Sexual dimorphism in neural structure and function

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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? We are focusing on several model systems to address this question, especially the Spinal Nucleus of the Bulbocavernosus (SNB), and parts of the brainstem and cerebellum, that we have previously linked to masculine sexual behaviour and the actions of the sex hormone testosterone on nerve cells. In particular, we will be focusing on the role of androgen receptors in establishing a male-typical caudal ventral medulla system for reproductive behaviour, and on the effects of the plasticizer Bisphenol A in disrupting this system. (2) How do androgens like testosterone change the behavior of lab animals and humans? Here, we will examine the effects of Bisphenol A on a variety of behaviours that are normally different between male and female rats, ranging from spatial cognition to mating. We are also studying the role of androgens in the ultrasonic vocalizations that are an important social signal 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, or reproductive opportunities - provoke a change in testosterone release in men and women. Presumably, this mechanism is an ancient adaptation that coordinates physiology and neural mechanisms with environmental opportunities. And lastly, we have been studying the effects of pregnancy on cognition, as pregnancy is a sort of natural experiment involving large fluctuations in sex hormones. Having found a surprising fetal-sex effect on maternal cognition, we are now investigating possible mechanisms by which fetuses affect their mothers' cognitive abilities, possibly through the actions of understudied hormones called lutropins.