We use the male golden hamster as a model system for studying adolescent maturation of social behaviors and their underlying neural circuits. We are especially interested in determining which aspects of maturation are dependent on the pubertal elevation in gonadal hormones and which aspects are hormone-independent, that is, related to age instead of pubertal status.
Some of our early work showed that adult male social behaviors, including sexual behavior, aggression, and scent marking, are compromised if adolescent development proceeds in the absence of testicular hormones. In addition, male hamsters that do not experience testosterone during adolescent development appear to be "socially awkward", showing inappropriate responses during social interactions and failing to learn from social experience. These results showed that testosterone, acting during puberty, organizes neural circuits underlying social behaviors, and we've proposed a two stage model of sexual differentiation, in which perinatal testosterone initially masculinizes the nervous system, and then a second wave of further masculinization occurs when testosterone levels rise again during puberty.
We've also found that the perinatal and pubertal periods are not two separate sensitive periods for brain organization by testosterone, but instead that puberty and adolescence are part of an extended period of postnatal sensitivity to organizational effects of hormones that begins at birth and ends sometime in late adolescence.
We are currently focused on the role of testicular hormones in adolescent maturation of social information processing. Male hamsters are a good model for this line of work, because they show an adolescent change in neural and behavioral responses to female pheromones that are required for successful reproduction. It appears that these female pheromones are rewarding to adults, but not juveniles, because adults will form a conditioned place preference to vaginal secretions that contain the pheromones, whereas juvenile hamsters do not. In addition, the pheromones activate certain elements of the mesocorticolimbic reward circuitry in adults, but not juveniles. We are now investigating the role of testosterone and dopamine in this adolescent change in the perception of this essential social stimulus.