The overall objectives of this proposal are to determine the exact location of neurons whih take up and retain androgen as such and those neurons which convert androgen to estrogen before nuclear uptake and retention, and to determine whether these sites of androgen uptake respond to androgen by modulating the release of FSH and LH from the pituitary gland. In order to accomplish these objectives, three principal approaches will be used. The first approach, autoradiography, will make use of the stereospecific properties of aromatization to locate those neurons which concentrate androgen and those neurons which convert androgen to estrogen before nuclear uptake and retention occurs. The second and tird approaches, stereotaxic implantation and radioimmunoassay, will be used to determine which of these sites respond to androgen by modulating the release of FSH and LH from the pituitary and modulating sexual behavior. Comparisons will be made in a number of species to determine the generality of the selective nuclear uptake and retention of unaromatized androgen (rat, mouse, hamster, guinea pig, and Rhesus Macaque (if available) and to determine the effects of androgen on a number of important physiologic parameters (rat and hamster).