The goal of the proposed research is a better understanding of the cellular mechanisms by which hormones affect brain function and behavior. The cellular actions of estradiol will be studied in relation to sexual behavior, locomotor activity, eating behavior, and luteinizing hormone release. The effects of estradiol on these measures could be mediated by the high-affinity estradiol-binding protein (estrogen receptor) found in some regions of the brain. When estradiol is bound to the receptor, the hormone-receptor complex migrates to the cell nucleus, where it could modulate RNA synthesis, thereby altering the activity of the cell. The subcellular distribution of the receptor will be determined under physiological conditions in female and male rats. Estradiol-induced behavioral changes will be correlated with the presence of estrogen receptors in cell nuclei of brain regions. For example, in females, cytoplasmic and nuclear estrogen receptors will be assayed throughout the estrous cycle and pregnancy. In males, levels of nuclear estrogen receptors (translocated by estrogens formed intraneuronally) will be assayed in rats who display differing levels of copulatory behavior. A second way to relate brain estrogen receptors to behavior is to use antiestrogens, agents which block most behavioral actions of estradiol and are used therapeutically in humans for the induction of ovulation. The neuroanatomical sites where antiestrogens affect several behaviors and neuroendocrine function will be specified by localized intracerebral implants of tritiated antiestrogens. Antiestrogens will be localized autoradiographically, and the sites where the implants block estradiol binding will be determined by estradiol immunofluorescence. The interactions of antiestrogens with estrogen receptors will be studied in specified areas of the brain. Five hypotheses about the mechanism of action of antiestrogens will be studied in detail. The hypotheses assess the functional significance of various aspects of receptor dynamics, including the replenishment of cytoplasmic receptors, the requirement for stable ligand-receptor complexes, and the binding of ligand-receptor complexes to acceptor sites in cell nuclei.