The Role of Social Context in Modulating Gene Expression, Neural Activity, and Neuroendocrine Response in Individuals of Varying Social Status Caitlin Williamson Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Graduate School of Arts and Sciences COLUMBIA UNIVERSITY 2018 © 2018 Caitlin Williamson All rights reserved ABSTRACT The Role of Social Context in Modulating Gene Expression, Neural Activity, and Neuroendocrine Response in Individuals of Varying Social Status Caitlin Williamson Social context, which includes both the direct social experience of individuals as well as the characteristics of their social network as a whole, has been shown to be an important modulator of behavior across species. However, relatively little is known about the role of social context in regulating the complex relationships between neurobiology, neuroendocrine response, and behavior in mammals. Historically, the neurobiology of social behavior has been studied at the dyadic level, looking at brief social interactions between pairs of individuals. Given that all social species live in groups, rather than pairs, it is essential that we begin to understand the role social context at the group level plays in regulating physiology. Throughout this thesis, I use a novel behavioral housing system to study how the characteristics of stable social groups and how instances of social opportunity, when individuals are ascending up a social hierarchy, are associated with differential brain gene expression, neuroendocrine output, and behavior. I first extensively analyze the social dynamics of male dominance hierarchies, showing that they are both consistent, in that males reliably form significantly linear dominance hierarchies, and unique, in that the characteristics of these hierarchies vary from group to group. I further prove that mice living in these social hierarchies are extremely socially competent, displaying the ability to respond appropriately to individuals of varying social status. I demonstrate that females are capable of forming dominance hierarchies as well, but that their hierarchies differ from those of males. I then use this foundational knowledge to investigate how these different hierarchy characteristics can lead to differences in physiology, how one’s social status is associated with brain gene expression and neuroendocrine response, and how disruption of a hierarchy through removal of the alpha male leads to robust behavioral as well as physiological consequences. Finally, I use the insights gained from this immediate early gene work to demonstrate the crucial role of the infralimbic/prelimbic region of the medial prefrontal cortex in regulating socially competent response to changing social contexts. Taken together, this work establishes the broad role social context plays in regulating the complex relationships between behavior, brain gene expression, neural activation, and neuroendocrine output. TABLE OF CONTENTS List of Figures .......... iii List of Tables .......... vi Acknowledgments .......... viii Dedication .......... xii Chapter 1 General Introduction .......... 1 Chapter 2 Temporal dynamics of social hierarchy formation and maintenance in male mice .......... 13 Chapter 3 Social context-dependent relationships between mouse dominance rank and plasma hormone levels .......... 65 Chapter 4 Social hierarchy position in female mice is associated with plasma corticosterone levels and estrogen- mediated gene expression in the ventromedial hypothalamus .......... 102 Chapter 5 Mouse social network dynamics and community structure are associated with plasticity-related gene expression .......... 148 Chapter 6 The behavioral and neuroendocrine response to social opportunity .......... 209 Study #1 Dynamic changes in social dominance and mPOA GnRH expression in male mice following social opportunity .......... 209 Study #2 Short-term changes in circulating plasma testosterone levels are not associated with social ascent .......... 246 i Study #3 Social status is associated with a behavioral, but not plasma testosterone, response to exogenous GnRH administration in mice .......... 259 Chapter 7 Immediate early gene activation throughout the brain is associated with dynamic changes in social context .......... 272 Chapter 8 Hypofunction of the infralimbic and prelimbic prefrontal cortex disrupts social opportunity behavior .......... 305 Chapter 9 General Conclusion .......... 329 ii LIST OF FIGURES Chapter 2 Main Text Figures 2.1 Median directional consistencies by relationship across cohorts .......... 26 2.2 Triangle transitivity by day .......... 28 2.3 Final Glicko ratings by cohort .......... 30 2.4 Temporal dynamics of individual Glicko ratings by cohort .......... 31 2.5 Correlation between Glicko ratings after each day and final Glicko ratings .......... 33 2.6 Changes in Gini coefficient in winning and losing by day .......... 36 2.7 Win proportions by alpha males across cohorts .......... 38 Supplemental Figures S2.1 Housing Vivarium .......... 57 S2.2 Valued and binarized matrices of wins and losses between all pairs of individuals across all cohorts .......... 58 S2.3 Interaction probabilities by rank .......... 60 S2.4 Triangle transitivity by day based on the last five observations per relationship .......... 61 S2.5 Gini coefficients of wins and losses against the top four most dominant Individuals .......... 62 S2.6 Difference in win proportions between alpha and beta males across cohorts .......... 63 S2.7 Location of agonistic interactions by cohort .......... 64 Chapter 3 Main Text Figures 3.1 Schematic of experimental timeline .......... 75 3.2 Testosterone and corticosterone in pair-housed males .......... 81 3.3 Rate of wins and losses by housing condition and despotism .......... 84 3.4 Plasma testosterone and plasma corticosterone levels by social rank across all hierarchies .......... 87 3.5 Plasma testosterone and plasma corticosterone levels by social rank in high and low despotism hierarchies .......... 88 Supplemental Figures S3.1 Housing Vivarium .......... 100 S3.2 Plasma testosterone and plasma corticosterone levels by social rank in high and low despotism hierarchies as determined by behavior only during the final two days of group housing .......... 101 iii Chapter 4 Main Text Figures 4.1 Female social hierarchies are significantly different from those of males .......... 117 4.2 Number of wins and losses differ between stages of the estrous cycle .......... 119 4.3 Plasma Corticosterone and Estradiol levels for dominant and subordinate females .......... 120 4.4 ERβ, PR, and OPRM1 mRNA levels in the VMH are higher for subordinate females .......... 121 Supplemental Figures S4.1 Housing vivarium .......... 144 S4.2 Glicko scores over the group housing period for all cohorts .......... 145 S4.3 ERα, GnRH, and OTR mRNA levels in the VMH do not differ between dominant and subordinate females .......... 146 S4.4 ERα, ERβ, PR, OTR, GnRH, and OPRM1 mRNA levels in the mPOA do not differ between dominant and subordinate females .......... 147 Chapter 5 Main Text Figures 5.1 Frequency and binarized win-loss sociomatrices .......... 166 5.2 Mice within overall social hierarchy establish separate hierarchically organized communities .......... 169 5.3 Location and frequency of agonistic interactions by subject .......... 170 5.4 Non-metric multidimensional scaling (nMDS) plot of individual space usage .......... 172 5.5 Individual network position are associated with dominance rank .......... 175 5.6 Brain gene expression and social dominance .......... 178 Supplemental Figures S5.1 Housing vivaria .......... 202 S5.2 Location of agonistic interactions by community .......... 203 S5.3 Half-weight association indices within and between communities .......... 204 S5.4 Changes in space usage evenness of giving and receiving aggression by days .......... 205 S5.5 Investigation of novel social stimuli are negatively associated with initial individual network position .......... 206 S5.6 Hippocampal DNMT3a expression is negatively associated with out-closeness in individuals in Community B but not Community A .......... 207 S5.7 mPOA DNMT1 and DNMT3a expression are not associated with out-closeness .......... 208 iv Chapter 6 Main Text Figures 6.1 Schematic of the social opportunity experimental design .......... 216 6.2 Behavioral changes following social opportunity .......... 222 6.3 Behavioral changes in subdominant males following the removal of the alpha male .......... 226 6.4 HPG measures correlated to social status and impacted by social opportunity .......... 229 6.5 Replication of behavioral changes following social opportunity .......... 252 6.6 Plasma testosterone changes in response to social opportunity .......... 253 6.7 Effect of GnRH administration on aggression in dominant and subordinate Individuals .......... 266 6.8 Effect of GnRH administration on testosterone response in dominant and subordinate individuals .......... 268 Supplemental Figures S6.1 Housing Vivarium .......... 243 S6.2 Frequency of wins and losses within one hour of the alpha male being Removed .......... 244 S6.3 David’s scores of animals during the one hour period following alpha male removal .......... 245 Chapter 7 Main Text Figures 7.1 Schematic of the social opportunity experimental design .......... 279 7.2 Behavioral changes in subdominant male following removal or non-removal of the alpha male .......... 285 7.3 Sample images of Fos staining in individuals from