Sisk 9602169 Puberty is a well-defined developmental phase when reproductive function and behaviors mature in animal species. The maturation process begins in a poorly defined manner and is propagated further by changes in gonadal steroid sensitivity. Unfortunately, a thorough understanding of the mechanisms triggering puberty has been elusive. Dr. Sisk's investigations focus on how androgenic steroid hormones, such as testosterone, influence brain function differently in reproductively immature and adult males. Juvenile males are relatively unresponsive to the effects of testosterone on behaviors related to reproduction, and Dr. Sisk is identifying the neuronal elements of prepubertal males responsible for the lack of responsivity and the underlying causes. In addition, the idea of puberty as a developmental stage during which steroid hormones can permanently shape brain organization and function are being addressed. These investigations will provide important contributions to an understanding of how brain processes change during puberty, and will also have more general applicability to an understanding of hormonal influences on the nervous system throughout the lifespan. These investigations contribute significantly to our understanding of species survival in the natural setting and the neurobiological basis for successful reproduction.