Georgia State University ScholarWorks @ Georgia State University Neuroscience Institute Dissertations Neuroscience Institute Spring 5-9-2016 Genetic and Epigenetic Mechanisms Underlying Stress-Induced Behavioral Change Katharine E. McCann Georgia State University Follow this and additional works at: https://scholarworks.gsu.edu/neurosci_diss Recommended Citation McCann, Katharine E., "Genetic and Epigenetic Mechanisms Underlying Stress-Induced Behavioral Change." Dissertation, Georgia State University, 2016. https://scholarworks.gsu.edu/neurosci_diss/25 This Dissertation is brought to you for free and open access by the Neuroscience Institute at ScholarWorks @ Georgia State University. It has been accepted for inclusion in Neuroscience Institute Dissertations by an authorized administrator of ScholarWorks @ Georgia State University. For more information, please contact [email protected]. GENETIC AND EPIGENETIC MECHANISMS UNDERLYING STRESS- INDUCED BEHAVIORAL CHANGE by KATHARINE E. MCCANN Under the Direction of Kim Levy Huhman, PhD ABSTRACT Social stress is the most common stressor experienced by humans and exposure to social stress is thought to cause or exacerbate neuropsychiatric illness. Social stress also leads to behavioral and physiological responses in many animal models that closely mirror the symptoms of fear and anxiety in humans. Our laboratory uses Syrian hamsters to study behavioral responses to social stress. Hamsters are highly territorial, but after losing an agonistic encounter, hamsters exhibit a striking behavioral change, abandoning all territorial aggression and instead becoming highly submissive. This behavioral shift is termed conditioned defeat. Epigenetic modifications, such as changes in histone acetylation, are a possible molecular mechanism underlying such behavioral shifts. Histone deacetylase (HDAC) inhibitors have been shown to enhance fear learning and conditioned place preference for drugs of abuse, while suppressing histone acetylation with histone acetyltransferase (HAT) inhibitors impairs long-term memory formation. The first goal of this study was to test the hypothesis that histone acetylation is a molecular mechanism underlying conditioned defeat. We found that animals given an HDAC inhibitor systemically before social defeat later exhibited increased conditioned defeat. This treatment also suppressed defeat-induced immediate-early gene activity in the infralimbic cortex but not the basolateral amygdala. Next, we demonstrated that administration of an HDAC inhibitor in the infralimbic cortex before defeat enhanced stress-induced behavioral responses while HAT inhibition blocked these behavioral changes. Although both males and females exhibit conditioned defeat, the behavioral expression is more pronounced in males. We next used transcriptomic analysis to investigate potential genetic mechanisms leading to this sexually dimorphic expression and to further delineate the role of acetylation in stress-induced behavioral changes. We sequenced the whole brain transcriptome of male and female hamsters as well as the transcriptome of basolateral amygdala, a nucleus necessary for the acquisition and expression of conditioned defeat, of dominant, subordinate, and control animals. Our analysis revealed that numerous genes relating to histone acetylation, including several HDACs, were differentially expressed in animals of different social status and between sexes. Together, these data support the hypotheses that histone modifications underlie behavioral responses to social stress and that some of these modifications are sexually dimorphic. INDEX WORDS: Conditioned defeat, Transcriptomics, Histone acetylation, Sex differences, Social stress GENETIC AND EPIGENETIC MECHANISMS UNDERLYING STRESS-INDUCED BEHAVIORAL CHANGE by KATHARINE E. MCCANN A Dissertation Submitted in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy in the College of Arts and Sciences Georgia State University 2016 Copyright by Katharine E. McCann 2016 GENETIC AND EPIGENETIC MECHANISMS UNDERLYING STRESS- INDUCED BEHAVIORAL CHANGE by KATHARINE E. MCCANN Committee Chair: Kim L. Huhman Committee: H. Elliot Albers Laura L. Carruth Kerry J. Ressler Walter Wilczynski Electronic Version Approved: Office of Graduate Studies College of Arts and Sciences Georgia State University May 2016 iv Dedication For my husband, my parents, and my brother for never letting me forget why I came back to school and why this research is important. v Acknowledgements First and foremost I want to thank my advisor, Dr. Kim Huhman. Kim, you have been an amazing mentor, role model, and friend. I could not have asked for a better graduate school experience or a better advisor to help get me here. You have taught me so much about how to be a good scientist and how to keep a balanced life without sacrificing success. I am incredibly grateful that you took that chance on me all those years ago! I also want to thank the members of my committee, Dr. Elliott Albers, Dr. Laura Carruth, Dr. Kerry Ressler, and Dr. Walt Wilczynski. Thank you Elliott for being a second mentor to me all through graduate school. I am excited for the opportunity to continue to work with and learn from you over the next year. To Laura, thank you for teaching me the importance of being a well-rounded scientist. I am a better scientist because of your mentorship. To Walt and Kerry, I would not have made it this far without your support and guidance. I dove in head first to the world of epigenetics and transcriptomics, and I may have drowned had it not been for you both. I also want to thank all of the members of both the Huhman and Albers labs who have supported and helped me throughout this entire process, especially Alisa. Alisa – you know we would all be lost without you. Your help and guidance in the lab is invaluable, but more importantly, I am happy to have found a life-long friend. Furthermore, this work would not have been possible without the support of my friends and family, the GSU DAR staff, the NI administration, and GSU IS&T. Lastly, I would like to thank Ken and Georganne Honeycutt. Knowing that I had people as genuine and supportive as the Honeycutts rooting for me has made reaching the finish line so much easier. vi TABLE OF CONTENTS Acknowledgements ............................................................................ v List of tables ..................................................................................... xi List of figures ................................................................................... xii 1 Introduction ................................................................................. 1 1.1 Animal models of human psychopathology: Using hamsters in a translational model of social stress-induced behavioral change ............. 1 1.2 Epigenetic mechanisms underlying conditioned defeat: The potential role of histone deacetylases ....................................................... 4 1.3 Genetic resources for non-traditional animal models using transcriptomics ........................................................................................ 7 1.4 Specific aims overview............................................................. 9 1.4.1 Specific Aim 1: Does inhibition of HDACs or HATs increase or decrease, respectively, social avoidance and submissive behavior after acute social defeat? ...................................................................... 9 1.4.2 Specific Aim 2: Does systemic HDAC inhibition during social defeat increase subsequent neuronal activity (as measured by Fos-immunoreactivity) in specific nodes of the neural circuit that mediates conditioned defeat? ................................................................ 9 1.4.3 Specific Aim 3: Are Class I HDACs highly expressed in the hamster amygdala and is their expression altered by social defeat? .. 10 vii 2 Pharmacological manipulation of histone acetylation modulates behavioral responses to acute social stress ............................................... 10 2.1 Introduction .......................................................................... 10 2.2 Materials and Methods .......................................................... 12 2.2.1 Animals ........................................................................... 12 2.2.2 Social defeat training ...................................................... 13 2.2.3 Social avoidance testing .................................................. 14 2.2.4 Cannulation and microinjections .................................... 15 2.2.5 Pharmacological agents .................................................. 16 2.2.6 Histology.......................................................................... 17 2.2.7 Immunohistochemistry for immediate-early gene c-fos ... 17 2.2.8 Statistical analysis .......................................................... 18 2.3 Results .................................................................................. 18 2.3.1 Systemic administration of an HDAC inhibitor before social stress enhances the acquisition of conditioned defeat .............. 18 2.3.2 Systemic administration of VPA also enhances acquisition of conditioned defeat in female hamsters ............................................ 21 2.3.3 Site-specific HDAC inhibition in the IL, but not in the BLA, alters behavioral responses to social defeat ....................................... 21 2.3.4 HAT inhibition in the IL blocks the acquisition of conditioned defeat .............................................................................