There are two principal purposes for the present research. One goal will be to gather and integrate information on the effects of gonadal steroids on the non-reproductive behaviors of several species of rodents, focusing on the behaviors that affect body weight and composition. A second goal of the program is to study, with biochemical methods, the mechanisms by which steroids affect brain tissue and, thus, behavior. A great deal of previous work indicates that gonadal steroids have very striking effects on many of the behaviors controlling body weight in a wide variety of species, including both human beings and nonhuman primates. In fact, the set-point about which body weight is regulated may be determined, in part, by the levels of circulating sex steroids. Specific projects will examine the effects of various combinations of brain (and peripheral nerve) lesions, endocrinectomies, and hormone treatments (both systemic and intracerebral) on these weight-regulating behaviors. The second portion of this program will attempt to determine the sites and mechanisms of action of gonadal hormones in the brain. Specific experiments will correlate brain uptake of radioactive steroids and behavioral responses to sex steroids when the steroids are administered in the dosages, injection routes, and vehicles, and time-courses that affect behavior. BIBLIOGRAPHIC REFERENCES: Roy, E.J., Maass, C.A., and Wade, G.N. Central action and a species comparison of the estrogenic effects of an antiestrogen on eating and body weight. Physiology and Behavior, 1977, 18, in press. Roy, E.J. and Wade, G.N. Binding of 3H-estradiol by brain cell nuclei and female rat sexual behavior: Inhibition by antiestrogens. Brain Research, 1977, in press.