Objectives: This proposal is designed to examine the neuroendocrine control of the synthesis and release of neuropeptide Y (NPY) in the hypothalamus of female rats following alterations in plasma levels of gonadal steroids. The proposed research should enhance our basic understanding of the reproductive neuroendocrine regulation of NPY biosynthesis and secretion which is part of our long-term objective to elucidate the function of NPY in the neuroendocrine events which precede ovulation. This knowledge may provide new insight into the fundamental neuroendocrine mechanisms which control reproduction and fertility and thereby facilitate our understanding of pathological changes which accompany infertility. Aims: 1. To examine the regulation of NPY secretion from the hypothalamus using in vivo and in vitro techniques. The role of LHRH, gonadal steroids, catecholamines, and two potential intracellular mechanisms involved in catecholaminergic modulation of NPY release will be explored using short-term cultures of medial basal hypothalamic fragments, push-pull perfusion and microdialysis of the medial basal hypothalamus, microdialysis of the anterior pituitary gland, and collection of pituitary portal blood. 2. To investigate the hypothesis that gonadal steroids regulate NPY biosynthesis in the basal hypothalamus of female rats. The effects of altered levels of gonadal steroids on NPY biosynthesis will be determined in ovariectomized rats treated with estrogen, estrogen and progesterone, or vehicle. These rats will receive injections of [3H] tyrosine into the third cerebral ventricle to examine, in vivo, the gonadal steroid dependency of the biosynthesis and posttranslational processing of NPY in the arcuate nucleus.