Mice to Meet You: The Impact of Testosterone on Social Behavior Across Social Context and Sex

Abstract

Previous research has demonstrated that sex hormones promote particular suites of behavior in a context-dependent manner and that sex differences in hormone concentration drive sex differences in behavior. However, previous research has limited its study of sex hormones to specific suites of social behavior – namely parenting, aggression, and mating – and used a narrow number of human-identifiable metrics to analyze social behavior. Thus, my thesis examines how sex hormones, and specifically testosterone (T), affect social behavior and sex differences in social behavior using a more expansive treatment of behavior. This more expansive treatment employs an unsupervised, computational approach to analyze behavior across several social contexts. With this treatment, I test the hypothesis that sex hormones bias animals into particular behavior states as a function of sex and social context by examining how social behavior changes in a low hormone state induced by gonadectomy and a low hormone state supplemented by a longitudinal dose of T. I subjected male and female CD1 mice to a resident-intruder paradigm in which they encountered three different social partners: CD1 males, CD1 females, and Balb/c males. Mice were tested in the paradigm on three, nonconsecutive days before and after surgery. Both gonadectomy and gonadectomy plus T treatment changed social behavior and sex differences in social behavior in a social context-dependent manner. However, T treatment exhibited less behavior change compared to gonadectomy in females, but not in males, suggesting that rapid fluctuations in T release may be required to restore intact behavior patterns in males. In addition, both gonadectomy and gonadectomy plus T treatment decreased sex differences in interactions with males and increased sex differences in interactions with females, suggesting that sex hormones interact with sex differences in the neural circuitry to produce sex- and context-dependent behavioral outcomes. In conclusion, these results demonstrate that sex hormones do not have a unilateral effect on behavior, but rather interact with internal and external factors to modulate social behavior.