Neuroendocrine Control of Pituitary Hormone Secretion: The molecular mechanism(s) by which steroid hormones regulate the release of hypothalamic releasing hormones and thereby control the release of pituitary hormones is not well defined. Three loci for steroid hormone action have been identified: extra-hypothalamic brain nuclei, the hypothalamus and the pituitary. Evidence from our laboratory has shown that subcellular fractions of specific brain regions are altered via steroid treatment. Thus the content and release of luteinizing hormone releasing hormone (LHRH) in hypothalamic (HYP) synaptosomes is changed with ovariectomy plus estrogens. We propose to continue our examination of the mechanism by which estrogens (E) alter the release of LHRH. Temporal studies of the hypothalamic content and releasability of LHRH from HYP synaptosomes has allowed a correlation of estrogen receptors in the HYP with the positive feedback of estrogens. Using subcellular fractionation and SDS-PAGE, we propose to search specific fractions of nerve terminals for proteins induced by estrogens and progestins. We will continue our studies of the in vitro release of LHRH, extend these to an examination of the effects of neurotransmitters on release. Finally, we will determine the estrogen dependence of neurotransmitter effect. From our previous results and those of others, we believe that cellular and subcellular fractionation of central nervous tissues known to be target sites for steroids into neurons, glia, and functional subcellular units offers the field of endocrinology unique models for the elucidation of mechanism(s) by which steroids regulate neuroendocrine systems.