Behavioural Endocrinology and Sexual Dimorphism of Brain and Behaviour

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Like the rest of the body, the nervous system takes on a male or female form and function due to the actions of sex hormones. Exploring these differences helps us learn about how the nervous system functions, specializes and remodels itself. To study the reciprocal relationships between hormones, the nervous system, and behaviour, we ask three basic questions: (1) How do sex hormones act on neural structures to cause them to take on male or female form? Our on-going research program focuses on model systems in the spinal cord, brainstem, and cerebellum, that we have previously linked to masculine sex-related behaviour and the actions of the sex steroid testosterone. In proposed research we will explore testosterone's influence on neural and genetic control of communicative behaviours active in sexual contexts. Additionally, we will map sex differences in previously understudied brainstem components of the male sexual circuitry. Other studies build on our work showing that the plasticizer bisphenol A (BPA) alters the structure of sex steroid-sensitive neurons in the spinal cord next, we will study effects in additional brain regions, and examine effects of BPA replacement substances that appear to have steroid-like actions of their own. We will also study how the effects of these substances on the structure of the brain are passed on to subsequent generations through epigenetic modification. (2) How do androgens like testosterone regulate behavioural processes? Several proposed experiments probe the role of androgens in the production of ultrasonic vocalizations, an important communicative behaviour in rats. We are interested in their signalling qualities, and relation to social and sexual development as determined by hormone exposure. In other work, we plan to thoroughly explore novel ways in which plasticizers, by mimicking steroids, alter the expression of normal sex differences in cognitive, emotional, and sexual behaviours in rats. (3) Reversing the relationship, how do behaviours and social cues alter sex hormones? Turning mostly to humans, we are interested in how ecologically-important environmental cues like dominance competitions, relationships, social settings, and reproductive opportunities provoke changes in testosterone release in men and women. Presumably, this mechanism is an ancient adaptation that coordinates physiology and neural mechanisms with environmental opportunities. Proposed studies probe endocrine reactivity in response to social inputs likes competition, teamwork, social exclusion, and mate stimuli. We will also systematically evaluate the impact of gender identity in determining social endocrine reactivity, alongside more traditional sex differences.