The goal of this research program is to elucidate fundamental neuroendocrine mechanisms mediating the activation of reproductive behavior. It involves an investigation of the interrelationship among hormones, brain, and behavior and includes methods and experimental approaches appropriate to the study of all three of these components of the integrated system that governs hormone-dependent behaviors. The proposed experiments focus on the neuroendocrine mechanisms regulating appetitive and consummatory male sexual behavior in Japanese quail (Coturnix japonica). In particular the related roles played by the catecholamine, dopamine (DA), and the steroid metabolizing enzyme, aromatase, in relation to the activation by testosterone (T) of male reproductive behavior will be investigated. The proposed work capitalizes on previous findings concerning the neuroendocrine control of male sexual behavior in quail that make this species a unique model for these investigations. Especially notable is the ability to localize reliably at the cellular level both the protein and the mRNA of brain aromatase. In this application, 13 experiments are proposed that are designed to analyze three specific aims relating to the interaction of DA and brain aromatase in relation to the effects of T on the neural circuit mediating male sexual behavior. Aim I concerns the differential regulation of appetitive and consummatory aspects of male sexual behavior. Lesion and tract tracing studies, along with histological measures of neural activation, are proposed to characterize the neural circuit mediating these two components of male behavior [Expts 1-6]. Aim II is designed to investigate the dopaminergic regulation of aromatase and will involve both in vivo and in vitro studies of this interaction [Expts 7-11]. Aim III focuses on the identification of sex differences in the connectivity and chemical neuroanatomy of steroid-sensitive brain areas and their relationship to sex differences in the hormonal activation of appetitive and consummatory aspects of male sexual behavior [Expts 12-13]. The elucidation of the mechanisms mediating steroid effects on a neural circuit is relevant to many significant issues facing the field of behavioral neuroscience. Steroid hormones have been found to have wide ranging effects on brain morphology and plasticity both during development and in adulthood. The study of steroid-neurotransmitter interactions also may provide insight into the etiology of sexually differentiated or steroid-dependent diseases.