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An ethologically relevant animal model of post-traumatic stress disorder

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Title:
An ethologically relevant animal model of post-traumatic stress disorder physiological, pharmacological and behavioral sequelae in rats exposed to predator stress and social instability
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Book
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English
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Zoladz, Phillip R
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University of South Florida
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Tampa, Fla
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Subjects

Subjects / Keywords:
PTSD
Glucocorticoids
Hippocampus
Amygdala
Antidepressants
Dissertations, Academic -- Psychology -- Doctoral -- USF   ( lcsh )
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non-fiction   ( marcgt )

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Summary:
ABSTRACT: Post-traumatic stress disorder (PTSD) is a debilitating mental illness that results from exposure to intense, life-threatening trauma. Some of the symptoms of PTSD include intrusive flashback memories, persistent anxiety, hyperarousal and cognitive impairments. The finding of reduced basal glucocorticoid levels, as well as a greater suppression of glucocorticoid levels following dexamethasone administration, has also been commonly observed in people with PTSD. Our laboratory has developed an animal model of PTSD which utilizes chronic psychosocial stress, composed of unavoidable predator exposure and daily social instability, to produce changes in rat physiology and behavior that are comparable to the symptoms observed in PTSD patients.The present set of experiments was therefore designed to 1) test the hypothesis that our animal model of PTSD would produce abnormalities in glucocorticoid levels that are comparable to those observed in people with PTSD, 2) examine the ability of antidepressant and anxiolytic agents to ameliorate the PTSD-like physiological and behavioral symptoms induced by our paradigm and 3) ascertain how long the physiological and behavioral effects of our stress regimen could be maintained. The experimental findings revealed that our animal model of PTSD produces a reduction in basal glucocorticoid levels and increased negative feedback sensitivity to the synthetic glucocorticoid, dexamethasone.In addition, chronic prophylactic administration of amitriptyline (tricyclic antidepressant) and clonidine (α-2-adrenergic receptor agonist) prevented a subset of the effects of chronic stress on rat physiology and behavior, but tianeptine (antidepressant) was the only drug to block the effects of chronic stress on all physiological and behavioral measures. The final experiment indicated that only a subset of the effects of chronic stress on rat physiology and behavior could be observed 4 months following the initiation of chronic stress, suggesting that some of the effects of our animal model diminish over time. Together, these findings further validate our animal model of PTSD and may provide insight into the mechanisms underlying trauma-induced changes in brain and behavior. They also provide guidance for pharmacotherapeutic approaches in the treatment of individuals suffering from PTSD.
Thesis:
Dissertation (Ph.D.)--University of South Florida, 2008.
Bibliography:
Includes bibliographical references.
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Mode of access: World Wide Web.
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by Phillip R. Zoladz.
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Title from PDF of title page.
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Document formatted into pages; contains 218 pages.
General Note:
Includes vita.

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aleph - 002004898
oclc - 352923285
usfldc doi - E14-SFE0002688
usfldc handle - e14.2688
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ABSTRACT: Post-traumatic stress disorder (PTSD) is a debilitating mental illness that results from exposure to intense, life-threatening trauma. Some of the symptoms of PTSD include intrusive flashback memories, persistent anxiety, hyperarousal and cognitive impairments. The finding of reduced basal glucocorticoid levels, as well as a greater suppression of glucocorticoid levels following dexamethasone administration, has also been commonly observed in people with PTSD. Our laboratory has developed an animal model of PTSD which utilizes chronic psychosocial stress, composed of unavoidable predator exposure and daily social instability, to produce changes in rat physiology and behavior that are comparable to the symptoms observed in PTSD patients.The present set of experiments was therefore designed to 1) test the hypothesis that our animal model of PTSD would produce abnormalities in glucocorticoid levels that are comparable to those observed in people with PTSD, 2) examine the ability of antidepressant and anxiolytic agents to ameliorate the PTSD-like physiological and behavioral symptoms induced by our paradigm and 3) ascertain how long the physiological and behavioral effects of our stress regimen could be maintained. The experimental findings revealed that our animal model of PTSD produces a reduction in basal glucocorticoid levels and increased negative feedback sensitivity to the synthetic glucocorticoid, dexamethasone.In addition, chronic prophylactic administration of amitriptyline (tricyclic antidepressant) and clonidine (-2-adrenergic receptor agonist) prevented a subset of the effects of chronic stress on rat physiology and behavior, but tianeptine (antidepressant) was the only drug to block the effects of chronic stress on all physiological and behavioral measures. The final experiment indicated that only a subset of the effects of chronic stress on rat physiology and behavior could be observed 4 months following the initiation of chronic stress, suggesting that some of the effects of our animal model diminish over time. Together, these findings further validate our animal model of PTSD and may provide insight into the mechanisms underlying trauma-induced changes in brain and behavior. They also provide guidance for pharmacotherapeutic approaches in the treatment of individuals suffering from PTSD.
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An Ethologically Relevant Animal Mode l of Post-Traumatic Stress Disorder: Physiological, Pharmacological and Behavioral Sequelae in Rats Exposed to Predator Stress and Social Instability by Phillip R. Zoladz A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy Department of Psychology College of Arts and Sciences University of South Florida Major Professor: David Diamond, Ph.D. Paula Bickford, Ph.D. Cheryl Kirstein, Ph.D. Edward Levine, Ph.D. Kristen Salomon, Ph.D. Date of Approval: November 5, 2008 Keywords: PTSD, glucocorticoids, hi ppocampus, amygdala, antidepressants Copyright 2008, Phillip R. Zoladz

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For my loving wife, Meagan. If it were not fo r you, I would never have made it this far.

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Acknowledgements I would like to thank Dr. David Diamond for his guidance and expertise. I truly appreciate all of the opportuni ties with which I have been provided, and I thank you for the encouragement and words of wisdom that you have offered me. I would also like to thank Dr. Paula Bickford, Dr. Ed Levine, Dr Cheryl Kristein and Dr. Kristen Salomon for being on my dissertation committee and Dr. Eric Bennett for agreeing to serve as the chairperson of my dissertation defense. Each of you has made this process very enjoyable for me. I would like to thank th e laboratory of Monika Fleshn er from the University of Colorado for assaying so many serum samples from this dissertation. I can truly say that it would not have gotten fini shed without your help! Also, my lab colleagues, Josh Halonen, Collin Park, Shyam Seetharaman a nd Alvin Jin, and I have developed very strong professional and personal re lationships over the past few years. I am very thankful for each one of you. I would also like to thank my family fo r all of their love and support. Meagan, you gave up everything for me to pursue my graduate studies, and I could never express how much you mean to me. I love you with al l of my heart. To my parents, you have always been there for me, and now as I start a life of my own, I only hope that I can be as good of a parent as you both have been to me. Finally, I would like to thank God for what He has done in my life. I have always need ed You, but it was not unt il recently that I accepted this need. Thank you for always loving me, even in spite of who I used to be.

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i Table of Contents List of Tables vii List of Figures viii Abstract xiii Chapter One: Background 1 Definition of Post-Traumatic Stress Disorder 1 Susceptibility to Post-Traumatic Stress Disorder 2 Heightened Arousal in Post -Traumatic Stress Disorder 2 Elevated Sympathetic Nervous System Activity 2 Contribution of the Parasy mpathetic Nervous System to Sympathetic Overdrive 7 Conclusion on Sympathetic Overdrive in Post-Traumatic Stress Disorder 8 Abnormal Functioning of the Hypothalamus-Pituitary-Adrenal Axis in Post-Traumatic Stress Disorder 10 Abnormal Baseline Levels of Cortisol and Its Hormone Precursors 11 Mechanisms Underlying Abnormal HypothalamusPituitary-Adrenal Axis Functioning in Post-Traumatic Stress Disorder 15 Structural and Functional Brain Abnormalities in Post-Traumatic Stress Disorder 17 Smaller Hippocampal Volume 17 Cognitive Impairments 19 Interactions between the Am ygdala and Prefrontal Cortex 20 Pharmacotherapy for Post-Traumatic Stress Disorder 22 Selective Serotonin Reuptake Inhibitors 22 Tricyclic Antidepressants and Monoamine Oxidase Inhibitors 23 Noradrenergic Modulators 25 The Antidepressant Tianeptine 26 Animal Models of Post-Traumatic Stress Disorder 28 Existing Models of Post-T raumatic Stress Disorder in Rodents 28 Our Laboratorys Recently Developed Animal Models of Post-Traumatic Stress Disorder 30

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ii Purpose of the Present Experiments 34 Chapter Two: Experiment One 35 Chronic Psychosocial Stress Produces a Reduction in Basal Glucocorticoid Levels in Rats: Further Validation of an Animal Model of PTSD 35 Methods 36 Rats 36 Psychosocial Stress Procedure 36 Acute Stress Sessions 36 Daily Social Stress 37 Assessment of Basal and St ress-Induced Glucocorticoid Levels 37 Preparation 37 Blood Sampling and Post-Mortem Dissection 38 Statistical Analyses 39 Experimental Design 39 Growth Rate, Adrenal Gland Weight and Thymus Weight 39 Corticosterone Levels 39 Results 40 Growth Rates 40 Adrenal Gland Weights 40 Thymus Weights 40 Corticosterone Levels 41 Discussion of Findings 42 Chapter Three: Experiment Two 46 Chronic Psychosocial Stress Result s in Enhanced Suppression of Corticosterone Levels following Dexamethasone Administration: Evidence for Enhanced Negative Feedback of the Hypothalamus-Pituitary-Adrenal Axis 46 Methods 47 Rats 47 Psychosocial Stress Procedure 47 Assessment of Post-Dexamethasone Basal and StressInduced Glucocorticoid Levels 47 Preparation 47 Pharmacological Manipulations 48 Blood Sampling and Post-Mortem Dissection 48 Statistical Analyses 49 Experimental Design 49 Growth Rate, Adrenal Gland Weights and Thymus Weights 49

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iii Corticosterone Levels 49 Results 50 Growth Rates 50 Adrenal Gland Weights 50 Thymus Weights 50 Corticosterone Levels 51 Discussion of Findings 54 Chapter Four: Experiment Three 58 Differential Effectiveness of the Pharmacological Agents Amitriptyline, Clonidine and Tianeptine in Blocking the PTSDLike Physiological and Behavioral Sequelae in Rats 58 Methods 60 Rats 60 Psychosocial Stress Procedure 60 Pharmacological Agents 62 Behavioral Testing 62 Behavioral Apparatus 63 Contextual and Cue Fear Memory 63 Elevated Plus Maze 64 Startle Response 64 Novel Object Recognition 65 Preparation for Blood Sampling 66 Blood Sampling and Ca rdiovascular Activity 66 Statistical Analyses 67 Experimental Design and General Analyses 67 Fear Memory 67 Elevated Plus Maze 68 Startle Response 68 Novel Object Recognition 68 Corticosterone Levels 69 Heart Rate and Blood Pressure 69 Growth Rates, Adrenal Gland Weights and Thymus Weights 69 Results 70 Fear Memory 70 Stress Session One 70 Stress Session Two 70 Context Test Immobility 72 Context Test Fecal Boli 73 Cue Test Immobility No Tone 74 Cue Test Immobility Tone 75 Cue Test Fecal Boli 76 Elevated Plus Maze 77

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iv Percent Time in Open Arms, 5-Minute Trial 77 Percent Time in Open Arms, First Minute 78 Ambulations, 5-Minute Trial 80 Ambulations, First Minute 81 Startle Response 82 90 dB Auditory Stimuli 82 100 dB Auditory Stimuli 83 110 Auditory Stimuli 84 Novel Object Recognition 85 Habituation 85 Training 87 Testing, 5-Minute Trial 88 Testing, First Minute 89 Corticosterone Levels 89 Cardiovascular Activity 91 Heart Rate 91 Systolic Blood Pressure 92 Diastolic Blood Pressure 94 Growth Rates 95 Adrenal Gland Weights 96 Thymus Weights 98 Discussion of Findings 99 Amitriptyline 101 Clonidine 105 Tianeptine 107 Limitations and Future Research 112 Summary and Applications to Pharmacotherapy for PostTraumatic Stress Disorder 113 Chapter Five: Experiment Four 115 Temporal Dynamics of the Physio logical and Behavi oral Sequelae Induced by Ch ronic Psychosocial Stress 115 Methods 115 Rats 115 Psychosocial Stress Procedure 116 Behavioral Testing 118 Behavioral Apparatus 118 Contextual and Cue Fear Memory 118 Elevated Plus Maze 119 Startle Response 119 Novel Object Recognition 119 Preparation for Blood Sampling 119 Blood Sampling and Ca rdiovascular Activity 119 Statistical Analyses 120

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v Experimental Design and General Analyses 120 Fear Memory 120 Elevated Plus Maze 120 Startle Response 121 Novel Object Recognition 121 Corticosterone Levels 122 Heart Rate and Blood Pressure 122 Growth Rates, Adrenal Gland Weights and Thymus Weights 122 Results 122 Fear Memory 122 Stress Session One 122 Stress Session Two 123 Stress Session Three 124 Context Test Immobility 124 Context Test Fecal Boli 125 Cue Test Immobility No Tone 127 Cue Test Immobility Tone 127 Cue Test Fecal Boli 127 Elevated Plus Maze 128 Percent Time in Open Arms, 5-Minute Trial 128 Percent Time in Open Arms, First Minute 128 Ambulations, 5-Minute Trial 130 Ambulations, First Minute 130 Startle Response 132 90 dB Auditory Stimuli 132 100 dB Auditory Stimuli 132 110 dB Auditory Stimuli 133 Novel Object Recognition 133 Habituation 133 Training 134 Testing 135 Corticosterone Levels 136 Cardiovascular Activity 136 Heart Rate 136 Systolic Blood Pressure 138 Diastolic Blood Pressure 138 Growth Rates 138 Adrenal Gland Weights 140 Thymus Weights 140 Discussion of Findings 141 Conclusions and Limitations 142 Chapter Six: Concluding Remarks 145

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vi References 149 About the Author End Page

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vii List of Tables Table 1 Growth Rates, Adrena l Gland Weights and Thymus Weights ( SEM) for the Groups in Experiment 1 41 Table 2 Growth Rates, Adrena l Gland Weights and Thymus Weights ( SEM) for the Psychosocial Stress and No Psychosocial Stress Gro ups (collapsed across all dexamethasone conditions) in Experiment 2 51 Table 3 Time (seconds SEM) Sp ent with Each Object during Object Recognition Training for all Groups in Experiment 3 87

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viii List of Figures Figure 1. Chronic Psychosocial Stress Produced a Reduction of Basal Glucocorticoid Levels in Rats 42 Figure 2. Chronic Psychosocial Stre ss Increases Sensitivity of the HPA Axis to Dexamethasone 52 Figure 3. Effects of Chronic Psyc hosocial Stress on Corticosterone Responses Following Different Doses of Dexamethasone 53 Figure 4. Amount of Immobility during the 3-Minute Chamber Exposure during Stress Session One 70 Figure 5. Amount of Immobility during the 3-Minute Chamber Exposure during Stress Session Two 71 Figure 6. Effects of Chronic Psyc hosocial Stress and Drug Treatment on Immobility during the 5-Minute Context Test 72 Figure 7. Effects of Chronic Psyc hosocial Stress and Drug Treatment on Fecal Boli Produced during the 5-Minute Context Test 74 Figure 8. Effects of Chronic Psyc hosocial Stress and Drug Treatment on Immobility during the First 3 Minutes of the Cue Test 75 Figure 9. Effects of Chronic Psyc hosocial Stress and Drug Treatment on Immobility during the Tone 76 Figure 10. Effects of Chronic Psyc hosocial Stress and Drug Treatment on Fecal Boli Produced during the 6-Minute Cue Test 77 Figure 11. Effects of Chronic Psyc hosocial Stress and Drug Treatment on Percent Time Spent in the Open Arms during the 5-Minute Trial on the Elevated Plus Maze 78 Figure 12. Effects of Chronic Psyc hosocial Stress and Drug Treatment on Percent Time Spent in the Open Arms during the First Minute of the 5-Minute Trial on the Elevated Plus Maze 79

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ix Figure 13. Effects of Chronic Psyc hosocial Stress and Drug Treatment on Ambulations Made during the 5-Minute Trial on the Elevated Plus Maze 80 Figure 14. Effects of Chronic Psyc hosocial Stress and Drug Treatment on Ambulations Made during the First Minute of the 5-Minute Trial on the Elevated Plus Maze 81 Figure 15. Effects of Chronic Psyc hosocial Stress and Drug Treatment on Startle Responses to the 90 dB Auditory Stimuli 82 Figure 16. Effects of Chronic Psyc hosocial Stress and Drug Treatment on Startle Responses to the 100 dB Auditory Stimuli 84 Figure 17. Effects of Chronic Psyc hosocial Stress and Drug Treatment on Startle Responses to the 110 dB Auditory Stimuli 85 Figure 18. Effects of Chronic Psyc hosocial Stress and Drug Treatment on Locomotor Activity during the 5-Minute Object Recognition Habituation Period 86 Figure 19. Effects of Chronic Psyc hosocial Stress and Drug Treatment on Object Recognition Memory during the Entire 5-Minute Testing Trial 88 Figure 20. Effects of Chronic Psyc hosocial Stress and Drug Treatment on Object Recognition Memory during the First Minute of the Testing Trial 89 Figure 21. Effects of Chronic Psyc hosocial Stress and Drug Treatment on Serum Corticosterone Levels 90 Figure 22. Effects of Chronic Psyc hosocial Stress and Drug Treatment on Heart Rate 92 Figure 23. Effects of Chronic Psyc hosocial Stress and Drug Treatment on Systolic Blood Pressure 93 Figure 24. Effects of Chronic Psyc hosocial Stress and Drug Treatment on Diastolic Blood Pressure 94 Figure 25. Effects of Chronic Psyc hosocial Stress and Drug Treatment on Growth Rate 96

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x Figure 26. Effects of Chronic Psyc hosocial Stress and Drug Treatment on Adrenal Gland Weight 97 Figure 27. Effects of Chronic Psyc hosocial Stress and Drug Treatment on Thymus Weight 98 Figure 28. Experimental Gr oups in Experiment 4 117 Figure 29. Amount of Immobility upon Chamber Exposure during Stress Session One 123 Figure 30. Amount of Immobility upon Chamber Exposure during Stress Session Two 123 Figure 31. Amount of Immobility upon Chamber Exposure during Stress Session Three 124 Figure 32. Effects of Differential Chronic Psychosocial Stress Paradigms on Immobility during the 5-Minute Context Test 125 Figure 33. Effects of Differential Chronic Psychosocial Stress Paradigms on Fecal Boli Produced during the 5-Minute Context Test 126 Figure 34. Effects of Differential Chronic Psychosocial Stress Paradigms on Immobility during the First 3 Minutes of the Cue Test 126 Figure 35. Effects of Differential Chronic Psychosocial Stress Paradigms on Immobility during the Last 3 Minutes of the Cue Test 127 Figure 36. Effects of Differential Chronic Psychosocial Stress Paradigms on Fecal Boli Produced during the 6-Minute Cue Test 128 Figure 37. Effects of Differential Chronic Psychosocial Stress Paradigms on Percent Time Spent in the Open Arms during the 5-Minute Trial on the Elevated Plus Maze 129 Figure 38. Effects of Differential Chronic Psychosocial Stress Paradigms on Percent Time Spent in the Open Arms during the First Minute of the 5-Minute Trial on the Elevated Plus Maze 129

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xi Figure 39. Effects of Differential Chronic Psychosocial Stress Paradigms on Ambulations Made during the 5-Minute Trial on the Elevated Plus Maze 130 Figure 40. Effects of Differential Chronic Psychosocial Stress Paradigms on Ambulations Made during the First Minute of the 5-Minute Trial on the Elevated Plus Maze 131 Figure 41. Effects of Differential Chronic Psychosocial Stress Paradigms on Startle Responses to the 90 dB Auditory Stimuli 131 Figure 42. Effects of Differential Chronic Psychosocial Stress Paradigms on Startle Responses to the 100 dB Auditory Stimuli 132 Figure 43. Effects of Differential Chronic Psychosocial Stress Paradigms on Startle Responses to the 110 dB Auditory Stimuli 133 Figure 44. Effects of Differential Chronic Psychosocial Stress Paradigms on Object Recognition Memory during the Entire 5-Minute Testing Trial 134 Figure 45. Effects of Differential Chronic Psychosocial Stress Paradigms on Object Recognition Memory during the First Minute of the Testing Trial 135 Figure 46. Effects of Differential Chronic Psychosocial Stress Paradigms on Serum Corticosterone Levels 136 Figure 47. Effects of Differential Chronic Psychosocial Stress Paradigms on Heart Rate 137 Figure 48. Effects of Differential Chronic Psychosocial Stress Paradigms on Systolic Blood Pressure 137 Figure 49. Effects of Differential Chronic Psychosocial Stress Paradigms on Diastolic Blood Pressure 138 Figure 50. Effects of Differential Chronic Psychosocial Stress Paradigms on Growth Rate 139

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xii Figure 51. Effects of Differential Chronic Psychosocial Stress Paradigms on Adrenal Gland Weight 139 Figure 52. Effects of Differential Chronic Psychosocial Stress Paradigms on Thymus Weight 140

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xiii An Ethologically Relevant Animal Mode l of Post-Traumatic Stress Disorder: Physiological, Pharmacological and Behavioral Sequelae in Rats Exposed to Predator Stress and Social Instability Phillip R. Zoladz ABSTRACT Post-traumatic stress disorder (PTSD) is a debilitating mental illness that results from exposure to intense, life-threatening trauma. Some of the symptoms of PTSD include intrusive flashback memories, pers istent anxiety, hyperar ousal and cognitive impairments. The finding of reduced basal gluc ocorticoid levels, as well as a greater suppression of glucocorticoid levels following dexamethas one administration, has also been commonly observed in people with PTSD Our laboratory has developed an animal model of PTSD which utilizes chronic psychosocial stress, composed of unavoidable predator exposure and daily social instabi lity, to produce changes in rat physiology and behavior that are comparable to the symptoms observed in PTSD patients. The present set of experiments was therefore designed to 1) test the hypothesis that our animal model of PTSD would produce abnormalities in glucocortico id levels that are comparable to those observed in people with PTSD, 2) examine th e ability of antidepre ssant and anxiolytic agents to ameliorate the PT SD-like physiological and behavioral symptoms induced by our paradigm and 3) ascertain how long the physiological and behavi oral effects of our stress regimen could be maintained.

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xiv The experimental findings revealed that our animal model of PTSD produces a reduction in basal glucocorticoid levels and increased negative feedback sensitivity to the synthetic glucocorticoid, dexamethasone. In addition, chronic prophylactic administration of amitriptyline (tricyclic an tidepressant) and clonidine ( 2-adrenergic receptor agonist) prevented a subset of the effects of chr onic stress on rat physiology and behavior, but tianeptine (antidepressant) was the only drug to block the effects of chronic stress on all physiological and behavioral measures. The fina l experiment indicated that only a subset of the effects of chronic st ress on rat physiology and behavior could be observed 4 months following the initiation of chronic stress, suggesting th at some of the effects of our animal model diminish over time. Together these findings further validate our animal model of PTSD and may provide insight in to the mechanisms underlying trauma-induced changes in brain and behavior. They also provide guidance for pharmacotherapeutic approaches in the treatment of individuals suffering from PTSD.

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1 Chapter One: Background Definition of Post-Traumatic Stress Disorder Individuals who are exposed to intense tr auma that threatens physical injury or death, such as rape, wartime combat and moto r vehicle accidents, ar e at significant risk for developing post-traumatic stress disorder (PTSD). People who develop PTSD respond to a traumatic experience with intense fear, helplessness or horror (American Psychiatric Association, 1994) and subsequently endure chronic psychological distress by repeatedly reliving their trauma through intrusive, flashback memories (Ehlers et al., 2004; Hackmann et al., 2004; Reynolds & Brewin, 1998; Reynolds & Brewin, 1999; Speckens et al., 2006; Speckens et al., 2007). These intrus ions are frequently precipitated by the presence of cues associated with the trau matic event; therefore, PTSD patients make great efforts to avoid stimuli that remind them of their trauma. The re-experiencing and avoidance symptoms of the disorder significantly hinder everyday functioning in PTSD patients and foster the development of several additional debilitating symptoms, including persistent anxiety, exaggerated startle, cognitive impairments, diminished extinction of conditioned fear and pharmacol ogical abnormalities, such as an increased sensitivity to yohimbine (Brewin et al., 2000; Elzinga & Bremner, 2002; Nemeroff et al., 2006; Newport & Nemeroff, 2000; Stam, 2007a).

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2 Susceptibility to Post-Traumatic Stress Disorder Only about 25% of traumatized indivi duals develop PTSD (Ozer et al., 2003; Ozer & Weiss, 2004; Yehuda, 2004). While nearly every traumatized person displays reexperiencing, avoidance and hyperarousal symp toms in the acute aftermath of trauma (McFarlane, 2000), only a minority continue to exhibit these symptoms for a period of at least 1 month and fulfill the requirements set forth by the Diagnostic and Statistical Manual of Mental Disorders (American Psychiatric Association, 1994) for a diagnosis of PTSD (Yehuda & LeDoux, 2007). Thus, in approximately 75% of traumatized individuals, the re-experienci ng, avoidance and hyperarousal symptoms subside within a 1-month time frame, and at least one-third of those who conti nue to display the symptoms at 1-month post-trauma recover w ithin 3 months (Kessler et al., 1995). Thus, the natural response to trauma is recovery, a nd only a subset of traumatized individuals develops chronic forms of the disorder. Heightened Arousal in Post -Traumatic Stress Disorder Elevated Sympathetic Nervous System Activity PTSD is characterized by a complex aberrant biological profile involving several physiological systems, one of which is the sympathetic nervous system (SNS). Extensive work has demonstrated that PTSD patients exhibit greater baseline and stress-induced elevations of sympathetic activity than cont rol subjects (Buckl ey & Kaloupek, 2001; Pole, 2007). In response to traumatic reminders and standard laborat ory stressors, people with PTSD display significantly greater increa ses in heart rate (HR), blood pressure (BP), skin conductance, epinephrine (EPI) and norepinephrine (NE) than do control subjects

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3 (Blanchard et al., 1982; Blanch ard et al., 1991; Casada et al., 1998; Kolb & Mutalipassi, 1992; Malloy et al., 1983; McFall et al., 1990; Orr et al., 1998; Pitman et al., 1987; Rabe et al., 2006; Schmahl et al., 2004; Shalev et al., 1993; Veazey et al., 2004). In addition, PTSD patients exhibit significant elevations of baseline HR, systolic BP and diastolic BP (Buckley & Kaloupek, 2001; Pole, 2007), findi ngs that resonate with recent work reporting an association between PTSD and increased risk for cardiovascular disease (Boscarino & Chang, 1999; Kubzansky et al., 2007; Sawchuk et al., 2005). A vast literature has also implicated in creased baseline noradrenergic activity in individuals suffering from PTSD. Several studi es have shown that PTSD patients exhibit abnormally high levels of baseline NE (G eracioti et al., 2001; Kosten et al., 1987; Southwick et al., 1999a; Strawn & Geracioti, 2008; Yehuda et al., 1998), levels that have been shown to positively correlate with th e severity of symptoms in PTSD patients (Geracioti et al., 2001). Another indication of accentuated symp athetic activity in people with PTSD is the hyperresponsivity they exhibi t to the administration of yohimbine, an 2 adrenergic receptor antagonist which blocks noradrenergic autoreceptors and leads to increased central norepinephr ine activity (Rasmusson et al ., 2000; Southwick et al., 1993; Southwick et al., 1999c; Southwick et al., 1999a; Southwick et al ., 1999b). Southwick and colleagues (Southwick et al., 1993) f ound that, following yohimbine administration, 70% of PTSD patients experi enced panic attacks, and 40% experienced flashbacks. PTSD patients also exhibited significantly greater HR, systolic BP, anxiety-related behavior and acoustic startle responses to the drug (Morgan et al., 1995b).

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4 Bremner and colleagues (Bremner et al., 1997a) suggested that these findings may be related to reduced NE catabolism in PTSD patients. To test this hypothesis, the investigators gave PTSD patients a single bolus of [F-18]2-fluoro-2-deoxyglucose, a compound that is taken up by high-glucose-usin g cells, immediately prior to intravenous injections of yohimbine. Approximately an hour later, the investigators measured cerebral metabolic activity in participants by employing positron emission tomography (PET). The PET scans revealed that, relative to healthy controls, PTSD patients displayed significantly lower levels of glucose metabolis m in several neocortical brain regions that are highly innervated by noradrenergic nerv e fibers, suggesting the presence of reduced NE catabolism in people with PTSD. The anxi ogenic effects of yohi mbine in people with PTSD have also been linked to the presence of fewer and less sensitive 2 adrenergic receptors and lower levels of plasma neurope ptide Y (NPY) in PTSD patients (Perry et al., 1990; Perry, 1994; Rasmusson et al., 2000). NPY is a peptide neurotransmitter that is colocalized with NE in most sympathetic nerv e fibers and within the locus coeruleus, an area of the dorsal pons that contains the ma jor cell bodies of the noradrenergic system. The peptide typically inhibits the release of the neurotransmitter with which it is colocalized. Rasmusson et al. (2000) found that PTSD patients had lower baseline plasma levels of NPY, as well as a smaller increas e in NPY levels in response to a yohimbine challenge paradigm. This finding could explain the presence of greater baseline NE levels, as well as greater reactivity to yohimbine, in PTSD patients. Related to the symptoms of hyperarousal and greater noradrenergic activity, an exaggerated startle response is often presente d as a core symptom of PTSD (Grillon et al.,

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5 1996). The startle response is defined as th e rapid sequence of flexor motor movements that occurs after the onset of a brieflypresented, intense stimulus (Morgan, 1997). Approximately 85-90% of trauma survivors with PTSD subjectively report having an increased startle response (S halev et al., 1997). However, empirical investigations examining the startle response in PTSD patient s have presented conflicting results. While some studies have found heightened startle in people with PTSD (Butler et al., 1990; Grillon et al., 1998; Morgan et al., 1995a; Mo rgan et al., 1996; Mo rgan et al., 1997; Orr et al., 1995; Shalev et al., 1997), others have found no differences between PTSD patients and control subjects (Elsesser et al., 2004; Grillon et al., 199 6; Lipschitz et al., 2005; Orr et al., 1997; Siegelaar et al ., 2006). The exaggerated startle response often observed in PTSD patients may not be due to a stable tra it of these individuals, but rather an acute state of conditioned fear or anxiety (e.g., antic ipatory anxiety) that they experience during the experimental assessment. In support of this hypothesis, several studies have found that manipulations of the experimental context or the presentation of explicit threat cues consistently leads to enhanced startle res ponses in PTSD patients (Grillon et al., 1998; Grillon & Morgan, 1999; Pole et al., 2003). Investigators have also faced the challe nge of determining whether or not the exaggerated startle response observed in peopl e with PTSD is a secondary effect of the disorder or a predisposing risk factor that increases ones susceptibility to develop the disorder. In a recent study, Guthrie and Brya nt (2005) assessed the auditory startle response of firefighters before and after th ey had been exposed to trauma. Although none of the firefighters who were exposed to trauma developed PTSD during the course of the

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6 study, they did display more symptoms (e.g., intrusive memories, avoidance) of the disorder after the trauma than firefighters w ho had not been exposed to a traumatic event. More importantly, the investig ators found that the magnitude of the pre-trauma startle response predicted the development of acute PTSD symptoms. These findings suggest that an exaggerated startle re sponse may not necessarily be a secondary effect of PTSD; rather, it could be a pre-existi ng factor that increases ones susceptibility to develop the disorder. Despite the inconsistent findings on baseli ne startle responses in PTSD patients, research has reliably shown that upon exposur e to briefly-presented, intense stimuli (e.g., loud tones), people with PTSD exhibit signif icantly greater autonomic reactivity than do controls (Metzger et al., 1999; Orr et al ., 1995; Orr et al., 1997; Shalev et al., 1997; Shalev et al., 2000; Siegelaa r et al., 2006). This includes a failure to physiologically habituate to the stimuli, in addition to the el icitation of greater autonomic responses from the onset of the stimuli. In a recent study, Siegelaar et al. (2006) found that although PTSD patients did not display an exaggera ted startle response, relative to control subjects, they did exhibit significantly great er autonomic reactivity, in the form of galvanic skin response, to the test stimuli. The investigators conte nded that the presence of greater autonomic activity following the pr esentation of startling stimuli may explain why PTSD patients subjectively report ex aggerated startle responses, despite not exhibiting them behaviorally. Ultimately, thes e findings suggest that while it is unclear whether or not individuals with PTSD exhibit a heightened baseline startle response, they do tend to display exaggerated autonomic r eactivity to sudden, intense stimulation.

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7 Contribution of the Parasympathetic Nerv ous System to Sympathetic Overdrive The parasympathetic nervous system (PNS ), which is metaphorically considered the brakes on the SNS since it reduces SNS activity, makes a significant contribution to the maintenance of HR (Berntson et al., 1993) The vagus nerve, which is an important part of the PNS, innervates the sinoatrial node on the right atrium of the heart, where electrical impulses are gene rated to trigger cardiac c ontraction. By modulating the sinoatrial node, the vagus nerve slows HR a nd helps to maintain a balance between the SNS and PNS. Vagal modulation of HR is impor tant for reactions to and recovery from stressful situations, and has been considered a possible mechanism for the differences in basal HR and changes in HR due to trauma-rela ted cues in individuals with PTSD (Sahar et al., 2001). Most studies monitoring PNS activity in PTSD patients have utilized heart-rate variability (HRV) as the primary dependent m easure. HRV is a measure of beat-to-beat alterations in heart rate, or more specificall y, the variability of the intervals between R waves. The two main frequency bands that are examined during HRV assessment are the Low-Frequency (LF) band (0.04 to 0.15 Hz), wh ich is influenced primarily by the SNS, and the High-Frequency (HF) band (0.15 to 0.40 Hz), which is influenced primarily by the PNS (Sahar et al., 2001). Cohen and co lleagues (Cohen et al., 1997; Cohen et al., 1998; Cohen et al., 2000a) found that, at rest PTSD patients displayed greater HR and lower HRV than healthy control subjects. Furt hermore, these patients demonstrated lower HF and higher LF components than controls, suggestive of enhanced sympathetic and reduced parasympathetic tone, respectively. Sahar et al. (2001) examined the vagal

PAGE 25

8 modulation of HR in PTSD patients in response to a mental challenge by using respiratory sinus arrhythmia (RSA) as their dependent measure. RSA is the natural fluctuation in heart rate that occurs during the breathing cycle, and changes in RSA have been shown to reflect activ ity of the vagus nerve (Berntson et al., 1993). Sahar and colleagues (Sahar et al., 2001) found that PTSD patients and traumatized control subjects did not differ on resting levels of parasympat hetic activity. However, when faced with a challenging arithmetic task, c ontrol subjects showed a significant increase in RSA (which was highly correlated with their HR), while PTSD patients showed no such increase. Thus, vagal mechanisms contributed to HR regulation in control subjects, but not in PTSD patients. These findings suggest that va gal modulation of HR may be impaired in PTSD patients, resulting in poor control of stress-induced changes in HR and increased risk for exaggerated sympathetic tone. Conclusion on Sympathetic Overdrive in Post-Traumatic Stress Disorder Sympathetic overdrive has been hypothesi zed to contribute to the hyperarousal symptoms observed in PTSD patients. It is al so potentially responsible for their enhanced acquisition of conditioned fear and their overconsolidation of the original traumatic memory (Cahill et al., 1994; Cahill & McGaugh, 1998; McGaugh et al., 1996; Pitman, 1989). Many researchers have used conditioning theory to explain the development of PTSD (Garakani et al., 2006; Wessa & Flor, 2002). These investigat ors have speculated that during the trauma, the plethora of cues (CSs) to which an individual is exposed becomes associated with the life-threatening e xperience (US) that he or she is enduring and eventually elicits feelings of intense f ear (CRs) similar to those (URs) experienced

PAGE 26

9 during the original traumatic event. In theo ry, individuals who are more susceptible to developing the disorder would exhibit more intense fear responses to the trauma, which would then be more strongly associated with the cues from the environment. This would subsequently cause these individuals to exhi bit exaggerated physiolo gical and behavioral responses to the presence of trauma-related cues and compel them to avoid reminders of their trauma. One mechanism that could explai n the enhanced consolidation of traumatic memories in PTSD patients is excessive adrenergic activity at the time of trauma (Cahill et al., 1994; Cahill & McGaugh, 1998; McGaugh et al., 1996; Pitman, 1989). Decades of animal research has shown that the admi nistration of EPI or NE following learning enhances the storage of emotional memories (Gold et al., 1977; Gold & Van Buskirk, 1975; McGaugh, 2004), and a substantial amount of work in traumatized people has found that those individuals w ho exhibit greater HR responses to the traumatic event are at a much greater risk of developing PTSD (Bryant et al., 2000; Bryant et al., 2004; Bryant, 2006; Bryant et al., 2007; Shalev et al., 1998; Zatz ick et al., 2005). As PTSD is a disorder of memory, in which an individual repeatedly relives his or her trauma through intrusive, flashback memories, an exaggerated sympathetic respons e to trauma could foster a development of a powerful, unrel enting traumatic memory that in some individuals becomes incapacitating over time. Although sympathetic activity facilitates a rapid response to threat in ones environment, chronic activation of the sy stem can have detrimental effects on an individuals health (McEwen, 1998; McEw en, 2003; McEwen & Wingfield, 2003). As mentioned above, some studies have indicated that PTSD is associated with increased

PAGE 27

10 risk for cardiovascular disease, including myocardial infarctions and atrioventricular conduction abnormalities (Boscarino & Chang, 1999; Kubzansky et al., 2007; Sawchuk et al., 2005). The finding of reduced PNS activ ity in PTSD patients could exacerbate this problem. Research has shown that diminished PNS activity is associated with increased susceptibility to cardiac arrhythmias and incr eased mortality in myocardial infarction patients (La Rovere et al., 1988; La Rovere et al., 1998; Verrier & Dickerson, 1994). Thus, the presence of chronic sympathetic activity and a hyperaroused physiological state can lead to a significant decline in the ove rall physical health of PTSD patients. Abnormal Functioning of the Hypothalamus-Pitu itary-Adrenal Axis in Post-Traumatic Stress Disorder Stress involves activation of the hypothalamus-pituitary-adrenal (HPA) axis, which entails the paraventricular nucleus of the hypothalamu s secreting corticotrophinreleasing hormone (CRH), whic h travels through the median eminence via the portal vasculature to the anterior pituitary gla nd. Within the anterior pituitary gland, CRH stimulates the release of adrenocorticotrophin (ACTH), which then circulates through the bloodstream to stimulate the adrenal cortex to synthesize and rele ase corticosteroids (primarily corticosterone in rodents and cortisol in humans). Corticosteroids help coordinate an individuals ab ility to cope with stress and divert energy to tissues with greater demands (de Kloet et al., 1999). Alt hough corticosteroids ar e critically involved in the stress response, they also play a role in regulating baseline physiology by influencing metabolism, the immune system a nd memory consolidation (de Kloet et al.,

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11 1999; Deuschle et al., 1997; Hartmann et al., 1997; Raison & M iller, 2003; Tsigos & Chrousos, 2002). Abnormal Baseline Levels of Cort isol and Its Hormone Precursors The HPA axis has been one of the most researched biological systems in people with PTSD. Researchers initially considered PTSD to be characterized by hypocortisolism, as a majority of the initial studies in this area of research reported abnormally low levels of baseline cortisol in people with PTSD (for reviews, see Yehuda, 2002; Yehuda, 2005). However, this view has st eadily evolved over the past decade, in light of new work that has reported baseline cortisol levels in PTSD patients that are either greater than, or no different from, t hose of controls (see de Kloet et al., 2006 for a review). Given such a complex set of findings, it has recently been suggested that there may be no static hypoor hypercortisolism in PTSD, but a tendency of HPA tone to hyperregulate in both [an] upward and downward direction (Stam, 2007a, p. 536). Researchers have addressed several factor s that could underlie the complexity of baseline cortisol findings in people with PT SD. One factor has been the considerable variability in the characteris tics of PTSD patients across st udies. According to Yehuda (2005, p. 373), the absence of cortisol alte rations in some studies [implies] that alterations associated with low cortisolare only present in a biologic subtype of PTSD (italics added for emphasis). The nature of baseline HPA axis alterations in PTSD patients may be dependent, at least in part, on the type of trauma that led to their psychopathology. For instance, a majority of the studies examining people with abuserelated (i.e., sexual or physical abuse, in cluding rape) PTSD ha ve reported greater

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12 baseline cortisol levels in PTSD patients than controls (Bremner et al., 2003a; De Bellis et al., 1999a; Elzinga et al., 2003; Inslicht et al., 2006a; Insl icht et al., 2006b; Lemieux & Coe, 1995), while a majority of the studies examining people with combat-related PTSD have reported lower baseline co rtisol levels in PTSD patient s than controls (Boscarino, 1996; Kanter et al., 2001; Thaller et al ., 1999; Yehuda et al., 1996b; Yehuda et al., 1993a). Other factors that could have influenced studies examining baseline cortisol levels in people with PTSD are the type (i.e., periphe ral vs. central) of cor tisol that was assayed and when (i.e., time of day) the assay was perf ormed. Most of the studi es in this area of research have used peripheral measures (e.g., urine, saliva, serum) to examine cortisol levels in PTSD patients (for reviews, see de Kloet et al., 2006; Yehuda, 2002; Yehuda, 2005). The only study to assess central levels of cortisol in people with PTSD reported that combat veterans with the disorder exhi bited significantly greater CSF cortisol levels than healthy controls (Baker et al., 2005). While cortisol is mostly free (i.e., unbound) and biologically active in CSF, it is largely bound to corticoste roid-binding globulin (CBG) in serum (Dunn et al., 1981; Pardridg e, 1981); and, one study found that people with PTSD displayed significantly greater leve ls of serum CBG than controls (Kanter et al., 2001). Thus, baseline cortisol levels in PT SD patients could vary based on the type of cortisol being measured. Many of the studies examining baseline cort isol levels in PTSD have collected biological samples for cortisol analysis at a single time point or have pooled the samples over a 12or 24-hour period. These methodol ogies could have failed to detect a

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13 difference between PTSD patients and control s ubjects due to measuring cortisol levels at a time of day when no true differences exist or by masking potential differences through pooling a number of samples spread across th e day. To address this issue and study the circadian rhythm of cortisol levels in PTSD patients, Yehuda et al. (1996b) examined baseline levels of cortisol in combat vete rans with PTSD at 30-minute intervals over a 24-hour period of bed rest. Their results reveal ed that individuals with PTSD had lower levels of cortisol than controls during the late evening (i.e., ~10:00 p.m.) and early morning (i.e., ~5:00 a.m.) hours, which appear ed to result from a prolonged nadir and short-lived peak response in the cycle of co rtisol release. In addition to this finding, several other studies reporting lower levels of cortisol in PTSD patients have collected samples for cortisol analysis in the early morning hours (Brand et al., 2006; Goenjian et al., 1996; King et al., 2001; Lindauer et al., 2006; Rohleder et al., 2004; Seedat et al., 2003; Wessa et al., 2006), suggesting that th is may be the time of day when these individuals displa y hypocortisolism. In addition to cortisol level abnormalities, investigators ha ve also reported significantly elevated levels of CRH in peopl e with PTSD (Baker et al., 1999; Geracioti et al., 2001). If most PTSD patients display abnormally low baseline cortisol levels, these findings would create a paradox that is how could PTSD patients exhibit lower baseline levels of cortisol if they have significantly elevated levels of CRH? Smith and colleagues (Smith et al., 1989) found that in a CRH challenge paradigm, PTSD patients displayed significantly lower leve ls of ACTH than healthy c ontrol subjects (however, see Kellner et al., 2003; Rasmusson et al., 2001) and Kellner et al (2000) reported

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14 significantly lower levels of ACTH in PTSD patients following the administration of cholecystokinin tetrapeptide (CCK-4), a poten t stimulator of ACTH. In addition, several studies have reported no differe nces in baseline ACTH levels between PTSD patients and controls (Baker et al., 2005; Duval et al., 2004; Kanter et al., 2001; Liberzon et al., 1999a; Newport et al., 2004; Neylan et al., 2003; Neylan et al., 2006; Otte et al., 2007; Rasmusson et al., 2001; Yehuda et al., 1996a; Yehuda et al., 2004b). One possibility is that PTSD patients have desensitized CRH r eceptors and/or enhanced negative feedback inhibition at the level of the pituitary, which results in a blunted release of ACTH upon CRH receptor stimulation. Support for this hypothesis has been provided by studies using the dexamethasone-CRH challenge paradigm (de Kloet et al., 2006). In this paradigm, participants are treated with dexamethasone, a synthetic glucocorticoid, the night before the experiment. Since the HPA axis is regul ated through a negative feedback system, the dexamethasone pre-treatment significantly re duces HPA axis activity. On the following morning, the participants are tr eated with CRH, and th eir levels of ACTH and cortisol are measured. The advantage of this paradigm is th at, since all participan ts are treated with a relatively high dose of dexamethasone the night prior to the st udy, by the time of CRH administration, both the PTSD patients and control subjects should display the same amount of dexamethasone-induced cortisol supp ression (i.e., the same baseline). Of the four studies examining the effects of this ch allenge paradigm on HPA axis functioning in PTSD patients, two (Rinne et al., 2002; Strohl e et al., 2008) have reported that, following CRH administration, participants with PTSD displayed significantly lower ACTH levels

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15 than controls. The other two (de Kloet et al., 2008; Muhtz et al., 2008) reported no significant group differences, wh ich are likely a result of using too high of a dose of dexamethasone (see Strohle et al., 2008). Ther efore, given that PTSD patients exhibited significantly less ACTH release upon CRH administration, it would suggest that the disorder is characterized by reduced CRH receptor sensitivity and/or enhanced glucocorticoid negative feedback at the level of the pituitary. Mechanisms Underlying Abnorma l Hypothalamus-Pituitary-Adre nal Axis Functioning in Post-Traumatic Stress Disorder Several hypotheses have been proposed to explain the abnormal HPA axis functioning observed in people with PTSD (de Kloet et al., 2006). As referenced above, one hypothesis has been that PTSD patients di splay pituitary insufficiency or reduced pituitary sensitivity to CRH stimulation. Alt hough findings have been mixed, the reports above indicating that PTSD patients exhi bited lower ACTH levels following CRH administration, relative to c ontrols, support this hypothesis. Another hypothesis has suggested that PTSD is ch aracterized by adrenal insufficiency or reduced adrenal sensitivity to ACTH. However, this scen ario seems unlikely, as non-pharmacological challenge paradigms have indicated that PT SD patients exhibit a robust stress-induced increase in cortisol that is greater than that of control subjects (Bremner et al., 2003a; Elzinga et al., 2003). Moreover, if adrenal insufficiency or desensitization were the reason for HPA axis dysfunction in PTSD, one would expect PTSD patients to exhibit lower cortisol levels than controls follo wing an ACTH challenge paradigm. On the contrary, the administration of ACTH has act ually been shown to result in significantly

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16 greater cortisol levels in peopl e with PTSD, relative to cont rol subjects (Rasmusson et al., 2001). Another hypothesis, which has received the most empirical support, is that PTSD patients have enhanced negative feedback inhi bition of the HPA axis. When cortisol is released into the bloodstream, it exerts negative feedback on the HPA axis by binding to glucocorticoid receptors th roughout the body. Research has shown that PTSD patients have an increased number and sensitivity of glucocorticoid receptors (Rohleder et al., 2004; Stein et al., 1997b; Yehuda et al., 1991; Yehuda et al ., 1993a; Yehuda et al., 1995). In addition, studies have repor ted an increased suppression of cortisol and ACTH in PTSD patients following the administration of dexamethasone, a synthetic glucocorticoid (Duval et al., 2004; Goenjian et al., 1996; Grossman et al ., 2003; Newport et al., 2004; Stein et al., 1997b; Yehuda et al., 1993b; Yehuda et al., 1995; Yehuda et al., 2002; Yehuda et al., 2004b). This finding suggests that dexamethasone produces greater negative feedback inhibition of the HPA axis in PTSD patients, which leads to a greater suppression of cortisol and ACTH in thes e individuals. Some have also observed increased activation of the p ituitary gland in PTSD patients following the administration of metyrapone, a glucocorticoid antagonist that blocks the conversion of 11-deoxycortisol to cortisol (or 11-deoxycortico terone to corticosterone in rodents) (Otte et al., 2006; Yehuda et al., 1996a). Both of these studies found that following the administration of metyrapone, PTSD patients exhibited a signifi cantly greater increase in ACTH and 11deoxycortisol, two of the primary precursors to co rtisol release, relative to controls. Since metyrapone prevents the production of cor tisol, it hinders the negative feedback

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17 component of the HPA axis. In theory, PTSD patients in these studies demonstrated greater increases in ACTH and 11-deoxyc ortisol because metyrapone removed the enhanced negative feedback inhibition initially present in these individuals. Structural and Functional Brain Abnormalities in Post-Traumatic Stress Disorder Smaller Hippocampal Volume Investigators have reported sma ller hippocampal volume in people who developed PTSD following combat exposure (Bre mner et al., 1995a; Gurvits et al., 1996; Hedges et al., 2003; Vythilingam et al., 2005; Woodward et al., 2006a), firefighting (Shin et al., 2004b), police work (Lindauer et al., 2004b; Lindauer et al., 2006), childhood abuse (Bremner et al., 1997b; Bremner et al ., 2003b; Stein et al., 1997a), and mixed types of events, such as motor vehicle accidents a nd assaults (Villarreal et al., 2002; Wignall et al., 2004; Winter & Irle, 2004). In general, these studies have detected smaller hippocampal volume in individuals with PTSD after adjusting for the total brain volume and age of each subject. Nevertheless, numerous other studies have not replicated these findings; they reported no differences in hippocampal volume between individuals diagnosed with PTSD and control subjects (Bonne et al., 2001; De Bellis et al., 1999b; De Bellis et al., 2001; Fennema-N otestine et al., 2002; Jatzko et al., 2006; Pederson et al., 2004; Schuff et al., 2001; Tupler & De Bellis, 2006; Yamasue et al., 2003; Yehuda et al., 2007). The inconsistencies of these findings ra ise an important issue: is hippocampal volume reduced by trauma, or is a smaller hippocampus a pre-existing risk factor that increases ones susceptibility to develop the disorder?

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18 Work conducted by Gilbertson and coll eagues (Gilbertson et al., 2002) had a substantial impact on how the scientific community interpreted smaller hippocampal volume in PTSD patients. These investigat ors used MRI to measure hippocampal volume of monozygotic twins discordant for trauma exposure, which, in this case, was combat. Consistent with previous findings, those i ndividuals who were exposed to combat and had developed PTSD exhibited smaller hippocampal volume than combat-exposed individuals who did not develop PTSD. Th e important finding, though, was that the nonexposed twin brothers of those individuals who developed PTSD also displayed smaller hippocampal volume than trauma-exposed indi viduals who did not develop PTSD. Thus, these individuals had smaller hippocampal vol ume than controls, even though they were not exposed to a traumatic event. This finding supported the idea that smaller hippocampal volume was a pre-existing familial ri sk factor that enhanced the likelihood of the combat-exposed brother to develop PTSD. In another study employing the same st rategy, Gilbertson et al. (2007) assessed allocentric (i.e., related to configural relationships am ong distal stimuli) spatial processing, a hippocampus-dependent task, in monozygotic twins discordant for trauma exposure, which was combat. The investigat ors found that those i ndividuals who were exposed to combat and had developed PTSD, as well as their twin brothers, made significantly more errors on the spatial task than those individuals who were exposed to combat and did not develop PTSD. These findings extended the earlier report by Gilbertson and colleagues by demonstrating that impaire d hippocampal function, in

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19 addition to smaller hippocampal volume, may also be a pre-existing familial risk factor for the development of PTSD. Cognitive Impairments Since there is extensive evidence supporting the presence of smaller hippocampal volume in PTSD patients, it is not surpri sing that numerous studies have reported declarative and working memory impairments, along with deficits in attention, in these individuals as well (Bremner et al., 1993; Bremner et al., 1995b; Bremner et al., 1995a; Gil et al., 1990; Gilbertson et al., 2001; Golier et al., 2002; Jenkins et al., 1998; Moradi et al., 1999; Sachinvala et al., 2000; Uddo et al., 1993; Vasterling et al., 1998; Yehuda et al., 2004a). Bremner and colleagues (Bremner et al ., 1993; Bremner et al., 1995b; Bremner et al., 1995a) reported verbal memory deficits in both combat-related and abuse-related PTSD patients. More importantly, Bremner et al. (1995a) found that these verbal memory deficits were significantly associated with the smaller right hippocampus of PTSD patients, suggesting the possibility of a re lationship between these two phenomena. Other work has reported that PTSD patients have si gnificant attentional impairments, which are believed to be due to a bias for the processing of emotional informa tion and the persistent intrusiveness of memories related to the traumatic ev ent (Bryant & Harvey, 1997; Buckley et al., 2000; Ehlers et al., 2006; Michael et al., 2005; Moradi et al., 2000; Paunovic et al., 2002). Some studies have reported enhanced memory for trauma-related information in PTSD patients (Golier et al., 2003; McNally, 1997), providing support for greater attentional resources de voted to processing emotional, especially trauma-relevant, information in these individuals.

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20 Interactions between the Amygdala and Prefrontal Cortex Extensive work has implicated involvement of the amygdala, an almond-shaped medial temporal lobe struct ure, in the acquisition and expression of fear memories (Fanselow & Gale, 2003; LeDoux, 2003; Mare n et al., 1996; Maren, 2003; McGaugh, 2002; McGaugh, 2004). Inactivation of the amygda la impairs the acquisition of fear conditioning in rodents (Gale et al., 2004; Maren, 1999; Wallace & Rosen, 2001; Wilensky et al., 1999), and people with lesions of the amygdala have difficulty acquiring conditioned fear (LaBar et al., 1995) and recognizing f earful stimuli (Adolphs, 2002; Scott et al., 1997; Wang et al., 2002). Likewise, neuroimaging studies in humans have consistently reported amygdala activation during fear conditioning (Buchel & Dolan, 2000; Cheng et al., 2003; Kni ght et al., 2004; LaBar et al ., 1998). Investigators have speculated that PTSD patients may display abnormal amygdala functioning, which would lead to an aberrant stress response and an enhanced am ygdala-induced augmentation of emotional memories (Elzinga & Bremner, 2002). Several studies have reported amygdala hyperresponsivity in PTSD patients during th e presentation of traumatic scripts and stimuli (Driessen et al., 2004; Hendler et al ., 2003; Liberzon et al ., 1999b; Pissiota et al., 2002; Protopopescu et al., 2005; Rauch et al., 1996; Shin et al ., 1997; Shin et al., 2004a), the presentation of non-trauma-rele vant emotional stimuli (Rauch et al., 2000; Shin et al., 2005; Williams et al., 2006) and during the acqui sition of fear conditioning (Bremner et al., 2005). Others have found a positive relati onship between activation of the amygdala and PTSD symptom severity (Armony et al ., 2005; Protopopescu et al., 2005; Rauch et

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21 al., 1996; Shin et al., 2004a). These findings s uggest an important role of the amygdala in the expression of PTSD symptomatology. The prefrontal cortex (PFC) is located in th e anterior part of th e frontal lobe and is involved in working memory processes, atte ntion, and decision making (Braver et al., 1997; Curtis & D'Esposito, 2003; Funahash i & Kubota, 1994; McCarthy et al., 1996; Postle et al., 2000). This area of the brain ha s been shown to play a major role in more complex cognition, such as the planning and or ganization of behavior (Koechlin et al., 1999; Koechlin et al., 2000; Tanji & Hoshi, 2001). Reciprocal conne ctions between the PFC and amygdala allow for dynamic interact ions between these two brain regions (Amaral & Insausti, 1992; Ghashghaei & Barbas, 2002; McDonald, 1987; McDonald, 1991; Sesack et al., 1989). The PFC allows fo r the inhibition of inappropriate cognitive and emotional responses that are mediated in part by the amygdala (Elzinga & Bremner, 2002). Such a role of the PFC has led resear chers to speculate that PTSD patients may have impaired PFC functioning and that such an impairment may allow for hyperactivity of the amygdala and exaggera ted emotional responsiveness. In agreement with this hypothesis, several studies have shown that PTSD patients have a smaller volume of major regions of the PFC (e.g., anterior cingulat e cortex, medial frontal gyrus) (Carrion et al., 2001; De Bellis et al., 2002; Fennema-Notestine et al., 2002; Rauch et al., 2003; Woodward et al., 2006b; Yamasue et al., 2003) and perform more poorly on tasks dependent upon an intact PFC (Koenen et al., 2001). In addition, the PFC is involved in the extinction of fear memories. Animal studies have shown that lesions of the medi al PFC impair the extinction of conditioned

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22 fear (Lebron et al., 2004), while stimulation of this area facilitates this process (Milad et al., 2004). Research has shown that PTSD patient s are impaired at extinguishing fear (Orr et al., 2000; Peri et al., 2000) and demonstrate reduced act ivity of PFC regions during extinction trials (Bremner et al., 2005). Moreover, these i ndividuals exhibit less activity of, or a complete failure to activate, PFC brain regions during the pr esentation of traumarelevant stimuli (Bremner, 1999; Bremner et al., 1999; Britton et al., 2005; Lanius et al., 2001; Lindauer et al., 2004a; Shin et al., 1999; Shin et al., 2004a). In theory, reduced activation of the PFC, in conjunction with amygdala hyperactivity, could promote the intrusive emotional thoughts and memories th at PTSD patients ofte n experience. Such a system could lead to greater governance of behavior by lower brain areas, such as the amygdala and hypothalamus, rather than the pr efrontal areas, which allow for adaptation, behavioral flexibility and coherent cognitive processing. Pharmacotherapy for Post-Traumatic Stress Disorder Selective Serotonin Reuptake Inhibitors The fact that a subset of people with PTSD exhibit significant improvement in some of their symptoms following treatment w ith selective serotonin reuptake inhibitors (SSRIs) suggests a role of th e serotonergic system in this disorder (Asnis et al., 2004; Davidson, 2003; Davis et al., 2006; Hidalgo & Davidson, 2000; Ipser et al., 2006; Stein et al., 2006). Research has shown that several SSRIs, such as fluoxetine, fluvoxamine and citalopram, exert positive e ffects on people with PTSD and lead to significant improvements in quality of lif e (Brady et al., 2000; Brady et al., 1995; Cava ljuga et al., 2003; Connor et al., 1999; Davi dson et al., 2001; De Boer et al., 1992; English et al.,

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23 2006; Escalona et al., 2002; Figgitt & McCl ellan, 2000; Friedman et al., 2007; Londborg et al., 2001; March, 1992; Mart enyi et al., 2002a; Martenyi et al., 2002b; Martenyi & Soldatenkova, 2006; McRae et al., 2004; Meltzer-Brody et al., 2000; Ne ylan et al., 2001; Robert et al., 2006; Schwartz & Rothbaum, 2002; Seedat et al., 2001; Smajkic et al., 2001; Van der Kolk et al., 1994). However, the response rates to SSRIs in PTSD patients rarely exceeds 60%, and full remission from the disorder is achieved following SSRI treatment only 20-30% of the time (Stein et al., 2002). In addition, SSRIs tend to blunt only the depressive components of PTSD, while having little effect on the memoryand anxiety-related symptoms of the disorder (Asnis et al., 2004; Boehnlein & Kinzie, 2007; Brady et al., 2000; Van der Kolk et al., 1994) Some forms of PTSD, such as combatrelated PTSD, are incredibly resistant to SSRI treatment (Jakovljevic et al., 2003; Rothbaum et al., 2008; Stein et al., 2002). SSRIs are also anxiogenic early in the treatment phase and only exert anxiolytic eff ects after a substantia l delay (Browning et al., 2007; Burghardt et al., 2004; Humble & Wi stedt, 1992). Given the numerous caveats to the efficacy of SSRIs in treating PTSD, there is a need for additional research in people with PTSD and in animal models of th e disorder to facilitate the development of more effective treatments for PTSD. Tricyclic Antidepressants and M onoamine Oxidase Inhibitors Tricyclic antidepressants, named for th eir three-carbon ring molecular structure, inhibit the reuptake of serot onin and NE to varying degrees They also antagonize, to a lesser extent, dopaminergic, histaminergic, adrenergic and cholinergic receptor sites, which often produces an array of adverse se condary side effects (Albucher & Liberzon,

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24 2002). Few randomized, placebo-controlled stud ies have been conducted to assess the effects of tricyclic antidepressants on PTSD but those that have been performed have reported positive effects on PTSD symptoma tology (Bisson, 2007). Some studies found that amitriptyline (Davidson et al., 1990; Davidson et al., 1993) and imipramine (Burstein, 1984; Frank et al., 1988; Kosten et al., 1991) significantly reduced global scores of PTSD severity and were particularly effective in ameliorating the avoidance, intrusion and re-experienci ng symptoms in PTSD patient s. Another study found that desipramine effectively reduced symptoms of depression in PTSD patients but had no effect on the anxiety-related symptoms that are specific to PTSD (Reist et al., 1989). Monoamine oxidase inhibitors (MAOIs) prevent the enzyme monoamine oxidase from breaking down monoamine transmitter substances. This leads to a significant increase in the synaptic release of monoa mines, such as dopamine, norepinephrine, epinephrine and serotonin. Several studies ha ve shown that MAOIs, such as phenelzine (Kosten et al., 1991; Shestatzky et al., 1988), br ofaromine (Baker et al., 1995; Katz et al., 1994) and moclobemide (Neal et al., 1997), are effective in re ducing avoidance, intrusion and hyperarousal symptoms associated with PTSD, and MAOIs appear to be more effective in treating PTSD than tricyclic antidepressants (Albuc her & Liberzon, 2002). Despite the positive effects of tricyclic antidepressants and MAOIs on PTSD symptoms, these agents are rarely used as the first line of tr eatment for PTSD and, instead, are typically only employed when SSR Is are ineffective (A lbucher & Liberzon, 2002). Due to the numerous side effects of both drug classes, the dropout rates for these agents are very high (e.g., 30-50%). Additiona lly, patients who take MAOIs must adhere

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25 to a special low tyramine diet to avoid a potential life-threatening hypertensive crisis. Thus, tricyclic antidepressants and MAOIs, a lthough effective treatments for some PTSD symptoms, are difficult to tolerate and therefore fre quently avoided. Noradrenergic Modulators People with PTSD have significantly elevated baseline le vels of NE and EPI and demonstrate adverse reactions (e.g., panic att acks, flashbacks) to agents that increase adrenergic activity, such as yohimbine. These adrenergic abnormalities are believed to contribute to the hyperarousal, intrusion and avoidance symptoms, as well as the sleep disturbances, that are often reported in PTSD patients (Boehnlein & Kinzie, 2007; Strawn & Geracioti, 2008). Thus, recent work has be gun testing the effect s of pharmacological agents that reduce adrenergic activity on PTSD symptomatology. Some studies have found that propranolol, a -adrenergic receptor antagonist, may be effective in preventing the disorders development (Pitman et al., 2002; Taylor & Cahill, 2002; Vaiva et al., 2003). For instance, Vaiva et al. (2003) found that propranolol treatment shortly after experiencing a traumatic event significantly reduced the incidence and symptoms of PTSD in individuals 2 months later, and Pitman and colleagues (Pitman et al., 2002) reported that post-trauma administration of propranolol ameliorated sympathetic responses to traumatic reminders at a 1-m onth follow-up visit. Additional work has shown that propranolol can effectively reduce PTSD symptoms if administered following the re-experiencing of a trauma (Taylor & Cahill, 2002), suggesting that it may be effective at preventing the reconsolidation of the traumatic memory (Brunet et al., 2008). These findings suggest that pr opranolol may be an effective treatment for PTSD if

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26 administered immediately after the traumatic event or after the re-experiencing of a traumatic event. Other work has shown that clonidine, an 2-adrenergic receptor agonist, and prazosin, an 1-adrenergic receptor antagonist, can signi ficantly ameliorate symptoms of heightened anxiety and hypera rousal in people with PTSD (Boehnlein & Kinzie, 2007). Clonidine works by facilitating 2-adrenergic autoreceptors, which ultimately leads to decreased NE levels. Though many studies have examined the effects of clonidine on PTSD and found it to be effective at reducing intrusive memories and hyperarousal (Harmon & Riggs, 1996; Porter & Bell, 1999; Viola et al., 1997), no randomized, placebo-controlled studies of clonidines effects on PTSD have been performed (Boehnlein & Kinzie, 2007). Prazosin, on the other hand, works by inhibiting postsynaptic 1-adrenergic receptors, which, similar to clonidine, leads to a reduction of NE activity. Recent work has shown that prazosin is an effective treatment for hyperarousal symptoms, intrusive thoughts, recurrent distressing dreams and sleep disturbances in PTSD (Brkanac et al., 2003; Peskind et al., 2003; Raskind et al., 2002; Raskind et al., 2003; Taylor & Raskind, 2002; Taylor et al ., 2006). Collectively, these studies suggest that the reduction of adrenerg ic activity in PTSD patients is an effective approach to ameliorating many of the disorders debilitating symptoms. The Antidepressant Tianeptine Tianeptine is most commonly known to exert antidepressant effects and ameliorate symptoms of MDD, but it has b een shown to have beneficial effects in treating PTSD as well (Onder et al., 2006). Early studies on tianeptines mechanism of

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27 action showed that the drug led to significantly lower extrace llular levels of serotonin, a finding that was hypothesized to result from enhanced serotoni n reuptake (Fattaccini et al., 1990; Labrid et al., 1992; Mennini et al., 1987; Mocaer et al., 1988). However, tianeptines effects on the serotonergic system may be an indirect consequence of the drugs influences on an alternative neurotrans mitter system because later studies failed to show any direct effects of tianeptine on sero tonergic neurotransmission (Pineyro et al., 1995a; Pineyro et al., 1995b). Additionally, rese arch has shown that tianeptine does not alter the density or affinity of any serotonin receptor subtype, and tianeptines affinity for the serotonin transporter is very low (Kat o & Weitsch, 1988; Svenni ngsson et al., 2007). Some have also contested the validity of the original studies on tianeptines mechanism of action based on technical limitations that were present at the time (Malagie et al., 2000). Recently, extensive work has suggested that tianeptines therapeutic effects are more associated with modulation of the glut amatergic system (Brink et al., 2006; Kasper & McEwen, 2008; Zoladz et al., in press) Glutamate is the primary excitatory neurotransmitter of the central nervous system, and one of its roles is to regulate calcium influx by acting on postsynaptic alpha-amino3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and N -methyl-D-aspartate (NMDA) receptors (Riedel et al., 2003). Extensive work has implicated hyperactivity of the glutamatergic system in the deleterious effects of stre ss on brain structure and f unction. Experiments conducted primarily on the hippocampus have shown that stress significantly increases glutamate levels (Bagley & Moghaddam, 1997; Lowy et al., 1993; Lowy et al., 1995; Moghaddam,

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28 1993; Reznikov et al., 2007), inhibits glutamat e uptake (Yang et al., 2005), increases the expression and binding of glutamate receptors (Bartanusz et al., 1995; Krugers et al., 1993; McEwen et al., 2002) and increases calcium currents (J oels et al., 2003). Accordingly, researchers have shown that administration of NMDA receptor antagonists blocks the effects of stress on behavioral, morphological a nd electrophysiological measures of hippocampal function (Kim et al., 1996; Magarinos & McEwen, 1995; Park et al., 2004). Tianeptine appears to protect the hippo campus and prefrontal cortex from the deleterious effects of stress by normaliz ing the stress-induced modulation of glutamatergic activity. Researchers have also shown that tianeptine inhibits the acute stress-induced increase in extra cellular levels of glutamate in the amygdala (Reznikov et al., 2007). In addition to its glutamatergic modulation, tianeptine reduces the expression of CRH mRNA in the amygdala and the bed nucl eus of the stria terminalis, a brain region that is highly innervated by amygdala fibe rs (Kim et al., 2006). CRH neurotransmission in both of these regions has been implicated in the expression of anxiety-like behaviors (Holsboer, 1999; Strohle & Holsboer, 2003). Th ese findings suggest that tianeptine could be an effective pharmacological treatment for PTSD. Animal Models of Post-Traumatic Stress Disorder Existing Models of Post-Traumatic Stress Disorder in Rodents Preclinical researchers have used several types of stressors to model aspects of PTSD in rodents (see Stam, 2007b for a review). Such stressors have included electric shock (Garrick et al., 2001; Li et al., 2006; Mild e et al., 2003; Pynoos et al., 1996; Rau et

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29 al., 2005; Sawamura et al., 2004; Servatius et al., 1995; Shimizu et al., 2004; Shimizu et al., 2006; Siegmund & Wotjak, 2007a; Siegm und & Wotjak, 2007b; Wakizono et al., 2007), underwater trauma (Cohen et al., 2004; Richter-Levin, 1998), stress-restress paradigms and single prolonged stress paradigms (Harvey et al., 2003; Khan & Liberzon, 2004; Kohda et al., 2007; Libe rzon et al., 1997; Takahashi et al., 2006) and exposure to predators (Adamec, 1997; Adamec et al., 2007; Adamec et al., 1999; Adamec et al., 2006; Adamec & Shallow, 1993; Blanchard et al., 1998; Park et al., 2001) or predatorrelated cues (Cohen et al., 2000b; Cohen et al ., 2004; Cohen et al., 2006; Cohen et al., 2007; Cohen & Zohar, 2004). The stressors empl oyed in these studies typically produced increased behavioral signs of anxiety, and in some cases, exaggerated startle, cognitive impairments, enhanced fear conditioning a nd reduced social interaction. Although these studies have reported physiol ogical and behavioral changes resembling those observed in people with PTSD, most have utilized only a small set of assessments, such as stressinduced changes in anxiety, without assessing other meas ures common in people with PTSD, such as an impairment in cogniti on. Moreover, many of these studies have evaluated stress-induced changes in responses for a relatively short period of time. Thus, while these studies have provided insight in to how stress or fear conditioning changes aspects of behavior and physio logy, the field would benefit from an animal model of PTSD that takes into account how trauma tic stress produces long-lasting PTSD-like changes in rats given multiple behavioral and physiological diagnostic tests.

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30 Our Laboratorys Recently Developed Animal Model of Post-Traumatic Stress Disorder Our laboratory has developed an animal m odel of PTSD in which rats are exposed to a cat (predator stress) on two separate oc casions, in conjunction with daily social stress, and tested 3 weeks after the second cat exposure (Zoladz et al., 2008). We found that rats stressed in this pa radigm exhibited reduced growth rate, greater adrenal gland weight, reduced thymus weight, heightened anxiety, an exaggerated startle response, impaired hippocampus-dependent memory, greater cardiovascular and corticosterone reactivity to an acute stressor and an exa ggerated physiological and behavioral response to yohimbine. Importantly, all of these phys iological and behavioral abnormalities are commonly observed in people with PTSD. Our animal model of PTSD was develope d to expose rats to conditions which, based on DSM-IV criteria, ar e analogous to conditions th at produce PTSD in people. Specifically, a subset of the DSM-IV criteria for the diagnosis of PTSD includes the following three conditions: (1) PTSD can be triggered by an event that involves threatened death or a threat to ones physical integrity; (2) a person's response to the event involves intense fear, he lplessness or horror; and (3) in the aftermath of the trauma, the person feels as if the traumatic event we re recurring, including a sense of reliving the experience (American Psychiatric Association, 1994). The behaviors that rats exhibit in re sponse to forced exposure to a cat are consistent with the first two components of the DSM-IV criteria for PTSD. That is, rats exhibit an intense fear response when exposed to a predator, which is a condition that is a threat to their survival. In addition, we have observed that rats typically direct their

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31 posture away from the cats gaze, which provides the rat with an element of control over its confrontation with the cat. As control critic ally influences the expression of the stress response, in general (Kim & Diamond, 2002) and a loss of control exacerbates behavioral and physiological re sponses to stress conditions (Amat et al., 2005; Bland et al., 2006; Bland et al., 2007; Kavushansky et al., 2006; Maier et al., 1993; Maier & Watkins, 2005; Shors et al., 1989), we immob ilized the rats during predator exposure. The immobilization component of our animal model, therefore, may provide a rodent analogue to the sense of helplessness and a lo ss of control which feature prominently in the DSM-IV criteria for PTSD. Another component of our model is that rats are exposed to the cat on two occasions, separated by 10 days. PTSD devel ops in some people only after they have repeated traumatic experiences (Resnick et al., 1995; Taylor & Cahill, 2002), and prolonged exposure to trauma increases the likelihood of developing symptoms of PTSD (Gurvits et al., 1996). Therefor e, the repeated inescapable cat exposure was designed to increase the likelihood that the manipulations would produce eff ects in the rats that could be broadly applied to people who develop PTSD as a result of multiple traumatic experiences. In addition, people who develop PT SD in response to only a single trauma experience powerful episodes of anxiety and pani c as a result of their repeated reliving of the trauma through intrusive, flashback memories (Reynolds & Brewin, 1999). As mentioned above, the repeated reliving of the original experience through disturbing intrusive memories is a criterion for the di agnosis of PTSD. The second exposure of the rats to the cat forced them to re-experience the original stress experience, which can be

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32 considered analogous to how people with PTSD re port that they feel as if they relive their original trauma when they have an intrusive memory of the experience. The second reason why the rats were re-expos ed to the cat pertained to the issue of predictability. The first predator expos ure occurred during the light cycle and the second predator exposure occurred during the dark cycle, thereby adding an element of unpredictability as to when the rats might re -experience the traumatic event. A lack of predictability in ones environment is a majo r factor in the development of PTSD, as a means with which to increase the susceptibility of a subset of people to develop PTSD in response to trauma, as well as to influence the later expression of PTSD symptoms (Orr et al., 1990; Regehr et al., 2000; Solom on et al., 1989; Solomon et al., 1988). Lastly, McEwen and colleagues observed increased spine density on dendritic arbors of amygdala neurons 10 days after a si ngle immobilization experience (Mitra et al., 2005). Therefore, the second stress session reinforced stress-induced changes in brain and behavior which were presumably initiate d by the first stress se ssion. In theory, the reinforcement of morphologica l plasticity in the amygdala through a reminder of the original experience would augment the PTSD -like syndrome in psychosocially stressed rats. The strengthening of plasticity in th e amygdala, which may be expressed in a number of different ways, such as dendrit ic hypertrophy (Fuchs et al., 2006; McEwen & Chattarji, 2004; Mitra et al., 2005; Vyas et al., 2002; Vyas et al., 2003; Vyas et al., 2006) or as stress-induced long-term potenti ation (Kavushansky & Richter-Levin, 2006; Manzanares et al., 2005; Vouimba et al., 2004; Vouimba et al., 2006), lends itself to experimentation via pharmacological manipulatio ns of the reconsolidation process, which

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33 is likely to occur in response to traumatic memory reca ll (Cai et al., 2006; Debiec et al., 2002; Debiec & LeDoux, 2004; Debiec & LeDoux, 2006; Maroun & Akirav, 2008; Nader et al., 2000; Przybyslaw ski et al., 1999; Przybyslawski & Sara, 1997; Sara, 2000; Suzuki et al., 2004). In addition to the two acute cat exposu res, we included chronic unstable housing conditions in the psychosocial stress paradigm to mimic the lack of social support and chronic mild stress experienced by people with PTSD (Andrews et al., 2003; Boscarino, 1995; Brewin et al., 2000; Solomon et al., 1989; Ullman & Filipas, 2001). We hypothesized that the daily anxiety produced by unstable housing would exacerbate any adverse effects on the rats induced by predator exposure, alone. This hypothesis was supported by our finding that th e combination of two cat exposur es with social instability produced greater anxiogenic effects on rat beha vior than either manipulation in isolation. Chronic social instability, alone, had no negative effects on behavior and may have even been beneficial for rats, as it led to a sma ll increase in growth rate and significantly greater motor activity on th e elevated plus maze. In sum, the primary goal of this preliminary work was to develop an animal model of PTSD based on the factors that are known to be involved in the etiology and persistence of PTSD symptoms in people. To accomplish this goal, we combined a lifethreatening stress experience (i.e., unavoidable predator ex posure) with a re-experiencing of the trauma and chronic social instability, all of which are well-described risk factors for PTSD. This approach enabled us to produce an animal model that targets the subset of people who actually develop PTSD in response to trauma and affords us the opportunity

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34 to explore the mechanisms responsible for the effects of traumatic stress on brain and behavior. Purpose of the Present Experiments The purpose of the present experiments was to further examine the neurobiological mechanisms responsible fo r the PTSD-like seque lae induced by our laboratorys animal model and to explore th e longevity of the effects induced by our chronic psychosocial stress paradigm. Specifical ly, the present set of experiments were designed to 1) test the h ypothesis that our animal m odel of PTSD would produce abnormalities in glucocorticoid levels that are comparable to those observed in people with PTSD, 2) examine the abil ity of antidepressant and anxiol ytic agents to ameliorate the PTSD-like physiological and behavioral symptoms induced by our laboratorys paradigm and 3) ascertain how long the phys iological and behavior al effects of our laboratorys stress regime n could be maintained.

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35 Chapter Two: Experiment One Chronic Psychosocial Stress Produces a Reduc tion in Basal Glucocorticoid Levels in Rats: Further Validation of an Animal Model of PTSD Although findings have been mixed, extens ive work has reported abnormally low baseline levels of cortisol in people with PTSD (for revi ews, see de Kloet et al., 2006; Yehuda, 2002; Yehuda, 2005). Additionally, some (B remner et al., 2003a; Elzinga et al., 2003), but not all (Geracioti et al., 2008), studi es have reported significantly greater stress-induced elevations of cortisol in PTSD patients, relative to control subjects. Therefore, to further validate our laborato rys animal model of PTSD, Experiment One was designed to examine the effects of chr onic psychosocial stress, composed of two acute predator exposures and daily social instability, on baseline and stress-induced serum corticosterone levels in rats. While previous studies in our laboratory have examined rat serum corticosterone levels following the proposed stress paradigm (Zoladz et al., 2008), these studies did not obtain undisturbed, baseline measures of corticosterone from psychosocially stressed animals. In each case, the rats were transported to the laboratory, and in some cases injected, pr ior to blood sampling, which could have induced a stress response in the rats. Moreover, the rats in these studies had been exposed to several behavioral assessments on the days prior to blood sampling. Both of these factors could have hindered an accurate interp retation of the data. Therefore, in order to obtain undisturbed, baseline measures of cortic osterone, the rats in the present study were

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36 exposed to only one endpoint manipulati on, which was blood sampling, and the first blood sample was obtained immediately afte r removing the rats from their housing rooms. In light of the PTSD literature, I hypothesized that rats exposed to chronic psychosocial stress would display significantl y lower baseline, but significantly greater stress-induced, corticosterone levels th an control (i.e., unstressed) animals. Methods Rats Experimentally nave adult male Spra gue-Dawley rats (225-250 g upon delivery) obtained from Charles River laboratories (Wilmington, Massachusetts) were used for the present experiment. The rats were housed on a 12-hr light/dark schedule (lights on at 0700) in standard Plexiglas cages (two per cag e) with free access to food and water. The colony room temperature and humidity were maintained at 20C and 60%, respectively. Upon arrival, all rats were given 1 week to acclimate to the housing room environment, as well as cage changing procedures, before any experimental manipulations took place. All procedures were approved by the Institutional Animal Care and Use Committee at the Univ ersity of South Florida. Psychosocial Stress Procedure Acute Stress Sessions Following the 1-week acclimation phase, rats were brought to the laboratory, weighed and assigned to psychosocial stress or no psychosocial stress groups (N = 10 rats/group). Rats in the psychosocial stress group were immobilized in plastic DecapiCones (Braintree Sc ientific; Braintree, MA) and placed in a perforated wedge-shaped Plexiglas enclosure (Braintree Scientific; Braintree, MA; 20 x

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37 20 x 8 cm). Then, the rats, still immobili zed in the plastic DecapiCones within the Plexiglas enclosure, were taken to the cat housing room where they were placed in a metal cage (24 x 21 x 20 in) with an adult fema le cat for 1 hour. Th e Plexiglas enclosure prevented any contact between the cat and rats, but the rats were still exposed to all nontactile sensory stimuli associated with the ca t. Canned cat food was smeared on top of the Plexiglas enclosure to direct cat activity towa rd the rats. An hour later, the rats were returned to the laboratory. Ra ts in the no psychosocial st ress group remained in their home cages in the laboratory fo r the 1-hour stress period. Rats were exposed to two acute stress sessions, which were separated by 10 days. The first stress session took place during the light cycle, between 0800 and 1300 hours, and the second stress session took place during the dark cycle, between 1900 and 2100 hours. Daily Social Stress Beginning on the day of the first stress session, rats in the psychosocial stress group were exposed to unstable housing conditions for the next 31 days. Rats in the psychosocial stress group we re still housed two per cage, but every day, their cohort pair combination was changed. Ther efore, no rat in the psychosocial stress group had the same cage mate on two consecutive days during the 31-day stress period. Assessment of Basal and Stress -Induced Glucocorticoid Levels Preparation Twenty days after the second stre ss session, rats in the psychosocial stress and no psychosocial stress groups were brought to the laboratory and weighed. Then, the hind legs of all rats were shaved to allow access to their saphenous veins. The rats were then taken back to the housing r oom and left undisturbed for the remainder of the day. The hind legs of all rats were shav ed 1 day prior to blood sampling to minimize

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38 the amount of time it took the experimenter to obtain baseline blood samples on the following day. Blood Sampling and Post-Mortem Dissection Twenty-four hours later, rats were brought, one cage (i.e., 2 rats) at a time, to a nearby procedure room for blood sampling. Petroleum jelly was applied to each rats hind leg, and the saphenous vein of each rat was punctured with a sterile, 27-gauge syringe needle. A 0.2 cc sample of blood was then collected from each rat in a microcentrifuge tube. The first blood sample was considered a baseline measure of corticosterone and wa s collected within 2 minutes after the rats were removed from the housing room. After obtaining this sample, the rats were immobilized in plastic DecapiCones for 20 mi nutes. Then, the rats were removed from the DecapiCones, and another 0.2 cc sample of blood was collected in a microcentrifuge tube via saphenous vein venipuncture. This blood sample served to examine the hormonal responses of rats to acute immobili zation stress. After co llecting this sample, the rats were returned to th eir home cages. An hour later, one last blood sample (trunk blood) was collected following rapid decapitatio n. This sample was collected to examine the recovery of corticosterone levels fo llowing acute immobilization stress. Following rapid decapitation, the adrenal and thymus gl ands were removed and weighed. Once all of the blood had clotted at room temperat ure, it was centrifuged (3000 rpm for 8 minutes), and the serum was extracted and stored at -80 C until assayed by Monika Fleshner at the University of Colorado at Boulder. Most studies have reported abnormal cortis ol levels in PTSD patients in the early morning hours, when the levels of cortisol reach their peak in people (Brand et al., 2006;

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39 Goenjian et al., 1996; King et al., 2001; Li ndauer et al., 2006; R ohleder et al., 2004; Seedat et al., 2003; Wessa et al., 2006). Since rats are nocturnal, thei r circadian rhythm is reversed (Meaney et al., 1992). Ra ts exhibit very low morning corticosterone levels that slowly rise throughout the day and peak in the early eveni ng hours (e.g., around 1800 hours). Thus, in order to avoid a floor effect and allow room for between-group differences in basal corticosterone levels, as well as to relate the present findings to the PTSD literature, all blood sampling for th is study took place between 1700 and 2000 hours. Statistical Analyses Experimental Design The present study utilized a single factor, between-subjects design. The between-subjects f actor was psychosocial stre ss (psychosocial stress, no psychosocial stress). Growth Rate, Adrenal Gland Weight and Thymus Weight Growth rates, expressed as grams per day (g/day), were cal culated for all rats by dividing their total body weight gained during the course of the experiment by the total number of days in the experiment (i.e., 31 days). The adrena l glands and thymuses were weighed and expressed as milligrams per 100 grams of body weight (mg/100 g b.w.). Independent samples t -tests were used to compare the growth rates, adrenal gland weights and thymus weights between the psychosocial stre ss and no psychosocial stress groups. Corticosterone Levels Since the purpose of the present experiment was to examine whether the proposed animal mode l of PTSD would produce reduced baseline glucocorticoid levels, a planned comparison (independent samples t -test) was used to

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40 compare the baseline corticosterone levels of the psychosocial stress and no psychosocial stress groups. Additionally, a mixed-m odel ANOVA was employed to analyze the corticosterone levels of the psychosocial stress and no psychos ocial stress groups from all three time points. In the ANOVA, psychosocia l stress served as the between-subjects factor, and time point (baseline, stress, retu rn-to-baseline) served as the within-subjects factor. For all statistical analyses, alpha wa s set at 0.05, and Holm-Sidak post hoc comparisons were employed when necessary. Results Growth Rates (see Table 1) The psychosocial stress group tended to disp lay a reduced growth rate, relative to the no psychosocial stress group, but this diffe rence did not reach sta tistical sign ificance, t (18) = 2.02, p = 0.058. Adrenal Gland Weights (see Table 1) The psychosocial stress group exhibited sign ificantly larger adrenal glands than the no psychosocial stress group, indica tive of chronic stress-induced adrenal hypertrophy, t (16) = 4.26, p < 0.001. Thymus Weights (see Table 1) The psychosocial stress group exhibited sign ificantly smaller thymuses than the no psychosocial stress group, indicative of chronic stress-induced suppression of the immune system, t (16) = 2.12, p = 0.05.

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41 Table 1 Growth Rates, Adrenal Gland Weights and Thym us Weights ( SEM) for the Groups in Experiment 1 Growth Rate Adrenal Gland Thymus Weight (g/day) Weight (mg/100 g b.w.) (mg/100 g b.w.) No Psychosocial Stress 4.75 0.26 7.45 0.64 115.18 7.31 Psychosocial Stress 3.72 0.43 10.66 0.44 96.47 4.98 Corticosterone Levels (see Figure 1) A planned comparison indicated that the psychosocial stress group (2.42 0.41 g/dL) displayed significantly lower baseli ne corticosterone levels than the no psychosocial stress group (3.96 0.43 g/dL), t (17) = 2.60, p < 0.05. The mixed-model ANOVA revealed a significant main effect of time point, F (2,32) = 23.19, p < 0.001. Post hoc tests indicated that both groups demonstrated a significant increase in corticosterone levels following 20 minutes of acute immobilization stress and that these levels remained signifi cantly elevated, relative to baseline, 1 hour later ( p s < 0.05). There was no significant ma in effect of psychosocial stress, F (1,16) = 0.85, and the Time Point x Psychosocial Stre ss interaction was not significant, F (2,32) = 0.38 ( ps > 0.05).

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42 Corticosterone ( g/dL) 0 2 4 6 8 10 12 No Psychosocial Stress Psychosocial Stress ImmobilizationHome Cage*Chronic Psychosocial Stress Produced a Reduction of Basal Glucocorticoid Levels0 min20 min 80 min Figure 1 Chronic psychosocial stress produced a reduction of basa l glucocorticoid levels in rats. The data are presented as mean corticosterone levels (g/dL) SEM. = p < 0.05 relative to the no psyc hosocial stress group. Discussion of Findings As expected, psychosocially stressed rats exhibited significantly larger adrenal glands, significantly smaller thymuses and a marginally significan t reduction in growth rate, relative to control rats. Yet, the most important finding of the present experiment is that rats exposed to chronic psychosocial st ress exhibited significantly lower baseline levels of corticosterone than control animals. This differe nce was observed in the early evening hours (i.e., 1700-2000 hours), a time when serum corticosterone levels begin to rise in rats, and is comparable to much of the literature in PTSD pa tients. Several studies have reported abnormally low baseline levels of cortisol in people with PTSD in the early morning hours, when levels of cortisol be gin to rise in humans (Brand et al., 2006; Goenjian et al., 1996; King et al., 2001; Li ndauer et al., 2006; R ohleder et al., 2004;

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43 Seedat et al., 2003; Wessa et al., 2006). However, as indicated above, the findings regarding baseline levels of cortisol in PTSD patients have been mixed, and the presence of abnormally low levels of ba seline cortisol may only be pres ent in a biologic subtype of PTSD (for reviews, see de Kloet et al., 2006; Yehuda, 2002; Yehuda, 2005) If this is the case, then it is important to consider what subtype of PTSD our laboratorys chronic psychosocial stress paradigm is modeling. Si nce abnormally low levels of baseline cortisol have predominantly been reporte d in patients with combat-related PTSD (Boscarino, 1996; Kanter et al., 2001; Thaller et al., 1999; Yehuda et al., 1996b; Yehuda et al., 1993a), it is possible that our stress regimen models a su btype related to that which is caused by exposure to wartime combat. Ho wever, future work must clarify what specific biologic subtypes of PTSD exist be fore such a conclusion can be drawn with certainty. Many animal models have reported that chronic stress, such as daily restraint stress (6 hours/day for 21 days), results in significantly elevated ba seline glucocorticoid levels (Blanchard et al., 1993; Kant et al., 1987; Lepsch et al., 2005; Marin et al., 2007; Mizoguchi et al., 2001; Patterson-Buckenda hl et al., 2001; Touyarot & Sandi, 2002). Few, however, have been shown to produce abnormally low baseline glucocorticoid levels similar to those re ported here. Those animal m odels that have reported significantly reduced baseline glucocorticoid levels have employed either the single prolonged stress paradigm or a stress-restress paradigm consisting of situational reminders of the original stress experience (Diehl et al., 2007; Ha rvey et al., 2003). The single prolonged stress paradigm involves exposing rats to 2 hours of restraint, followed

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44 by 20 minutes of swim stress, which is then terminated with exposure to ether vapors until anesthesia is induced. Investigators have reported that, up to 1 week later, such a paradigm results in abnormally low baseline glucocorticoid levels and enhanced negative feedback of the HPA axis, among other behavi oral impairments (e.g., heightened anxiety, cognitive impairments, exaggerated startle response) (Diehl et al., 2007; Harada et al., 2008; Harvey et al., 2003; Iwamoto et al., 2007 ; Kohda et al., 2007; Liberzon et al., 1997; Takahashi et al., 2006; Wang et al., 2008). The present expe riment therefore extends these findings by demonstrating that simila r HPA axis abnormalities can be produced in rats by exposure to acute predator stress and daily social instability more than 4 weeks after the initial stress experience. Psychosocially stressed rats did not disp lay a greater acute stress-induced increase in corticosterone levels than control animals. This null effect could potentially be due to the time of day during which the blood sample s were collected. Previous work has shown that the stress-induced increase in rodent corticosterone levels is not as robust during the dark cycle as it is during the light cycle (Kant et al., 1986; Yamada & Iwasaki, 1994). Therefore, it is possible that psychosocially stressed animals were limited in the extent to which their corticosterone levels could be increased by immobilizat ion. Additionally, this null finding, although unexpected, is consiste nt with some of the PTSD literature reporting a blunted stress-induced increase in cortisol levels in PTSD patients. For instance, Geracioti et al. (2008) found that combat veterans with PTSD, despite reporting significantly greater levels of anxiety, exhibited a si gnificant reduction of CSF CRH levels and peripheral cortisol levels while watching a trauma-related film. Importantly,

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45 this effect was not observed when the same combat veterans were exposed to a neutral film about oil painting. Some animal models of PTSD have also reported a blunted glucocorticoid response to acute stress in animals that have developed PTSD-like behaviors. Harvey et al. (2006) found that pr eviously-stressed rats exhibited significantly lower corticosterone levels than control animals following 20 minutes of acute swim stress. In addition, Louvart et al. (2005) reported that previously-shocked animals displayed a smaller increase in corticosterone levels in response to a situational reminder of the shock than controls. Investigators have contended that these findings are a result of stress-induced changes in HPA axis function th at results in enhanced negative feedback inhibition. Thus, in these referenced studies, the same acute stress-induced increase in corticosterone levels that was observed in c ontrol animals would theoretically result in significantly greater glucocorti coid receptor occupancy in pr eviously stressed animals and, ultimately, lead to a much greater s uppression of their corticosterone levels. The findings of Experiment One indicate that the our laboratorys animal model of PTSD, composed of two acute predator exposures and daily social instability, produces changes in HPA axis functioning that are co mparable to those observed in people with PTSD. Specifically, rats exposed to this ch ronic psychosocial stress paradigm exhibited significantly lower baseline gluc ocorticoid levels than contro l animals, and this effect was observed at a time of the circadian rhyt hm during which similar effects have been reported in PTSD patients. Therefore, this study provides further validation of our laboratorys animal model of PTSD and prom otes its use to further investigate the mechanisms underlying trauma-induced changes in brain and behavior.

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46 Chapter Three: Experiment Two Chronic Psychosocial Stress Results in Enhan ced Suppression of Corticosterone Levels following Dexamethasone Administration: Ev idence for Enhanced Negative Feedback of the Hypothalamus-Pituitary-Adrenal Axis Extensive work has suggested that peopl e with PTSD may exhibit abnormally low baseline levels of cortisol due to the presen ce of enhanced negative feedback of the HPA axis (de Kloet et al., 2006). Several studies have found that PTSD patients have an increased number and sensitivity of glucocor ticoid receptors (Rohleder et al., 2004; Stein et al., 1997b; Yehuda et al., 1991; Yehuda et al., 1993a; Yehuda et al., 1995). In addition, a majority of the PTSD literature has reported an increased suppression of cortisol and ACTH in people with PTSD following the administration of dexamethasone, a synthetic glucocorticoid (Duval et al., 2004; Goenjian et al., 1996; Grossman et al., 2003; Newport et al., 2004; Stein et al., 1997b; Yehuda et al., 1993b; Yehuda et al., 1995; Yehuda et al., 2002; Yehuda et al., 2004b). These findings suggest that dexamethasone results in greater negative feedback inhibition of the HPA axis presumably due to the presence of more glucocorticoid receptors, in PTSD patients, which leads to a greater suppression of cortisol and ACTH in these individuals. Taking these findings into consideration, Experiment Two was designed to examine th e effects of chronic psychosocial stress, composed of two acute predator exposu res and daily social instability, on the corticosterone response in rats to the dexa methasone suppression test. I hypothesized that

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47 psychosocially stressed rats would exhibit a significantly gr eater suppression of corticosterone levels than control rats following the administration of dexamethasone. Methods Rats The same weight range and strain of rats as well as the housing conditions, that were employed in Experiment One were used in the present experime nt. Upon arrival, all rats were given 1 week to acclimate to the housing room environment and cage changing procedures before any experimental mani pulations took place. All procedures were approved by the Institutional Animal Care a nd Use Committee at the University of South Florida. Psychosocial Stress Procedure Following the 1-week acclimation phase, rats were brought to the laboratory, weighed and assigned to psychosocial stress or no psychosocial stress groups (N = 40 rats/group). Afterwards, each group of rats was exposed to the same respective manipulations that were utilized in Experime nt One. That is, rats in the psychosocial stress group were given two acute cat exposures in conjunction with daily social stress, while rats in the no psychosocial stress group were give n two laboratory exposures (remaining in their home cages) and had the same cage mates throughout the duration of the experiment. Assessment of Post-Dexamethasone Basal and Stress-Induced Glucocorticoid Levels Preparation Twenty days after the second stre ss session, rats in the psychosocial stress and no psychosocial stress groups we re brought to the laboratory and weighed. As

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48 in Experiment One, the hind legs of all rats were then shaved to allow access to their saphenous veins. The rats were then taken b ack to the housing room and left undisturbed for the remainder of the day. Pharmacological Manipulations On the following day, between 1100 and 1400 hours, rats were taken to th e procedure room, one cage at a time, where they were administered subcutaneous (s.c.) injections of dexamethasone (10 g/kg, 25 g/kg, 50 g/kg) or vehicle at a volume of 1 ml/kg. These doses were chosen because previous work indicated that they produced a modest suppression of corticosterone levels in control rats (Lurie et al., 1989). Ten rats from each of the psychosocial stress and no psychosocial stress groups were ra ndomly assigned to receive s.c. injectio ns of one of the three doses of dexamethasone or the vehicle solution, for a total of 10 rats per group. Dexamethasone (Sigma-Aldrich, St. Louis, MO) was dissolved in a vehicle solution consisting of sodium sulfite (1 mg/ml) and sodium citrate (19.4 mg /ml), which were both dissolved in distilled water. Immediately following the administration of dexamethasone or vehicle, the rats were returned to th e housing room until the commencement of blood sampling. Blood Sampling and Post-Mortem Dissection Six hours following dexamethasone or vehicle administration, th ree blood samples (baseline, stress and return-to-baseline) were obtai ned from all rats, following th e procedures utilized in Experiment One. Following rapid decapitati on, the adrenal and thymus glands were removed and weighed. All blood sampling took place between 1700 and 2100 hours. Once all of the blood had clotted at room te mperature, it was centrifuged (3000 rpm for 8

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49 minutes), and the serum was extracted and stored at -80 C until assayed by Monika Fleshner at the University of Colorado at Boulder. Statistical Analyses Experimental Design The present study utilized a between-subjects, 2 x 4 factorial design. The between-subjects factor s were psychosocial stress (psychosocial stress, no psychosocial stress) a nd dexamethasone (vehicle and 10 g/kg, 25 g/kg or 50 g/kg of dexamethasone). Growth Rate, Adrenal Gland Weights and Thymus Weights Growth rates, expressed as grams per day (g/day), were cal culated for all rats by dividing their total body weight gained during the course of the experiment by the total number of days in the experiment (i.e., 31 days). The adrena l glands and thymuses were weighed and expressed as milligrams per 100 grams of body weight (mg/100 g b.w.). Two-way ANOVAs were used to analyze the growth rates, adrenal gland weights and thymus weights, with psychosocial stress and dexa methasone serving as the between-subjects factors in each case. Corticosterone Levels A mixed-model ANOVA was employed to analyze the corticosterone levels of all groups fr om the three time points. In the ANOVA, psychosocial stress and dexamethasone served as the between-subjects factors, and time point (baseline, stress, return-to-baseline) served as the within-subjects factor. For all statistical analyses, alpha wa s set at 0.05, and Holm-Sidak post hoc comparisons were employed when necessary. Since dexamethasone administration took place on the final day of the experiment, it was predicted that the drug would have no

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50 effect on growth rate and adrenal gland or t hymus weights. As this was confirmed via the statistical analyses below, Table 2 presents th e predicted effects of psychosocial stress on growth rate and adrenal gland and thymus we ights, collapsed across all drug conditions. Results Growth Rates (see Table 2) The growth rate analysis revealed a signi ficant main effect of psychosocial stress, F (1,72) = 9.67, p < 0.01, indicating that the psychosocia l stress group had a significantly lower growth rate than the no psychosocial stress group. There was no significant main effect of dexamethasone, F (3,72) = 1.80, and the Psychosocial Stress x Dexamethasone interaction was not significant, F (3,72) = 1.01 ( ps > 0.05). Adrenal Gland Weights (see Table 2) The analysis of adrenal gland weights revealed a significant main effect of psychosocial stress, F (1,72) = 8.42, p < 0.01, indicating that the psychosocial stress group had significantly larger adre nal glands than the no psyc hosocial stress group. There was no significant main effect of dexamethasone, F (3,72) = 1.56, and the Psychosocial Stress x Dexamethasone interac tion was not significant, F (3,72) = 0.03 ( ps > 0.05). Thymus Weights (see Table 2) The analysis of thymus wei ghts revealed a significant main effect of psychosocial stress, F (1,70) = 35.89, p < 0.001, indicating that the ps ychosocial stress group had significantly smaller thymuses than the no psychosocial stress group. There was no significant main effect of dexamethasone, F (3,70) = 2.67, and the Ps ychosocial Stress x Dexamethasone interaction was not significant, F (3,70) = 1.77 ( ps > 0.05).

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51 Table 2 Growth Rates, Adrenal Gland Weights and Thymus Weights ( SEM) for the Psychosocial Stress and No Psychosocial Stress Groups (collapsed across all dexamethasone conditions) in Experiment 2 Growth Rate Adrenal Gland Thymus Weight (g/day) Weight (mg/100 g b.w.) (mg/100 g b.w.) No Psychosocial Stress 5.39 0.18 9.70 0.39 113.77 3.34 Psychosocial Stress 4.65 0.16 11.32 0.39 90.08 2.59 Corticosterone Levels (See Figures 2 and 3) The mixed-model ANOVA revealed a significant main effect of time point, F (2,126) = 102.31, p < 0.001. Post hoc tests indicated that overall, rats demonstrated a significant increase in corticosterone levels following 20 minutes of acute immobilization stress and that these levels significantly declined, yet remained elevated relative to baseline, 1 hour later ( ps < 0.05). There was also a si gnificant main effect of dexamethasone, F (3,63) = 67.47, p < 0.001. Post hoc tests rev ealed that, as expected, dexamethasone led to a significant reduction in circulating corticos terone levels. More specifically, the rats treated with 10 g/kg or 25 g/kg of dexamethasone displayed significantly lower corticosterone levels than the rats treated with vehicle, and the rats treated with 50 g/kg of dexamethasone exhibited si gnificantly lower corticosterone

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52 levels than the rats treated with vehicle or the two lower doses of dexamethasone. There was no significant main effect of psychosocial stress, F (1,63) = 1.28, p > 0.05. Chronic Psychosocial Stress Increases Sensitivity of th e HPA Axis to Dexamethasone0 min Corticosterone ( g/dL) 0 2 4 6 8 10 12 14 16 18 20 20 min 80 min Immobilization Home Cage* # No Psych Stress Vehicle Psych Stress Vehicle No Psych Stress 10 g/kg Psych Stress 10 g/kg No Psych Stress 25 g/kg Psych Stress 25 g/kg No Psych Stress 50 g/kg Psych Stress 50 g/kg Figure 2 Chronic psychosocial stress increases sensitivity of the HPA axis to dexamethasone. The data are presented as mean corticosterone levels (g/dL) SEM. = p < 0.05 (all dexamethasone-treated groups re lative to the vehicle-treated groups); = p < 0.05 relative to 25 g/kg dexamethasone-treated no psychosocial stress group; # = p < 0.05 relative to 10 g/kg dexamethasone-treated no psychosocial stress group. The Time Point x Dexamethasone, F (6,126) = 8.68, and Time Point x Psychosocial Stress x Dexamethasone, F (6,126) = 4.12, interactions were significant ( ps < 0.001). Post hoc tests indicated that 10 g/kg of dexamethasone did not prevent the acute stress-induced increase in corticosterone levels in either the psychosocial stress or no psychosocial stress groups; however, it did lead to a greater suppression of postimmobilization corticosterone levels in the psychosocial stress group. The administration of 25 g/kg of dexamethasone prevented the acute stress-induced increase in corticosterone levels in the ps ychosocial stress group only. Finally, 50 g/kg of

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53 dexamethasone tended to produce lower baseline and post-immobilization corticosterone levels in the psychosocial stress group, relative to the no ps ychosocial stress group, although these comparisons did not achieve statistical significance ( p s = 0.07). The Time Point x Psychosocial Stress, F (2,126) = 0.92, and Psychosocial Stress x Dexamethasone, F (3,63) = 1.38, interactions were not significant ( ps > 0.05). Vehicle Corticosterone ( g/dL) 0 2 4 6 8 10 12 14 No Psychosocial Stress Psychosocial Stress 0 min20 min 80 min ImmobilizationHome Cage 10 g/kg Dexamethasone Corticosterone ( g/dL) 0 2 4 6 8 10 12 14 No Psychosocial Stress Psychosocial Stress *0 min20 min 80 min ImmobilizationHome Cage 25 g/kg Dexamethasone Corticosterone ( g/dL) 0 2 4 6 8 10 12 14 No Psychosocial Stress Psychosocial Stress 0 min20 min 80 min ImmobilizationHome Cage* 50 g/kg Dexamethasone Corticosterone ( g/dL) 0 2 4 6 8 10 12 14 No Psychosocial Stress Psychosocial Stress 0 min20 min 80 min ImmobilizationHome Cage Effects of Chronic Psychosocial St ress on Corticosterone Responses following Different Doses of Dexamethasone Administration Figure 3 Effects of chronic psyc hosocial stress on corticosterone responses following different doses of dexamethasone. The data ar e presented as mean corticosterone levels (g/dL) SEM. = p < 0.05 relative to the no ps ychosocial stress group; = p = 0.07 relative to the no psyc hosocial stress group.

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54 Discussion of Findings In contrast to Experiment One, vehicle-tr eated psychosocially stressed rats did not display significantly lower baseline corticoste rone levels than vehicle-treated control animals. This null effect is likely due to the f act that rats in the present experiment were not left undisturbed for the entire day lead ing up to blood sampling, as was the case in Experiment One. Rats in the present expe riment were injected 6 hours prior to blood sampling, which could have potentially influenc ed baseline HPA axis functioning for the remainder of the day. As expected, dexamethasone-treated animal s, in general, displayed significantly lower baseline corticosterone levels than vehicle-treated an imals. In addition, relative to vehicle, the two higher doses of dexameth asone significantly blunt ed the immobilizationinduced increase in corticosterone levels and led to significantly lower corticosterone levels in all rats an hour later. As in Expe riment One, psychosocially stressed rats also exhibited significantly larger adrenal gla nds, significantly smaller thymuses and a significant reduction in growth ra te, relative to control rats. The most important finding of the presen t experiment, however, is that chronic psychosocial stress, involving tw o acute predator exposures a nd daily social instability, resulted in enhanced negative feedback se nsitivity to the synt hetic glucocorticoid, dexamethasone. Psychosocially stressed animal s displayed a greater suppression of postdexamethasone corticosterone levels in a doseand time-dependent manner. In response to 10 g/kg of dexamethasone, psychosocially stressed rats exhibite d a greater recovery of corticosterone levels th an controls animals an hour following exposure to 20 minutes

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55 of immobilization. The 25 g/kg dose of dexamethasone prevented the acute immobilization-induced increase in corticostero ne levels in only the psychosocial stress group, and the 50 g/kg dose led to marginally lower corticosterone levels in the psychosocial stress group, relativ e to controls, at baseline and an hour following the 20 minutes of immobilization. These findings suggest that the stress regimen employed in this experiment results in enhanced negativ e feedback inhibition of the HPA axis. More specifically, since the doses of dexamethasone that were used in this study do not cross the blood-brain barrier (Meijer et al., 1998; Sc hinkel et al., 1995), th e findings indicate that this enhanced negative feedback o ccurs at the level of the pituitary gland. These findings are consistent with a major ity of the PTSD literature. A number of studies have reported that PTSD patients ha ve an increased number and sensitivity of glucocorticoid receptors (Rohled er et al., 2004; Stein et al ., 1997b; Yehuda et al., 1991; Yehuda et al., 1993a; Yehuda et al., 1995) a nd display an increased suppression of cortisol and ACTH following the administration of dexame thasone (Duval et al., 2004; Goenjian et al., 1996; Grossman et al., 2003; Newport et al., 2004; Stein et al., 1997b; Yehuda et al., 1993b; Yehuda et al., 1995; Ye huda et al., 2002; Yehuda et al., 2004b). Some studies have also obser ved increased activation of the pituitary gland in PTSD patients following the administration of mety rapone, which investigators believe to be due to the fact that metyrapone removes th e enhanced negative feedback inhibition initially present in these individuals (Otte et al., 2 006; Yehuda et al., 1996a). Collectively, these findings have implicated en hanced negative feedba ck inhibition in the HPA axis abnormalities observed in people with PTSD.

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56 Rarely have investigators tested for th e presence of enhanced negative feedback inhibition of the HPA axis in animal models of PTSD. Only two studies have conducted such assessments. Liberzon et al. (1997) found that rats exposed to a single prolonged stress paradigm subsequently (i.e., 1 week later) exhibited a blunted restraint stressinduced increase in ACTH levels following the administration of cortisol. In addition, similar to the present findings, Kohda et al. ( 2007) reported that rats exposed to a single prolonged stress paradigm subsequently (i.e., 1 week later) exhibite d a blunted restraint stress-induced increase in corticosterone levels following the administration of dexamethasone. Both of these findings suggest that the single prolonged stress paradigm produces changes in HPA axis function that resemble enhanced negative feedback inhibition and are comparable to the present set of data. The commonalities in HPA responses between psychosocially stressed rats from the present studies and traumatized people w ith PTSD further validate the use of this chronic psychosocial stress paradigm to e xplore the mechanisms underlying emotional trauma-induced changes in brain and behavior. Nevertheless, future work concerning the neurobiological bases of the present effects should examine other markers of enhanced negative feedback inhibition of the HPA axis, such as enhanced glucocorticoid receptor expression in key areas of the brain (e.g., an terior pituitary gland, hippocampus). Future studies will also need to explore the e ffect of metyrapone or dexamethasone-CRH challenge paradigms on pituitary function (e .g., ACTH release). Our laboratory already has preliminary data indicating that rats e xposed to the psychosocial stress regimen exhibit significantly greater baseline levels of CRH mRNA in the paraventricular nucleus

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57 of the hypothalamus than control animals ( unpublished findings). This finding suggests that psychosocially stressed rats might al so display abnormally high CRH levels, which would also be consistent with the PTSD literature. Future work, however, must be conducted to verify this hypothesis.

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58 Chapter Four: Experiment Three Differential Effectiveness of the Pharmacological Agents Amitriptyline, Clonidine and Tianeptine in Blocking the PTSD-Like Physio logical and Behavioral Sequelae in Rats A subset of people with PTSD exhibit si gnificant improvement in their symptoms following treatment with SSRIs (Asnis et al ., 2004; Davidson, 2003; Davis et al., 2006; Hidalgo & Davidson, 2000; Ipser et al., 2006; Stei n et al., 2006). At th is time, the SSRIs sertraline and paroxetine are the only two medications that have been approved by the Food and Drug Administration (FDA) for the treatment of PTSD (Albucher & Liberzon, 2002; Barrett et al., 2005; Van der Kolk, 2001; Vaswani et al., 2003). However, SSRIs tend to blunt only the depressive components of PTSD, while having little effect on the memoryand anxiety-related symptoms of th e disorder (Asnis et al., 2004; Boehnlein & Kinzie, 2007; Brady et al., 2000; Van der Kolk et al., 1994). In a ddition, some forms of PTSD, such as combat-related PTSD, are incredibly resistant to SSRI treatment (Jakovljevic et al., 2003; Rothbaum et al., 2008; Stein et al., 2002). They can even produce severe adverse side effects, incl uding sleep disruption, headache, abdominal pain, sexual dysfunction, agita tion, nausea and weight gain, which significantly interfere with an individuals daily life (Asnis et al ., 2004; Boehnlein & Kinzie, 2007; Brady et al., 2000; Van der Kolk et al., 1994). Thus, there is a need for additional pharmacological research in people with PTSD and in animal models of the disorder to facilitate the development of more effective pha rmacotherapy for PTSD patients.

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59 The purpose of Experiment Three was to ascertain whether chronic prophylactic administration of amitriptyline, clonidine and tianeptine would ameliorate the physiological and behavioral sequelae induced by chronic psychosocial stress in rats. Amitriptyline is a tricyclic antidepressant that has been reported to significantly ameliorate many symptoms of PTSD, especially those relate d to intrusion, avoidance and re-experiencing (Davidson et al., 1990; Davidson et al., 1993). Clonidine is an anxiolytic and 2 adrenergic receptor agonist that, via the facilitation of adrenergic autoreceptor activity, leads to a significan t reduction in NE levels throughout the central nervous system. As PTSD is characterized by abnor mally high levels of NE, researchers have contended that clonidine s hould ameliorate many of the symptoms of PTSD, and especially those related to hyperarousal (B oehnlein & Kinzie, 2007). However, as of now, there have been no randomized, placebo-controlled studies on the efficacy of clonidine in treating people with PTSD. The final experimental treatment was tianeptine, an antidepressant. While this agent is most commonly know n to exert antidepressant effects and ameliorate symptoms of majo r depression, it has been shown to have beneficial effects in PTSD patients as we ll (Onder et al., 2006). Moreover, numerous studies in rodents have provi ded support for tianeptines us e in treating stress-related psychopathologies, as it bl ocks the adverse effects of stress on cognitive, electrophysiological, morphological and molecular measures of hippocampal functioning (Diamond et al., 2004; Kasper & McEwen, 2008; McEwen et al., 2002; McEwen & Olie, 2005; Uzbay, 2008). To emphasize that the design of the present experiment had clinical relevance, administration of the pharmacological agents did not begin until the day after

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60 the stress paradigm commenced. Treatment be ginning 24 hours after exposing rats to an intense stressor is potentially relevant to treatment applications begun in people within 24 hours of a traumatic experience and may highli ght the importance of quickly beginning a treatment regimen soon after experiencing intense trauma. Methods Rats The same weight range and strain of rats as well as the housing conditions, that were employed in Experiments One and Two we re used in the pres ent experiment. Upon arrival, all rats were given 1 week to acclimate to the housing room environment and cage changing procedures before any experimental manipulations took place. All procedures were approved by the Institutional Animal Care and Use Committee at the University of South Florida. Psychosocial Stress Procedure PTSD is a disorder of memory, and indi viduals suffering from PTSD experience chronic psychological distress by repeatedly reliving their trauma through intrusive, flashback memories (Ehlers et al., 2004; Hackmann et al., 2004; Reynolds & Brewin, 1998; Reynolds & Brewin, 1999; Speckens et al., 2006; Speckens et al., 2007). Therefore, to incorporate a rat analog of a traumatic memory into our animal model of PTSD, we developed a paradigm to quantify th e memory for the acute cat exposures that are a part of the psychosocial stress procedure (Halonen et al., 2006). This paradigm was included in the psychosocial stress procedure in the present experime nt to assess, during behavioral testing, the long-term me mory of the acute cat exposures.

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61 Following the 1-week acclimation phase, rats were brought to the laboratory and then assigned to psychosocial stress or no psychosocial stress groups (N = 60 rats/group). Afterwards, rats from each group were exposed to a chamber for 3 minutes. During the last 30 seconds of the 3-minute chamber exposure, a 74-dB, 2500 Hz tone was presented to the rats. The chamber ( 25.50 x 30 x 29 cm; Coulbourn Instruments; Allentown, PA) consisted of tw o aluminum sides, an aluminum ceiling, and a Plexiglas front and back. The floor of the chamber c onsisted of 18 stainle ss steel rods, spaced 1.25 cm apart. The rats were not exposed to footshock at any time in the chamber. The sole purpose of exposing rats to th e chamber was to allow rats in the psychosocial stress group to associate the chamber (cont extual fear conditioning) a nd tone [auditory (cue) fear conditioning] with the acute stress experience (i.e., immobilization plus cat exposure) and measure their memory for the experience (v ia an assessment of immobility in the chamber) during behavioral testing. Locomoto r activity in the chamber was measured during the acute stress sessions and behavioral testing by a 24-cell infrared activity monitor (Coulbourn Instruments; Allentown, PA) mounted on the top of the chamber, which used the emitted infrared body heat image (1300 nm) from the animals to detect their movement. Immobility was defined as periods of inactivity lasting at least seven seconds. Following the 3-minute chamber expos ure, rats in the psychosocial stress group were exposed to 1 hour of immobilization during cat exposure (as per the methods in Experiments One and Two), while rats in the no psychosocial stress group remained in their home cages in the laboratory for a yoked period of time. Both groups of rats were weighed following the 1-hour period and then returned to their housing rooms. As per

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62 Experiments One and Two, this entire process (i.e., acute stress sess ion) was repeated 10 days later (during the dark cy cle on Day 11), and beginning with the day of the first stress session, rats in the psychosocial stress group were exposed to unstable housing conditions for the next 31 days. Pharmacological Agents Twenty-four hours after the first stress session (i.e., Day 2), all rats began receiving daily intraperitoneal (i.p.) injections of amitrip tyline (5 or 10 mg/kg), clonidine (0.01 or 0.05 mg/kg), tianeptine (10 mg/kg), or vehicle (dist illed water). The injections occurred every day throughout the 31-day peri od of psychosocial st ress and also during behavioral testing. Drug administration was continued during behavioral testing to prevent withdrawal effects from influencing rat behavior. The injections were always administered in the morning (between 0900 and 1200 hours) at a volume of 1 ml/kg. Ten rats from each of the psychosocial stre ss and no psychosocial stress groups were randomly assigned to each of the drug c onditions, for a total of 10 rats per group. Amitriptyline and clonidine were obtained fr om Sigma-Aldrich (St. Louis, MO), while tianeptine was provided by Servier Pharmaceuticals (France). Behavioral Testing Three weeks after the second stress session (Day 32), rats were given tests to measure their fear memory, anxiety, startle, learning and memory, cardiovascular activity and corticosterone activity. The 3-week delay from the second stress session to behavioral testing was based on comparable time periods employed in other studies on the effects of stress on brain and behavior (Adamec & Shallow, 1993; Cook & Wellman,

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63 2004; Magarinos et al., 1996; McLaughlin et al., 2007; Park et al., 2001 ; Watanabe et al., 1992a; Watanabe et al., 1992c; Watanabe et al., 1992b). Additionally, work from our laboratory has previously shown that the ch ronic psychosocial stress paradigm employed in the present experiment produces significant changes in rat physiology and behavior that can be detected 3 weeks following the s econd stress session (Zoladz et al., 2008). On the first 4 days of behavioral testing (Days 32-35), all rats were taken to the procedure room across from the rat housing rooms, where they received i.p. injections of the drug appropriate to the condition to which they ha d been assigned. Then, they were taken to the laboratory and left undisturbed for 30 minutes before testing began. All behavioral testing took place during the light cycle, between 0800 and 1500 hours. Behavioral Apparatus Contextual and Cue Fear Memory On Day 32, rat behavior in response to the chamber (context test) and tone (cue test) that were previously paired with the acute stress sessions was examined. Rats were placed in the same chamber that they were exposed to during each of the two stress se ssions for 5 minutes, and their immobility was recorded, as per the methods described above. An hour after the 5-minute context test, the rats were placed in a novel chamber that ha d different lighting, wa lls and flooring from that of the chamber in which they were placed during each of the tw o stress sessions. The rats were placed in the novel chamber for a total of 6 minutes (cue test). Three minutes into the cue test, the rats we re presented with a 74-dB, 2500 Hz tone that continuously played for the remainder of the 6-minute testing period. The amount of immobility recorded during the first 3 minutes of the cue test (i.e., no tone) provi ded a measure of the

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64 general fear of a novel place, while the amount of immobility recorded during the last 3 minutes of the cue test (i.e., tone) provided a measure of the fear response to the cue that was, in the psychosocial stress group, speci fically associated w ith the two acute cat exposures. Elevated Plus Maze The elevated plus maze (EPM) is a routine test of anxiety in rodents (Korte & De Boer, 2003) and cons ists of two open arms (10.80 x 50.17 cm) and two closed arms (10.80 x 50.17 cm) that intersect each other to form the shape of a plus sign. On Day 33, the rats were placed on the EPM for 5 minutes, and their behavior was scored by 48 infrared photobeams (located along the perimeter of the open and closed arms), which were connected to a computer program (Motor Monitor, Hamilton-Kinder, San Diego, CA). The primary dependent measures of interest were the amount of time rats spent in the open arms and the number of ambulations made by each rat. An arm entry was scored by the computer program only when a rats entire body had moved from one arm into a new arm (e.g., the entire body of the rat moved from the closed arms into an open arm). Thus, the computer program would begin tallying ope n arm time only after a rat had completely entered an open arm. An ambulation was scored by the computer program each time a rat crossed a photobeam sensor. Thus, the ambulations score consisted of the total number of beam breaks made by each rat during the 5-minute trial and served as a measure of motor activit y. Between each testing session, the EPM was wiped down with a 25% ethanol solution. Startle Response One hour after the EPM assessment, acoustic startle testing was administered. The rats were placed insi de a small Plexiglas box (18.50 x 9.75 x 9.75 cm),

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65 which was inside a larger startle monito r cabinet (Hamilton-Kinder; San Diego, CA; 35.56 x 27.62 x 49.53 cm). The small Plexiglas box within this cabinet contained a sensory transducer on which the rats were placed at the beginning of the trial. The sensory transducer was connected to a com puter (Startle Monitor computer program; Hamilton-Kinder; San Diego, CA), which record ed the startle responses by measuring the maximum amount of force (in Newtons) that ra ts exerted on the sensory transducer for a period of 250 ms after the presentation of each auditory stimulus. To control for any differences in body weight, the sensitivity of th e sensory transducer was adjusted prior to each trial via a Vernier adjust ment with a sensitivity range of 0-7 arbitrary units. The startle trial began with a 5-minute acclima tion period, followed by the presentation of 24 bursts of white noise (50 ms each), eight from each of three auditory intensities (90, 100, and 110 dB). The noise bursts we re presented in sequential or der (i.e. eight bursts at 90 dB, followed by eight bursts at 100 dB, followed by eight bursts at 110 dB), and the time between each noise burst varied pseudora ndomly between 25 and 55 seconds. Upon the commencement of the first noise burst, th e startle apparatus provided uninterrupted background white noise (57 dB). Novel Object Recognition The novel object recognition (NOR) task was a modified version of that which was empl oyed by Baker and Kim (2002). On Day 34, the rats were placed in an open field (Ham ilton-Kinder, San Diego, CA 40 x 47 x 70 cm) for 5 minutes to acclimate to the environm ent. Their behavior was monitored by a Logitech camera that was mounted on the ceiling overlooking the open field. This camera was connected to a computer program known as ANY-Maze (Stoelting; Wood Dale, IL),

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66 which scored rat behavior. Twenty-four hours later (Day 35), the rats were placed in the same open field with two identical (plastic/m etal) objects for 5 minut es. The objects were in opposite corners of the open field and secure d to the flooring to prevent the rats from displacing them. The objects were counterbala nced across rats, as were the corners in which the objects were placed. Three hours later, the rats were returned to the open field for a final 5-minute test trial, but this time the open field contained a replica of the object that had been there before and a novel objec t. During this testi ng session, greater time spent by the rats in proximity to the novel versus familiar object was an indication of intact memory for the familiar object. The tim e that each rat spent with the objects during training and testing was quan tified by specifying a 16 cm2 zone around the objects for the ANY-maze software to score the dura tion of investigatory behavior. Preparation for Blood Sampling Immediately following the 3-hour object recognition test, the hind legs of all rats were shaved to allow access to their saphenous veins, as per Experiments One and Two. Blood Sampling and Cardiovascular Activity On the final day of behavioral testing (Day 36), rats were brought, one cage at a time, to a nearby procedure room for blood sampling. Then, baseline and post-stress samples of blood were collected from the rats, as per the methods employed in E xperiments One and Two. Immediately after collecting the post-immo bilization blood sample, the rats were placed in Plexiglas tubes within a warming test chamber to increase th eir body temperature. This enhanced blood flow to their tails, and allow HR and BP to be assessed using a tail cuff fitted with photoelectric sensors (IITC Life Scien ce; Woodland Hills, CA). Once their body

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67 temperature reached approximately 32 C, th ree HR and BP recordings were obtained from each rat (these three recordings were averaged to create single HR and BP data points for each rat). An hour later, one la st blood sample (trunk blood) was collected following rapid decapitation. Then, the adrenal glands and thymuses were removed and weighed. Once all of the blood had clotted at room temperature, it was centrifuged (3000 rpm for 8 minutes), and the serum was extrac ted and stored at 80 C until assayed by Monika Fleshner at the Universi ty of Colorado at Boulder. Statistical Analyses Experimental Design and General Analyses The present study utilized a between-subjects, 2 x 6 factorial design. The independent variables were psychosocial stress (psychosocial stress, no psychosocial stress) and drug (vehicle, amitriptyline 5 and 10 mg/kg, clonidine 0.01 and 0.05 mg/kg, ti aneptine 10 mg/kg). In most cases, two-way, between-subjects ANOVAs were us ed to analyze the data from the physiological and behavioral assessments, with psychosocial stress and drug serving as the between-subjects factors. Planned comparisons (independent samples t -tests) were also conducted between groups th at were predicted to differ a priori For all analyses, alpha was set at 0.05, and Holm Sidak post hoc tests were employed when necessary. Fear Memory The amount of immobility from each chamber exposure (Stress Session 1, Stress Session 2, Context Test, Cue Test No Tone, Cue Test Tone) was analyzed separately. The number of fecal boli that rats produced in the chamber was also analyzed for the Context and Cue Tests. For each assessment, two-way, between-subjects

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68 ANOVAs were used to analyze behavior. Ps ychosocial stress and drug served as the between-subjects factors in each case. Elevated Plus Maze The amount of time that rats spent in the open arms of the EPM was calculated as a percent of the total tr ial time. The percent time that rats spent in the open arms, as well as the number of ambulations that rats made on the EPM were analyzed with two-way, between-subject s ANOVAs. Each of these analyses was performed for the entire 5-minut e testing trial and for the first minute of the testing trial, with psychosocial stress and drug serving as the between-subjects factors in each case. Startle Response Startle responses to each of the three auditory stimulus intensities (90, 100 and 110 dB) were analyz ed separately. In each case, two-way, between-subjects ANOVAs were employed to an alyze the data, with psychosocial stress and drug serving as the be tween-subjects factors. Novel Object Recognition For habituation, a two-way, between-subjects ANOVA was used to compare overall locomotor ac tivity across all groups with psychosocial stress and drug serving as the between-subjec ts factors. The amount of time that rats spent in each area of the open field during th e habituation phase was also analyzed to assure that the rats did not display a pr eference for one area of the open field over another. For the analysis, the open field was divided into four square quadrants via the ANY-Maze computer program. The amount of ti me that rats spent in each of the quadrants was analyzed with a mixed-mode l ANOVA, with psychosocial stress and drug serving as the between-subjects factors and ti me spent in each quadrant serving as the within-subjects factor. Fo r training, paired samples t -tests were first conducted to

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69 determine whether the rats within each gr oup spent a comparable amount of time with each object replica (to rule out object preferen ce effects). Then, the to tal time that rats spent with both object replicas during trai ning was compared across groups by using twoway, between-subjects ANOVAs, with psyc hosocial stress and dr ug serving as the between-subjects factors. For testing, a ra tio time score was calculated for each group by taking the time that rats spent with the novel object and dividing it by the time that rats spent with the familiar object (i.e., ratio time = time with novel object / time with familiar object). The ratio times were compared across groups by utilizing two-way, betweensubjects ANOVAs, with psychosocial stress and drug again serving as the betweensubjects factors. This was performed for the entire 5-minute testing trial and for the first minute of the testing trial. Corticosterone Levels A mixed-model ANOVA was used to analyze corticosterone levels at the three time points. Psychosocial st ress and drug served as the between-subjects factors, and tim e point (baseline, stress, re turn-to-baseline) served as the within-subjects factor. Heart Rate and Blood Pressure The HR, systolic BP and diastolic BP data were analyzed with two-way, between-subjects ANOVAs, with psychosocial stress and drug serving as the between-subjects factors. Growth Rates, Adrenal Gland Weights and Thymus Weights Growth rates, expressed as grams per day (g/day), were cal culated for all rats by dividing their total body weight gained during the course of the experiment by the total number of days in the experiment (i.e., 31 days). The adrena l glands and thymuses were weighed and

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70 expressed as milligrams per 100 grams of body weight (mg/100 g b.w.). Two-way, between-subjects ANOVAs were used to analy ze the growth rates, adrenal gland weights and thymus weights, with psychosocial stre ss and drug serving as the between-subjects factors in each case. Results Fear Memory Stress Session One (see Figure 4) For the analysis of immobility during the 3minute chamber exposure during stress sessi on one, there were no significant main effects of psychosocial stress, F (1,104) = 0.48, or drug, F (5,104) = 0.84, and the Psychosocial Stress x Drug inte raction was not significant, F (5,104) = 1.13 ( ps > 0.05). Amount of Immobility upon Chamber Exposure During Stress Session 1VEH % Immobility 0 20 40 60 80 No Psychosocial Stress Psychosocial Stress AMI-5AMI-10C-0.01C-0.05TIA-10 Figure 4 Amount of immobility during the 3-minute chamber exposure during stress session one. The data are presented as mean percent immobility SEM. Stress Session Two (see Figure 5) For the analysis of immobility during the 3minute chamber exposure during st ress session two, there was a significant main effect of

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71 psychosocial stress, indicating that the ps ychosocial stress groups spent significantly more time immobile than the no psychosocial stress groups, F (1,103) = 7.55, p < 0.01. There was no significant main effect of drug, F (5,103) = 0.48, and the Psychosocial Stress x Drug interaction was not significant, F (5,103) = 0.96 ( ps > 0.05). Planned comparisons were also conducted between groups that were predicted to differ a priori The vehicle-treated psychosoc ial stress group spent signifi cantly more time immobile than the vehicle-treated no psychosocial stress group, t (17) = 2.73, p < 0.05. Groups of psychosocially stressed rats that were treated with 0.01, t (18) = 2.19, or 0.05, t (16) = 2.26, of clonidine were the only other psyc hosocial stress groups that displayed significantly greater imm obility than their resp ective control groups ( ps < 0.05). Amount of Immobility upon Chamber Exposure During Stress Session 2VEH % Immobility 0 20 40 60 80 No Psychosocial Stress Psychosocial Stress AMI-5AMI-10C-0.01C-0.05TIA-10* * * Figure 5 Amount of immobility during the 3-minute chamber exposure during stress session two. The data are presented as mean percent immobility SEM. = p < 0.05 relative to the vehicle-treate d no psychosocial stress group; = p < 0.05 relative to the respective drug-treated no psychosocial stress group.

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72 Effects of Chronic Psychosocial Stress and Drug Treatment on Immobility during the Context TestVEH % Immobility 0 20 40 60 80 No Psychosocial Stress Psychosocial Stress AMI-5AMI-10C-0.01C-0.05TIA-10* Figure 6 Effects of chronic psychosocial stress and drug treatment on immobility during the 5-minute context test. The data are presen ted as mean percent immobility SEM. = p < 0.05 relative to the vehicle-tr eated no psychosocial stress group; = p < 0.05 relative to the vehicle-treated psychosocial stress group; = p < 0.05 relative to the respective drug-treated no psyc hosocial stress group. Context Test Immobility (see Figure 6) For the analysis of immobility during the 5-minute context test, there were signifi cant main effects of psychosocial stress, F (1,97) = 11.96, and drug, F (5,97) = 3.90, and the Psychosocial Stress x Drug interaction was significant, F (5,97) = 2.56 ( ps < 0.05). Post hoc tests indicated that the vehicle-treated psychosocial stress group spent significantly mo re time immobile than the vehicle-treated no psychosocial stress group. Chronic treatment with 5 or 10 mg/kg of amitriptyline or 10 mg/kg of tianeptine in groups that were ps ychosocially stressed prevented the chronic stress-induced increase in immobility, as evid enced by significantly less immobility than the vehicle-treated psychosocial stress group and a lack of statisti cal significance relative

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73 to each of the groups respect ive drug-treated no psychosocial stress group. The group of psychosocially stressed rats treated with 0.01 mg/kg of clonidine also did not exhibit significantly greater i mmobility than its respective dr ug-treated control group; however, the amount of immobility displayed by this grou p was not statistically different from that of the vehicle-treated psychosocial stress group. Context Test Fecal Boli (see Figure 7) The analysis of fecal boli produced during the context test revealed significant main effects of psychosocial stress, F (1,97) = 15.45, and drug, F (5,97) = 4.09 ( ps < 0.01). The psychosocial stress groups produced significantly more fecal boli than the no psyc hosocial stress groups, and groups that were treated with 5 mg/kg of amitr iptyline produced significantly more fecal boli than groups that were treated with 10 mg/kg of amitripty line or tianeptine. The Psychosocial Stress x Drug interaction was not significant, F (5,97) = 0.87, p > 0.05. Planned comparisons were also conducted between groups th at were predicted to differ a priori The vehicle-treated psychosocial stress group produced significantly more fecal boli than the vehicle-treated no psychosocial stress group, t (17) = 2.81, p < 0.05. Chronic treatment with 10 mg/kg of amitriptyline, 0.01 mg/kg of clonidine or 10 mg/kg of tianeptine in groups that were psychosocially stressed preven ted the stress-induced increase in fecal boli, as evidenced by the presence of significantly fewer fecal boli deposits than the vehicle-treated psychosocial stress group and a lack of statis tical significance relative to each of the groups respective drug-treated no psychos ocial stress groups. While the group of psychosocially stressed rats treated with 0.05 mg/kg of clonidine did not defecate more than the vehicle-treated control animals, t (17) = 1.14, p > 0.05, they did produce

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74 significantly more fecal boli than th eir respective drug-treated controls, t (18) = 2.40, p < 0.05. Effects of Chronic Psychosocial Stress and Drug Treatment on Fecal Boli Produced during the Context TestVEH Fecal Boli 0 1 2 3 4 No Psychosocial Stress Psychosocial Stress AMI-5AMI-10C-0.01C-0.05TIA-10* Figure 7 Effects of chronic ps ychosocial stress and drug treatment on fecal boli produced during the 5-minute context test. The data are presented as mean number of fecal boli SEM. = p < 0.05 relative to the vehicl e-treated no psychosocial stress group; = p < 0.05 relative to the vehicle-tr eated psychosocial stress group; = p < 0.05 relative to the respec tive drug-treated no ps ychosocial stress group. Cue Test Immobility No Tone (i.e., Novel Environment) (see Figure 8) For the analysis of immobility during the first 3 minutes of the cue test, there were significant main effects of psychosocial stress, F (1,100) = 9.40, and drug, F (5,100) = 2.72, and the Psychosocial Stress x Drug in teraction was significant, F (5,100) = 5.73 ( ps < 0.05). Post hoc tests indicated that chronic treatment with 0.05 mg/kg of clonidine in rats that were psychosocially stressed led to significantly greater immobility than all other groups.

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75 Effects of Chronic Psychosocial Stress and Drug Treatment on Immobility in a Novel EnvironmentVEH % Immobility 0 20 40 60 80 No Psychosocial Stress Psychosocial Stress AMI-5AMI-10C-0.01C-0.05TIA-10# Figure 8 Effects of chronic psychosocial stress and drug treatment on immobility during the first 3 minutes of the cue test. The data are presented as mean percent immobility SEM. # = p < 0.05 relative to all other groups. Cue Test Immobility Tone (see Figure 9) For the analysis of immobility during the tone, there was no significant main effect of drug, F (5,100) = 2.02, p > 0.05. There was a significant main effect of psychosocial stress, F (1,100) = 12.04, and the Psychosocial Stress x Drug in teraction was significant, F (5,100) = 2.71 ( ps < 0.05). Post hoc tests indicated that the vehicle-treated psychosocial stress group spent significantly more time immobile than the vehicle-treate d no psychosocial stress group. Additionally, chronic treatment with 10 mg/kg of amitripty line in groups that we re not psychosocially stressed led to significantly greater immobility than the vehicle-treated no psychosocial stress group. Chronic treatment with 5 or 10 mg/kg of amitriptylin e or 10 mg/kg of tianeptine in groups that were psychosocially stressed pr evented the chronic stress-

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76 induced increase in immobility, as evidenced by a lack of statistical significance relative to each of the groups respective drug -treated no psychosocial stress group. Effects of Chronic Psychosocial Stress and Drug Treatment on Immobility during the Cue TestVEH % Immobility 0 20 40 60 80 No Psychosocial Stress Psychosocial Stress AMI-5AMI-10C-0.01C-0.05TIA-10* * * Figure 9 Effects of chronic psychosocial stress and drug treatment on immobility during the tone. The data are presented as mean percent immobility SEM. = p < 0.05 relative to the vehicle-treated no psychosocial stress group; = p < 0.05 relative to the respective drug-treated no psyc hosocial stress group. Cue Test Fecal Boli (see Figure 10) The analysis of fecal boli produced during the cue test revealed a significant ma in effect of psychosocial stress, F (1,100) = 7.34. The psychosocial stress groups produced significantly more fecal boli during the cue test than the no psychosocial stress groups. There was no significant main effect of drug, F (5,100) = 2.19, and the Psychosocial Stress x Dr ug interaction was not significant, F (5,100) = 0.57 ( ps > 0.05). Planned comparisons were also conducted between groups that were predicted to differ a priori There was no significant di fference between the vehicletreated psychosocial stress group and the ve hicle-treated no psychosocial stress group,

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77 t (17) = 1.90, p > 0.05. The psychosocial stress group th at was chronically treated with 0.05 mg/kg of clonidine produced significantly less fecal boli than the vehicle-treated psychosocial stress group, t (18) = 3.36, p < 0.01. Effects of Chronic Psychosocial Stress and Drug Treatment on Boli Produced during the Cue TestVEH Fecal Boli 0 1 2 3 4 5 No Psychosocial Stress Psychosocial Stress AMI-5AMI-10C-0.01C-0.05TIA-10 Figure 10 Effects of chronic psychosocial stress and drug treatment on fecal boli produced during the 6-minute cue test. The data are presented as mean number of fecal boli SEM. = p < 0.05 relative to the vehicle-tr eated psychosocial stress group. Elevated Plus Maze Percent Time in Open Arms, 5-Minute Trial (see Figure 11) For the analysis of percent time in the open arms during the 5-minute trial on the EPM, there were no significant main effects of psychosocial stress, F (1,100) = 2.89, or drug, F (5,100) = 1.14, and the Psychosocial Stress x Drug in teraction was not significant, F (5,100) = 1.16 ( ps > 0.05). Planned comparisons were also conducted between groups that were predicted to differ a priori The vehicle-treated psychosocial stre ss group spent signif icantly less time in the open arms of the EPM than the vehicle-treated no psychosocial stress group, t (15)

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78 = 2.44, p < 0.05. Chronic treatment with 10 mg/kg of amitriptyline, 0.01 or 0.05 mg/kg of clonidine or 10 mg/kg of tianep tine in groups that were psyc hosocially stressed prevented the chronic stress-induced decrease in open arm exploration, as evidenced by the presence of significantly great er percent time spent in th e open arms than the vehicletreated psychosocial stress group or a lack of statistical significance relative to each of the groups respective drug-treated no psychosocial stress group. Effects of Chronic Psychosocial Stress and Drug Treatment on Anxiety on the EPM (5-Minute Trial)VEH % Time Spent in the Open Arms 0 10 20 30 40 50 60 No Psychosocial Stress Psychosocial Stress AMI-5AMI-10C-0.01C-0.05TIA-10* Figure 11 Effects of chronic psychosocial st ress and drug treatment on percent time spent in the open arms during the 5-minute tria l on the elevated plus maze. The data are presented as mean percent time spent in the open arms SEM. = p < 0.05 relative to the vehicle-treated no psychosocial stress group; = p < 0.05 relative to the vehicletreated psychosocial stress group. Percent Time in Open Arms, First Minute (see Figure 12) For the analysis of percent time in the open arms during the firs t minute of the 5-minute trial on the EPM, there was a significant main ef fect of psychosocial stress, F (1,102) = 4.79, and the Psychosocial Stress x Drug in teraction was significant, F (5,102) = 3.03 ( ps < 0.05). The

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79 vehicle-treated psychosocial stress group spent significantly less time in the open arms of the EPM than the vehicle-treated no psychosoc ial stress group. Chronic treatment with 0.01 mg/kg of clonidine in th e group that was not psychos ocially stressed led to significantly less open arm expl oration on the EPM, relative to the vehicle-treated no psychosocial stress group. Chronic treatment w ith 5 or 10 mg/kg of amitriptyline, 0.01 or 0.05 mg/kg of clonidine or 10 mg/kg of tiane ptine in groups that were psychosocially stressed prevented the chronic stress-indu ced decrease in open arm exploration, as evidenced by the presence of significantly gr eater percent time spent in the open arms than the vehicle-treated psychosocial stress group or a lack of statistical significance relative to each of the gr oups respective drug-treated no psychosocial stress group. Effects of Chronic Psychosocial Stress and Drug Treatment on Anxiety on the EPM (First Minute)VEH % Time Spent in the Open Arms 0 20 40 60 80 100 No Psychosocial Stress Psychosocial Stress AMI-5AMI-10C-0.01C-0.05TIA-10* Figure 12 Effects of chronic psychosocial st ress and drug treatment on percent time spent in the open arms during the first minute of the 5-minute trial on the elevated plus maze. The data are presented as mean percent time spent in the open arms SEM. = p < 0.05 relative to the vehicle-treated no psychosocial stress group; = p < 0.05 relative to the vehicle-treated psychosocial stress group.

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80 Effects of Chronic Psychosocial Stress and Drug Treatment on Motor Activity on the EPM (5-Minute Trial)VEH Total Ambulations 0 50 100 150 200 250 300 350 No Psychosocial Stress Psychosocial Stress AMI-5AMI-10C-0.01C-0.05TIA-10* Figure 13 Effects of chronic psychosocial st ress and drug treatment on ambulations made during the 5-minute trial on the elevated plus maze. The data are presented as mean number of ambulations SEM. = p < 0.05 relative to the vehicle-treated no psychosocial stress group. Ambulations, 5-Minute Trial (see Figure 13) For the analysis of ambulations made during the 5-minute trial on the EPM, there was no significant main effect of psychosocial stress, F (1,100) = 3.70, and the Psychosocia l Stress x Drug interaction was not significant, F (5,100) = 0.52 ( ps > 0.05). There was a significant main effect of drug, F (5,100) = 4.48, p < 0.001. Planned comparisons were also conducted between groups that were predicted to differ a priori There was no significant difference between the number of ambulations made by the vehicle-treated psychosocia l stress group and the vehicle-treated no psychosocial stress group on the EPM, t (16) = 0.16, p > 0.05. Chronic treatment with 10 mg/kg of amitriptyline, t (15) = 2.67, or 10 mg/kg of tianeptine, t (16) = 2.38, in groups that were not psychosocially st ressed led to a signifi cantly greater number

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81 of ambulations on the EPM, relative to the vehicle-treated no psychosocial stress group ( ps < 0.05). Effects of Chronic Psychosocial Stress and Drug Treatment on Motor Activity on the EPM (First Minute)VEH Total Ambulations 0 10 20 30 40 50 60 No Psychosocial Stress Psychosocial Stress AMI-5AMI-10C-0.01C-0.05TIA-10* * Figure 14 Effects of chronic psychosocial st ress and drug treatment on ambulations made during the first minute of the 5-minute trial on the elevated plus maze. The data are presented as mean number of ambulations SEM. = p < 0.05 relative to the vehicletreated no psychosocial stress group. Ambulations, First Minute (see Figure 14) For the analysis of ambulations made during the first minute of the 5-minute trial on the EPM, there was no significant main effect of psychosocial stress, F (1,100) = 0.16, and the Psychosocial Stress x Drug interaction was not significant, F (5,100) = 1.57 (ps > 0.05). There was a significant main effect of drug, F (5,100) = 2.43, p < 0.05. Planned comparisons were also conducted between groups that were predicted to differ a priori There was no significant difference between the number of ambulations made by the vehicle-treated psychosocial stress group and the vehicle-treated no ps ychosocial stress group on the EPM, t (16) = 1.37, p >

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82 0.05. Chronic treatment with 5 mg/kg, t (15) = 2.24, or 10 mg/kg, t (15) = 2.96, of amitriptyline in groups that were not psychosocially stressed and 5 mg/kg of amitriptyline, t (15) = 2.24, or 0.01 mg/kg of clonidine, t (16) = 2.16, in groups that were psychosocially stressed led to a significantly greater number of ambulations on the EPM, relative to the vehicle-treate d no psychosocial stress group ( p s < 0.05). Effects of Chronic Psychosocial Stress and Drug Treatment on Startle Response to 90 dB Auditory StimuliVEH Startle Response (Newtons) 0.0 0.1 0.2 0.3 0.4 0.5 No Psychosocial Stress Psychosocial Stress AMI-5AMI-10C-0.01C-0.05TIA-10* Figure 15 Effects of chronic psychosocial stre ss and drug treatment on startle responses to the 90 dB auditory stimuli. The data are presented as mean startle response (Newtons) SEM. = p < 0.05 relative to the vehicle-tr eated no psychosocial stress group; = p < 0.05 relative to the vehicle-trea ted psychosocial stress group. Startle Response 90 dB Auditory Stimuli (see Figure 15) For the analysis of st artle responses to the 90 dB auditory stimuli, there was no signi ficant main effect of psychosocial stress, F (1,102) = 3.40, p > 0.05. There was a significant main effect of drug, F (5,102) = 3.84, and the Psychosocial Stress x Drug interaction was significant, F (5,102) = 2.74 ( ps <

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83 0.05). Post hoc tests indicated that the vehicle-treated psyc hosocial stress group exhibited significantly greater startle responses than the vehicle-treated no psychosocial stress group. Chronic treatment with 5 or 10 mg /kg of amitriptyline, 0.01 or 0.05 mg/kg of clonidine or 10 mg/kg of tianep tine in groups that were psyc hosocially stressed prevented the chronic stress-induced increase in startle response, as evidenced by the presence of significantly lower startle responses than the vehicle-treated psychos ocial stress group or a lack of statistical significance relative to each of the groups respective drug-treated no psychosocial stress group. 100 dB Auditory Stimuli (see Figure 16) For the analysis of startle responses to the 100 dB auditory stimuli, there was no significant main effect of drug, F (5,98) = 1.39, p > 0.05. There was a significant main effect of psychosocial stress, F (1,98) = 7.29, and the Psychosocial Stress x Drug interaction was significant, F (5,98) = 2.32 ( ps < 0.05). Post hoc tests indicated that the vehicl e-treated psychosocial stress group exhibited significantly greater startle responses than the vehicle-treated no psychosocial stress group. Chronic treatment with 10 mg/kg of amitriptyline, 0.05 mg/kg of clonidine or 10 mg/kg of tianeptine in groups that were ps ychosocially stressed prevented the chronic stress-induced increase in startle response, as evidenced by the presence of significantly lower startle responses than the vehicl e-treated psychosocial stress group. The psychosocial stress groups treated with 5 mg/kg of amitriptyline or 0.01 mg/kg of clonidine did not exhibit signi ficantly greater startle respons es than the vehicle-treated control group; however, neith er of the groups displayed significantly lower startle responses than the vehicletreated psychosocial stress gr oup, and the psychosocial stress

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84 group treated with 5 mg/kg of amitriptyline de monstrated significan tly greater startle responses than its respectiv e drug-treated control group. Effects of Chronic Psychosocial Stress and Drug Treatment on Startle Response to 100 dB Auditory StimuliVEH Startle Response (Newtons) 0.0 0.2 0.4 0.6 0.8 1.0 1.2 No Psychosocial Stress Psychosocial Stress AMI-5AMI-10C-0.01C-0.05TIA-10* Figure 16 Effects of chronic psychosocial stre ss and drug treatment on startle responses to the 100 dB auditory stimuli. The data are presented as mean star tle response (Newtons) SEM. = p < 0.05 relative to the vehicle-tr eated no psychosocial stress group; = p < 0.05 relative to the vehicle-trea ted psychosocial stress group; = p < 0.05 relative to the respective drug-treated no psychosocial stress group. 110 dB Auditory Stimuli (see Figure 17) For the analysis of startle responses to the 110 dB auditory stimuli, th ere were no significant main e ffects of psychosocial stress, F (1,100) = 1.42, or drug, F (5,100) = 1.49, and the Psychosocia l Stress x Drug interaction was not significant, F (5,100) = 1.92 (ps > 0.05). Planned comparisons were also conducted between groups that were predicted to differ a priori The vehicle-treated psychosocial stress group tended to exhibit gr eater startle responses than the vehicletreated no psychosocial stress group, although this difference did not achieve statistical

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85 significance, t (16) = 2.06, p = 0.056. Chronic treatment with 5 or 10 mg/kg of amitriptyline, 0.01 or 0.05 mg/kg of clonidine or 10 mg/kg of tianeptine in groups that were psychosocially stressed prevented this marginally significant, chronic stress-induced increase in startle response, as evidenced by the presence of significantly lower startle responses than the vehicle-tr eated psychosocial stress group or a lack of statistical significance relative to each of the groups respective drugtreated no psychosocial stress group. Effects of Chronic Psychosocial Stress and Drug Treatment on Startle Response to 110 dB Auditory StimuliVEH Startle Response (Newtons) 0.0 0.5 1.0 1.5 2.0 2.5 3.0 No Psychosocial Stress Psychosocial Stress AMI-5AMI-10C-0.01C-0.05TIA-10* Figure 17 Effects of chronic psychosocial stre ss and drug treatment on startle responses to the 110 dB auditory stimuli. The data are presented as mean star tle response (Newtons) SEM. = p < 0.056 relative to the vehicle-trea ted no psychosocial stress group; = p < 0.05 relative to the vehicle-trea ted psychosocial stress group. Novel Object Recognition Habituation (see Figure 18) The analysis of locomoto r activity in the open field during the 5-minute habituation phase revealed significant main effects of psychosocial stress, F (1,104) = 8.25, and drug, F (5,104) = 9.27 ( ps < 0.01). In genera l, rats that had

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86 been psychosocially stressed traveled significan tly less distance in the open field than rats that had not been psychosoci ally stressed. In addition, rats that were treated with 0.05 mg/kg of clonidine, independe nt of psychosocial stress, traveled significantly less distance than all other groups. The Psychos ocial Stress x Drug interaction was not significant, F (5,104) = 0.40, p > 0.05. Effects of Chronic Psychosocial Stress and Drug Treatment on Locomotor Activity during OR HabituationVEH Distance Traveled (m) 0 2 4 6 8 10 No Psychosocial Stress Psychosocial Stress AMI-5AMI-10C-0.01C-0.05TIA-10# # Figure 18 Effects of chronic psychosocial stress and drug treatment on locomotor activity during the 5-minute object recognition habituation period. The data are presented as mean distance traveled (m) SEM. # = p < 0.05 relative to all groups that were not treated with 0.05 mg/kg of clonidine. The analysis of time that the rats spent in each area of the open field revealed no significant main effect of quadrant, F (3,309) = 1.26, psychosocial stress, F (1,103) = 0.54, or drug, F (5,103) = 1.00, and the Quadrant x Psychosocial Stress, F (3,309) = 2.54, Quadrant x Drug, F (15,309) = 1.33, Psychosocial Stress x Drug, F (5,103) = 0.43, and Quadrant x Psychosocial Stress x Drug, F (15,309) = 1.61, interactions were not significant ( ps > 0.05; data not shown).

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87 Table 3 Time (seconds SEM) Spent with Each Ob ject during Object R ecognition Training for all Groups in Experiment 3 Paired t -test Object 1 Object 2 = p < 0.05 No Psychosocial Stress Vehicle 10.54 1.89 9.87 1.19 t (9) = 0.03 5 mg/kg Amitriptyline 5.87 0.88 6.26 1.50 t (9) = 0.37 10 mg/kg Amitriptyline 9.03 2.37 7.77 1.29 t (9) = 0.46 0.01 mg/kg Clonidine 11.85 1.94 7.13 0.85 t (9) = 2.78* 0.05 mg/kg Clonidine 6.70 1.89 9.55 2.90 t (9) = 0.83 Tianeptine 8.07 1.50 9.76 0.98 t (9) = 0.84 Psychosocial Stress Vehicle 6.31 1.38 13.88 5.32 t (9) = 1.34 5 mg/kg Amitriptyline 5.90 0.91 9.46 1.63 t (9) = 1.86 10 mg/kg Amitriptyline 8.41 1.12 9.53 2.82 t (9) = 0.36 0.01 mg/kg Clonidine 7.80 1.30 6.32 0.87 t (9) = 1.02 0.05 mg/kg Clonidine 12.20 3.30 5.05 1.91 t (9) = 1.55 Tianeptine 7.40 1.49 6.38 0.96 t (9) = 0.93 Training (see Table 3) Within-group comparisons indicated that most groups spent a comparable amount of time with each of the objects that were placed in the open

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88 field during object recognition tr aining (see Table 3), suggesti ng that no object preference effects were present. Only one group, the 0.01 mg/kg clonidine-tr eated no psychosocial stress group, spent more time with one object than the othe r. A between-groups comparison of the total amount of time spent with both objects during training revealed no significant main effects of psychosocial stress, F (1,103) = 0.27, or drug, F (5,103) = 0.82, and the Psychosocial Stress x Drug interaction was not significant, F (5,103) = 0.99 ( ps > 0.05; data not shown). These findings in dicated that all groups spent a comparable amount of time with bot h objects during training. Effects of Chronic Psychosocial Stress and Drug Treatment on Object Recognition Memory (5-Minute Trial)VEH Ratio Time 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 No Psychosocial Stress Psychosocial Stress AMI-5AMI-10C-0.01C-0.05TIA-10 Figure 19 Effects of chronic psychosocial stress and drug treatment on object recognition memory during the entire 5-minute testing trial. The da ta are presented as mean ratio time SEM. Testing, 5-Minute Trial (see Figure 19) The analysis comparing the ratio times of all groups during the 5-minute object recognition testing session revealed no significant

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89 main effects of psychosocial stress, F (1,87) = 0.80, or drug, F (5,87) = 0.52, and the Psychosocial Stress x Drug inte raction was not significant, F (5,87) = 1.17 ( ps > 0.05). Effects of Chronic Psychosocial Stress and Drug Treatment on Object Recognition Memory (First Minute)VEH Ratio Time 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 No Psychosocial Stress Psychosocial Stress AMI-5AMI-10C-0.01C-0.05TIA-10 Figure 20 Effects of chronic psychosocial stress and drug treatment on object recognition memory during the first minute of th e testing trial. The da ta are presented as mean ratio time SEM. Testing, First Minute (see Figure 20) The analysis comparing the ratio times of all groups during the first minute of the testi ng trial revealed no signi ficant main effects of psychosocial stress, F (1,68) = 1.56, or drug, F (5,68) = 1.34, and the Psychosocial Stress x Drug interaction was not significant, F (5,68) = 1.44 ( ps > 0.05). Corticosterone Levels (see Figure 21) For the analysis of serum corticoster one levels, there was no significant main effect of psychosocial stress, F (1,97) = 0.02, p > 0.05. There was, how ever, a significant main effect of time point, F (2,194) = 487.29, p < 0.001. Post hoc tests indicated that rats demonstrated a significant increase in corticos terone levels following 20 minutes of acute

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90 immobilization stress and that these levels de clined, but remained significantly elevated relative to baseline, 1 hour later. Vehicle Corticosterone ( g/dL) 0 5 10 15 20 25 30 35 No Psychosocial Stress Psychosocial Stress ImmobilizationHome Cage 0 min20 min 80 min Corticosterone ( g/dL) 0 5 10 15 20 25 30 35 No Psychosocial Stress Psychosocial Stress Amitriptyline (5 mg/kg) ImmobilizationHome Cage 0 min20 min 80 min Corticosterone ( g/dL) 0 5 10 15 20 25 30 35 No Psychosocial Stress Psychosocial Stress Amitriptyline (10 mg/kg) ImmobilizationHome Cage 0 min20 min 80 min Corticosterone ( g/dL) 0 5 10 15 20 25 30 35 No Psychosocial Stress Psychosocial Stress Clonidine (0.01 mg/kg) ImmobilizationHome Cage 0 min20 min 80 min Corticosterone ( g/dL) 0 5 10 15 20 25 30 35 No Psychosocial Stress Psychosocial Stress ImmobilizationHome Cage 0 min20 min 80 minClonidine (0.05 mg/kg) Corticosterone ( g/dL) 0 5 10 15 20 25 30 35 No Psychosocial Stress Psychosocial Stress Tianeptine (10 mg/kg) ImmobilizationHome Cage 0 min20 min 80 minEffects of Chronic Psychosocial Stress and Drug Treatment on Serum Corticosterone Levels * Figure 21 Effects of chronic psychosocial stress and drug treatment on serum corticosterone levels. The data are presented as mean serum corticos terone levels (g/dL) SEM. = p < 0.05 relative to th e respective no psychos ocial stress group. There was also a significant main effect of drug, F (5,97) = 24.00, p < 0.001. Post hoc tests indicated that rats treated with 5 mg/kg of amitriptyline displayed significantly lower corticosterone levels than all other groups except for those treated with tianeptine or 10 mg/kg of amitriptyline. In addition, ra ts treated with 10 mg /kg of amitriptyline exhibited significantly lower corticosterone levels than all other groups, except for those

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91 treated with 5 mg/kg of amitriptyline. Lastly, rats that were treated with tianeptine had significantly lower corticosterone levels than rats treated with vehicle or 0.01 mg/kg of clonidine. The Time Point x Psychosocial Stress interaction was not significant, F (2,194) = 0.34, p > 0.05. However, the Time Point x Drug interaction was significant, F (10,194) = 8.91, p < 0.001. Post hoc tests indicated that both doses of amitriptyline, particularly the 10 mg/kg dose, significantly blunted the acute immobilization-induced increase in serum corticosterone levels. Tianeptin e had a similar effect, although not as pronounced as that of amitriptyline. The Psychosocial Stress x Drug, F (5,97) = 2.70, and Time Point x Psychosocial Stress x Drug, F (10,194) = 2.21, interactions were also significant (ps < 0.05). Post hoc tests revealed that psychosocia lly stressed rats treated with 10 mg/kg of amitriptyline exhibited significantly lower cortic osterone levels than the controls treated with 10 mg/kg of amitriptyline an hour fo llowing 20 minutes of immobilization. In contrast, 0.01 mg/kg of clonidine prevented the reduction in corticosterone levels an hour following immobilization in the psychosocial stress group only. Cardiovascular Activity Heart Rate (see Figure 22) For the analysis of heart rate, there were no significant main effects of psychosocial stress, F (1,81) = 0.05, or drug, F (5,81) = 1.15 ( ps > 0.05). The Psychosocial Stress x Drug inter action was significant, F (5,81) = 3.99 ( p < 0.01). Post hoc tests indicated that the vehicle-treated psychosocial stress group exhibited significantly greater heart rate than the vehicle-treated no psychosocial stress group. Chronic treatment with 5 or 10 mg /kg of amitriptyline, 0.01 or 0.05 mg/kg of

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92 clonidine or 10 mg/kg of tianep tine in groups that were psyc hosocially stressed prevented the chronic stress-induced increase in heart rate, as evidenced by the presence of significantly lower heart rate than the vehicle-treated psyc hosocial stress group or a lack of statistical signifi cance relative to each of the groups respective drug-treated no psychosocial stress group. Effects of Chronic Psychosocial Stress and Drug Treatment on Heart RateVEH Heart Rate (bpm) 0 350 375 400 425 450 No Psychosocial Stress Psychosocial Stress AMI-5AMI-10C-0.01C-0.05TIA-10* Figure 22 Effects of chronic psychosocial stre ss and drug treatment on heart rate. The data are presented as mean heart rate (bpm) SEM. = p < 0.05 relative to the vehicletreated no psychosocial stress group; = p < 0.05 relative to the vehicle-treated psychosocial stress group; = p < 0.05 relative to the respective drug-treated no psychosocial stress group. Systolic Blood Pre ssure (see Figure 23) For the analysis of systolic blood pressure, there was no significant main effect of psychosocial stress, F (1,86) = 1.90, p > 0.05. There was a significant main effect of drug, F (5,86) = 11.80, and the Psychosocial Stress x Drug interaction was significant, F (5,86) = 3.60 ( ps < 0.01). Post hoc tests

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93 indicated that the vehicletreated psychosocial stress gr oup had significantly higher systolic blood pressure than the vehicletreated no psychosocial stress group. Chronic treatment with 5 or 10 mg/kg of amitripty line in groups that were not psychosocially stressed led to significantly gr eater systolic blood pressure than the vehicle-treated no psychosocial stress group. Chronic treatment w ith 5 or 10 mg/kg of amitriptyline, 0.01 or 0.05 mg/kg of clonidine or 10 mg/kg of tiane ptine in groups that were psychosocially stressed prevented the chronic stress-induced increase in systolic blood pressure, as evidenced by the presence of significantly lowe r systolic blood pressure than the vehicletreated psychosocial stress group or a lack of statistical significance relative to each of the groups respective drug-treated no psychosocial stress group. Effects of Chronic Psychosocial Stress and Drug Treatment on Systolic Blood PressureVEH Systolic Blood Pressure (mm Hg) 0 105 120 135 150 No Psychosocial Stress Psychosocial Stress AMI-5AMI-10C-0.01C-0.05TIA-10* * Figure 23 Effects of chronic psychosocial st ress and drug treatment on systolic blood pressure. The data are presented as mean systolic blood pressure (mm Hg) SEM. = p < 0.05 relative to the vehicle-treated no psychosocial stress group; = p < 0.05 relative to the vehicle-treated psychosocial stress group.

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94 Effects of Chronic Psychosocial Stress and Drug Treatment on Diastolic Blood PressureVEH Diastolic Blood Pressure (mm Hg) 0 70 80 90 100 110 No Psychosocial Stress Psychosocial Stress AMI-5AMI-10C-0.01C-0.05TIA-10* * * Figure 24 Effects of chronic psychosocial stre ss and drug treatment on diastolic blood pressure. The data are presented as mean diastolic blood pressure (mm Hg) SEM. = p < 0.05 relative to the vehicle-treated no psychosocial stress group; = p < 0.05 relative to the vehicle-treated psychosocial stress group; = p < 0.05 relative to th e respective drugtreated no psychosocial stress group. Diastolic Blood Pressure (see Figure 24) For the analysis of diastolic blood pressure, there were significant main effects of psychosocial stress, F (1,86) = 9.67, and drug, F (5,86) = 21.78, and the Psychosocial Stress x Drug interaction was significant, F (5,86) = 6.11 ( ps < 0.01). Post hoc tests indicated that the vehicle-tr eated psychosocial stress group had significantly hi gher diastolic blood pressure than the vehicle-treated no psychosocial stress group. A dditionally, chronic treatment with 5 or 10 mg/kg of amitriptyline in groups that were not psychos ocially stressed led to significantly greater diastolic blood pressure than the vehicle-treated no psychosocial stress group. Chronic treatment with 10 mg/kg of am itriptyline, 0.01 or 0.05 mg/kg of clonidine or 10 mg/kg of

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95 tianeptine in psychosocially stressed rats led to significantly lower diastolic blood pressure than the vehicle-treated psychos ocial stress group. However, psychosocially stressed rats that were treated with 10 mg /kg of amitriptyline still displayed significantly greater diastolic blood pressure than the ve hicle-treated no psychosocial stress group, and psychosocially stressed rats th at were treated with 0.01 mg/kg of clonidine still exhibited significantly greater diastolic blood pressure than its respective drug-treated no psychosocial stress group. Growth Rates (see Figure 25) For the analysis of growth rate, th ere was no significant main effect of psychosocial stress, F (1,100) = 0.61, p > 0.05. There was a significant main effect of drug, F (5,100) = 11.78, and the Psychosocial Stre ss x Drug interaction was significant, F (5,100) = 13.42 (ps < 0.001). Post hoc tests indicated that the vehicle-treated psychosocial stress group had a significantly lower growth rate than the vehicle-treated no psychosocial stress group. Additionally, chr onic treatment with 5 or 10 mg/kg of amitriptyline or 0.05 mg/kg of clonidine in gr oups that were not psychosocially stressed led to significantly lower growth rates than the vehicle-treated no psychosocial stress group. Chronic treatment with 5 or 10 mg/kg of amitriptyline, 0.01 mg /kg of clonidine or 10 mg/kg of tianeptine in groups that were ps ychosocially stressed prevented the chronic stress-induced reduction of growth rate, as evidenced by the presence of significantly greater growth rates than th e vehicle-treated psychosocia l stress group or a lack of statistical significance relati ve to each of the group s respective drug-treated no psychosocial stress group. However, the psyc hosocial stress group treated with 5 mg/kg

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96 of amitriptyline still exhibite d a significantly lower growth ra te than the vehicle-treated no psychosocial stress group. Effects of Chronic Psychosocial Stress and Drug Treatment on Growth RateVEH Growth Rate (g/day) 0 1 2 3 4 5 6 No Psychosocial Stress Psychosocial Stress AMI-5AMI-10C-0.01C-0.05TIA-10* *#* * Figure 25 Effects of chronic psychosocial stre ss and drug treatment on growth rate. The data are presented as mean growth rate (g/day) SEM. = p < 0.05 relative to the vehicle-treated no psychosocial stress group; # = p < 0.05 relative to all other groups; = p < 0.05 relative to the vehicle-tr eated psychosocia l stress group; = p < 0.05 relative to the respective drugtreated no psychosocial stress group. Adrenal Gland Weights (see Figure 26) For the analysis of adrenal gland weights, there was no significant main effect of psychosocial stress, F (1,97) = 0.89, p > 0.05. There was a significant main effect of drug, F (5,97) = 10.53, and the Psychosocial Stress x Drug interaction was significant, F (5,97) = 3.26 ( ps < 0.01). Post hoc tests indicated that the vehicle-treated psychosocial stress group had significantly larger adrenal glands than the vehicle-tr eated no psychosocial stress group. Additionally, chronic treatment with 10 mg/kg of amitriptyline or 0.05

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97 mg/kg of clonidine in groups that were not psychosocially stressed led to significantly larger adrenal glands than the vehicle-tr eated no psychosocial stress group. Chronic treatment with 5 mg/kg of am itriptyline, 0.01 or 0.05 mg/kg of clonidine or 10 mg/kg of tianeptine in groups that were psychosocially stressed pr evented the chronic stressinduced hypertrophy of the adrenal glands, as evidenced by a lack of a statistically significant increase in adrenal gland weight relative to each of the groups respective drug-treated no psychosocial stress group. Inte restingly, the psychosocial stress group treated with 10 mg/kg of amitriptyline e xhibited significantly lower adrenal gland weights than its respectiv e drug-treated control group. Effects of Chronic Psychosocial Stress and Drug Treatment on Adrenal Gland WeightVEH Adrenal Gland Weight (mg / 100 g b.w.) 0 9 10 11 12 13 14 15 No Psychosocial Stress Psychosocial Stress AMI-5AMI-10C-0.01C-0.05TIA-10* * * Figure 26 Effects of chronic psychosocial st ress and drug treatment on adrenal gland weight. The data are presented as mean adre nal gland weight (mg/100 g b.w.) SEM. = p < 0.05 relative to the vehicle-tr eated no psychosocial stress group; = p < 0.05 relative to the respective drug-treate d no psychosocial stress group.

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98 Effects of Chronic Psychosocial Stress and Drug Treatment on Thymus WeightVEH Thymus Weight (mg / 100 g b.w.) 0 75 90 105 120 135 No Psychosocial Stress Psychosocial Stress AMI-5AMI-10C-0.01C-0.05TIA-10* * Figure 27 Effects of chronic psychosocial stre ss and drug treatment on thymus weight. The data are presented as mean thymus weight (mg/100 g b.w.) SEM. = p < 0.05 relative to the vehicle-treate d no psychosocial stress group; = p < 0.05 relative to the vehicle-treated psychosocial stress group; = p < 0.05 relative to the respective drugtreated no psychosocial stress group. Thymus Weights (see Figure 27) For the analysis of thymus weights, there was no significant main effect of drug, F (5,91) = 1.42, p > 0.05. There was a significant main effect of psychosocial stress, F (1,91) = 17.12, and the Psychosocial Stress x Drug interaction was significant, F (5,91) = 6.49 ( ps < 0.001). Post hoc analyses indicated that the vehicle-treated psychosocial stress group tended to exhibit smaller thymus es than the vehicle-treated no psychosocial stress group, yet this difference did not reach statistical significance. Additionally, chronic treatment with 10 mg/kg of amitripty line in groups that we re not psychosocially stressed led to significantly smaller thymuses than the vehicle-treated no psychosocial

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99 stress group. Chronic treatment with 5 mg/ kg of amitriptyline or 0.01 or 0.05 mg/kg of clonidine in groups that were psychosocially stressed le d to significantly smaller thymuses than the vehicle-treated no psychos ocial stress group. Chronic treatment with 10 mg/kg of amitriptyline or 10 mg/kg of tianeptine prevented the slight decrease in thymus weight induced by chronic psychosocia l stress, as evidenced by the presence of significantly greater thymus weights than th e vehicle-treated psychosocial stress group and/or a lack of a statistically significant decreases in thymus weight relative to each of the groups respective drug-treate d no psychosocial stress group. Discussion of Findings Consistent with our previous work (Zolad z et al., 2008), vehicl e-treated rats that were exposed to chronic psychosocial stress, composed of two acute predator exposures and daily social instability, e xhibited reduced growth rate, greater adrenal gland weight, heightened anxiety, an exagge rated startle response, greate r blood pressure reactivity to an acute stressor and intact memories for the context and cue that were associated with the two cat exposures. In cont rast to our prior findings, however, the vehicle-treated psychosocially stressed rats did not display a significant impairment of object recognition memory or significantly reduced thymus weight s, relative to vehicletreated control (i.e., unstressed) animals. Nonetheless, it is impor tant to note that these effects were in the hypothesized direction. That is to say, vehicle-treated psycho socially stressed rats spent less time with the novel object and had smaller thymuses, albeit both non-significantly, than vehicle-treated control animals. One possi ble explanation for the lack of statistical significance is that the chroni c injections in the present study acted as a chronic mild

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100 stressor in control rats, wh ich added considerable variab ility to their data on these measures. Studies in rodents have reported that chronic m ild stress in the form of repeated injections can signi ficantly alter the morphology of neurons in the prefrontal cortex (Weaver et al., 2005; Wellman, 2001). Ther efore, chronic inject ions in the present study could have adversely influe nced rat physiology and behavior. Another finding that is in conflict with our previous work is that the vehicletreated psychosocially stressed rats demonstr ated significantly greater HR than vehicletreated control rats following exposure to an acute stressor on the final day of testing. Previously, we reported that the present psychosocial stress paradigm resulted in significantly lower HR, compared to controls, followi ng acute stress on the final day of testing (Zoladz et al., 2008). Nevertheless, the HR exhibited by psychosocially stressed rats in the present study (409.85 7.30 bpm) wa s very similar to the HR exhibited by psychosocially stressed rats in our previous work (413.25 9.93 bpm). What appears to be the cause of the inconsistent effects between the findings of the present study and those of our previous work is the HR exhi bited by the control animals in each case. Vehicle-treated control rats displayed much lower HR in the present study (385.61 8.11 bpm) than that which was displayed by c ontrols in the prior study (462.88 11.43 bpm). In theory, vehicle-treated cont rols could have exhibited mu ch lower HR in the present study because the chronic mild stress of re peated injections protected them against responding as strongly to the acu te stressor as the more nave animals that were utilized in our prior work.

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101 Amitriptyline Both doses of the tricyclic antidepressa nt amitriptyline blocke d the expression of fear-related behaviors in psychosocially stresse d rats in response to the context and cue that were paired with the two cat exposures. These fear responses served as a measure of memory for the acute stress experiences a nd rat analogs of a traumatic memory in humans. As traumatic memories are a sour ce of psychological dist ress in people with PTSD, these findings suggest that amitriptyline could serve to effectively reduce the strength of traumatic memories and conse quentially diminish the intrusion and reexperiencing symptoms endured by PTSD patients. One caveat to this interpretation, however, is that extensive work has reported amitriptyline-induced memory impairments in both humans (Kerr et al., 1996; Liljequist et al., 1978; Mat tila et al., 1978; Spring et al., 1992; van Laar et al., 2002) and rodents (E verss et al., 2005; G onzalez-Pardo et al., 2008; Kumar & Kulkarni, 1996), findings that may be related to the drugs anticholinergic side effects (Pavone et al., 1997). Therefore, the a ttenuation of contextual and cue fear conditioning in psychosocially stressed rats treated with amitriptyline could simply be due to its amnestic side effects, rather than a specific amelioration of the chronic stress-induced behavi oral sequelae. On the othe r hand, studies reporting amitriptyline-induced memory impairments have administered the drug prior to learning. In the present experiment, amitriptyline trea tment did not begin until 24 hours after the first pairing of the context and cue with th e cat exposure. Therefore, a more likely explanation of the present findings is that amitriptyline blunted the augmentation of contextual and cue fear conditi oning in psychosocially stress ed rats that occurred in

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102 response to the second cat exposure on Da y 11 of the paradigm. Another possible explanation of these findings is that amitriptyline increased general locomotor activity, thus reducing overall immobility. Amitriptyline-treated control animals did display a significantly greater amount of motor activity on the EPM than vehicle-treated animals, but the same effect was not observed duri ng the open field habituation period on the following day. In addition, the finding that amitrip tyline, at least at the higher dose, led to significantly fewer fecal boli deposits in psychosocially stressed rats during the context test supports the notion that the observed effects were not by-pr oducts of drug-induced changes in locomotor activity. Both doses of amitriptyline were at leas t partially effective in preventing the chronic stress-induced increase in startl e responses, but only the 10 mg/kg dose of amitriptyline blocked the effects of chroni c psychosocial stress on anxiety, as measured by rat behavior on the EPM. These findings are consistent with other work in the rodent literature reporting that amitriptyline exerts anxiolytic effects in control animals (Bodnoff et al., 1988; Zajaczkowski & Gorka, 1993) a nd blocks stress-induced increases in anxiety-like behavior and startle (Orsetti et al., 2007; Poltyrev & Weinstock, 2004; West & Weiss, 2005). Research in humans has also shown that amitriptyline significantly blunts startle responses (Phillips et al., 2000) Thus, amitriptyline ap pears to have potent anxiolytic effects that may effectively ame liorate the hyperarousal symptoms related to PTSD. Amitriptyline also led to significantly lower serum corticosterone levels in rats and was particularly effective in blunting the immobilization-indu ced increase in these

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103 levels on the final day of testing. This finding is consistent with several studies in the rodent literature reporting that chronic amitriptyline administration results in significantly reduced basal and stress-induced levels of ACTH and corticosterone in rats (Barden, 1999; Reul et al., 1993). Amitriptyline appear s to accomplish these effects by enhancing the negative feedback inhibition of the HPA axis. Investigators have shown that chronic amitriptyline administration leads to an up-regulation of gluc ocorticoid receptor expression and enhanced glucocorticoid re ceptor binding in se veral brain regions (Barden, 1999; Pariante & Mill er, 2001; Przegalinski & Budzis zewska, 1993; Reul et al., 1993). Interestingly, in the present study, there was an additive effect of amitriptyline and psychosocial stress on the recovery of serum corticosterone levels following immobilization. Psychosocially stressed rats that were treated with amitriptyline, particularly the 10 mg/kg dose, exhibited signi ficantly lower corticosterone levels at the 80 minute time point than amitriptyline-treated controls. In theory, chronic amitriptyline and psychosocial stress synergis tically facilitated the produc tion of enhanced negative feedback of the HPA axis, which led to a more rapid recovery of stress-induced serum corticosterone levels in these rats. Despite the positive effects of amitriptyline on the chronic stress-induced physiological and behavioral sequelae in rats, there were adverse side effects of the drug that should be considered. For instance, chronic amitriptyline treatment resulted in significantly greater stress-induced increases in systolic and diastolic blood pressure than vehicle. Most work in both humans and rode nts has reported that chronic amitriptyline treatment results in increased heart rate, postural hypotensi on and increased

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104 cardiotoxicity (Balcioglu et al., 1991; Fiedler et al., 1986; H ong et al., 1974; Joubert et al., 1985; Kopera, 1978; Low & Opfer-Gehrking, 1992; Yokota et al., 1987). The results presented here are novel in that they reveal that chronic amitr iptyline treatment has unfavorable effects on stress-induced changes in cardiovascular activity. Amitriptyline also led to a significant reducti on in growth rate in rats, particularly at the higher dose of the drug. Although count erintuitive, 10 mg/ kg of amitriptyline significantly reduced growth rates in the cont rol rats, an effect that was reversed by exposure to chronic psychosocial stress. Sim ilar findings were observed with regards to adrenal gland and thymus weights. The highe r dose of amitriptyline led to significantly larger adrenal glands and significantly smaller thymuses than vehicle in control animals, and exposure to chronic psychosocial stress significantly blunted each of these effects. These findings suggest that, in the present ex periment, there was an interaction between amitriptyline treatment and chronic psychos ocial stress, in which the physiological consequences of the drug were more prom inent in those rats that were unstressed. Another finding of interest is that upon disse ction of these animals, there were a large number of adhesions observed on the internal organs, such as the liver, intestines and spleen, and the mortality rate for rats chroni cally treated with amitriptyline (3 out of 40, or 7.5%) was greater than the mortality rates fo r rats chronically treated with clonidine (0 out of 40, or 0%) or tianeptine (0 out of 20, or 0%). Thus, despite its ability to prevent the effects of psychosocial stress on anxiety-like behavior and st artle and the development of a powerful traumatic memory, the adverse phys iological side effects of amitriptyline could be a major limitation to its use in the treatment of people with PTSD.

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105 Clonidine Neither dose of clonidine prevented the expression of fear-related behaviors in psychosocially stressed rats in response to the context and cue that were paired with the two cat exposures. Although psychosocially st ressed rats chronically treated with 0.01 mg/kg of clonidine did not display significantl y greater immobility dur ing the context test than vehicle-treated control rats ( p = 0.15), the within-drug co ntrast (i.e., clonidinetreated psychosocial stress group vs. clonidine-treated controls) was marginally significant ( p = 0.06). These findings should be inte rpreted cautiously, however. Since clonidine is an 2-adrenergic receptor agonist a nd significantly reduces central noradrenergic activity, it can have sedative side effects at higher doses (Millan et al., 2000). In the present study, the higher dose of clonidine did result in a significant reduction of locomotor activity in the open field during OR habituation. On the other hand, clonidine had no significant effect s on motor activity on the EPM, and psychosocially stressed rats treated with 0.05 mg/kg of clonidine still produced significantly more fecal boli during the context test than the no psychosocial stress group treated with 0.05 mg/kg of clonidine. One study also reported that clonidines sedative effects are not observed until doses greater th an 0.1 mg/kg are employed (Millan et al., 2000). Therefore, the data suppor t the notion that clonidine is ineffective in blunting the expression of a traumatic memory in rats. Both doses of clonidine, and in particular the 0.05 mg/ kg dose, blocked the effects of psychosocial stress on anxiet y and startle, as well as cardi ovascular responses to acute immobilization. However, the higher dose of clonidine led to a significantly reduced

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106 growth rate in controls, which was exacerbate d by chronic psychosocial stress. It also resulted in significantly increased adrenal gland weights in control animals. Lastly, neither dose of clonidine prevented the chr onic psychosocial stress-induced decrease in thymus weights. Thus, despite its amelioration of the chronic stre ss-induced behavioral and cardiovascular sequelae, clonidine was ineffective at preventing the remaining physiological changes induced by our laboratorys stress regimen. Since people with PTSD have significan tly elevated baseline NE levels and demonstrate adverse reactions (e.g., panic att acks, flashbacks) to agents that increase these levels (e.g., yohimbine), pharmacological agents that reduce noradrenergic activity could be effective treatments for people with PTSD (Boehnlein & Kinzie, 2007; Strawn & Geracioti, 2008). Some studies have reported that propranolol, a -adrenergic receptor antagonist, may be an effective treatment for PTSD if administered immediately after the traumatic event or after the re-experiencing of a traumatic event (Pitman et al., 2002; Taylor & Cahill, 2002; Vaiva et al., 2003). Other work has found that prazosin, an 1adrenergic receptor antagonist, reduces hype rarousal symptoms, intrusive thoughts, recurrent distressing dreams and sleep dist urbances in PTSD (Brkanac et al., 2003; Peskind et al., 2003; Raskind et al., 2002; Raskind et al., 2003; Taylor & Raskind, 2002; Taylor et al., 2006). However, despite the cas e of clonidines use in treating PTSD, no randomized, placebo-controlled studies of clonidines effects on PTSD have been performed. The present findings suggest that cl onidine may be particularly effective in ameliorating the anxiety, hyperarousal (e.g., exaggerated startle response) and

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107 cardiovascular components of PTSD. They also highlight the need for clinical research addressing the effectiveness of clonidi ne as a treatment for the disorder. Tianeptine In the present experiment, tianeptine was the only pharmacological agent to prevent the effects of chronic psychosocial stress on all physiol ogical and behavioral measures. Tianeptine completely blocked the expression of fear-related behaviors in psychosocially stressed rats in response to the context and cue that were paired with the two cat exposures. It also prevented the e ffects of psychosocial st ress on anxiety, startle, cardiovascular reactivity to an acute stresso r, growth rate, adrenal gland weight and thymus weight. These findings suggest that tianeptine could be a premier treatment for PTSD. The present findings may be related to previous work reporting that chronic, but not acute, administration of tianeptine si gnificantly impairs the acquisition and expression of conditioned fear in rats (Burghardt et al., 2004). These effects appear to be more related to the anxiolytic, rather than memory-impairing, properties of tianeptine, as numerous studies have shown that tianeptine treatment enhances, rather than impairs, hippocampus-dependent learni ng and memory (Jaffard et al., 1991; Meneses, 2002; Munoz et al., 2005). Interestingly, the same i nvestigators reporting tianeptines effects on fear conditioning found that acute ad ministration of the SSRI citalopram enhanced the acquisition of auditory fear conditioning, while chronic treatment with the drug impaired the acquisition and expression of conditioned fear. Thus, tianeptine appears to

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108 demonstrate long-term anxiolytic effects that are similar to SSRIs, without having the acute anxiogenic effects typi cally found with these agents. In the present study, tianeptine signif icantly attenuated the immobilizationinduced increase in serum corticosterone levels This finding is consistent with previous work indicating that tianep tine reduces stress-induced activation of the HPA axis (Delbende et al., 1991). Additionally, tianep tine, relative to vehi cle, resulted in significantly lower systolic BP in co ntrol animals following 20 minutes of immobilization. Few studies have examined the effects of tianeptine on cardiovascular activity, but those that have investigated the phenome non have typically reported no effects of the drug on HR or BP (Juvent et al., 1990; Lasnier et al., 1991). On the other hand, one study did report that tianeptine resulted in signifi cantly reduced diastolic BP (Lechin et al., 2006). The effects of tianeptin e on cardiovascular ac tivity in the present study are not likely due to acute effects of th e drug. Our laboratory has preliminary data indicating that tianeptine doe s not prevent an acute stress-induced increase in BP (unpublished findings). In this particular study, rats were treated with 10 mg/kg of tianeptine or vehicle 30 minutes prior to a 15-minute exposure to predator stress. Animals that were exposed to the cat for 15 minutes exhibited significant elevations of systolic and diastolic BP, regardless of whether or not they had received tianeptine. In other words, tianeptine was ineffec tive in preventing the acute st ress-induced increase in blood pressure. Thus, the ability of tianeptine to prevent the effects of chronic psychosocial stress on cardiovascular reactivity to an acute stressor is most likely attributable to its effects on general anxiety. Although speculativ e, tianeptine theore tically enabled the

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109 psychosocially stressed rats to cope better with the daily mild stress of social instability and also with future acute stressors, such as the 20-minute exposure to immobilization on the final day of testing. Chronic treatment with tianeptine also prevented the effects of chronic psychosocial stress on all of the other physio logical endpoints, including growth rate, adrenal gland weight and thymus weight. Pr evious work in rodents has reported that tianeptine had no effect on the chronic st ress-induced adrenal gland hypertrophy or reduction in growth rate (Magarinos et al., 1999; Watanabe et al., 1992b). However, these studies utilized a different st ressor (restraint stress 6 hours per day for 21 days) than that which was employed here, which could accoun t for the apparent discrepancies. The finding that tianeptine prevented any chroni c stress-induced atrophy of the thymus is consistent with work demonstrating that tianeptine significantly interacts with the immune system. For instance, several studies have shown th at tianeptine prevents the adverse effects of cytokines on brain bioc hemistry and peripheral measures of inflammation in the rat (Castanon et al., 2001; Plaisant et al., 2003b; Plaisant et al., 2003a). Thus, an interesting avenue of futu re research would involve exploring the contribution of tianeptine-immune system inte ractions to its anti -stress effects on rat physiology and behavior. Early studies on tianeptines mechanism of action showed that the drug led to significantly lower extracellular levels of serotonin, a finding that was hypothesized to result from enhanced serotonin reuptake (F attaccini et al., 1990; Labrid et al., 1992; Mennini et al., 1987; Mocaer et al., 1988) However, tianeptines effects on the

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110 serotonergic system may be an indirect consequence of the drugs influences on an alternative neurotransmitter system because later studies failed to show any direct effects of tianeptine on serotonergic neurotransmi ssion (Pineyro et al., 1995a; Pineyro et al., 1995b). Additionally, research has shown that tianeptine does not alter the density or affinity of any serotonin receptor subtype, and tianeptines affinity for the serotonin transporter is very low (Kato & Weitsch, 1988; Svenningsson et al., 2007). Some have also contested the validity of the original studies on tianeptines mechanism of action based on technical limitations that were present at the time (Malagie et al., 2000). Recent work has suggested that its therap eutic effects may be more associated with modulation of the glutamatergic syst em (Brink et al., 2006; Kasper & McEwen, 2008; Zoladz et al., in press). Extensive wo rk has implicated h yperactivity of the glutamatergic system in the deleterious eff ects of stress on brain structure and function (Bagley & Moghaddam, 1997; Bartanusz et al., 1995; Joels et al., 2003 ; Kim et al., 1996; Krugers et al., 1993; Lowy et al., 1993; Lowy et al., 1995; Magarinos & McEwen, 1995; McEwen et al., 2002; Moghaddam, 1993; Park et al., 2004; Reznikov et al., 2007; Yang et al., 2005), and tianeptine appears to protect brain regions that are highly susceptible to stress, such as the hippocampus and prefrontal cortex, from the deleterious effects of stress by normalizing the stress-induced m odulation of glutamatergic activity. For instance, tianeptine has been shown to prevent stress-induced increases in NMDA channel currents, as well as the ratio of NMDA:non-NMDA receptor currents, in the CA3 region of the hippocampus (Kole et al., 2002). It also inhibits the acute stress-induced increase in extracellular leve ls of glutamate in the basola teral amygdala (Reznikov et al.,

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111 2007). In addition to its glutamatergic modul ation, tianeptine reduces the expression of CRH mRNA in the amygdala and the bed nucleus of the stria terminalis, a brain region that is highly innervated by amygdala fibe rs (Kim et al., 2006). CRH neurotransmission in both of these regions has been implicated in the expression of anxiety-like behaviors (Holsboer, 1999; Strohle & Holsboer, 2003). T hus, tianeptines effects on glutamatergic and CRH activity in these various brain regions may play an important role in its ability to reverse the effects of chronic stress on the expression of an xiety-like behaviors. Uzbay and colleagues found that tianeptine reduced the intensity (Ceyhan et al., 2005) and delayed the onset (Uzbay et al., 2007 ) of pentylenetetrazole-induced seizures in rodents. The latter effect was blocked by the administra tion of caffeine, a nonspecific adenosine receptor antagonist, and 8-cy clopentyl-1,3-dipropylxanthine, an A1 receptorspecific antagonist. However, administration of the A2 receptor-specific antagonist, 8-(3chlorostyryl) caffeine, had no effect on the tianeptine-induced delay of seizure onset, suggesting that tianeptines anticonvulsant properties are dependent upon activation of A1 adenosine receptors. Since previous wo rk has shown that activation of A1 adenosine receptors has anxiolytic effects (Florio et al., 1998; Jain et al., 1995; Prediger et al., 2004; Prediger et al., 2006), this specific categor y of adenosinergic receptors could be responsible, at least in part, for tianeptines anxiolytic effect s in rodents (Burghardt et al., 2004; File et al., 1993; File & Mabbutt, 1991; Pi llai et al., 2004) a nd in the depressed population (Defrance et al., 1988; Wilde & Benfield, 1995). In sum, tianeptine was the only pharmacol ogical agent to prevent the effects of chronic psychosocial stress on all physiological and behavi oral measures. Extensive

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112 preclinical research has shown that exposure to stress result s in a significant increase in glutamate activity, and tianeptines antidepressant properties have been attributed to its ability to normalize this hyperactivity of the glutamatergic sy stem. It is therefore likely that at least some of the behavioral change s observed in our animal model of PTSD are a result of stress-induced altera tions in glutamate function. Furthermore, it is possible that abnormalities in glutamatergic function also underlie the pathology of PTSD (Chambers et al., 1999; Nair & Singh, 2008; Reul & Nu tt, 2008), in which case tianeptine would certainly be an optimal choice to tr eat individuals with the disorder. Limitations and Future Research The design of this experiment does not di stinguish between th e acute and chronic effects of amitriptyline, clonidine and tianeptine on rat physiology and behavior. Rats were administered these pharmacological ag ents not only on Days 2-31 of the chronic psychosocial stress paradigm, but throughout behavioral testing as well. The drug administration continued during behavioral testing to prevent withdrawal effects from influencing rat behavior. Importantly, our laboratory does have preliminary data indicating that chronic tianeptine treatment prevents the effects of the current stress regimen on all physiological and behavioral me asures even if it is administered only during Days 2-31 and discontinued at th e commencement of behavioral testing. Nevertheless, future work should examine the effects of the present compounds on the stress-induced changes in rat physiology and be havior when they are administered during the chronic stress period only and during behavioral testing only.

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113 Summary and Application to Pharmacotherapy for Post-Traumatic Stress Disorder A subset of people with PTSD show si gnificant improvement in their symptoms following treatment with SSRIs (Asnis et al ., 2004; Davidson, 2003; Davis et al., 2006; Hidalgo & Davidson, 2000; Ipser et al., 2006; St ein et al., 2006). However, SSRIs tend to blunt only the depressive com ponents of PTSD, while having little effect on the memoryand anxiety-related symptoms of the disorder (Asnis et al., 2004; Boehnlein & Kinzie, 2007; Brady et al., 2000; Van der Kolk et al ., 1994). In addition, some forms of PTSD, such as combat-related PTSD, are incredibly resistant to SSRI treatment (Jakovljevic et al., 2003; Rothbaum et al., 2008; Stein et al., 2002). These ag ents also have anxiogenic effects early in the treatment phase and only exert their antidepressant effects after a substantial delay (Browning et al., 2007; Bu rghardt et al., 2004; Humble & Wistedt, 1992). Thus, there is an urgent need to develop alternative pharmacotherapeutic interventions for the treatment of PTSD. The present experiment examined the ab ility of amitriptyline, clonidine and tianeptine to prevent the deve lopment of PTSD-like sequelae in rats exposed to chronic psychosocial stress. The tricyclic antidepressant amitriptyline was effective in reducing the memories for the context and cue that we re associated with the acute cat exposures, and it ameliorated the stress-induced increase in anxiety and startle. However, this agent had adverse side effects, as it significantly increased cardiovascular reactivity in control animals and led to adverse physiological r eactions, including reduced growth rate, increase adrenal gland weight and internal adhesions. Thus, despite its positive effects,

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114 the adverse physiological side effects of amitriptyline could be a major limitation to its use in the treatment of people with PTSD. Clonidine also blocked the effects of chronic psychosocial stress on anxiety and startle, but in contrast to amitriptyline, prevented the stress-induced changes in cardiovascular reactivity to an acute stresso r as well. However, it did not prevent the expression of fear-related behaviors in psychosocially stressed rats upon exposed to the context and cue that were paired with the acute cat exposures. Cloni dine also had some adverse side effects of its own, including a significant reduction in growth rate and a significant increase in adrenal gland weight. Th us, clonidine may be particularly effective in ameliorating the anxiety, hyperarousal (e.g., exaggerated star tle response) and cardiovascular components of PTSD, but have li ttle effect on the st rength of a traumatic memory. Lastly, tianeptine was the only pharmacological agent to prevent the effects of chronic psychosocial stress on a ll physiological and behavioral endpoints. It completely blocked the expression of fear-related behavi ors in psychosocially stressed rats in response to the context and cue that were paired with the two cat exposures and prevented the effects of psychosocial stress on anxiety, startle, car diovascular reactivity to an acute stressor, growth rate, adrenal gland weight and thymus weight. Collectively, these findings illustrate the differential effectiv eness of these three treatments in blocking the PTSD-like sequelae in rats, and the profile of tianeptine as the most effective agent provides guidance for pharmacotherapeutic appr oaches in the treatment of individuals suffering from PTSD.

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115 Chapter Five: Experiment Four Temporal Dynamics of the Physiological and Behavioral Sequelae Induced by Chronic Psychosocial Stress People with chronic PTSD display physiol ogical and behavioral symptoms of the disorder years after the original trauma took place. These symptoms develop acutely after experiencing the trauma and progressively worsen to eventually produce full-blown PTSD. A valid animal model of PTSD should be able to demonstrate PTSD-like effects on physiology and behavior long af ter the initial stress exposur e. Therefore, the purpose of Experiment Four was to examine whether or not the stress regimen employed in the previous experiments would produce physiological and behavioral changes in rats that would be present for a longer period of time. It was also designed to explore the contribution of an additional, third, acute st ress session and irregular rather than just daily, social instability to the maintenance of the PTSD-like effects for this extended period of time. Methods Rats The same weight range and strain of rats as well as the housing conditions, that were employed in Experiments One, Two and Three were used in the present experiment. Upon arrival, all rats were given 1 week to acclimate to the housing room environment and cage changing procedures before any e xperimental manipulations took place. All

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116 procedures were approved by the Institutional Animal Care and Use Committee at the University of South Florida. Psychosocial Stress Procedure Following the 1-week acclimation phase, rats were brought to the laboratory and then randomly assigned to one of four groups (see Figure 28; N = 10 rats per group). In contrast to Experiments One through Three, each of the four groups was exposed to three, as opposed to two, acute stress sessions. Du ring each stress session, as in Experiment Three, the rats were exposed to a chamber for 3 minutes (with a 30-second tone presented at the end of the 3-minute period). Then, the rats were either immob ilized and exposed to a cat or placed back in their home cages fo r 1 hour. As before, the first stress session occurred during the light cycle, betwee n 0800 and 1300 hours, while the second stress session occurred 10 days later during the da rk cycle, between 1900 and 2100 hours. The third and final stress session took place 3 weeks following the second stress session during the light cycle, between 0800 and 1300 hours. Of the four groups in the present experiment, three were exposed to chronic psychosocial stress and one was a control, no psychosocial stress, group. Each of the three psychosocial stress groups was exposed to the same manipulations until the third stress session. That is, these groups were exposed to the chamber followed by immobilization plus cat exposure during the first and second stress sessions, as well as daily randomized housing throughout the 31-day period leading up to the third stress session. During the third stress session (Day 32), rats in psychos ocial stress group 1 were exposed to the chamber for 3 minutes followed by a 1-hour exposure to their home

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117 cages. Rats in psychosocial stress group 2 and psychosocial stress group 3 were exposed to the chamber for 3 minutes follo wed by 1 hour of immobilization during cat exposure. These procedures ar e illustrated in Figure 28. Figure 28 Experimental groups in Experiment 4. Following the third stress session, each of the three psychosocial stress groups was exposed to randomized housing. As in the previous experiments, psychosocial groups 1 and 2 were exposed to daily randomized housing for the 12 weeks following the third stress session. In contrast psychosocial stress group 3 was exposed to irregular randomized housing for the next 12 weeks. In other words, the cage mates in this group

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118 were randomized every 1-4 days. The strate gy behind this manipulation was to add an additional element of unpredictability to the stress experience. The typical daily randomized housing procedure, although effective for the 31-day paradigm, is somewhat predictable in that it occurs at approximatel y the same time every day, and if continued for an extended period of time, coul d eventually become ineffective. Behavioral Testing Twelve weeks after the thir d stress session (i.e., Day 116), rats were given tests to measure their fear memory, anxiety, startle, learning and memory, cardiovascular activity and corticosterone activity. On the first 4 da ys of behavioral testing (Days 116-119), all rats were brought to the laboratory and left undisturbed for 30 minutes before testing began. All behavioral testing took place dur ing the light cycle, between 0800 and 1500 hours. Behavioral Apparatus All rats in the pr esent experiment were exposed to the same physiological and behavioral testing procedures that were employed in Experiment Three. Thus, these procedures will only be briefly addressed here. Contextual and Cue Fear Memory On Day 116, rat behavior in response to the chamber (context test) and tone (cue test) that were previously paired with the acute stress sessions was examined. Testing adhered to the procedures employed in Experiment Three.

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119 Elevated Plus Maze On Day 117, the rats were placed on the EPM for 5 minutes, and their behavior was scored according to the procedures employed in Experiment Three. Startle Response One hour after the EPM assessment, acoustic startle testing was administered according to the procedures employed in Experiment Three. Novel Object Recognition On Day 118, the rats were pl aced in an open field for 5 minutes to acclimate to the environment. Their behavior was monitored and scored according to the procedures employed in E xperiment Three. Twenty-four hours later (Day 119), the rats were given novel object recognition training and testing according to the procedures employed in Experiment Three. Preparation for Blood Sampling Immediately following the 3-hour object recognition test, the hind legs of all rats were shaved to allow access to their saphenous veins, as per Experiments One through Three. Blood Sampling and Cardiovascular Activity On the final day of behavioral testing (Day 120), three blood samples, as well as measures of heart rate and blood pressure, were collected, according to the pr ocedures utilized in Experiment Three. Following rapid decapitation, the adrenal and thymus glands were removed and weighed. Once all of the blood had clotted at room te mperature, it was centrifuged (3000 rpm for 8 min), and the serum was extracted and stored at -80 C until assaye d by Monika Fleshner at the University of Colorado at Boulder.

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120 Statistical Analyses Experimental Design and General Analyses The present study utilized a single factor, between-subjects design. The indepe ndent variable was psychosocial stress (psychosocial stress group 1, psychosocial stress group 2, psychosocial stress group 3, no psychosocial stress). In most cases, one-w ay, between-subjects ANOVAs were used to analyze the data from the physiological and behavioral assessments, with psychosocial stress serving as the between-subjects fact ors. Planned comparisons (independent samples t -tests) were also conducted between eac h of the psychosocial stress groups and the no psychosocial stress group. For all anal yses, alpha was set at 0.05, and Holm-Sidak post hoc tests were employed when necessary. Fear Memory The amount of immobility dur ing each chamber exposure (Stress Session 1, Stress Session 2, Stress Session 3, Co ntext Test, Cue Test No Tone, Cue Test Tone) was analyzed separately. For each test, one-way, between-subjects ANOVAs were used to analyze behavior. Ps ychosocial stress served as the betweensubjects factor in each case. Elevated Plus Maze The amount of time that rats spent in the open arms of the EPM was calculated as a percent of the total tr ial time. The percent time that rats spent in the open arms, as well as the number of ambulations that rats made on the EPM were analyzed with one-way, between-subject s ANOVAs. Each of these analyses was performed for the entire 5-minut e testing trial and for the first minute of the testing trial, with psychosocial stress serving as th e between-subjects factor in each case.

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121 Startle Response Startle responses to each of the 3 auditory stimulus intensities (90, 100 and 110 dB) were analyzed separatel y. In each case, one-w ay, between-subjects ANOVAs were employed to analyze the data, with psychosocial stress serving as the between-subjects factor. Novel Object Recognition For habituation, a one-way, between-subjects ANOVA was used to compare overall locomotor ac tivity across all groups with psychosocial stress serving as the between-subjects factor. The amount of time that rats spent in each area of the open field during the habituation pha se was also analyzed to assure that the rats did not display a preference for one ar ea of the open field over another. For the analysis, the open field was divided into four square quadrants via the ANY-Maze computer program. The amount of time that rats spent in each of the quadrants was analyzed with a mixed-model ANOVA, with psychosocial stress serv ing as the betweensubjects factor and time spen t in each quadrant serving as th e within-subjects factor. For training, paired samples t -tests were first conducted to de termine whether th e rats within each group spent a comparable amount of time w ith each object replica (to rule out object preference effects). Then, the to tal time that rats spent with both object replicas during training was compared across groups by using one-way, between-subjects ANOVAs, with psychosocial stress servi ng as the between-subjects factor. For testing, a ratio time score was calculated for each group by taking the time that rats spent with the novel object and dividing it by the time that rats spent with the fam iliar object (i.e., ratio time = time with novel object / time with familiar obj ect). The ratio times were compared across groups by utilizing one-way, between-subjects ANOVAs, with psychosocial stress again

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122 serving as the between-subjects factor. This wa s performed for the en tire 5-minute testing trial and for the first minute of the testing trial. Corticosterone Levels A mixed-model ANOVA was used to analyze corticosterone levels at the three time points. Psychosocial stress served as the betweensubjects factor, and time point (baseline, stress, return-to-baseline) served as the withinsubjects factor. Heart Rate and Blood Pressure The HR, systolic BP and diastolic BP data were analyzed with one-way, between-subjects ANOV As, with psychosocial stress serving as the between-subjects factor. Growth Rates, Adrenal Gland Weights and Thymus Weights Growth rates, expressed as grams per day (g/day), were cal culated for all rats by dividing their total body weight gained during the course of the experiment by the total number of days in the experiment (i.e., 115 days). The adrena l glands and thymuses were weighed and expressed as milligrams per 100 grams of body weight (mg/100 g b.w.). The growth rate, adrenal gland weights and thymus weight s were analyzed with one-way, betweensubjects ANOVAs, with psychosocial stress serving as the between-subjects factor. Results Fear Memory Stress Session One (see Figure 29) The analysis of immobility during the 3minute chamber exposure during stress session one revealed a significant main effect of psychosocial stress, F (3,35) = 3.07, p < 0.05. However, post hoc analyses did not indicate any significant differenc es between the groups.

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123 Amount of Immobility upon Chamber Exposure During Stress Session 1No Psych Stress % Immobility 0 20 40 60 80 Psych Stress 1 Psych Stress 2 Psych Stress 3 Figure 29 Amount of immobility upon chamber exposure during stress session one. The data are presented as mean percent immobility SEM. Stress Session Two (see Figure 30) The analysis of immobility during the 3minute chamber exposure during st ress session two revealed no si gnificant main effect of psychosocial stress, F (3,35) = 1.79, p > 0.05. Amount of Immobility upon Chamber Exposure During Stress Session 2No Psych Stress % Immobility 0 20 40 60 80 Psych Stress 1 Psych Stress 2 Psych Stress 3 Figure 30 Amount of immobility upon chamber exposure during stress session two. The data are presented as mean percent immobility SEM.

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124 Stress Session Three (see Figure 31) The analysis of immobility during the 3minute chamber exposure during stress session th ree revealed no significant main effect of psychosocial stress, F (3,33) = 2.63, p = 0.067. However, planned comparisons indicated that psychosocial stress group 1, t (16) = 2.31, and psychosocial stress group 2, t (16) = 2.85, spent significantly more time immobile than the no psychosocial stress group ( ps < 0.05). Amount of Immobility upon Chamber Exposure During Stress Session 3No Psych Stress % Immobility 0 20 40 60 80 Psych Stress 1 Psych Stress 2 Psych Stress 3* Figure 31 Amount of immobility upon chamber exposure during stress session three. The data are presented as mean percent immobility SEM. = p < 0.05 relative to the no psychosocial stress group. Context Test Immobility (see Figure 32) The analysis of immobility during the 5minute context test revealed a significan t main effect of psychosocial stress, F (3,34) = 14.79, p < 0.001. Post hoc tests indicated th at psychosocial stress group 1 spent significantly more time immob ile than the no psychosocial stress group, and psychosocial stress group 2 spent significantly more time immobile than all other groups.

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125 Effects of Differential Chronic Psychosocial Stress Paradigms on Immobility during the Context TestNo Psych Stress % Immobility 0 20 40 60 80 Psych Stress 1 Psych Stress 2 Psych Stress 3*# Figure 32 Effects of differential chronic ps ychosocial stress paradigms on immobility during the 5-minute context test. The data are presented as mean percent immobility SEM. = p < 0.05 relative to the no psychosocial stress group; # = p < 0.05 relative to all other groups. Context Test Fecal Boli (see Figure 33) The analysis of fecal boli produced during the 5-minute context test revealed a si gnificant main effect of psychosocial stress, F (3,35) = 7.51, p < 0.001. Post hoc tests indicated th at psychosocial stress group 2 produced significantly more fecal boli th an the no psychosocial stress group, and psychosocial stress group 1 produced significantl y more fecal boli than all other groups.

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126 Effects of Differential Chronic Psychosocial Stress Paradigms on Fecal Boli Produced during the Context TestNo Psych Stress Fecal Boli 0 1 2 3 4 5 6 Psych Stress 1 Psych Stress 2 Psych Stress 3*# Figure 33 Effects of differential chronic ps ychosocial stress paradigms on fecal boli produced during the 5-minute context test. The data are presented as mean number of fecal boli SEM. = p < 0.05 relative to the no psychosocial stress group; # = p < 0.05 relative to all other groups. Effects of Differential Chronic Psychosocial Stress Paradigms on Immobility in a Novel EnvironmentNo Psych Stress % Immobility 0 20 40 60 80 Psych Stress 1 Psych Stress 2 Psych Stress 3 Figure 34 Effects of differential chronic ps ychosocial stress paradigms on immobility during the first 3 minutes of the cue test. The data are presented as mean percent immobility SEM.

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127 Cue Test Immobility No Tone (i.e., Novel Environment) (see Figure 34) The analysis of immobility during the first 3 minutes of the cue test revealed no significant main effect of psychosocial stress, F (3,34) = 2.09, p > 0.05. Cue Test Immobility Tone (see Figure 35) The analysis of immobility during the last 3 minutes of the cue test revealed no significant main effect of psychosocial stress, F (3,33) = 2.73, p = 0.059. However, planned co mparisons indicated that psychosocial stress group 1, t (16) = 2.23, and psychosocial stress group 2, t (16) = 3.30, spent significantly more time immobile than the no psychosocial stress group ( ps < 0.05). Effects of Differential Chronic Psychosocial Stress Paradigms on Immobility during the ToneNo Psych Stress % Immobility 0 20 40 60 80 Psych Stress 1 Psych Stress 2 Psych Stress 3* Figure 35 Effects of differential chronic ps ychosocial stress paradigms on immobility during the tone. The data ar e presented as mean percent immobility SEM. = p < 0.05 relative to the no psyc hosocial stress group. Cue Test Fecal Boli (see Figure 36) The analysis of fecal boli produced during the 6-minute cue test revealed no signifi cant main effect of psychosocial stress, F (3,35) = 1.73, p > 0.05.

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128 Effects of Differential Chronic Psychosocial Stress Paradigms on Fecal Boli Produced during the Cue TestNo Psych Stress Fecal Boli 0 1 2 3 4 5 6 Psych Stress 1 Psych Stress 2 Psych Stress 3 Figure 36 Effects of differential chronic ps ychosocial stress paradigms on fecal boli produced during the 6-minute cue test. The data are presented as mean number of fecal boli SEM. Elevated Plus Maze Percent Time in Open Arms, 5-Minute Trial (see Figure 37) The analysis of percent time spent in the open arms during the 5-minute trial on the EPM revealed no significant main effect of psychosocial stress, F (3,33) = 0.43, p > 0.05. Percent Time in Open Arms, First Minute (see Figure 38) The analysis of percent time spent in the open arms during the first minute of the 5-minute trial on the EPM revealed a significant main effect of psychosocial stress, F (3,31) = 5.28, p < 0.01. Post hoc tests indicated that each of the psyc hosocial stress groups sp ent significantly less time in the open arms than the no psychosocial stress group.

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129 Effects of Differential Chronic Psychosocial Stress Paradigms on Anxiety on the EPM (5-Minute Trial)No Psych Stress % Time Spent in the Open Arms 0 5 10 15 20 25 30 35 Psych Stress 1 Psych Stress 2 Psych Stress 3 Figure 37 Effects of differential chronic psyc hosocial stress paradigms on percent time spent in the open arms during the 5-minute tria l on the elevated plus maze. The data are presented as mean percent time spent in the open arms SEM. Effects of Differential Chronic Psychosocial Stress Paradigms on Anxiety on the EPM (First Minute)No Psych Stress % Time Spent in the Open Arms 0 20 40 60 80 Psych Stress 1 Psych Stress 2 Psych Stress 3* * Figure 38 Effects of differential chronic psyc hosocial stress paradigms on percent time spent in the open arms during the first minute of the 5-minute trial on the elevated plus maze. The data are presented as mean percent time spent in the open arms SEM. = p < 0.05 relative to the no psychosocial stress group.

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130 Ambulations, 5-Minute Trial (see Figure 39) The analysis of ambulations made during the 5-minute trial on the EPM revealed no significant main ef fect of psychosocial stress, F (3,35) = 0.73, p > 0.05. Effects of Differential Chronic Psychosocial Stress Paradigms on Motor Activity on the EPM (5-Minute Trial ) No Psych Stress Total Ambulations 0 25 50 75 100 125 150 175 200 Psych Stress 1 Psych Stress 2 Psych Stress 3 Figure 39 Effects of differential chronic psyc hosocial stress paradigms on ambulations made during the 5-minute trial on the elevated plus maze. The data are presented as mean percent time spent in the open arms SEM. Ambulations, First Minute (see Figure 40) The analysis of ambulations made during the first minute of the 5-minute tria l on the EPM revealed no significant main effect of psychosocial stress, F (3,35) = 1.77, p > 0.05.

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131 Effects of Differential Chronic Psychosocial Stress Paradigms on Motor Activity on the EPM (First Minute ) No Psych Stress Total Ambulations 0 10 20 30 40 Psych Stress 1 Psych Stress 2 Psych Stress 3 Figure 40 Effects of differential chronic psyc hosocial stress paradigms on ambulations made during the first minute of the 5-minute trial on the elevated plus maze. The data are presented as mean percent time spent in the open arms SEM. Effects of Differential Chronic Psychosocial Stress Paradigms on Startle Response to 90 dB Auditory Stimul i No Psych Stress Startle Response (Newtons) 0.0 0.1 0.2 0.3 0.4 Psych Stress 1 Psych Stress 2 Psych Stress 3 Figure 41 Effects of differential chronic ps ychosocial stress paradigms on startle responses to the 90 dB auditory stimuli. The data are presen ted as mean startle response (Newtons) SEM.

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132 Startle Response 90 dB Auditory Stimuli (see Figure 41) The analysis of startle responses to the 90 dB auditory stimuli revealed no significan t main effect of psychosocial stress, F (3,35) = 1.57, p > 0.05. 100 dB Auditory Stimuli (see Figure 42) The analysis of startle responses to the 100 dB auditory stimuli revealed no signifi cant main effect of psychosocial stress, F (3,34) = 2.30, p > 0.05. Effects of Differential Chronic Psychosocial Stress Paradigms on Startle Response to 100 dB Auditory Stimul i No Psych Stress Startle Response (Newtons) 0.00 0.25 0.50 0.75 1.00 1.25 1.50 Psych Stress 1 Psych Stress 2 Psych Stress 3 Figure 42 Effects of differential chronic ps ychosocial stress paradigms on startle responses to the 100 dB auditory stimuli. The da ta are presented as m ean startle response (Newtons) SEM.

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133 Effects of Differential Chronic Psychosocial Stress Paradigms on Startle Response to 110 dB Auditory Stimul i No Psych Stress Startle Response (Newtons) 0.0 0.5 1.0 1.5 2.0 2.5 Psych Stress 1 Psych Stress 2 Psych Stress 3 Figure 43 Effects of differential chronic ps ychosocial stress paradigms on startle responses to the 110 dB auditory stimuli. The da ta are presented as m ean startle response (Newtons) SEM. 110 dB Auditory Stimuli (see Figure 43) The analysis of startle responses to the 110 dB auditory stimuli revealed no signifi cant main effect of psychosocial stress, F (3,34) = 1.62, p > 0.05. Novel Object Recognition Habituation The analysis of locomotor activ ity in the open field during the 5minute habituation phase revealed no signifi cant main effect of psychosocial stress, F (3,35) = 0.68, p > 0.05 (data not shown). The analysis of time that the rats spent in each area of the open field revealed no significant main effects of quadrant, F (3,105) = 1.05, or psychosocial stress, F (3,35) = 0.91, and the Quadrant x Psychosocial Stress interaction was not significant, F (9,105) = 0.40 (ps > 0.05; data not shown). These findings

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134 indicated that the rats did not display a preference for one area of the open field over another. Training. Within-group comparisons showed that the no psychosocial stress group, t (9) = 0.81, psychosocial stress group 1, t (9) = 0.72, psychosocial stress group 2, t (9) = 1.30, and psychosocial stress group 3, t (8) = 0.91, spent a comparable amount of time with each of the objects that were placed in the open field during object recognition training ( p s > 0.05; data not shown), indicating that no object preference effects were present. Moreover, a between-groups comparis on of the total amount of time spent with both objects during training reve aled no significant main effe ct of psychosocial stress, F (3,35) = 1.44, p > 0.05, indicating that all groups sp ent a comparable amount of time with both objects during tr aining (data not shown). Effects of Differential Chronic Psychosocial Stress Paradigms on Object Recognition Memory (5-Minute Trial ) No Psych Stress Ratio Time 0.0 0.5 1.0 1.5 2.0 2.5 Psych Stress 1 Psych Stress 2 Psych Stress 3 Figure 44 Effects of differential chronic psychosocial stress paradigms on object recognition memory during the entire 5-minute testing trial. The da ta are presented as mean ratio time SEM. = p < 0.05 relative to the no psychosocial stress group.

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135 Effects of Differential Chronic Psychosocial Stress Paradi g ms on Ob j ect Reco g nition Memor y ( First Minute ) No Psych Stress Ratio Time 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 Psych Stress 1 Psych Stress 2 Psych Stress 3* * Figure 45 Effects of differential chronic psychosocial stress paradigms on object recognition memory during the first minute of th e testing trial. The da ta are presented as mean ratio time SEM. = p < 0.05 relative to the no psychosocial stress group. Testing The analysis comparing the ratio tim es of all groups during the 5-minute object recognition testing sessi on revealed no significant main effect of psychosocial stress, F (3,29) = 1.23, p > 0.05 (see Figure 44). The analysis comparing the ratio times of all groups during the first minute of the testing trial revealed a signifi cant main effect of psychosocial stress, F (3,20) = 6.29, p < 0.01 (see Figure 45). Post hoc contrasts indicated that each of the 3 psychosoci al stress groups exhibited signifi cantly lower ratio times than the no psychosocial stress group ( ps < 0.05).

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136 Effects of Differential Chronic Psychosocial Stress Paradigms on Serum Corticos terone Levels Corticosterone ( g/dL) 0 5 10 15 20 No Psychosocial Stress Psychosocial Stress 1 Psychosocial Stress 2 Psychosocial Stress 3 ImmobilizationHome Cage 0 min20 min 80 min Figure 46 Effects of differential chronic psychosocial stress paradigms on serum corticosterone levels. The data are pres ented as mean corticosterone levels ( g/dL) SEM. Corticosterone Levels (see Figure 46) The analysis of corticosterone levels revealed a significant main effect of time point, F (2,62) = 138.41, p < 0.001. Post hoc tests indicate d that all groups displayed significantly elevated serum corticosterone levels, relative to baseline, following 20 minutes of acute immobilization stress and that these levels remained elevated an hour later ( p s < 0.05). There was no significant ma in effect of psychosocial stress, F (3,31) = 1.11, and the Time Point x Psychosocial Stre ss interaction was not significant, F (6,62) = 0.93 ( ps > 0.05). Cardiovascular Activity Heart Rate (see Figure 47) The analysis of heart ra te revealed no significant main effect of psychosocial stress, F (3,22) = 0.17, p > 0.05.

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137 Effects of Differential Chronic Psychosocial Stress Paradigms on Heart RateNo Psych Stress Heart Rate (bpm) 0 350 375 400 425 Psych Stress 1 Psych Stress 2 Psych Stress 3 Figure 47 Effects of differential chronic psychosocial stress pa radigms on heart rate. The data are presented as mean heart rate (bpm) SEM. Effects of Differential Chronic Psychosocial Stress Paradigms on Systolic Blood PressureNo Psych Stress Systolic Blood Pressure (mm Hg) 0 90 100 110 120 130 140 Psych Stress 1 Psych Stress 2 Psych Stress 3* Figure 48 Effects of differential chronic psyc hosocial stress paradigms on systolic blood pressure. The data are presented as mean systolic blood pressure (mm Hg) SEM. = p < 0.05 relative to the no stress group.

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138 Systolic Blood Pre ssure (see Figure 48) The analysis of systolic blood pressure revealed a significant main effect of psychosocial stress, F (3,22) = 3.46, p < 0.05. Post hoc tests indicated that psychosocial stress group 3 exhibited significan tly greater systolic blood pressure than the no psychosocial stress group. Effects of Differential Chronic Psychosocial Stress Paradigms on Diastolic Blood PressureNo Psych Stress Diastolic Blood Pressure (mm Hg) 0 60 70 80 90 100 Psych Stress 1 Psych Stress 2 Psych Stress 3* Figure 49 Effects of differential chronic ps ychosocial stress paradigms on diastolic blood pressure. The data are presented as mean diastolic blood pressure (mm Hg) SEM. = p < 0.05 relative to the no psychosocial stress group. Diastolic Blood Pressure (see Figure 49) The analysis of diastolic blood pressure revealed a significant main effect of psychosocial stress, F (3,22) = 3.13, p < 0.05. Post hoc tests indicated that psychosocial stre ss group 3 exhibited significantly greater diastolic blood pressure than the no psychosocial stress group. Growth Rates (see Figure 50) The analysis of growth rate revealed no significant main effect of psychosocial stress, F (3,34) = 0.54, p > 0.05.

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139 Effects of Differential Chronic Psychosocial Stress Paradigms on Growth RateNo Psych Stress Growth Rate (g / day) 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 Psych Stress 1 Psych Stress 2 Psych Stress 3 Figure 50 Effects of differential chronic psyc hosocial stress paradigms on growth rate. The data are presented as mean growth rate (g/day) SEM. Effects of Differential Chronic Psychosocial Stress Paradigms on Adrenal Gland WeightNo Psych Stress Adrenal Gland Weight (mg / 100 g b.w.) 0 2 4 6 8 10 Psych Stress 1 Psych Stress 2 Psych Stress 3 Figure 51 Effects of differential chronic psyc hosocial stress paradigms on adrenal gland weight. The data are presented as mean adrenal gland weight (mg/100 g b.w.) SEM.

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140 Adrenal Gland Weights (see Figure 51) The analysis of adrenal glands weight revealed no significan t main effect of psychosocial stress, F (3,34) = 0.73, p > 0.05. Effects of Differential Chronic Psychosocial Stress Paradigms on Thymus WeightNo Psych Stress Thymus Weight (mg / 100 g b.w.) 0 20 40 60 80 100 Psych Stress 1 Psych Stress 2 Psych Stress 3* Figure 52 Effects of differential chronic ps ychosocial stress paradigms on thymus weight. The data are presented as mean t hymus weight (mg/100 g b.w.) SEM. = p < 0.05 relative to the no psychosocial stress group; = p = 0.057 relative to the no psychosocial stress group. Thymus Weights (see Figure 52) The analysis of thymus we ight revealed a significant main effect of psychosocial stress, F (3,35) = 3.76, p < 0.05. Post hoc tests indicated that psychosocial stress group 3 exhibited significantly smaller thymuses than the no psycho social stress group. Moreover, psychosocial stress group 2 tended to display smaller thymuses than the no psychosocial stress group, although this differe nce did not reach sta tistical significance.

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141 Discussion of Findings The most important finding of the present e xperiment is that at least some of the PTSD-like physiological and behavioral e ffects induced by the chronic psychosocial stress paradigm employed in Experiments On e through Three could be maintained for at least 4 months following the initial stress se ssion. Psychosocial stress group 1, which was given two acute cat exposures and daily social instability throughout the entire experiment, displayed significantly greater f ear responses to the context and cue that were paired with the acute cat exposures, heightened anxiety on the EPM and impaired object recognition memory, relative to the no psychosocial stress (i.e., control) group. However, psychosocial stress group 1 did not ex hibit an exaggerated startle response to any auditory stimulus intensity or reduced gr owth rate, larger adre nal glands or smaller thymuses than the controls. These findings sugg est that some of the effects of our chronic stress regimen, and in particular the physiol ogical effects, diminish over time, even with the continued presence of daily social instability. Psychosocial stress group 2 exhibited physiological and behavioral effects (i.e., significant fear responses to the context and cue tests, heightened anxiety on the EPM, impaired object recognition memory) that we re very similar to those observed in psychosocial stress group 1. Like psychosoc ial stress group 1, psychosocial stress group 2 did not exhibit an exaggerated startle respons e to any auditory stimulus intensity or a reduced growth rate, larger adrenal glands or smaller thymuses than the controls. One major difference between these two groups, however, was that psychosocial stress group 2 displayed a significantly greater fear res ponse, at least with regards to immobility, to

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142 the context that was paired with the acute cat exposures than all other groups. These findings indicate that the addi tional cat exposure resulted onl y in a stronger contextual fear memory for the acute cat exposures and did not reinforce the physiological and behavioral changes that were l acking in psychosocial stress group 1. Similar to psychosocial stress groups 1 and 2, psychosocial stress group 3 exhibited heightened anxiet y on the EPM and impaired ob ject recognition memory. Interestingly, however, psychosocial stress group 3 displayed some physiological and behavioral effects that were markedly different from those of the other psychosocial stress groups. First, psychosocial stress group 3 did not exhibit a significant fear response to the context or tone that was paired with the acute cat exposures. Moreover, psychosocial stress group 3 was the only psychosocial stress group to display significantly greater blood pre ssure and smaller thymuses than the control group. Since the only difference between psychosocial stre ss groups 2 and 3 was the type of social instability to which each was exposed, these findings suggest that the irregular social instability resulted in stronger effects on contextual and cue fear memory, as well as the physiological responses of rats to an acute stressor, than daily social instability. Conclusions and Limitations The results of this final experiment provi de insight into the temporal and social factors that mediate the length of time that trauma-induced changes in rat physiology and behavior last. This is the first study to report physiological and behavioral changes in rats subjected to a chronic psychosoc ial stress paradigm more than 4 months after the stress regimen began. The findings of this experiment indicate that some of the PTSD-like

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143 behavioral changes (i.e., intact fear memor y, heightened anxiety, cognitive impairments) produced by our laboratorys stress paradigm can be maintained up to 115 days poststress. One caveat to these findings is that in every psychosocial stress group, the social instability manipulation continued until the beginning of behavioral testing. Thus, the observed effects may have been caused, at least in part, by the presence of social instability until behavioral testing. Perhaps the most interesti ng finding of the present expe riment was that irregular social instability led to an impairment of the memories for the context and cue that were previously paired with the acute cat e xposures and exacerbated the stress-induced physiological changes in rats. Psychosocial stress group 3 was the only stress group to display significantly greater cardiovascular reactivity to an acute stressor and a significantly smaller thymus than the no psychosocial stress group. Most studies, and even those from our own laboratory, that have employed unstable housing conditions in a stress paradigm have used daily social instability to demonstrate its adverse effects on rat physiology and behavior (Baran et al., 2005; Baranyi et al ., 2005; Gerges et al., 2004; Haller et al., 2004; Lemaire et al., 1997; Pa rk et al., 2001). The strategy behind using the irregular social stress in th e present experiment was to make the unstable housing more unpredictable. The typical daily randomized housing procedure, although effective for the 31-day paradigm, is somewhat predictable in that it occurs at approximately the same time every day, and if continued for an extended period of time, could eventually become ineffective. Therefore, I reasoned that the irregular social stress could exacerbate the physiological and behavioral effects of the daily social instabili ty and increase the

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144 likelihood that rats would e xhibit PTSD-like abnormalities for a longer period of time. The present findings demonstrate that the elemen t of predictability in day-to-day stressors may play a major role in the development of chronic PTSD.

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145 Chapter Six: Concluding Remarks PTSD is a debilitating mental illness that is characterized by the repeated reliving of a life-threatening traumatic event through intrusive, flashback memories. People with PTSD display an array of physiological and behavioral symptoms, including persistent anxiety, exaggerated startle, heightened autonomic activity, impaired HPA axis functioning, cognitive impairments and impair ed extinction of conditioned fear. Despite scientific advances over the past couple of decades, the neurobiological mechanisms underlying the development and maintenance of PTSD remain unclear. Moreover, there are currently no pharmacological agents that effectively treat both the dynamic memory (e.g., intrusive memories, re-experiencing symptoms) and st able trait (e.g., anxiety, hyperarousal) components of the disorder. Thus the need for a valid animal model of PTSD to use for preclinical research has become an issue of growing importance. Many of the symptoms of PTSD (e.g., he ightened anxiety, ex aggerated startle response, cognitive impairments, etc.) can be experienced by people suffering from other mental illnesses such as major depressive disorder, panic disorder or generalized anxiety disorder. Thus, an animal model of PTSD should produce physiologi cal and behavioral changes that are unique to the disorder as it is observed in humans. Some of the symptoms of PTSD that set it apart from other disorders include the presence of a powerful and intrusive memory of the traumatic event, abnormally low levels of glucocorticoids and enhanced suppression of glucocorticoid levels following the

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146 administration of dexamethasone. While ot her mental illnesses have also been characterized by abnormal HPA axis functi oning, PTSD is the only disorder to be characterized by abnormal reductions in basal cortisol levels and an enhanced suppression of cortisol in the dexamethas one suppression test (M arshall et al., 2002; Yehuda, 2002; Yehuda, 2005; Yehuda et al., 1993a ). For instance, major depressive disorder is characterized by chronically el evated glucocorticoid levels and reduced glucocorticoid suppression following the administration of dexamethasone (Pariante & Lightman, 2008). In contrast to people with PTSD, patients suffering from MDD also display an abnormally low number of glucocor ticoid receptors. Previous work from our laboratory has already demonstrated that the present psychosocial stress regimen produces heightened anxiety, an exaggerated startle response, cognitive impairments, heightened cardiovascular reactivity and hype rresponsivity to yohimbine (Zoladz et al., 2008). The present work has extended these find ings by demonstrating th at it also results in a powerful memory for the two isolat ed stress experiences and produces HPA abnormalities that are commonly observed in pe ople with PTSD. In conjunction with our previous work, these findings further suppor t that this psychosocial stress regimen produces physiological and behavioral change s that specifically model those found in PTSD. Experiment Three also indicated that th is model demonstrates predictive validity. That is to say, compounds that were predicted to ameliorate stress-induced changes in rat physiology and behavior and have led to im provements in some symptom clusters of PTSD were shown to ameliorate some of the physiological and behavioral sequelae

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147 induced by our chronic psychosocial stress para digm. Thus, this paradigm could be used in future research to guide the developmen t of new pharmacotherapeutic approaches to the treatment of PTSD. The differential eff ectiveness of the pharmacological agents examined in Experiment Three, particularly th e profile of tianeptine as the most effective agent, suggests that abnormal glutamater gic functioning may be involved in this regimens stress-induced changes in rat physiology and behavior. Finally, the last study provided evidence th at some of the effects induced by our chronic psychosocial stress paradigm could be maintained for at least 4 months following the first stress exposure. As PT SD is often a chronic disorder that affects people for most of their lives, such a finding indicates that this paradigm could serve to examine the neurobiological correlates of chronic PTSD as well. The reason why the exaggerated startle response, along with some of the ot her effects that we normally detect (e.g., reduced growth rate, increase adrenal gland we ight, etc.), was not observed in our typical psychosocial stress paradigm at 4 months post-st ress should be examined further in future work. Collectively, these studies have provided insight into the mechanisms underlying trauma-induced changes in brain and behavior and should advance our understanding of the biological basis of PTSD. Yet, mu ch remains to be known regarding the neurobiological underpinnings of the present effects. Future studies should examine the effects of the present psychos ocial stress manipulations on neuroplasticity within brain regions that play a major role in PTSD, such as the PFC, amygdala and hippocampus and

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148 whether or not these changes correlate with the observed alterations in rat physiology and behavior.

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149 References Adamec, R. (1997). Transmitter systems invol ved in neural plasticity underlying increased anxiety and defense: implica tions for understanding anxiety following traumatic stress. Neurosci Biobehav Rev 21, 755-765. Adamec, R., Muir, C., Grimes, M., & Pearce y, K. (2007). Involvement of noradrenergic and corticoid receptors in the consolida tion of the lasting anxiogenic effects of predator stress. Behav Brain Res 179, 192-207. Adamec, R. E., Blundell, J., & Burton, P. ( 2006). Relationship of the predatory attack experience to neural plasticity, pCREB e xpression and neuroendocrine response. Neurosci Biobehav Rev 30, 356-375. Adamec, R. E., Burton, P., Shallow, T., & Budgell, J. (1999). NMDA receptors mediate lasting increases in anxiety-like beha vior produced by the stress of predator exposure: implications for a nxiety associated with posttraumatic stress disorder. Physiol Behav 65, 723-737. Adamec, R. E. & Shallow, T. (1993). Las ting effects on rodent anxiety of a single exposure to a cat. Physiol Behav 54, 101-109. Adolphs, R. (2002). Neural systems for recognizing emotion. Curr Opin Neurobiol 12, 169-177. Albucher, R. C. & Liberzon, I. (2002). Ps ychopharmacological treatment in PTSD: a critical review. J Psychiatr Res 36, 355-367.

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150 Amaral, D. G. & Insausti, R. (1992). Retrograd e transport of D-[3H]-aspartate injected into the monkey amygdaloid complex. Exp Brain Res 88, 375-388. Amat, J., Baratta, M. V., Paul, E., Bland, S. T., Watkins, L. R., & Maier, S. F. (2005). Medial prefrontal cortex de termines how stressor contro llability affects behavior and dorsal raphe nucleus. Nat Neurosci 8, 365-371. American Psychiatri c Association (1994). Diagnostic and Statistical Manual of Mental Disorders: DSM-IV (4th ed.) Washington, D.C.: Am erican Psychiatric Association. Andrews, B., Brewin, C. R., & Rose, S. (2003). Gender, social support, and PTSD in victims of violent crime. J Trauma Stress 16, 421-427. Armony, J. L., Corbo, V., Clement, M. H., & Brunet, A. (2005). Amygdala response in patients with acute PTSD to masked and unmasked emotional facial expressions. Am J Psychiatry 162, 1961-1963. Asnis, G. M., Kohn, S. R., Henderson, M., & Brown, N. L. (2004). SSRIs versus nonSSRIs in post-traumatic stress disorder: an update w ith recommendations. Drugs 64, 383-404. Bagley, J. & Moghaddam, B. (1997). Tempor al dynamics of glutamate efflux in the prefrontal cortex and in the hippocampus following repeated stress: effects of pretreatment with saline or diazepam. Neuroscience 77, 65-73.

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151 Baker, D. G., Diamond, B. I., Gillette, G., Ha mner, M., Katzelnick, D., Keller, T., et al. (1995). A double-blind, randomized, placebocontrolled, multi-center study of brofaromine in the treatment of post-traumatic stress disorder. Psychopharmacology 122, 386-389. Baker, D. G., Ekhator, N. N., Kasckow, J. W., Dashevsky, B., Horn, P. S., Bednarik, L., et al. (2005). Higher levels of basal serial CSF cortisol in combat veterans with posttraumatic stress disorder. Am J Psychiatry 162 992-994. Baker, D. G., West, S. A., Ni cholson, W. E., Ekhator, N. N., Kasckow, J. W., Hill, K. K., et al. (1999). Serial CSF corticotr opin-releasing hormone levels and adrenocortical activity in combat veterans with posttraumatic stress disorder. Am J Psychiatry 156, 585-588. Baker, K. B. & Kim, J. J. (2002). Effects of stress and hippocampal NMDA receptor antagonism on recognition memory in rats. Learn Mem 9, 58-65. Balcioglu, A., Bozkurt, A., & Kayaalp, S. O. (1991). Comparison of the cardiovascular effects of amineptine with those of amitriptyline and imipramine in anaesthetized rats. Arch Int Pharmacodyn Ther 309, 64-74. Baran, S. E., Campbell, A. M., Kleen, J. K., Foltz, C. H., Wright, R. L., Diamond, D. M., et al. (2005). Combination of high fat diet and chronic stress retracts hippocampal dendrites. NeuroReport 16, 39-43. Baranyi, J., Bakos, N., & Haller, J. (2005). Social instability in female rats: the relationship between st ress-related and anxiety-like consequences. Physiol Behav 84, 511-518.

PAGE 169

152 Barden, N. (1999). Regulation of corticostero id receptor gene expression in depression and antidepressant action. J Psychiatry Neurosci 24, 25-39. Barrett, B., Byford, S., & Knapp, M. (2005). Evidence of cost-effective treatments for depression: a systematic review. J Affect Disord 84, 1-13. Bartanusz, V., Aubry, J. M., Pagliusi, S., J ezova, D., Baffi, J., & Kiss, J. Z. (1995). Stress-induced changes in messenger RNA levels of N-methyl-D-aspartate and AMPA receptor subunits in selected regions of the rat hippocampus and hypothalamus. Neuroscience 66, 247-252. Berntson, G. G., Cacioppo, J. T., & Quigley, K. S. (1993). Respiratory sinus arrhythmia: autonomic origins, physiological mechanisms, and psychophysiological implications. Psychophysiology 30, 183-196. Bisson, J. I. (2007). Pharmacological trea tment of post-traumatic stress disorder. Adv Psychiatr Treat 13, 119-126. Blanchard, D. C., Sakai, R. R., McEwen, B ., Weiss, S. M., & Blanchard, R. J. (1993). Subordination stress: behavioral, br ain, and neuroendocrine correlates. Behav Brain Res 58 113-121. Blanchard, E. B., Kolb, L. C., Pallmeyer, T. P., & Gerardi, R. J. (1982). A psychophysiological study of post traumatic stress disorder in Vietnam veterans. Psychiatr Q 54, 220-229. Blanchard, E. B., Kolb, L. C., Prins, A., Ga tes, S., & McCoy, G. C. (1991). Changes in plasma norepinephrine to combat-relate d stimuli among Vietnam veterans with posttraumatic stress disorder. J Nerv Ment Dis 179 371-373.

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153 Blanchard, R. J., Nikulina, J. N., Sakai, R. R., McKittrick, C., McEwen, B., & Blanchard, D. C. (1998). Behavioral and endocrine change following chronic predatory stress. Physiol Behav 63, 561-569. Bland, S. T., Schmid, M. J., Greenwood, B. N ., Watkins, L. R., & Maier, S. F. (2006). Behavioral control of the stressor modulates stress-induced changes in neurogenesis and fibroblast growth factor-2. NeuroReport 17, 593-597. Bland, S. T., Tamlyn, J. P., Barrientos, R. M., Greenwood, B. N., Watkins, L. R., Campeau, S., et al. (2007). Expression of fibroblast growth factor-2 and brainderived neurotrophic factor mRNA in the medial prefrontal cortex and hippocampus after uncontrollabl e or controllable stress. Neuroscience 144 12191228. Bodnoff, S. R., Suranyi-Cadotte, B., Aitken, D. H., Quirion, R., & Meaney, M. J. (1988). The effects of chronic antidepressant treatment in an animal model of anxiety. Psychopharmacology 95, 298-302. Boehnlein, J. K. & Kinzie, J. D. (2007). Ph armacologic reduction of CNS noradrenergic activity in PTSD: the case for clonidine and prazosin. J Psychiatr Pract 13, 72-78. Bonne, O., Brandes, D., Gilboa, A., Gomori, J. M., Shenton, M. E., Pitman, R. K., et al. (2001). Longitudinal MRI study of hippocampal volume in trauma survivors with PTSD. Am J Psychiatry 158, 1248-1251. Boscarino, J. A. (1995). Post-traumatic st ress and associated disorders among Vietnam veterans: the significance of comb at exposure and social support. J Trauma Stress 8, 317-336.

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154 Boscarino, J. A. (1996). Posttraumatic stress disorder, exposure to combat, and lower plasma cortisol among Vietnam veterans: findings and clinical implications. J Consult Clin Psychol 64, 191-201. Boscarino, J. A. & Chang, J. (1999). Electrocardiogram abnormalities among men with stress-related psychiatric disorders: implications for coronary heart disease and clinical research. Ann Behav Med 21 227-234. Brady, K., Pearlstein, T., Asnis, G. M., Baker, D., Rothbaum, B., Sikes, C. R., et al. (2000). Efficacy and safety of sertraline treatment of posttraumatic stress disorder: a randomized controlled trial. JAMA 283 1837-1844. Brady, K. T., Sonne, S. C., & Roberts, J. M. (1995). Sertraline treatment of comorbid posttraumatic stress disorder and alcohol dependence. J Clin Psychiatry 56 502505. Brand, S. R., Engel, S. M., Canfield, R. L ., & Yehuda, R. (2006). The effect of maternal PTSD following in utero trauma exposure on behavior and temperament in the 9month-old infant. Ann N Y Acad Sci 1071, 454-458. Braver, T. S., Cohen, J. D., Nystrom, L. E., Jonides, J., Smith, E. E., & Noll, D. C. (1997). A parametric study of prefrontal cortex involvement in human working memory. Neuroimage 5, 49-62. Bremner, J. D. (1999). Alterations in brain structure and function associated with posttraumatic stress disorder. Semin Clin Neuropsychiatry 4, 249-255.

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155 Bremner, J. D., Innis, R. B., Ng, C. K., Stai b, L. H., Salomon, R. M., Bronen, R. A., et al. (1997a). Positron emission tomography measurement of cerebral metabolic correlates of yohimbine administration in combat-related posttraumatic stress disorder. Arch Gen Psychiatry 54, 246-254. Bremner, J. D., Randall, P., Scott, T. M., Br onen, R. A., Seibyl, J. P., Southwick, S. M., et al. (1995a). MRI-based measurement of hippocampal volume in patients with combat-related posttraumatic stress disorder. Am J Psychiatry 152, 973-981. Bremner, J. D., Randall, P., Scott, T. M., Capelli, S., Delaney, R., McCarthy, G., et al. (1995b). Deficits in short-term memory in adult survivors of childhood abuse. Psychiatry Res 59, 97-107. Bremner, J. D., Randall, P., Vermetten, E., Staib, L., Bronen, R. A., Mazure, C., et al. (1997b). Magnetic resonance imaging-based measurement of hippocampal volume in posttraumatic stress disorder related to childhood physical and sexual abuse--a preliminary report. Biol Psychiatry 41, 23-32. Bremner, J. D., Scott, T. M., Delaney, R. C., Southwick, S. M., Mason, J. W., Johnson, D. R., et al. (1993). Deficits in shor t-term memory in posttraumatic stress disorder. Am J Psychiatry 150, 1015-1019. Bremner, J. D., Staib, L. H., Kaloupek, D., Southwick, S. M., Soufer, R., & Charney, D. S. (1999). Neural correlates of exposur e to traumatic pictures and sound in Vietnam combat veterans with and w ithout posttraumatic stress disorder: a positron emission tomography study. Biol Psychiatry 45, 806-816.

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156 Bremner, J. D., Vermetten, E., Schmahl, C., Vaccarino, V., Vythilingam, M., Afzal, N., et al. (2005). Positron emission tomographic imaging of neural correlates of a fear acquisition and extin ction paradigm in women with childhood sexual-abuserelated post-traumatic stress disorder. Psychol Med 35, 791-806. Bremner, J. D., Vythilingam, M., Vermetten, E., Adil, J., Khan, S., Nazeer, A., et al. (2003a). Cortisol response to a cognitive stress challeng e in posttraumatic stress disorder (PTSD) related to childhood abuse. Psychoneuroendocrinol 28, 733-750. Bremner, J. D., Vythilingam, M., Verme tten, E., Southwick, S. M., McGlashan, T., Nazeer, A., et al. (2003b). MRI and P ET study of deficits in hippocampal structure and function in women with childhood sexual abuse and posttraumatic stress disorder. Am J Psychiatry 160, 924-932. Brewin, C. R., Andrews, B., & Valentine, J. D. (2000). Meta-analysis of risk factors for posttraumatic stress disorder in trauma-exposed adults. J Consult Clin Psychol 68, 748-766. Brink, C. B., Harvey, B. H., & Brand, L. (2006). Tianeptine: a novel atypical antidepressant that may provide new insi ghts into the biomolecular basis of depression. Recent Patents CNS Drug Discov 1, 29-41. Britton, J. C., Phan, K. L., Taylor, S. F., Fi g, L. M., & Liberzon, I. (2005). Corticolimbic blood flow in posttraumatic stress diso rder during script-driven imagery. Biol Psychiatry 57 832-840. Brkanac, Z., Pastor, J. F., & St orck, M. (2003). Prazosin in PTSD. J Am Acad Child Adolesc Psychiatry 42, 384-385.

PAGE 174

157 Browning, M., Reid, C., Cowen, P. J., Goodwi n, G. M., & Harmer, C. J. (2007). A single dose of citalopram increases fear recognition in healthy subjects. J Psychopharmacol 21, 684-690. Brunet, A., Orr, S. P., Tremblay, J., Robert son, K., Nader, K., & Pitman, R. K. (2008). Effect of post-retriev al propranolol on psychophysiologic responding during subsequent script-driven traumatic imag ery in post-traumatic stress disorder. J Psychiatr Res 42, 503-506. Bryant, R. A. (2006). Longitudinal psychophysio logical studies of heart rate: mediating effects and implications for treatment. Ann N Y Acad Sci 1071 19-26. Bryant, R. A. & Harvey, A. G. (1997). Attent ional bias in posttraumatic stress disorder. J Trauma Stress 10, 635-644. Bryant, R. A., Harvey, A. G., Guthrie, R. M., & Moulds, M. L. (2000). A prospective study of psychophysiological arousal, acute stress disorder, and posttraumatic stress disorder. J Abnorm Psychol 109, 341-344. Bryant, R. A., Marosszeky, J. E., Crooks, J., & Gurka, J. A. (2004). Elevated resting heart rate as a predictor of posttraumatic stre ss disorder after seve re traumatic brain injury. Psychosom Med 66, 760-761. Bryant, R. A., Salmon, K., Sinclair, E., & Davi dson, P. (2007). Heart rate as a predictor of posttraumatic stress disorder in children. Gen Hosp Psychiatry 29, 66-68. Buchel, C. & Dolan, R. J. (2000). Classical fear conditioning in functional neuroimaging. Curr Opin Neurobiol 10, 219-223.

PAGE 175

158 Buckley, T. C., Blanchard, E. B., & Neill, W. T. (2000). Information processing and PTSD: a review of the empirical literature. Clin Psychol Rev 20, 1041-1065. Buckley, T. C. & Kaloupek, D. G. (2001). A meta-analytic examination of basal cardiovascular activity in posttraumatic stress disorder. Psychosom Med 63, 585594. Burghardt, N. S., Sullivan, G. M., McEwen, B. S., Gorman, J. M., & LeDoux, J. E. (2004). The selective serotonin reuptake inhi bitor citalopram in creases fear after acute treatment but reduces fear with chronic treatment: a comparison with tianeptine. Biol Psychiatry 55, 1171-1178. Burstein, A. (1984). Treatment of post-traumatic stress disorder with imipramine. Psychosomatics 25, 681-687. Butler, R. W., Braff, D. L., Rausch, J. L., Jenkins, M. A., Sprock, J., & Geyer, M. A. (1990). Physiological eviden ce of exaggerated startle response in a subgroup of Vietnam veterans with combat-related PTSD. Am J Psychiatry 147, 1308-1312. Cahill, L. & McGaugh, J. L. (1998). Mechan isms of emotional arousal and lasting declarative memory. Trends Neurosci 21, 294-299. Cahill, L., Prins, B., Weber, M., & McGa ugh, J. L. (1994). Beta-adrenergic activation and memory for emotional events. Nature 371, 702-704. Cai, W. H., Blundell, J., Han, J., Greene, R. W., & Powell, C. M. (2006). Postreactivation glucocorticoids impair recall of established fear memory. J Neurosci 26, 95609566.

PAGE 176

159 Carrion, V. G., Weems, C. F., Eliez, S., Pa twardhan, A., Brown, W., Ray, R. D., et al. (2001). Attenuation of frontal asymmetry in pediatric posttraumatic stress disorder. Biol Psychiatry 50, 943-951. Casada, J. H., Amdur, R., Larsen, R., & Liberzon, I. (1998). Psychophysiologic responsivity in posttraumatic stress di sorder: generalized hyperresponsiveness versus trauma specificity. Biol Psychiatry 44, 1037-1044. Castanon, N., Bluthe, R. M., & Dantzer, R. (2001). Chronic treatment with the atypical antidepressant tianeptine attenuates si ckness behavior induced by peripheral but not central lipopolysaccharide and in terleukin-1 beta in the rat. Psychopharmacology 154, 50-60. Cavaljuga, S., Licanin, I., Mulabegovic, N., & Potkonjak, D. (2003). Therapeutic effects of two antidepressant agents in the treat ment of posttraumatic stress disorder (PTSD). Bosn J Basic Med Sci 3, 12-16. Ceyhan, M., Kayir, H., & Uzbay, I. T. (2005). Investigation of the effects of tianeptine and fluoxetine on pentylenetetrazo le-induced seizures in rats. J Psychiatr Res 39, 191-196. Chambers, R. A., Bremner, J. D., Moghaddam, B., Southwick, S. M., Charney, D. S., & Krystal, J. H. (1999). Glutamate and pos t-traumatic stress disorder: toward a psychobiology of dissociation. Semin Clin Neuropsychiatry 4 274-281. Cheng, D. T., Knight, D. C., Smith, C. N., Stein, E. A., & Helmstetter, F. J. (2003). Functional MRI of human am ygdala activity during Pavlovian fear conditioning: stimulus processing versus response expression. Behav Neurosci 117, 3-10.

PAGE 177

160 Cohen, H., Benjamin, J., Geva, A. B., Matar, M. A., Kaplan, Z., & Kotler, M. (2000a). Autonomic dysregulation in panic disorder and in post-traumatic stress disorder: application of power spectrum analysis of heart rate variability at rest and in response to recollection of trauma or panic attacks. Psychiatry Res 96, 1-13. Cohen, H., Benjamin, J., Kaplan, Z., & Kotle r, M. (2000b). Admini stration of high-dose ketoconazole, an inhibitor of steroid synt hesis, prevents posttraumatic anxiety in an animal model. Eur Neuropsychopharmacol 10, 429-435. Cohen, H., Kaplan, Z., Matar, M. A., Loewen thal, U., Kozlovsky, N., & Zohar, J. (2006). Anisomycin, a protein synthesis inhi bitor, disrupts traumatic memory consolidation and attenu ates posttraumatic stress response in rats. Biol Psychiatry 60, 767-776. Cohen, H., Kaplan, Z., Matar, M. A., Loewen thal, U., Zohar, J., & Richter-Levin, G. (2007). Long-lasting behavioral effects of j uvenile trauma in an animal model of PTSD associated with a failure of the autonomic nervous system to recover. Eur Neuropsychopharmacol 17, 464-477. Cohen, H., Kotler, M., Matar, M. A., Kapla n, Z., Loewenthal, U., Miodownik, H., et al. (1998). Analysis of heart rate variability in posttraumatic stress disorder patients in response to a trauma-related reminder. Biol Psychiatry 44, 1054-1059. Cohen, H., Kotler, M., Matar, M. A., Kapl an, Z., Miodownik, H., & Cassuto, Y. (1997). Power spectral analysis of heart rate variability in posttraumatic stress disorder patients. Biol Psychiatry 41, 627-629.

PAGE 178

161 Cohen, H. & Zohar, J. (2004). An animal m odel of posttraumatic st ress disorder: the use of cut-off behavioral criteria. Ann N Y Acad Sci 1032, 167-178. Cohen, H., Zohar, J., Matar, M. A., Zee v, K., Loewenthal, U., & Richter-Levin, G. (2004). Setting apart the affected: the use of behavioral criteria in animal models of post traumatic stress disorder. Neuropsychopharmacology 29, 1962-1970. Connor, K. M., Sutherland, S. M., Tupler, L. A., Malik, M. L., & Davidson, J. R. (1999). Fluoxetine in post-traumatic stress diso rder. Randomised, double-blind study. Br J Psychiatry 175, 17-22. Cook, S. C. & Wellman, C. L. (2004). Chroni c stress alters dendritic morphology in rat medial prefrontal cortex. J Neurobiol 60, 236-248. Curtis, C. E. & D'Esposito, M. (2003). Persiste nt activity in the pref rontal cortex during working memory. Trends Cogn Sci 7, 415-423. Davidson, J., Kudler, H., Smith, R., Mahorney, S. L., Lipper, S., Hammett, E., et al. (1990). Treatment of posttraumatic stress disorder with amitriptyline and placebo. Arch Gen Psychiatry 47, 259-266. Davidson, J. R. (2003). Treatment of posttraumatic stress disorder: the impact of paroxetine. Psychopharmacol Bull 37 76-88. Davidson, J. R., Kudler, H. S., Saunders, W. B., Erickson, L., Smith, R. D., Stein, R. M., et al. (1993). Predicting response to amitrip tyline in posttraumatic stress disorder. Am J Psychiatry 150, 1024-1029.

PAGE 179

162 Davidson, J. R., Rothbaum, B. O., Van der Kol k, B. A., Sikes, C. R., & Farfel, G. M. (2001). Multicenter, double-blind comparis on of sertraline an d placebo in the treatment of posttraumatic stress disorder. Arch Gen Psychiatry 58, 485-492. Davis, L. L., Frazier, E. C., Williford, R. B., & Newell, J. M. (2006). Long-term pharmacotherapy for post-tra umatic stress disorder. CNS Drugs 20, 465-476. De Bellis, M. D., Baum, A. S., Birmaher, B ., Keshavan, M. S., Eccard, C. H., Boring, A. M., et al. (1999a). Developmental traumato logy. Part I: biologic al stress systems. Biol Psychiatry 45, 1259-1270. De Bellis, M. D., Hall, J., Boring, A. M., Frustaci, K., & Moritz, G. (2001). A pilot longitudinal study of hippocampal volumes in pediatric maltreatment-related posttraumatic stress disorder. Biol Psychiatry 50, 305-309. De Bellis, M. D., Keshavan, M. S., Clark, D. B., Casey, B. J., Giedd, J. N., Boring, A. M., et al. (1999b). Developmental traumatology. Part II: brain development. Biol Psychiatry 45 1271-1284. De Bellis, M. D., Keshavan, M. S., Shifflett, H ., Iyengar, S., Beers, S. R., Hall, J., et al. (2002). Brain structures in pediatric maltreatment-re lated posttraumatic stress disorder: a sociodemographically matched study. Biol Psychiatry 52, 1066-1078. De Boer, M., Op den Velde, W., Falger, P. J. R., Hovens, J. E., De Groen, J. H. M., & Van Duijn, H. (1992). Fluvoxamine treatm ent for chronic PTSD: A pilot study. Psychother Psychosom 57, 158-163.

PAGE 180

163 de Kloet, C., Geuze, E., Heijnen, C., Lentjes, E., Manuel, R., van Pe lt, J., et al. (2008). Differences in the response to the combined DEX-CRH test between PTSD patients with and without co-morbid depressive disorder. Psychoneuroendocrinol 33, 313-320. de Kloet, C. S., Vermetten, E., Geuze, E., Kavelaars, A., Heijnen, C. J., & Westenberg, H. G. (2006). Assessment of HPA-axis f unction in posttraumatic stress disorder: pharmacological and non-pharmacologi cal challenge tests, a review. J Psychiatr Res 40, 550-567. de Kloet, E. R., Oitzl, M. S., & Joels, M. (1999). Stress and cognition: are corticosteroids good or bad guys? Trends Neurosci 22 422-426. Debiec, J. & LeDoux, J. E. (2004). Disruption of reconsolidation but not consolidation of auditory fear conditioning by noradre nergic blockade in the amygdala. Neuroscience 129, 267-272. Debiec, J. & LeDoux, J. E. (2006). Noradrenergic signaling in the amygdala contributes to the reconsolidation of fear memo ry: treatment implications for PTSD. Ann N Y Acad Sci 1071, 521-524. Debiec, J., LeDoux, J. E., & Nader, K. (2002) Cellular and systems reconsolidation in the hippocampus. Neuron 36, 527-538. Defrance, R., Marey, C., & Kamoun, A. (1988). Antidepressant and anxiolytic activities of tianeptine: an overvie w of clinical trials. Clin Neuropharmacol 11, S74-S82.

PAGE 181

164 Delbende, C., Contesse, V., Mocaer, E., Kamoun, A., & Vaudry, H. (1991). The novel antidepressant, tianeptine, reduces stre ss-evoked stimulation of the hypothalamopituitary-adrenal axis. Eur J Pharmacol 202, 391-396. Deuschle, M., Schweiger, U., Weber, B., Gotth ardt, U., Krner, A., Schmider, J., et al. (1997). Diurnal activity and pulsatility of the hypothalamus-pituitary-adrenal system in male depressed pa tients and healthy controls. J Clin Endocrinol Metab 82, 234-238. Diamond, D. M., Campbell, A., Park, C. R ., & Vouimba, R. M. (2004). Preclinical research on stress, memory, and the brai n in the development of pharmacotherapy for depression. Eur Neuropsychopharmacol 14, S491-S495. Diehl, L. A., Silveira, P. P., Leite, M. C., Cr ema, L. M., Portella, A. K., Billodre, M. N., et al. (2007). Long lasting sex-specific effects upon behavior and S100b levels after maternal separation and exposur e to a model of post-traumatic stress disorder in rats. Brain Res 1144, 107-116. Driessen, M., Beblo, T., Mertens, M., Piefke, M., Rullkoetter, N., Silva-Saavedra, A., et al. (2004). Posttraumatic stress disorder and fMRI activation pa tterns of traumatic memory in patients with borderline personality disorder. Biol Psychiatry 55 603611. Dunn, J. F., Nisula, B. C., & Rodbard, D. ( 1981). Transport of steroid hormones: binding of 21 endogenous steroids to both testosterone-binding globulin and corticosteroid-binding globulin in human plasma. J Clin Endocrinol Metab 53, 58-68.

PAGE 182

165 Duval, F., Crocq, M. A., Guillon, M. S., Mokran i, M. C., Monreal, J., Bailey, P., et al. (2004). Increased adrenocorticotropi n suppression after dexamethasone administration in sexually abused adolescen ts with posttraumatic stress disorder. Ann N Y Acad Sci 1032, 273-275. Ehlers, A., Hackmann, A., & Michael, T. (2004). Intrusive re-experiencing in posttraumatic stress disorder: phenomenology, theory, and therapy. Memory 12 403415. Ehlers, A., Michael, T., Chen, Y. P., Payne, E., & Shan, S. (2006). Enhanced perceptual priming for neutral stimuli in a traumatic context: a pathway to intrusive memories? Memory 14, 316-328. Elsesser, K., Sartory, G., & Tackenberg, A. (2004). Attention, heart rate, and startle response during exposure to trauma-releva nt pictures: a comparison of recent trauma victims and patients with posttraumatic stress disorder. J Abnorm Psychol 113, 289-301. Elzinga, B. M. & Bremner, J. D. (2002). Are the neural substrates of memory the final common pathway in posttraumatic stress disorder (PTSD)? J Affect Disord 70, 117. Elzinga, B. M., Schmahl, C. G., Vermetten, E., van Dyck, R., & Bremner, J. D. (2003). Higher cortisol levels following exposure to traumatic reminders in abuse-related PTSD. Neuropsychopharmacology 28 1656-1665.

PAGE 183

166 English, B. A., Jewell, M., Jewell, G., Ambrose, S., & Davis, L. L. (2006). Treatment of chronic posttraumatic stress disorder in co mbat veterans with citalopram: an open trial. J Clin Psychopharmacol 26, 84-88. Escalona, R., Canive, J. M., Calais, L. A., & Davidson, J. R. (2002). Fluvoxamine treatment in veterans with combat-re lated post-traumatic stress disorder. Depress Anxiety 15, 29-33. Everss, E., Arenas, M. C., Vinader-Caer ols, C., Monleon, S., & Parra, A. (2005). Piracetam counteracts the effects of amitr iptyline on inhibitory avoidance in CD1 mice. Behav Brain Res 159 235-242. Fanselow, M. S. & Gale, G. D. (2003). The amygdala, fear, and memory. Amygdala in Brain Function: Basic and Clinical Approaches 985, 125-134. Fattaccini, C. M., Bolanos-Jimenez, F., Gozlan, H., & Hamon, M. (1990). Tianeptine stimulates uptake of 5-hydroxytryptamine in vivo in the rat brain. Neuropharmacology 29 1-8. Fennema-Notestine, C., Stein, M. B., Kennedy, C. M., Archibald, S. L., & Jernigan, T. L. (2002). Brain morphometry in female vict ims of intimate partner violence with and without posttrauma tic stress disorder. Biol Psychiatry 52, 1089-1101. Fiedler, V. B., Martorana, P. A., & Nitz, R. E. (1986). Protective act ions of carbocromene against amitriptyline-induced cardiot oxicity in anesthetized rats. Arch Int Pharmacodyn Ther 279, 103-120. Figgitt, D. P. & McClellan, K. J. (2000). Fl uvoxamine. An updated review of its use in the management of adults with anxiety disorders. Drugs 60, 925-954.

PAGE 184

167 File, S. E., Andrews, N., & al Farhan, M. (1993). Anxiogenic responses of rats on withdrawal from chronic ethanol treatment: effects of tianeptine. Alcohol Alcohol 28, 281-286. File, S. E. & Mabbutt, P. S. (1991). Effects of tianeptine in animal-models of anxiety and on learning and memory. Drug Dev Res 23, 47-56. Florio, C., Prezioso, A., Papaioannou, A., & Ve rtua, R. (1998). Adenosine A1 receptors modulate anxiety in CD1 mice. Psychopharmacology 136, 311-319. Frank, J. B., Kosten, T. R., Giller, E. L., & Dan, E. (1988). A randomized clinical trial of phenelzine and imipramine for posttraumatic stress disorder. Am J Psychiatry 145, 1289-1291. Friedman, M. J., Marmar, C. R., Baker, D. G., Sikes, C. R., & Farfel, G. M. (2007). Randomized, double-blind comparison of sertraline and placebo for posttraumatic stress disorder in a Department of Veterans Affairs setting. J Clin Psychiatry 68, 711-720. Fuchs, E., Flugge, G., & Czeh, B. (2006). Re modeling of neuronal networks by stress. Front Biosci 11, 2746-2758. Funahashi, S. & Kubota, K. (1994). Wo rking memory and prefrontal cortex. Neurosci Res 21, 1-11. Gale, G. D., Anagnostaras, S. G., Godsil, B. P., Mitchell, S., Nozawa, T., Sage, J. R., et al. (2004). Role of the basolateral amygda la in the storage of fear memories across the adult lifetime of rats. J Neurosci 24, 3810-3815.

PAGE 185

168 Garakani, A., Mathew, S. J., & Charney, D. S. (2006). Neurobiology of anxiety disorders and implications for treatment. Mt Sinai J Med 73 941-949. Garrick, T., Morrow, N., Shalev, A. Y., & Et h, S. (2001). Stress-induced enhancement of auditory startle: an animal model of posttraumatic stress disorder. Psychiatry 64, 346-354. Geracioti, T. D., Baker, D. G., Ekhator, N. N., West, S. A., Hill, K. K., Bruce, A. B., et al. (2001). CSF norepinephrine concentra tions in posttraumatic stress disorder. Am J Psychiatry 158, 1227-1230. Geracioti, T. D., Baker, D. G., Kasckow, J. W., Strawn, J. R., Jeffrey, M. J., Dashevsky, B. A., et al. (2008). Effects of tr auma-related audiovisual stimulation on cerebrospinal fluid norepinephrine an d corticotropin-releasing hormone concentrations in post-tr aumatic stress disorder. Psychoneuroendocrinol 33 416424. Gerges, N. Z., Alzoubi, K. H., Park, C. R., Diamond, D. M., & Alkadhi, K. A. (2004). Adverse effect of the combination of hypothyroidism and chronic psychosocial stress on hippocampus-dependent memory in rats. Behav Brain Res 155, 77-84. Ghashghaei, H. T. & Barbas, H. (2002). Pathways for emotion: interactions of prefrontal and anterior temporal pathways in the amygdala of the rhesus monkey. Neuroscience 115, 1261-1279. Gil, T., Calev, A., Greenberg, D., Kugelm ass, S., & Lerer, B. (1990). Cognitive functioning in post-trau matic stress disorder. J Trauma Stress 3, 29-45.

PAGE 186

169 Gilbertson, M. W., Gurvits, T. V., Lasko, N. B., Orr, S. P., & Pitman, R. K. (2001). Multivariate assessment of explicit memory function in combat veterans with posttraumatic stress disorder. J Trauma Stress 14 413-432. Gilbertson, M. W., Shenton, M. E., Ciszewski, A ., Kasai, K., Lasko, N. B., Orr, S. P., et al. (2002). Smaller hippocampal volume pred icts pathologic vulnerability to psychological trauma. Nat Neurosci 5, 1242-1247. Gilbertson, M. W., Williston, S. K., Paulus, L. A., Lasko, N. B., Gurvits, T. V., Shenton, M. E., et al. (2007). Configural cue performance in identical twins discordant for posttraumatic stress disorder: theoretical im plications for the role of hippocampal function. Biol Psychiatry 62 513-520. Goenjian, A. K., Yehuda, R., Pynoos, R. S., St einberg, A. M., Tashjian, M., Yang, R. K., et al. (1996). Basal cortisol, dexamethasone suppression of cortisol, and MHPG in adolescents after the 1988 earthquake in Armenia. Am J Psychiatry 153, 929-934. Gold, P. E., van Buskirk, R., & Haycoc k, J. W. (1977). Effects of posttraining epinephrine injections on retenti on of avoidance training in mice. Behav Biol 20, 197-204. Gold, P. E. & Van Buskirk, R. B. (1975) Facilitation of time-dependent memory processes with posttrial epinephrine injections. Behav Biol 13 145-153. Golier, J. A., Yehuda, R., Lupien, S. J., & Harvey, P. D. (2003). Memory for traumarelated information in Holocaust survivors with PTSD. Psychiatry Res 121 133143.

PAGE 187

170 Golier, J. A., Yehuda, R., Lupien, S. J., Harvey, P. D., Grossman, R., & Elkin, A. (2002). Memory performance in Holocaust survi vors with posttraumatic stress disorder. Am J Psychiatry 159, 1682-1688. Gonzalez-Pardo, H., Conejo, N. M., Arias, J. L., Monleon, S., Vinader-Caerols, C., & Parra, A. (2008). Changes in brain oxidative metabolism induced by inhibitory avoidance learning and acute ad ministration of amitriptyline. Pharmacol Biochem Behav 89, 456-462. Grillon, C. & Morgan, C. A. (1999). Fear-potenti ated startle conditioni ng to explicit and contextual cues in Gulf War veterans with posttraumatic stress disorder. J Abnorm Psychol 108 134-142. Grillon, C., Morgan, C. A., Davis, M., & Southwick, S. M. (1998). Effects of experimental context and explicit threat cues on ac oustic startle in Vietnam veterans with posttraumatic stress disorder. Biol Psychiatry 44 1027-1036. Grillon, C., Morgan, C. A., Southwick, S. M., Davis, M., & Charney, D. S. (1996). Baseline startle amplitude and prepulse inhibition in Vietnam veterans with posttraumatic stress disorder. Psychiatry Res 64, 169-178. Grossman, R., Yehuda, R., New, A., Schmeidler J., Silverman, J., Mitropoulou, V., et al. (2003). Dexamethasone suppression test find ings in subjects with personality disorders: associations with posttrauma tic stress disorder and major depression. Am J Psychiatry 160, 1291-1298.

PAGE 188

171 Gurvits, T. V., Shenton, M. E., Hokama, H., Oh ta, H., Lasko, N. B., Gilbertson, M. W., et al. (1996). Magnetic resonance imaging st udy of hippocampal volume in chronic, combat-related posttraumatic stress disorder. Biol Psychiatry 40, 1091-1099. Guthrie, R. M. & Bryant, R. A. (2005). Audito ry startle response in firefighters before and after trauma exposure. Am J Psychiatry 162, 283-290. Hackmann, A., Ehlers, A., Speckens, A., & Clark, D. M. (2004). Characteristics and content of intrusive memories in PTSD and their changes with treatment. J Trauma Stress 17, 231-240. Haller, J., Baranyi, J., Bakos, N., & Halasz, J. (2004). Social instabil ity in female rats: effects on anxiety and buspirone efficacy. Psychopharmacology 174, 197-202. Halonen, J., Zoladz, P. R., & Diamond, D. M. (2006). Post-training immobilization of rats during predator exposure increases the magnitude and resistance to extinction of conditioned fear. Soc Neurosci Abst 36 829.6. Harada, K., Yamaji, T., & Matsuoka, N. (2008). Activation of the serotonin 5-HT2C receptor is involved in the enhanced anxiet y in rats after single-prolonged stress. Pharmacol Biochem Behav 89, 11-16. Harmon, R. J. & Riggs, P. D. (1996). Clonidi ne for posttraumatic stress disorder in preschool children. J Am Acad Child Adolesc Psychiatry 35, 1247-1249. Hartmann, A., Veldhuis, J. D., Deuschle, M., Standhardt, H., & Heuser, I. (1997). Twenty-four hour cortisol release profiles in patients with Alzheimer's and Parkinson's disease compared to normal controls: ultradian secretory pulsatility and diurnal variation. Neurobiol Aging 18, 285-289.

PAGE 189

172 Harvey, B. H., Brand, L., Jeeva, Z., & Stein, D. J. (2006). Cortical/hippocampal monoamines, HPA-axis changes and aver sive behavior fo llowing stress and restress in an animal model of post-traumatic stress disorder. Physiol Behav 87, 881-890. Harvey, B. H., Naciti, C., Brand, L., & Stein, D. J. (2003). Endocrine, cognitive and hippocampal/cortical 5HT 1A/2A receptor changes evoked by a time-dependent sensitisation (TDS) stress model in rats. Brain Res 983, 97-107. Hedges, D. W., Allen, S., Tate, D. F., Thatcher, G. W., Miller, M. J., Rice, S. A., et al. (2003). Reduced hippocampal volume in alcohol and substance naive Vietnam combat veterans with posttraumatic stress disorder. Cogn Behav Neurol 16 219224. Hendler, T., Rotshtein, P., Yeshurun, Y., Weiz mann, T., Kahn, I., Ben Bashat, D., et al. (2003). Sensing the invisibl e: differential sensitivity of visual cortex and amygdala to traumatic context. Neuroimage 19, 587-600. Hidalgo, R. B. & Davidson, J. R. (2000). Sele ctive serotonin reuptak e inhibitors in posttraumatic stress disorder. J Psychopharmacol 14, 70-76. Holsboer, F. (1999). The rationale for cortic otropin-releasing hormone receptor (CRH-R) antagonists to treat de pression and anxiety. J Psychiatr Res 33 181-214. Hong, W. K., Mauer, P., Hoch man, R., Caslowitz, J. G., & Paraskos, J. A. (1974). Amitriptyline cardiotoxicity. Chest 66 304-306.

PAGE 190

173 Humble, M. & Wistedt, B. (1992). Serotonin, pa nic disorder and agor aphobia: short-term and long-term efficacy of citalopram in panic disorders. Int Clin Psychopharmacol 6, 21-39. Inslicht, S. S., Marmar, C. R., Neylan, T. C., Metzler, T. J., Hart, S. L., Otte, C., et al. (2006a). Increased cortisol in women with intimate partner violence-related posttraumatic stress disorder. Ann N Y Acad Sci 1071, 428-429. Inslicht, S. S., Marmar, C. R., Neylan, T. C., Metzler, T. J., Hart, S. L., Otte, C., et al. (2006b). Increased cortisol in women w ith intimate partner violence-related posttraumatic stress disorder. Psychoneuroendocrinol 31, 825-838. Ipser, J., Seedat, S., & Stein, D. J. (2006) Pharmacotherapy for post-traumatic stress disorder: a systematic review and meta-analysis. S Afr Med J 96, 1088-1096. Iwamoto, Y., Morinobu, S., Takahashi, T., & Yamawaki, S. (2007). Single prolonged stress increases contextual freezing and the expression of glycine transporter 1 and vesicle-associated membrane prot ein 2 mRNA in the hippocampus of rats. Prog Neuropsychopharmacol Biol Psychiatry 31 642-651. Jaffard, R., Mocaer, E., Poignant, J. C., Micheau, J., Marighetto, A., Meunier, M., et al. (1991). Effects of tianeptine on spontaneous alternation, simple and concurrent spatial discrimination learning and on alcohol -induced alternation deficits in mice. Behav Pharmacol 2, 37-46. Jain, N., Kemp, N., Adeyemo, O., Buchana n, P., & Stone, T. W. (1995). Anxiolytic activity of adenosine receptor activation in mice. Br J Pharmacol 116, 2127-2133.

PAGE 191

174 Jakovljevic, M., Sagud, M., & Mi haljevic-Peles, A. (2003). Ol anzapine in the treatmentresistant, combat-related PTSD: a series of case reports. Acta Psychiatr Scand 107, 394-396. Jatzko, A., Rothenhofer, S., Schmitt, A., Gaser, C., Demirakca, T., Weber-Fahr, W., et al. (2006). Hippocampal volume in chronic posttraumatic stress disorder (PTSD): MRI study using two differe nt evaluation methods. J Affect Disord 94, 121-126. Jenkins, M. A., Langlais, P. J., Delis, D., & Cohen, R. (1998). Learning and memory in rape victims with posttraumatic stress disorder. Am J Psychiatry 155, 278-279. Joels, M., Velzing, E., Nair, S., Verkuyl, J. M ., & Karst, H. (2003). Acute stress increases calcium current amplitude in rat hippocampus: temporal changes in physiology and gene expression. Eur J Neurosci 18, 1315-1324. Joubert, P. H., Starke, D. D ., Van Reenen, O., & Venter, C. P. (1985). A comparison of the cardiovascular effects and subjec tive tolerability of binedaline and amitriptylene in healthy volunteers. Eur J Clin Pharmacol 27, 667-670. Juvent, M., Douchamps, J., Delcourt, E., Kost ucki, W., Dulcire, C., d'Hooge, D., et al. (1990). Lack of cardiovascular side eff ects of the new tric yclic antidepressant tianeptine: a double-blind, placebo-controlled study in young healthy volunteers. Clin Neuropharmacol 13, 48-57. Kant, G. J., Leu, J. R., Anderson, S. M., & Mougey, E. H. (1987). Effects of chronic stress on plasma corticosterone, ACTH and prolactin. Physiol Behav 40, 775-779.

PAGE 192

175 Kant, G. J., Mougey, E. H., & Meyerhoff, J. L. (1986). Diurnal variation in neuroendocrine response to stress in rats: plasma ACTH, beta-endorphin, betaLPH, corticosterone, prolactin a nd pituitary cyclic AMP responses. Neuroendocrinology 43, 383-390. Kanter, E. D., Wilkinson, C. W., Radant, A. D ., Petrie, E. C., Dobie, D. J., McFall, M. E., et al. (2001). Glucocorti coid feedback sensitivity and adrenocortical responsiveness in posttrau matic stress disorder. Biol Psychiatry 50, 238-245. Kasper, S. & McEwen, B. S. (2008). Neurobiological and clinical effects of the antidepressant tianeptine. CNS Drugs 22, 15-26. Kato, G. & Weitsch, A. F. (1988). Neurochemical profile of tianeptine, a new antidepressant drug. Clin Neuropharmacol 11, S43-S50. Katz, R. J., Lott, M. H., Arbus, P., Crocq, L., Herlobsen, P., Lingjaerde, O., et al. (1994). Pharmacotherapy of post-traumatic stress disorder with a novel psychotropic. Anxiety 1, 169-174. Kavushansky, A. & Richter-Levin, G. (2006). Effects of stress and corticosterone on activity and plasticity in the amygdala. J Neurosci Res 84, 1580-1587. Kavushansky, A., Vouimba, R. M., Cohen, H., & Richter-Levin, G. (2006). Activity and plasticity in the CA1, the dentate gyrus and the amygdala following controllable vs. uncontrollable water stress. Hippocampus 16, 35-42. Kellner, M., Wiedemann, K., Yassouridis, A ., Levengood, R., Guo, L. S., Holsboer, F., et al. (2000). Behavioral and endocrine response to cholecy stokinin tetrapeptide in patients with posttraumatic stress disorder. Biol Psychiatry 47 107-111.

PAGE 193

176 Kellner, M., Yassouridis, A., Hubner, R., Baker, D. G., & Wiedemann, K. (2003). Endocrine and cardiovascula r responses to co rticotropin-releas ing hormone in patients with posttraumatic stress disorder: a role for atrial natriuretic peptide? Neuropsychobiology 47, 102-108. Kerr, J. S., Powell, J., & Hindmarch, I. (1996). The effects of reboxetine and amitriptyline, with and without alcohol on cognitive function and psychomotor performance. Br J Clin Pharmacol 42, 239-241. Kessler, R. C., Sonnega, A., Bromet, E ., Hughes, M., & Nelson, C. B. (1995). Posttraumatic stress disorder in the national comorbidity survey. Arch Gen Psychiatry 52 1048-1060. Khan, S. & Liberzon, I. (2004). Topiramate atte nuates exaggerated acoustic startle in an animal model of PTSD. Psychopharmacology 172, 225-229. Kim, J. J. & Diamond, D. M. (2002). The stre ssed hippocampus, synaptic plasticity and lost memories. Nat Rev Neurosci 3, 453-462. Kim, J. J., Foy, M. R., & Thompson, R. F. (1996). Behavioral stress modifies hippocampal plasticity through N-methyl -D-aspartate receptor activation. Proc Natl Acad Sci U S A 93, 4750-4753. Kim, S. J., Park, S. H., Choi, S. H., Moon, B. H., Lee, K. J., Kang, S. W., et al. (2006). Effects of repeated tianeptine treatment on CRF mRNA expression in nonstressed and chronic mild stress-exposed rats. Neuropharmacology 50 824-833. King, J. A., Mandansky, D., King, S., Fletcher, K. E., & Brewer, J. (2001). Early sexual abuse and low cortisol. Psychiatry Clin Neurosci 55, 71-74.

PAGE 194

177 Knight, D. C., Cheng, D. T., Smith, C. N., Stein, E. A., & Helmstetter, F. J. (2004). Neural substrates mediating human delay and trace fear conditioning. J Neurosci 24, 218-228. Koechlin, E., Basso, G., Pietrini, P., Panzer, S., & Grafman, J. (1999). The role of the anterior prefrontal cortex in human cognition. Nature 399, 148-151. Koechlin, E., Corrado, G., Pietrini, P., & Grafma n, J. (2000). Dissociating the role of the medial and lateral anterior pref rontal cortex in human planning. Proc Natl Acad Sci U S A 97, 7651-7656. Koenen, K. C., Driver, K. L., Oscar-Berman, M ., Wolfe, J., Folsom, S., Huang, M. T., et al. (2001). Measures of pr efrontal system dysfuncti on in posttraumatic stress disorder. Brain Cogn 45, 64-78. Kohda, K., Harada, K., Kato, K., Hoshino, A., Motohashi, J., Yamaji, T., et al. (2007). Glucocorticoid receptor activation is involved in produci ng abnormal phenotypes of single-prolonged stress rats: a putative post-traumatic stre ss disorder model. Neuroscience 148, 22-33. Kolb, L. C. & Mutalipassi, L. R. (1992). Th e conditioned emotional response: a sub-class of the chronic delayed post-t raumatic stress disorder. Psychiatr Ann 12, 979-987. Kole, M. H., Swan, L., & Fuchs, E. (2002). The antidepressant tiane ptine persistently modulates glutamate receptor currents of the hippocampal CA3 commissural associational synapse in chronically stressed rats. Eur J Neurosci 16, 807-816. Kopera, H. (1978). Anticholinergic and blood pre ssure effects of mianserin, amitriptyline and placebo. Br J Clin Pharmacol 5, 29S-34S.

PAGE 195

178 Korte, S. M. & De Boer, S. F. (2003). A r obust animal model of state anxiety: fearpotentiated behaviour in the elevated plus-maze. Eur J Pharm 463, 163-175. Kosten, T. R., Frank, J. B., Dan, E., McD ougle, C. J., & Giller, E. L. (1991). Pharmacotherapy for posttraumatic st ress disorder using phenelzine or imipramine. J Nerv Ment Dis 179, 366-370. Kosten, T. R., Mason, J. W., Giller, E. L., Ostroff, R. B., & Harkness, L. (1987). Sustained urinary norepinephrine and ep inephrine elevation in post-traumatic stress disorder. Psychoneuroendocrinol 12, 13-20. Krugers, H. J., Koolhaas, J. M., Bohus, B., & Korf, J. (1993). A single social stressexperience alters glutam ate receptor-binding in ra t hippocampal CA3 area. Neurosci Lett 154, 73-77. Kubzansky, L. D., Koenen, K. C., Spiro, A., Vokonas, P. S., & Sparrow, D. (2007). Prospective study of posttraumatic stress di sorder symptoms and coronary heart disease in the Normative Aging Study. Arch Gen Psychiatry 64 109-116. Kumar, S. & Kulkarni, S. K. (1996). Influence of antidepressant drugs on learning and memory paradigms in mice. Indian J Exp Biol 34 431-435. La Rovere, M. T., Bigger, J. T., Marcus, F. I., Mortara, A., & Schwartz, P. J. (1998). Baroreflex sensitivity and heart-rate va riability in prediction of total cardiac mortality after myocardial infarction. Lancet 351, 478-484. La Rovere, M. T., Specchia, G., Mortara, A., & Schwartz, P. J. (1988). Baroreflex sensitivity, clinical correla tes, and cardiovascular mort ality among patients with a first myocardial infarction. A prospective study. Circulation 78, 816-824.

PAGE 196

179 LaBar, K. S., Gatenby, J. C., Gore, J. C., Le Doux, J. E., & Phelps, E. A. (1998). Human amygdala activation during conditioned f ear acquisition and extinction: a mixedtrial fMRI study. Neuron 20, 937-945. LaBar, K. S., LeDoux, J. E., Spencer, D. D., & Phelps, E. A. (1995). Impaired fear conditioning following unilateral te mporal lobectomy in humans. J Neurosci 15, 6846-6855. Labrid, C., Mocaer, E., & Kamoun, A. ( 1992). Neurochemical and pharmacological properties of tianeptine, a novel antidepressant. Br J Psychiatry 15 56-60. Lanius, R. A., Williamson, P. C., Densmore, M ., Boksman, K., Gupta, M. A., Neufeld, R. W., et al. (2001). Neural correlates of tr aumatic memories in posttraumatic stress disorder: a functional MRI investigation. Am J Psychiatry 158 1920-1922. Lasnier, C., Marey, C., Lapeyre, G., Delall eau, B., & Ganry, H. (1991). Cardiovascular tolerance to tianeptine. Presse Med 20 1858-1863. Lebron, K., Milad, M. R., & Quirk, G. J. (2004). Delayed recall of fear extinction in rats with lesions of ventral me dial prefrontal cortex. Learn Mem 11, 544-548. Lechin, F., van der, D. B., Hernandez, G., Orozco, B., Rodriguez, S., & Baez, S. (2006). Acute effects of tianeptine on circulating neurotransmitters and cardiovascular parameters. Prog Neuropsychopharmacol Biol Psychiatry 30 214-222. LeDoux, J. (2003). The emotional brain, fear, and the amygdala. Cell Mol Neurobiol 23 727-738.

PAGE 197

180 Lemaire, V., Taylor, G. T., & Mormede, P. (1997). Adrenal axis activation by chronic social stress fails to inhibit gonadal function in male rats. Psychoneuroendocrinol 22, 563-573. Lemieux, A. M. & Coe, C. L. (1995). Abuse-related posttraumatic stress disorder: evidence for chronic neuroendoc rine activation in women. Psychosom Med 57, 105-115. Lepsch, L. B., Gonzalo, L. A., Magro, F. J., DeLucia, R., Scavone, C., & Planeta, C. S. (2005). Exposure to chronic stress increas es the locomotor response to cocaine and the basal levels of cortic osterone in adolescent rats. Addict Biol 10, 251-256. Li, S., Murakami, Y., Wang, M., Maeda, K ., & Matsumoto, K. (2006). The effects of chronic valproate and diazepam in a mouse model of posttraumatic stress disorder. Pharmacol Biochem Behav 85, 324-331. Liberzon, I., Abelson, J. L., Flagel, S. B., Raz, J., & Young, E. A. (1999a). Neuroendocrine and psychophysiologic responses in PTSD: a symptom provocation study. Neuropsychopharmacology 21 40-50. Liberzon, I., Krstov, M., & Young, E. A. (1997) Stress-restress: effects on ACTH and fast feedback. Psychoneuroendocrinol 22, 443-453. Liberzon, I., Taylor, S. F., Am dur, R., Jung, T. D., Chamberlain, K. R., Minoshima, S., et al. (1999b). Brain activation in PTSD in response to trauma-related stimuli. Biol Psychiatry 45 817-826.

PAGE 198

181 Liljequist, R., Seppala, T., & Mattila, M. J. (1978). Amitriptylineand mianserin-induced changes in acquisition of pair ed-association learning-task. Br J Clin Pharmacol 5, 149-153. Lindauer, R. J., Booij, J., Habraken, J. B., Uy lings, H. B., Olff, M., Carlier, I. V., et al. (2004a). Cerebral blood flow changes dur ing script-driven imagery in police officers with posttraumatic stress disorder. Biol Psychiatry 56, 853-861. Lindauer, R. J., Olff, M., van Meijel, E. P ., Carlier, I. V., & Gersons, B. P. (2006). Cortisol, learning, memory, and attenti on in relation to smaller hippocampal volume in police officers with posttraumatic stress disorder. Biol Psychiatry 59, 171-177. Lindauer, R. J., Vlieger, E. J., Jalink, M., Ol ff, M., Carlier, I. V., Majoie, C. B., et al. (2004b). Smaller hippocampal volume in Dutc h police officers with posttraumatic stress disorder. Biol Psychiatry 56, 356-363. Lipschitz, D. S., Mayes, L. M., Rasmusson, A. M., Anyan, W., Billingslea, E., Gueorguieva, R., et al. (2005). Baseline and modulated acoustic startle responses in adolescent girls with posttraumatic stress disorder. J Am Acad Child Adolesc Psychiatry 44 807-814. Londborg, P. D., Hegel, M. T., Goldstein, S., Goldstein, D., Himmelhoch, J. M., Maddock, R., et al. (2001). Sertraline treatment of posttraumatic stress disorder: results of 24 weeks of open-label continuation treatment. J Clin Psychiatry 62, 325-331.

PAGE 199

182 Louvart, H., Maccari, S., Ducrocq, F., Thomas, P., & Darnaudery, M. (2005). Long-term behavioural alterations in female rats after a single intense footshock followed by situational reminders. Psychoneuroendocrinol 30 316-324. Low, P. A. & Opfer-Gehrking, T. L. (1992) Differential effects of amitriptyline on sudomotor, cardiovagal, and adrenerg ic function in human subjects. Muscle Nerve 15, 1340-1344. Lowy, M. T., Gault, L., & Yamamoto, B. K. (1993). Adrenalectomy attenuates stressinduced elevations in extracellular glut amate concentrations in the hippocampus. J Neurochem 61, 1957-1960. Lowy, M. T., Wittenberg, L., & Yamamoto, B. K. (1995). Effect of acute stress on hippocampal glutamate levels and spectri n proteolysis in young and aged rats. J Neurochem 65, 268-274. Lurie, S., Kuhn, C., Bartolome, J., & Schanbe rg, S. (1989). Differential sensitivity to dexamethasone suppression in an animal model of the DST. Biol Psychiatry 26, 26-34. Magarinos, A. M., Deslandes, A., & McEwe n, B. S. (1999). Effects of antidepressants and benzodiazepine treatments on the de ndritic structure of CA3 pyramidal neurons after chronic stress. Eur J Pharm 371, 113-122. Magarinos, A. M. & McEwen, B. S. (1995). St ress-induced atrophy of apical dendrites of hippocampal CA3c neurons: involvement of glucocorticoid secretion and excitatory amino acid receptors. Neuroscience 69 89-98.

PAGE 200

183 Magarinos, A. M., McEwen, B. S., Flugge, G ., & Fuchs, E. (1996). Chronic psychosocial stress causes apical dendritic atrophy of hippocampal CA3 pyramidal neurons in subordinate tree shrews. J Neurosci 16 3534-3540. Maier, S. F., Grahn, R. E., Kalman, B. A., Sutton, L. C., Wiertelak, E. P., & Watkins, L. R. (1993). The role of the amygdala and dorsal raphe nucleus in mediating the behavioral consequences of inescapable shock. Behav Neurosci 107, 377-388. Maier, S. F. & Watkins, L. R. (2005). Stre ssor controllability and learned helplessness: the roles of the dorsal raphe nucleus, sero tonin, and corticotropin-releasing factor. Neurosci Biobehav Rev 29, 829-841. Malagie, I., Deslandes, A., & Gardier, A. M. (2000). Effects of acute and chronic tianeptine administration on se rotonin outflow in rats: co mparison with paroxetine by using in vivo microdialysis. Eur J Pharmacol 403, 55-65. Malloy, P. F., Fairbank, J. A., & Keane, T. M. (1983). Validation of a multimethod assessment of posttraumatic stress disorders in Vietnam veterans. J Consult Clin Psychol 51, 488-494. Manzanares, P. A. R., Isoardi, N. A., Carrer, H. F., & Molina, V. A. (2005). Previous stress facilitates fear memory, attenu ates GABAergic inhibition, and increases synaptic plasticity in th e rat basolateral amygdala. J Neurosci 25, 8725-8734. March, J. S. (1992). Fluoxetin e and fluvoxamine in PTSD. Am J Psychiatry 149, 413. Maren, S. (1999). Neurotoxic basolateral amygda la lesions impair l earning and memory but not the performance of conditional fear in rats. J Neurosci 19, 8696-8703.

PAGE 201

184 Maren, S. (2003). The amygdala, synap tic plasticity, and fear memory. Ann N Y Acad Sci 985, 106-113. Maren, S., Aharonov, G., Stote, D. L., & Fans elow, M. S. (1996). N-methyl-D-aspartate receptors in the basolateral amygdala are required for both acquisition and expression of conditional fear in rats. Behav Neurosci 110, 1365-1374. Marin, M. T., Cruz, F. C., & Planeta, C. S. (2007). Chronic restraint or variable stresses differently affect the behavior, corticoste rone secretion and b ody weight in rats. Physiol Behav 90, 29-35. Maroun, M. & Akirav, I. (2008). Arousal and stress effects on consolidation and reconsolidation of recognition memory. Neuropsychopharmacology 33 394-405. Marshall, R. D., Blanco, C., Printz, D., Liebowitz, M. R., Klein, D. F., & Coplan, J. (2002). A pilot study of noradrenergic a nd HPA axis functioning in PTSD vs. panic disorder. Psychiatry Res 110 219-230. Martenyi, F., Brown, E. B., Zhang, H., Koke S. C., & Prakash, A. (2002a). Fluoxetine v. placebo in prevention of relapse in post-traumatic st ress disorder. Br J Psychiatry 181, 315-320. Martenyi, F., Brown, E. B., Zhang, H., Pr akash, A., & Koke, S. C. (2002b). Fluoxetine versus placebo in posttraumatic stress disorder. J Clin Psychiatry 63, 199-206. Martenyi, F. & Soldatenkova, V. (2006). Fluoxe tine in the acute treatment and relapse prevention of combat-related post-traumatic stress disorder: analysis of the veteran group of a placebo-controlled, randomized clinical trial. Eur Neuropsychopharmacol 16, 340-349.

PAGE 202

185 Mattila, M. J., Liljequist, R., & Seppala, T. (1978). Effects of amitriptyline and mianserin on psychomotor skills and memory in man. Br J Clin Pharmacol 5, 53S-55S. McCarthy, G., Puce, A., Constable, R. T., Krystal, J. H., Go re, J. C., & Goldman-Rakic, P. (1996). Activation of human prefrontal cortex during spatial and nonspatial working memory tasks measured by functional MRI. Cereb Cortex 6, 600-611. McDonald, A. J. (1987). Organization of amygdaloid projections to the mediodorsal thalamus and prefrontal cortex: a fluore scence retrograde transport study in the rat. J Comp Neurol 262, 46-58. McDonald, A. J. (1991). Organization of amygdalo id projections to th e prefrontal cortex and associated striatum in the rat. Neuroscience 44 1-14. McEwen, B. S. (1998). Stress, adaptation, and disease: allostasis and allostatic load. Ann N Y Acad Sci 840, 33-44. McEwen, B. S. (2003). Mood disorders and allostatic load. Biol Psychiatry 54, 200-207. McEwen, B. S. & Chattarji, S. (2004). Mo lecular mechanisms of neuroplasticity and pharmacological implications: the example of tianeptine. Eur Neuropsychopharmacol 14, S497-S502. McEwen, B. S., Magarinos, A. M., & Reagan, L. P. (2002). Structural plasticity and tianeptine: cellular and molecular targets. Eur Psychiatry 17 318S-330S. McEwen, B. S. & Olie, J. P. (2005). Neur obiology of mood, anxiety, and emotions as revealed by studies of a unique antidepressant: tianeptine. Mol Psychiatry 10, 525-537.

PAGE 203

186 McEwen, B. S. & Wingfield, J. C. (2003). The concept of allostasis in biology and biomedicine. Horm Behav 43, 2-15. McFall, M. E., Murburg, M. M., Ko, G. N ., & Veith, R. C. (1990). Autonomic responses to stress in Vietnam combat veterans with posttraumatic stress disorder. Biol Psychiatry 27 1165-1175. McFarlane, A. C. (2000). Posttraumatic st ress disorder: a model of the longitudinal course and the role of risk factors. J Clin Psychiatry 61, 15-20. McGaugh, J. L. (2002). Memory consolidation and the amygdala: a systems perspective. Trends Neurosci 25, 456. McGaugh, J. L. (2004). The amygdala modulates the consolidation of memories of emotionally arousing experiences. Annu Rev Neurosci 27, 1-28. McGaugh, J. L., Cahill, L., & Roozendaal, B. (1996). Involvement of the amygdala in memory storage: interaction with other brain systems. Proc Natl Acad Sci U S A 93, 13508-13514. McLaughlin, K. J., Gomez, J. L., Baran, S. E., & Conrad, C. D. (2007). The effects of chronic stress on hippocampal morphology a nd function: an evaluation of chronic restraint paradigms. Brain Res 1161, 56-64. McNally, R. J. (1997). Implic it and explicit memory for tr auma-related information in PTSD. Ann N Y Acad Sci 821, 219-224. McRae, A. L., Brady, K. T., Mellman, T. A., Sonne, S. C., Killeen, T. K., Timmerman, M. A., et al. (2004). Comparison of nefaz odone and sertraline for the treatment of posttraumatic stress disorder. Depress Anxiety 19 190-196.

PAGE 204

187 Meaney, M. J., Aitken, D. H., Sharma, S., & Viau, V. (1992). Basal ACTH, corticosterone and corticosterone-binding globulin levels over the diurnal cycle, and age-related changes in hippocampal type I and type II cortic osteroid receptor binding capacity in young and aged handled and nonhandled rats. Neuroendocrinology 55, 204-213. Meijer, O. C., de Lange, E. C., Breimer, D. D ., de Boer, A. G., Workel, J. O., & de Kloet, E. R. (1998). Penetration of dexamethasone into brain glucocor ticoid targets is enhanced in mdr1A P-gl ycoprotein knockout mice. Endocrinology 139, 17891793. Meltzer-Brody, S., Connor, K. M., Churchill, E., & Davids on, J. R. (2000). Symptomspecific effects of fluoxetine in post-traumatic stress disorder. Int Clin Psychopharmacol 15, 227-231. Meneses, A. (2002). Tianeptine: 5-HT uptake sites and 5-HT1-7 receptors modulate memory formation in an autoshaping Pavlovian/instrumental task. Neurosci Biobehav Rev 26, 309-319. Mennini, T., Mocaer, E., & Garattini, S. ( 1987). Tianeptine, a selective enhancer of serotonin uptake in rat brain. Naunyn Schmiedebergs Arch Pharmacol 336 478482. Metzger, L. J., Orr, S. P., Berry, N. J., Ahern, C. E., Lasko, N. B., & Pitman, R. K. (1999). Physiologic reactivity to star tling tones in women with posttraumatic stress disorder. J Abnorm Psychol 108, 347-352.

PAGE 205

188 Michael, T., Ehlers, A., & Halligan, S. L. (2005). Enhanced priming for trauma-related material in posttraumatic stress disorder. Emotion 5, 103-112. Milad, M. R., Vidal-Gonzalez, I., & Quirk, G. J. (2004). Electrical stimulation of medial prefrontal cortex reduces conditioned fear in a tem porally specific manner. Behav Neurosci 118 389-394. Milde, A. M., Sundberg, H., Roseth, A. G., & Murison, R. (2003). Proactive sensitizing effects of acute stress on acoustic startl e responses and experimentally induced colitis in rats: relationship to corticosterone. Stress 6, 49-57. Millan, M. J., Lejeune, F., Gobert, A., Brocco, M., Auclair, A., Bosc, C., et al. (2000). S18616, a highly potent spiroimidazoline a gonist at alpha(2)adrenoceptors: influence on monoaminergic transmi ssion, motor function, and anxiety in comparison with dexmedetomidine and clonidine. J Pharmacol Exp Ther 295, 1206-1222. Mitra, R., Jadhav, S., McEwen, B. S., Vyas, A., & Chattarji, S. (2005). Stress duration modulates the spatiotempor al patterns of spine form ation in the basolateral amygdala. Proc Natl Acad Sci U S A 102, 9371-9376. Mizoguchi, K., Yuzurihara, M., Ishige, A., Sasa ki, H., Chui, D. H., & Tabira, T. (2001). Chronic stress differentially regulates glucocorticoid negative feedback response in rats. Psychoneuroendocrinol 26, 443-459. Mocaer, E., Rettori, M. C., & Kamoun, A. (1988). Pharmacological antidepressive effects and tianeptine-induced 5-HT uptake increase. Clin Neuropharmacol 11 S32-S42.

PAGE 206

189 Moghaddam, B. (1993). Stress preferentially incr eases extraneuronal le vels of excitatory amino acids in the prefrontal cortex : comparison to hippocampus and basal ganglia. J Neurochem 60, 1650-1657. Moradi, A. R., Doost, H. T., Taghavi, M. R ., Yule, W., & Dalgleish, T. (1999). Everyday memory deficits in children and adolescents with PTSD: performance on the Rivermead Behavioural Memory Test. J Child Psychol Psychiatry 40, 357-361. Moradi, A. R., Taghavi, R., Neshat-Doost, H. T., Yule, W., & Dalgleish, T. (2000). Memory bias for emotional information in children and adolescents with posttraumatic stress disorder: a preliminary study. J Anxiety Disord 14, 521-534. Morgan, C. A. (1997). Startle res ponses in individuals with PTSD. National Center for PTSD Clinical Quarterly 7, 65-69. Morgan, C. A., Grillon, C., Lubin, H., & S outhwick, S. M. (1997). Startle reflex abnormalities in women with sexual assault-related postt raumatic stress disorder. Am J Psychiatry 154, 1076-1080. Morgan, C. A., Grillon, C., Southwick, S. M., Davis, M., & Charney, D. S. (1995a). Fearpotentiated startle in postt raumatic stress disorder. Biol Psychiatry 38, 378-385. Morgan, C. A., Grillon, C., Southwick, S. M., Davis, M., & Charney, D. S. (1996). Exaggerated acoustic startle reflex in Gu lf War veterans with posttraumatic stress disorder. Am J Psychiatry 153, 64-68. Morgan, C. A., Grillon, C., Southwick, S. M., Na gy, L. M., Davis, M., Krystal, J. H., et al. (1995b). Yohimbine facilita ted acoustic startle in combat veterans with posttraumatic stress disorder. Psychopharmacology 117, 466-471.

PAGE 207

190 Muhtz, C., Wester, M., Yassouridis, A ., Wiedemann, K., & Kellner, M. (2008). A combined dexamethasone/corticotropin-rele asing hormone test in patients with chronic PTSD: first preliminary results. J Psychiatr Res 42, 689-693. Munoz, C., Park, C. R., Campbell, A. M., & Diamond, D. M. (2005). The enhancement of long-term (24 hr) spatial memory by tianeptine, memantine and CPP supports the hypothesis that a reduction of NMDA receptor activity during learning will enhance memory. Soc Neurosci Abst 35, 887.10. Nader, K., Schafe, G. E., & LeDoux, J. E. (2000). Fear memories require protein synthesis in the amygdala for r econsolidation af ter retrieval. Nature 406, 722-726. Nair, J. & Singh, A. S. (2008). The role of the glutamatergic system in posttraumatic stress disorder. CNS Spectr 13, 585-591. Neal, L. A., Shapland, W., & Fox, C. (1997) An open trial of moclobemide in the treatment of post-traumatic stress disorder. Int Clin Psychopharmacol 12, 231237. Nemeroff, C. B., Bremner, J. D., Foa, E. B ., Mayberg, H. S., North, C. S., & Stein, M. B. (2006). Posttraumatic stress disorder : A state-of-the-science review. J Psychiatr Res 40, 1-21. Newport, D. J., Heim, C., Bonsall, R., Miller A. H., & Nemeroff, C. B. (2004). Pituitaryadrenal responses to standard and lowdose dexamethasone suppression tests in adult survivors of child abuse. Biol Psychiatry 55 10-20. Newport, D. J. & Nemeroff, C. B. (2000). Ne urobiology of posttraumatic stress disorder. Curr Opin Neurobiol 10, 211-218.

PAGE 208

191 Neylan, T. C., Lenoci, M., Maglione, M. L., Rose nlicht, N. Z., Metzler, T. J., Otte, C., et al. (2003). Delta sleep response to metyra pone in post-traumatic stress disorder. Neuropsychopharmacology 28, 1666-1676. Neylan, T. C., Metzler, T. J., Schoenfeld, F. B ., Weiss, D. S., Lenoci, M., Best, S. R., et al. (2001). Fluvoxamine and sleep disturba nces in posttraumatic stress disorder. J Trauma Stress 14, 461-467. Neylan, T. C., Otte, C., Yehuda, R., & Marm ar, C. R. (2006). Neur oendocrine regulation of sleep disturbances in PTSD. Ann N Y Acad Sci 1071, 203-215. Onder, E., Tural, U., & Aker, T. ( 2006). A comparative study of fluoxetine, moclobemide, and tianeptine in the treatme nt of posttraumatic stress disorder following an earthquake. Eur Psychiatry 21, 174-179. Orr, S. P., Claiborn, J. M., Altman, B., Forgue, D. F., de Jong, J. B., Pitman, R. K., et al. (1990). Psychometric profile of posttra umatic stress disorder, anxious, and healthy Vietnam veterans: correlatio ns with psychophysiologic responses. J Consult Clin Psychol 58, 329-335. Orr, S. P., Lasko, N. B., Metzger, L. J., Berry, N. J., Ahern, C. E., & Pitman, R. K. (1998). Psychophysiologic assessment of women with posttraumatic stress disorder resulting from childhood sexual abuse. J Consult Clin Psychol 66 906913. Orr, S. P., Lasko, N. B., Metzger, L. J., & Pitman, R. K. (1997). Physiologic responses to non-startling tones in Vietnam veterans with post-traumatic stress disorder. Psychiatry Res 73, 103-107.

PAGE 209

192 Orr, S. P., Lasko, N. B., Shalev, A. Y., & Pitman, R. K. (1995). Physiologic responses to loud tones in Vietnam veterans with posttraumatic stress disorder. J Abnorm Psychol 104 75-82. Orr, S. P., Metzger, L. J., Lasko, N. B., M acklin, M. L., Peri, T., & Pitman, R. K. (2000). De novo conditioning in trauma-exposed individuals with and without posttraumatic stress disorder. J Abnorm Psychol 109, 290-298. Orsetti, M., Canonico, P. L., Dellarole, A., Co lella, L., Di Brisco, F., & Ghi, P. (2007). Quetiapine prevents anhedonia indu ced by acute or chronic stress. Neuropsychopharmacology 32, 1783-1790. Otte, C., Lenoci, M., Metzler, T., Yehuda, R ., Marmar, C. R., & Neylan, T. C. (2007). Effects of metyrapone on hypot halamic-pituitary-adrenal axis and sleep in women with post-traumatic stress disorder. Biol Psychiatry 61, 952-956. Otte, C., Muhtz, C., Daneshkhah, S., Yassourid is, A., Kiefer, F., Wiedemann, K., et al. (2006). Mineralocorticoid receptor function in posttraumatic stress disorder after pretreatment with metyrapone. Biol Psychiatry 60 784-787. Ozer, E. J., Best, S. R., Lipsey, T. L., & We iss, D. S. (2003). Predictors of posttraumatic stress disorder and symptoms in adults: a meta-analysis. Psychol Bull 129 52-73. Ozer, E. J. & Weiss, D. S. (2004). Who develops posttraumatic stress disorder? Curr Dir Psychol Sci 13, 169-172. Pardridge, W. M. (1981). Transport of pr otein-bound hormones into tissues in vivo. Endocr Rev 2, 103-123.

PAGE 210

193 Pariante, C. M. & Lightman, S. L. (2008). Th e HPA axis in major depression: classical theories and new developments. Trends Neurosci 31 464-468. Pariante, C. M. & Miller, A. H. (2001). Gl ucocorticoid receptors in major depression: relevance to pathophysiology and treatment. Biol Psychiatry 49, 391-404. Park, C. R., Campbell, A. M., & Diamond, D. M. (2001). Chronic psychosocial stress impairs learning and memory and increases sensitivity to yohimbine in adult rats. Biol Psychiatry 50, 994-1004. Park, C. R., Fleshner, M., & Diamond, D. M. (2004). An NMDA antagonist can impair, protect or have no effect on memory depe nding on training parameters and stress at the time of retrieval. Soc Neurosci Abst 34, 776.22. Patterson-Buckendahl, P., Rusnak, M., Fukuha ra, K., & Kvetnansky, R. (2001). Repeated immobilization stress reduces rat vertebral bone growth and osteocalcin. Am J Physiol Regul Integr Comp Physiol 280, R79-R86. Paunovic, N., Lundh, L.-G., & Ost, L.-G. (2002). Attentional memory bias for emotional information in crime victims with acute posttraumatic stress disorder. J Anxiety Disord 16, 675-692. Pavone, F., Battaglia, M., & Sansone, M. ( 1997). Prevention of amitriptyline-induced avoidance impairment by tacrine in mice. Behav Brain Res 89 229-236. Pederson, C. L., Maurer, S. H., Kaminski, P. L., Zander, K. A., Peters, C. M., StokesCrowe, L. A., et al. ( 2004). Hippocampal volume and memory performance in a community-based sample of women with pos ttraumatic stress disorder secondary to child abuse. J Trauma Stress 17, 37-40.

PAGE 211

194 Peri, T., Ben Shakhar, G., Orr, S. P ., & Shalev, A. Y. (2000). Psychophysiologic assessment of aversive conditioning in posttraumatic stress disorder. Biol Psychiatry 47 512-519. Perry, B. D. (1994). Neurobiol ogical sequelae of childhood tr auma: PTSD in children. In: Murburg M, editor. Catecholamine Function in Post-Traumatic Stress Disorder: Emerging Concepts Washington, D.C.: APA Press, p. 233-256. Perry, B. D., Southwick, S. M., Yehuda, R., & Giller, E. L. (1990). Adrenergic receptor regulation in posttraumatic stress disorder. In: Giller EL, editor. Biological Assessment and Treatment of Posttraumatic Stress Disorder Washington, D.C.: American Psychiatric Press, p. 87-114. Peskind, E. R., Bonner, L. T., Hoff, D. J ., & Raskind, M. A. (2003). Prazosin reduces trauma-related nightmares in older men with chronic posttraumatic stress disorder. J Geriatr Psychiatry Neurol 16, 165-171. Phillips, M. A., Langley, R. W., Bradshaw, C. M., & Szabadi, E. (2000). The effects of some antidepressant drugs on prepulse inhibi tion of the acoustic startle (eyeblink) response and the N1/P2 auditory evoked response in man. J Psychopharmacol 14, 40-45. Pillai, A. G., Munoz, C., & Ch attarji, S. (2004). The antidep ressant tianeptine prevents the dendritic hypertrophy in the amygdala and increase in anxiety induced by chronic stress in the rat. Soc Neurosci Abst 34, 762.1.

PAGE 212

195 Pineyro, G., Deveault, L., Blier, P., Dennis, T., & de Montigny, C. (1995a). Effect of acute and prolonged tianeptine administ ration on the 5-HT transporter: electrophysiological, biochemical and ra dioligand studies in the rat brain. Naunyn Schmiedebergs Arch Pharmacol 351 111-118. Pineyro, G., Deveault, L., de Montigny, C., & Blier, P. (1995b). Effect of prolonged administration of tianeptine on 5-HT neurotransmission: an electrophysiological study in the rat hippocampus and dorsal raphe. Naunyn Schmiedebergs Arch Pharmacol 351 119-125. Pissiota, A., Frans, O., Fernandez, M., von Knorring, L., Fischer, H., & Fredrikson, M. (2002). Neurofunctional correlates of posttraumatic stress disorder: a PET symptom provocation study. Eur Arch Psychiatry Clin Neurosci 252, 68-75. Pitman, R. K. (1989). Post-traumatic stress disorder, hormones, and memory. Biol Psychiatry 26 221-223. Pitman, R. K., Orr, S. P., Forgue, D. F ., de Jong, J. B., & Claiborn, J. M. (1987). Psychophysiologic assessment of posttrau matic stress disorder imagery in Vietnam combat veterans. Arch Gen Psychiatry 44, 970-975. Pitman, R. K., Sanders, K. M., Zusman, R. M ., Healy, A. R., Cheema, F., Lasko, N. B., et al. (2002). Pilot study of secondary prevention of posttraumatic stress disorder with propranolol. Biol Psychiatry 51 189-192. Plaisant, F., Dommergues, M., Sp edding, M., Cecchelli, R., Brillault, J., Kato, G., et al. (2003a). Neuroprotective properties of tianeptine: intera ctions with cytokines. Neuropharmacology 44, 801-809.

PAGE 213

196 Plaisant, F., Dommergues, M. A., Spedding, M., & Gressens P. (2003b). Neuroprotective properties of tianeptine against neonatal excitotoxic brain le sions: effects of cytokines. Pediatr Res 53 541A. Pole, N. (2007). The psychophysiology of posttrau matic stress disorder: a meta-analysis. Psychol Bull 133, 725-746. Pole, N., Neylan, T. C., Best, S. R., Orr, S. P., & Marmar, C. R. (2003). Fear-potentiated startle and posttraumatic stress symptoms in urban police officers. J Trauma Stress 16, 471-479. Poltyrev, T. & Weinstock, M. (2004). Ge nder difference in the prevention of hyperanxiety in adult prenatally stre ssed rats by chronic treatment with amitriptyline. Psychopharmacology 171, 270-276. Porter, D. M. & Bell, C. C. (1999). The use of clonidine in post-traum atic stress disorder. J Natl Med Assoc 91, 475-477. Postle, B. R., Stern, C. E., Rosen, B. R., & Corkin, S. (2000). An fM RI investigation of cortical contributions to spatial a nd nonspatial visual working memory. Neuroimage 11, 409-423. Prediger, R. D., Batista, L. C., & Takahash i, R. N. (2004). Adenosine A1 receptors modulate the anxiolytic -like effect of ethanol in th e elevated plus-maze in mice. Eur J Pharmacol 499, 147-154.

PAGE 214

197 Prediger, R. D., da Silva, G. E., Batista, L. C., Bittencourt, A. L., & Takahashi, R. N. (2006). Activation of adenosine A1 receptors reduces anxiety-like behavior during acute ethanol withdr awal (hangover) in mice. Neuropsychopharmacology 31, 2210-2220. Protopopescu, X., Pan, H., Tuescher, O., Cloitr e, M., Goldstein, M., Engelien, W., et al. (2005). Differential time courses and sp ecificity of amygdala activity in posttraumatic stress disorder subjec ts and normal control subjects. Biol Psychiatry 57, 464-473. Przegalinski, E. & Budziszewska, B. (1993). The effect of long-term treatment with antidepressant drugs on the hippocampal mineralocorticoid and glucocorticoid receptors in rats. Neurosci Lett 161, 215-218. Przybyslawski, J., Roullet, P., & Sara, S. J. (1999). Attenuation of emotional and nonemotional memories after their reactivati on: role of beta adrenergic receptors. J Neurosci 19 6623-6628. Przybyslawski, J. & Sara, S. J. (1997). Recons olidation of memory after its r eactivation. Behav Brain Res 84, 241-246. Pynoos, R. S., Ritzmann, R. F., Steinberg, A. M., Goenjian, A., & Prisecaru, I. (1996). A behavioral animal model of posttraumatic stress disorder featuring repeated exposure to situational reminders. Biol Psychiatry 39, 129-134. Rabe, S., Dorfel, D., Zollner, T., Maercker A., & Karl, A. (2006). Cardiovascular correlates of motor vehicle accident relate d posttraumatic stress disorder and its successful treatment. Appl Psychophysiol Biofeedback 31, 315-330.

PAGE 215

198 Raison, C. L. & Miller, A. H. (2003). Wh en not enough is too much: the role of insufficient glucocorticoid signaling in the pathophysiology of stress-related disorders. Am J Psychiatry 160, 1554-1565. Raskind, M. A., Peskind, E. R., Kanter, E. D ., Petrie, E. C., Radant, A., Thompson, C. E., et al. (2003). Reduction of nightmares and other PTSD symptoms in combat veterans by prazosin: a placebo-controlled study. Am J Psychiatry 160, 371-373. Raskind, M. A., Thompson, C., Petrie, E. C., Dobi e, D. J., Rein, R. J., Hoff, D. J., et al. (2002). Prazosin reduces nightmares in co mbat veterans with posttraumatic stress disorder. J Clin Psychiatry 63, 565-568. Rasmusson, A. M., Hauger, R. L., Morgan, C. A., Bremner, J. D., Charney, D. S., & Southwick, S. M. (2000). Low baseline and yohimbine-stimulated plasma neuropeptide Y (NPY) levels in combat-related PTSD. Biol Psychiatry 47 526539. Rasmusson, A. M., Lipschitz, D. S., Wang, S., Hu, S., Vojvoda, D., Bremner, J. D., et al. (2001). Increased pituitary and adrenal re activity in premenopausal women with posttraumatic stress disorder. Biol Psychiatry 50, 965-977. Rau, V., DeCola, J. P., & Fanselow, M. S. (2005). Stress-induced enhancement of fear learning: an animal model of posttraumatic stress disorder. Neurosci Biobehav Rev 29, 1207-1223. Rauch, S. L., Shin, L. M., Segal, E., Pitma n, R. K., Carson, M. A., McMullin, K., et al. (2003). Selectively reduced regional cort ical volumes in post-traumatic stress disorder. NeuroReport 14 913-916.

PAGE 216

199 Rauch, S. L., Van der Kolk, B. A., Fisler, R. E ., Alpert, N. M., Orr, S. P., Savage, C. R., et al. (1996). A symp tom provocation study of posttrau matic stress disorder using positron emission tomography and script-driven imagery. Arch Gen Psychiatry 53, 380-387. Rauch, S. L., Whalen, P. J., Shin, L. M., Mc Inerney, S. C., Macklin, M. L., Lasko, N. B., et al. (2000). Exaggerated amygdala res ponse to masked facial stimuli in posttraumatic stress disord er: a functional MRI study. Biol Psychiatry 47, 769776. Regehr, C., Hill, J., & Glancy, G. D. (2000). Individual predictors of traumatic reactions in firefighters. J Nerv Ment Dis 188, 333-339. Reist, C., Kauffmann, C. D., Haier, R. J., Sangdahl, C., Demet, E. M., Chicz-DeMet, A., et al. (1989). A controlled trial of desipramine in 18 men with posttraumatic stress disorder. Am J Psychiatry 146, 513-516. Resnick, H. S., Yehuda, R., Pitman, R. K., & Foy, D. W. (1995). E ffect of previous trauma on acute plasma cortisol level following rape. Am J Psychiatry 152 16751677. Reul, J. M. & Nutt, D. J. (2008). Glutamate and cortisol: a critical confluence in PTSD? J Psychopharmacol 22, 469-472. Reul, J. M., Stec, I., Soder, M., & Holsboer, F. (1993). Chronic treatment of rats with the antidepressant amitriptyline attenuates the ac tivity of the hypotha lamic-pituitaryadrenocortical system. Endocrinology 133, 312-320.

PAGE 217

200 Reynolds, M. & Brewin, C. R. (1998). Intr usive cognitions, coping strategies and emotional responses in depression, post-traumatic stress di sorder and a nonclinical population. Behav Res Ther 36, 135-147. Reynolds, M. & Brewin, C. R. (1999). In trusive memories in depression and posttraumatic stress disorder. Behav Res Ther 37, 201-215. Reznikov, L. R., Grillo, C. A., Piroli, G. G., Pa sumarthi, R. K., Reagan, L. P., & Fadel, J. (2007). Acute stress-mediated increases in ex tracellular glutamate levels in the rat amygdala: differential effects of antidepressant treatment. Eur J Neurosci 25, 3109-3114. Richter-Levin, G. (1998). Acute and long-term behavioral correlat es of underwater trauma: potential relevance to st ress and post-stress syndromes. Psychiatry Res 79, 73-83. Riedel, G., Platt, B., & Micheau, J. (2003). Glutamate receptor function in learning and memory. Behav Brain Res 140, 1-47. Rinne, T., de Kloet, E. R., Wouters, L., Go ekoop, J. G., DeRijk, R. H., & van den, B. W. (2002). Hyperresponsiveness of hypothalamic-pituitary-adrenal axis to combined dexamethasone/corticotropin-releasing hor mone challenge in female borderline personality disorder subjects with a history of sustained childhood abuse. Biol Psychiatry 52 1102-1112. Robert, S., Hamner, M. B., Ulmer, H. G., Lorberbaum, J. P., & Durkalski, V. L. (2006). Open-label trial of escitalopram in the treatment of posttraumatic stress disorder. J Clin Psychiatry 67, 1522-1526.

PAGE 218

201 Rohleder, N., Joksimovic, L., Wolf, J. M ., & Kirschbaum, C. ( 2004). Hypocortisolism and increased glucocorticoid sensitivity of pro-Infla mmatory cytokine production in Bosnian war refugees with posttraumatic stress disorder. Biol Psychiatry 55, 745-751. Rothbaum, B. O., Killeen, T. K., Davidson, J. R., Brady, K. T., Connor, K. M., & Heekin, M. H. (2008). Placebo-controlled trial of risperidone augmentation for selective serotonin reuptak e inhibitor-resistant civilian posttraumatic stress disorder. J Clin Psychiatry 69, 520-525. Sachinvala, N., von Scotti, H., McGuire, M., Fa irbanks, L., Bakst, K., McGuire, M., et al. (2000). Memory, attention, function, and mood among patients with chronic posttraumatic stress disorder. J Nerv Ment Dis 188 818-823. Sahar, T., Shalev, A. Y., & Porges, S. W. (2001). Vagal modulation of responses to mental challenge in posttraumatic stress disorder. Biol Psychiatry 49, 637-643. Sara, S. J. (2000). Retrieval and reconsolidation: toward a neurobiology of remembering. Learn Mem 7, 73-84. Sawamura, T., Shimizu, K., Nibuya, M., Waki zono, T., Suzuki, G., Tsunoda, T., et al. (2004). Effect of paroxetine on a model of posttraumatic stress disorder in rats. Neurosci Lett 357, 37-40. Sawchuk, C. N., Roy-Byrne, P., Goldberg, J ., Manson, S., Noonan, C., Beals, J., et al. (2005). The relationship between post-trau matic stress disorder, depression and cardiovascular disease in an American Indian tribe. Psychol Med 35, 1785-1794.

PAGE 219

202 Schinkel, A. H., Wagenaar, E., Van Deemter, L., Mol, C. A. A. M., & Borst, P. (1995). Absence of the mdr1a P-glycoprotein in mice affects tissue distribution and pharmacokinetics of dexamethasone, digoxin, and cyclosporin A. J Clin Invest 96, 1698-1705. Schmahl, C. G., Elzinga, B. M., Ebner, U. W., Simms, T., Sanislow, C., Vermetten, E., et al. (2004). Psychophysiological reactivity to traumatic and abandonment scripts in borderline personality and posttraumatic stress disorder s: a preliminary report. Psychiatry Res 126, 33-42. Schuff, N., Neylan, T. C., Lenoci, M. A., Du, A. T., Weiss, D. S., Marmar, C. R., et al. (2001). Decreased hippocampal N-acetylaspartate in the absence of atrophy in posttraumatic stress disorder. Biol Psychiatry 50, 952-959. Schwartz, A. C. & Rothbaum, B. O. (2002). Re view of sertraline in post-traumatic stress disorder. Expert Opin Pharmacother 3, 1489-1499. Scott, S. K., Young, A. W., Calder, A. J., He llawell, D. J., Aggleton, J. P., & Johnson, M. (1997). Impaired auditory recognition of fear and anger following bilateral amygdala lesions. Nature 385, 254-257. Seedat, S., Lockhat, R., Kaminer, D., ZunguDirwayi, N., & Stein, D. J. (2001). An open trial of citalopram in adolescents with post-traumatic stress disorder. Int Clin Psychopharmacol 16, 21-25. Seedat, S., Stein, M. B., Kennedy, C. M., & Ha uger, R. L. (2003). Plasma cortisol and neuropeptide Y in female victim s of intimate partner violence. Psychoneuroendocrinol 28, 796-808.

PAGE 220

203 Servatius, R. J., Ottenweller, J. E., & Natelson, B. H. (1995) Delayed startle sensitization distinguishes rats exposed to one or thr ee stress sessions: furthe r evidence toward an animal model of PTSD. Biol Psychiatry 38, 539-546. Sesack, S. R., Deutch, A. Y., Roth, R. H., & Bunney, B. S. (1989). Topographical organization of the efferent projections of the medial prefrontal cortex in the rat: an anterograde tract-tracing study with Phaseolus vulgaris leucoagglutinin. J Comp Neurol 290, 213-242. Shalev, A. Y., Orr, S. P., & Pitman, R. K. (1993). Psychophysiologic assessment of traumatic imagery in Israeli civilian pa tients with posttraumatic stress disorder. Am J Psychiatry 150, 620-624. Shalev, A. Y., Peri, T., Brandes, D., Freedma n, S., Orr, S. P., & Pitman, R. K. (2000). Auditory startle response in trauma survivors with posttraumatic stress disorder: a prospective study. Am J Psychiatry 157 255-261. Shalev, A. Y., Peri, T., Orr, S. P., Bonne, O., & Pitman, R. K. (1997). Auditory startle responses in help-seeking trauma survivors. Psychiatry Res 69 1-7. Shalev, A. Y., Sahar, T., Freedman, S., Peri, T., Glick, N., Brandes, D., et al. (1998). A prospective study of heart rate response following trauma and the subsequent development of posttraumatic stress disorder. Arch Gen Psychiatry 55, 553-559. Shestatzky, M., Greenberg, D., & Lerer, B. ( 1988). A controlled trial of phenelzine in posttraumatic stress disorder. Psychiatry Res 24, 149-155.

PAGE 221

204 Shimizu, K., Kikuchi, A., Wakizono, T., Suzuki G., Toda, H., Sawamura, T., et al. (2006). An animal model of posttraumatic st ress disorder in rats using a shuttle box. Nihon Shinkei Seishin Yakurigaku Zasshi 26 93-99. Shimizu, K., Sawamura, T., Nibuya, M., Nakai, K., Takahashi, Y., & Nomura, S. (2004). An animal model of posttraumatic stress disorder and its validity: effect of paroxetine on a PTSD model in rats. Nihon Shinkei Seishin Yakurigaku Zasshi 24, 283-290. Shin, L. M., Kosslyn, S. M., McNally, R. J., Alpert, N. M., Thompson, W. L., Rauch, S. L., et al. (1997). Visual imagery and perception in posttraumatic stress disorder: a positron emission tomographic investigation. Arch Gen Psychiatry 54, 233-241. Shin, L. M., McNally, R. J., Kosslyn, S. M ., Thompson, W. L., Rauch, S. L., Alpert, N. M., et al. (1999). Regional cerebral blood flow during script-driven imagery in childhood sexual abuse-related PTSD: a PET investigation. Am J Psychiatry 156, 575-584. Shin, L. M., Orr, S. P., Carson, M. A., Rauch, S. L., Macklin, M. L., Lasko, N. B., et al. (2004a). Regional cerebral blood flow in the amygdala and medial prefrontal cortex during traumatic imagery in ma le and female Vietnam veterans with PTSD. Arch Gen Psychiatry 61, 168-176. Shin, L. M., Shin, P. S., Heckers, S., Krangel, T. S., Macklin, M. L., Orr, S. P., et al. (2004b). Hippocampal function in posttraumatic stress disorder. Hippocampus 14, 292-300.

PAGE 222

205 Shin, L. M., Wright, C. I., Cannistraro, P. A ., Wedig, M. M., McMullin, K., Martis, B., et al. (2005). A functional magnetic resonance imaging study of amygdala and medial prefrontal cortex responses to overtly presented fearful faces in posttraumatic stress disorder. Arch Gen Psychiatry 62, 273-281. Shors, T. J., Seib, T. B., Levine, S., & Thompson, R. F. (1989). Inescapable versus escapable shock modulates long-term potentiation in the rat hippocampus. Science 244, 224-226. Siegelaar, S. E., Olff, M., Bour, L. J., V eelo, D., Zwinderman, A. H., van Bruggen, G., et al. (2006). The auditory startle respon se in post-traumatic stress disorder. Exp Brain Res 174 1-6. Siegmund, A. & Wotjak, C. T. (2007a). A mouse model of posttraumatic stress disorder that distinguishes between c onditioned and sensitised fear. J Psychiatr Res 41, 848-860. Siegmund, A. & Wotjak, C. T. (2007b). Hypera rousal does not depend on trauma-related contextual memory in an animal mo del of posttraumatic stress disorder. Physiol Behav 90, 103-107. Smajkic, A., Weine, S., Duric-Bijedic, Z., Bo skailo, E., Lewis, J., & Pavkovic, I. (2001). Sertralilne, paroxetine and venlafaxine in refugee post traumatic stress disorder with depression symptoms. Med Arh 55, 35-38. Smith, M. A., Davidson, J., Ritchie, J. C., K udler, H., Lipper, S., Chappell, P., et al. (1989). The corticotropin-rel easing hormone test in pa tients with posttraumatic stress disorder. Biol Psychiatry 26, 349-355.

PAGE 223

206 Solomon, Z., Mikulincer, M., & Avitzur, E. (1988). Coping, locus of control, social support, and combat-related posttraumatic stress disorder: a prospective study. J Pers Soc Psychol 55, 279-285. Solomon, Z., Mikulincer, M., & Benbenishty, R. (1989). Locus of control and combatrelated post-traumatic stress disorder: the intervening role of battle intensity, threat appraisal and coping. Br J Clin Psychol 28 131-144. Southwick, S. M., Bremner, J. D., Rasmusson, A., Morgan, C. A., Arnsten, A., & Charney, D. S. (1999a). Role of norep inephrine in the pathophysiology and treatment of posttraumatic stress disorder. Biol Psychiatry 46, 1192-1204. Southwick, S. M., Krystal, J. H., Morgan, C. A., Johnson, D., Nagy, L. M., Nicolaou, A., et al. (1993). Abnormal noradrenergic f unction in posttraumatic stress disorder. Arch Gen Psychiatry 50, 266-274. Southwick, S. M., Morgan, C. A., Charney, D. S., & High, J. R. (1999b). Yohimbine use in a natural setting: effects on posttraumatic stress disorder. Biol Psychiatry 46, 442-444. Southwick, S. M., Paige, S., Morgan, C. A., Bremner, J. D., Krystal, J. H., & Charney, D. S. (1999c). Neurotransmitter alterations in PTSD: catecholamines and serotonin. Semin Clin Neuropsychiatry 4, 242-248. Speckens, A. E., Ehlers, A., Hackmann, A., & Clark, D. M. (2006). Changes in intrusive memories associated with imaginal reliving in posttraumatic stress disorder. J Anxiety Disord 20, 328-341.

PAGE 224

207 Speckens, A. E., Ehlers, A., Hackmann, A., Ruths, F. A., & Clark, D. M. (2007). Intrusive memories and rumination in patie nts with post-traumatic stress disorder: a phenomenological comparison. Memory 15, 249-257. Spring, B., Gelenberg, A. J., Garvin, R ., & Thompson, S. (1992). Amitriptyline, clovoxamine and cognitive function: a placebo-controlled comparison in depressed outpatients. Psychopharmacology 108 327-332. Stam, R. (2007a). PTSD and stress sensitisati on: a tale of brain and body. Part 1: human studies. Neurosci Biobehav Rev 31, 530-557. Stam, R. (2007b). PTSD and stre ss sensitisation: a tale of br ain and body. Part 2: animal models. Neurosci Biobehav Rev 31, 558-584. Stein, D. J., Ipser, J. C., & Seedat, S. (2006). Pharmacotherapy for post traumatic stress disorder (PTSD). Cochrane Database Syst Rev 1, CD002795. Stein, M. B., Kline, N. A., & Matloff, J. L. (2002). Adjunctive olanzapine for SSRIresistant combat-related PTSD: a double-blind, placebo-controlled study. Am J Psychiatry 159 1777-1779. Stein, M. B., Koverola, C., Hanna, C., To rchia, M. G., & McClarty, B. (1997a). Hippocampal volume in women victimized by childhood sexual abuse. Psychol Med 27, 951-959. Stein, M. B., Yehuda, R., Koverola, C., & Hanna, C. (1997b). Enhanced dexamethasone suppression of plasma cor tisol in adult women trau matized by childhood sexual abuse. Biol Psychiatry 42 680-686.

PAGE 225

208 Strawn, J. R. & Geracioti, T. D. (2008). Noradrenergic dysfunction and the psychopharmacology of posttraumatic stress disorder. Depress Anxiety 25 260271. Strohle, A. & Holsboer, F. (2003). Stress re sponsive neurohormones in depression and anxiety. Pharmacopsychiatry 36, S207-S214. Strohle, A., Scheel, M., Modell, S., & Hols boer, F. (2008). Blunted ACTH response to dexamethasone suppression-CRH stimula tion in posttraumatic stress disorder. J Psychiatr Res 42 1185-1188. Suzuki, A., Josselyn, S. A., Frankland, P. W., Masushige, S., Silva, A. J., & Kida, S. (2004). Memory reconsolidation and extin ction have distinct temporal and biochemical signatures. J Neurosci 24 4787-4795. Svenningsson, P., Bateup, H., Qi, H., Takamiya, K., Huganir, R. L., Spedding, M., et al. (2007). Involvement of AMPA receptor phos phorylation in antidepressant actions with special reference to tianeptine. Eur J Neurosci 26 3509-3517. Takahashi, T., Morinobu, S., Iwamoto, Y., & Yamawaki, S. (2006). Effect of paroxetine on enhanced contextual fear induced by single prolonged stress in rats. Psychopharmacology 189, 165-173. Tanji, J. & Hoshi, E. (2001). Behavioral planning in the prefrontal cortex. Curr Opin Neurobiol 11 164-170. Taylor, F. & Cahill, L. (2002). Propranolol for reemergent posttraumatic stress disorder following an event of retraumatization: a case study. J Trauma Stress 15, 433437.

PAGE 226

209 Taylor, F. & Raskind, M. A. (2002). The alpha 1-adrenergic antagonist prazosin improves sleep and nightmares in civilian trauma posttraumatic stress disorder. J Clin Psychopharmacol 22, 82-85. Taylor, F. B., Lowe, K., Thompson, C., McFall, M. M., Peskind, E. R., Kanter, E. D., et al. (2006). Daytime prazosin reduces psychological distress to trauma specific cues in civilian trauma posttraumatic stress disorder. Biol Psychiatry 59, 577-581. Thaller, V., Vrkljan, M., Hotujac, L., & Th akore, J. (1999). The potential role of hypocortisolism in the pathophysiology of PTSD and psoriasis. Coll Antropol 23, 611-619. Touyarot, K. & Sandi, C. (2002). Chronic re straint stress induces an isoform-specific regulation on the neural cell adhesion molecule in the hippocampus. Neural Plast 9, 147-159. Tsigos, C. & Chrousos, G. P. (2002). Hypothalamic-pituita ry-adrenal axis, neuroendocrine factors and stress. J Psychosom Res 53, 865-871. Tupler, L. A. & De Bellis, M. D. (2006). Segmented hippocampal volume in children and adolescents with posttraumatic stress disorder. Biol Psychiatry 59, 523-529. Uddo, M., Vasterling, J. J., Brailey, K., & Sutk er, P. B. (1993). Memory and attention in post-traumatic stress disorder. J Psychopathol Behav Assess 15 43-52. Ullman, S. E. & Filipas, H. H. (2001). Predic tors of PTSD symptom severity and social reactions in sexual assault victims. J Trauma Stress 14, 369-389.

PAGE 227

210 Uzbay, T. I. (2008). Tianeptine: Potentia l influences on neuroplasticity and novel pharmacological effects. Prog Neuropsychopharmacol Biol Psychiatry 32 915924. Uzbay, T. I., Kayir, H., & Ceyhan, M. (2007) Effects of tianeptin e on onset time of pentylenetetrazole-induced seizures in mice: possibl e role of adenosine A1 receptors. Neuropsychopharmacology 32, 412-416. Vaiva, G., Ducrocq, F., Jezequel, K., Averland, B., Lestavel, P., Brunet, A., et al. (2003). Immediate treatment with propranolol d ecreases posttraumatic stress disorder two months after trauma. Biol Psychiatry 54, 947-949. Van der Kolk, B. A. (2001). The psyc hobiology and psychopharmacology of PTSD. Hum Psychopharmacol 16, S49-S64. Van der Kolk, B. A., Dreyfuss, D., Michaels, M., Shera, D., Berkowitz R., Fisler, R., et al. (1994). Fluoxetine in posttraumatic stress disorder. J Clin Psychiatry 55 517522. van Laar, M. W., Volkerts, E. R., Verbaten, M. N., Trooster, S., van Megen, H. J., & Kenemans, J. L. (2002). Differential e ffects of amitriptylin e, nefazodone and paroxetine on performance and brain indices of visual selective attention and working memory. Psychopharmacology 162, 351-363. Vasterling, J. J., Brailey, K., Constans, J. I., & Sutker, P. B. (1998). Attention and memory dysfunction in posttraumatic stress disorder. Neuropsychology 12 125133.

PAGE 228

211 Vaswani, M., Linda, F. K., & Ramesh, S. ( 2003). Role of selectiv e serotonin reuptake inhibitors in psychiatric diso rders: a comprehensive review. Prog Neuropsychopharmacol Biol Psychiatry 27, 85-102. Veazey, C. H., Blanchard, E. B., Hickling, E. J., & Buckley, T. C. (2004). Physiological responsiveness of motor ve hicle accident survivors w ith chronic posttraumatic stress disorder. Appl Psychophysiol Biofeedback 29, 51-62. Verrier, D. L. & Dickerson, L. W. (1994). Cent ral nervous system a nd behavioral factors in vagal control of cardi ac arrhythmogenesis. In: Levy MM, Schwartz J, editors. Vagal Control of the Heart Armonk, NY: Futura, p. 557-577. Villarreal, G., Hamilton, D. A., Petropoulos, H., Driscoll, I., Rowland, L. M., Griego, J. A., et al. (2002). Reduced hippocampal vol ume and total white matter volume in posttraumatic stress disorder. Biol Psychiatry 52, 119-125. Viola, J., Ditzler, T., Batzer, W., Harazin, J., Adams, D., Lettich, L., et al. (1997). Pharmacological management of post-traum atic stress disorder: clinical summary of a five-year retrospective study, 1990-1995. Mil Med 162, 616-619. Vouimba, R. M., Munoz, C., & Diamond, D. M. (2006). Differential effects of predator stress and the antidepressant tianepti ne on physiological plasticity in the hippocampus and basolateral amygdala. Stress 9, 29-40. Vouimba, R. M., Yaniv, D., Diamond, D., & Richter-Levin, G. (2004). Effects of inescapable stress on LTP in the amygdala versus the dentate gyrus of freely behaving rats. Eur J Neurosci 19, 1887-1894.

PAGE 229

212 Vyas, A., Bernal, S., & Chattarji, S. ( 2003). Effects of chronic stress on dendritic arborization in the centra l and extended amygdala. Brain Res 965, 290-294. Vyas, A., Jadhav, S., & Chattarji, S. ( 2006). Prolonged behavioral stress enhances synaptic connectivity in the basolateral amygdala. Neuroscience 143, 387-393. Vyas, A., Mitra, R., Shankaranarayana Rao, B. S., & Chattarji, S. (2002). Chronic stress induces contrasting patterns of de ndritic remodeling in hippocampal and amygdaloid neurons. J Neurosci 22, 6810-6818. Vythilingam, M., Luckenbaugh, D. A., Lam, T., Morgan, C. A., Lipschitz, D., Charney, D. S., et al. (2005). Smaller head of the hippocampus in Gulf War-related posttraumatic stress disorder. Psychiatry Res 139 89-99. Wakizono, T., Sawamura, T., Shimizu, K., Nibuya, M., Suzuki, G., Toda, H., et al. (2007). Stress vulnerabilities in an animal model of post-traumatic stress disorder. Physiol Behav 90, 687-695. Wallace, K. J. & Rosen, J. B. (2001). Neurotoxic lesions of the la teral nucleus of the amygdala decrease conditioned fear but not unconditioned fear of a predator odor: comparison with electrolytic lesions. J Neurosci 21 3619-3627. Wang, K., Hoosain, R., Li, X., Zhou, J., Wang, C., Fu, X., et al. (2002). Impaired recognition of fear in a Chinese man with bilateral cingulate and unilateral amygdala damage. Cogn Neuropsychol 19, 641-652. Wang, W., Liu, Y., Zheng, H., Wang, H. N., Jin, X., Chen, Y. C., et al. (2008). A modified single-prolonged stress mode l for post-traumatic stress disorder. Neurosci Lett 441, 237-241.

PAGE 230

213 Watanabe, Y., Gould, E., Cameron, H. A., Da niels, D. C., & McEwen, B. S. (1992a). Phenytoin prevents stressand corticosterone-induced atroph y of CA3 pyramidal neurons. Hippocampus 2, 431-435. Watanabe, Y., Gould, E., Daniels, D. C ., Cameron, H., & McEwen, B. S. (1992b). Tianeptine attenuates stress-induced mo rphological changes in the hippocampus. Eur J Pharmacol 222, 157-162. Watanabe, Y., Gould, E., & McEwen, B. S. (1992c). Stress induces atrophy of apical dendrites of hippocampal CA3 pyramidal neurons. Brain Res 588, 341-345. Weaver, I. C., Champagne, F. A., Brown, S. E ., Dymov, S., Sharma, S., Meaney, M. J., et al. (2005). Reversal of maternal progra mming of stress responses in adult offspring through methyl supplementation: altering epigenetic marking later in life. J Neurosci 25, 11045-11054. Wellman, C. L. (2001). Dendritic reorganization in pyramidal neurons in medial prefrontal cortex after chronic corticosterone administration. J Neurobiol 49, 245253. Wessa, M. & Flor, H. (2002). Posttraumatic stress disorder and trauma memory: a psychobiological perspective. Z Psychosom Med Psychother 48, 28-37. Wessa, M., Rohleder, N., Kirschbaum, C., & Fl or, H. (2006). Altered cortisol awakening response in posttraumatic stress disorder. Psychoneuroendocrinol 31, 209-215. West, C. H. & Weiss, J. M. (2005). A selectiv e test for antidepressant treatments using rats bred for stress-induced reduction of motor activity in the swim test. Psychopharmacology 182, 9-23.

PAGE 231

214 Wignall, E. L., Dickson, J. M., Vaughan, P., Fa rrow, T. F., Wilkinson, I. D., Hunter, M. D., et al. (2004). Smaller hippocampal volume in patients with recent-onset posttraumatic stress disorder. Biol Psychiatry 56, 832-836. Wilde, M. I. & Benfield, P. (1995). Tian eptine: a review of its pharmacodynamic and pharmacokinetic properties, and therapeuti c efficacy in depression and coexisting anxiety and depression. Drugs 49, 411-439. Wilensky, A. E., Schafe, G. E., & LeDoux, J. E. (1999). Functional inactivation of the amygdala before but not after auditory fear conditioning prevents memory formation. J Neurosci 19 RC48. Williams, L. M., Kemp, A. H., Felmingham, K., Barton, M., Olivieri G., Peduto, A., et al. (2006). Trauma modulates amygdala a nd medial prefrontal responses to consciously attended fear. Neuroimage 29, 347-357. Winter, H. & Irle, E. (2004). Hippocampal volume in adult burn patients with and without posttraumatic stress disorder. Am J Psychiatry 161, 2194-2200. Woodward, S. H., Kaloupek, D. G., Streeter, C. C., Kimble, M. O., Reiss, A. L., Eliez, S., et al. (2006a). Hippocampal volume, PTSD and alcoholism in combat veterans. Am J Psychiatry 163, 674-681. Woodward, S. H., Kaloupek, D. G., Streeter, C. C., Martinez, C., Schaer, M., & Eliez, S. (2006b). Decreased anterior cingulat e volume in combat-related PTSD. Biol Psychiatry 59 582-587. Yamada, K. & Iwasaki, T. (1994). Diurnal va riation in passive a voidance response and serum corticosterone in rats. Shinrigaku Kenkyu 65 173-180.

PAGE 232

215 Yamasue, H., Kasai, K., Iwanami, A., Ohta ni, T., Yamada, H., Abe, O., et al. (2003). Voxel-based analysis of MRI reveals anterior cingulate gray-matter volume reduction in posttraumatic stress disorder due to terrorism. Proc Natl Acad Sci U S A 100, 9039-9043. Yang, C. H., Huang, C. C., & Hsu, K. S. (2005) Behavioral stress enhances hippocampal CA1 long-term depression through the bl ockade of the glutamate uptake. J Neurosci 25, 4288-4293. Yehuda, R. (2002). Current status of cortisol findings in post-traumatic stress disorder. Psychiatr Clin North Am 25, 341-68. Yehuda, R. (2004). Risk and resilience in posttraumatic stress disorder. J Clin Psychiatry 65 Suppl 1, 29-36. Yehuda, R. (2005). Neuroendocrine aspects of PTSD. Handb Exp Pharmacol 169 371403. Yehuda, R., Boisoneau, D., Lowy, M. T., & Gi ller, E. L. (1995). Dose-response changes in plasma cortisol and lymphocyte glucocorticoid receptors following dexamethasone administration in combat veterans with and without posttraumatic stress disorder. Arch Gen Psychiatry 52, 583-593. Yehuda, R., Boisoneau, D., Mason, J. W., & Giller, E. L. (1993a). Glucocorticoid receptor number and cortisol excretion in mood, anxiety, and psychotic disorders. Biol Psychiatry 34, 18-25.

PAGE 233

216 Yehuda, R., Golier, J. A., Halligan, S. L., & Harvey, P. D. (2004a). Learning and memory in Holocaust survivors with posttraumatic stress disorder. Biol Psychiatry 55 291-295. Yehuda, R., Golier, J. A., Halligan, S. L., Meaney, M., & Bierer, L. M. (2004b). The ACTH response to dexamethasone in PTSD. Am J Psychiatry 161, 1397-1403. Yehuda, R., Golier, J. A., Tischler, L., Harv ey, P. D., Newmark, R., Yang, R. K., et al. (2007). Hippocampal volume in aging comb at veterans with and without posttraumatic stress disorder: relation to risk and resilience factors. J Psychiatr Res 41, 435-445. Yehuda, R., Halligan, S., Grossman, R., Golier, A., & Wong, C. (2002). The cortisol and glucocorticoid receptor re sponse to low dose dexamethasone administration in aging combat veterans and holocaust survivors with and without posttraumatic stress disorder. Biol Psychiatry 52, 393-403. Yehuda, R. & LeDoux, J. (2007). Response variation following trauma: a translational neuroscience approach to understanding PTSD. Neuron 56, 19-32. Yehuda, R., Levengood, R. A., Schmeidler, J., Wilson, S., Guo, L. S., & Gerber, D. (1996a). Increased pituitary activation following metyrapone administration in post-traumatic stress disorder. Psychoneuroendocrinol 21, 1-16. Yehuda, R., Lowy, M. T., Southwick, S. M., Shaffer, D., & Giller, E. L. (1991). Lymphocyte glucocorticoid re ceptor number in posttraumatic stress disorder. Am J Psychiatry 148, 499-504.

PAGE 234

217 Yehuda, R., Siever, L. J., Teicher, M. H., Levengood, R. A., Gerber, D. K., Schmeidler, J., et al. (1998). Plasma norepinep hrine and 3-methoxy-4-hydroxyphenylglycol concentrations and severity of depression in combat posttraumatic stress disorder and major depressive disorder. Biol Psychiatry 44 56-63. Yehuda, R., Southwick, S. M., Krystal, J. H., Bremner, D., Charney, D. S., & Mason, J. W. (1993b). Enhanced suppression of cortisol following dexamethasone administration in posttraumatic stress disorder. Am J Psychiatry 150, 83-86. Yehuda, R., Teicher, M. H., Trestman, R. L., Levengood, R. A., & Siever, L. J. (1996b). Cortisol regulation in posttraumatic st ress disorder and major depression: a chronobiological analysis. Biol Psychiatry 40, 79-88. Yokota, S., Ishikura, Y., & Ono, H. (1987). Card iovascular effects of paroxetine, a newly developed antidepressant, in anestheti zed dogs in comparison with those of imipramine, amitriptyline and clomipramine. Jpn J Pharmacol 45, 335-342. Zajaczkowski, W. & Gorka, Z. (1993). The e ffects of single and re peated administration of MAO inhibitors on acoustic startle response in rats. Pol J Pharmacol 45, 157166. Zatzick, D. F., Russo, J., Pitman, R. K., Rivara, F., Jurkovich, G., & Roy-Byrne, P. (2005). Reevaluating the association betw een emergency department heart rate and the development of posttraumatic stre ss disorder: a public health approach. Biol Psychiatry 57, 91-95.

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218 Zoladz, P. R., Conrad, C. D., Fleshner, M., & Diamond, D. M. (2008). Acute episodes of predator exposure in conjunction with ch ronic social instability as an animal model of post-traumatic stress disorder. Stress 11 259-281. Zoladz, P. R., Park, C. R., Munoz, C., Fl eshner, M., & Diamond, D. M. (in press). Tianeptine: an antidepressant with memory-protective properties. Curr Neuropharmacol

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About the Author Phillip R. Zoladz received his Bachel or of Arts degree in Psychology from Wheeling Jesuit University in 2004 and his Mast er of Arts degree in Psychology from the University of South Florida in 2006. During hi s graduate studies at the University of South Florida, Phillip focuse d his research efforts on deve loping a better understanding of the neurobiological mechanisms of post-tr aumatic stress disorder and has presented his research findings at several national conferences. He has al so published several original data papers and literature re views in well-respected scientif ic journals. As a graduate student, Phillip gained extensive teaching experience by instructing several undergraduate courses, including Research Methods in Psychology, Psychology of Learning and Physiological Psyc hology. Phillip is a devout Ch ristian by faith and enjoys spending time with his beautiful wife, Meagan.