The long-term objective is to determine the role of Neuropeptide Y (NPY) in hypothalamic and hypophysial neuroendocrine control of luteinizing hormone (LH) secretion in the rat. The research addresses fundamental questions concerning NPY, which has been found in the rat and human brain in higher concentration than any peptide previously described and has been shown to affect LH and growth hormone (GH) secretion in vitro and in vivo. This research should yield important data about the role of NPY in basic neuroendocrine mechanisms which regulate reproductive hormone secretion. Aims: 1. Immunohistochemical methods will be used to precisely determine the anatomical relationships between NPY, luteinizing hormone releasing hormone (LHRH), and catecholamine (CA) containing cell bodies and terminals in the hypothalamus and pituitary gland. 2. Hypothalamic and pituitary homogenates will be examined for the presence of receptors which bind iodinated NPY in a saturable and reversible manner. 3. To examine the hypothesis that NPY influences LH release through effects on hypothalamic CAs and/or LHRH, hypothalamic fragments and slices will be perfused with medium containing NPY. The perfusate and tissue fragments will be collected and analyzed by RIA to measure the release of LHRH, and by HPLC with electrochemical detection to measure changes in CAs. 4. The direct effects of NPY on luteotrophs will be examined further using perfused columns of anterior pituitary cells exposed to NPY in the presence and absence of LHRH. 5. The potential sensitivity of hypothalamic NPY neurons to serum levels of gonadal steroids will be examined in female rats sacrificed at each stage of the estrous cycle and at specific times after ovariectomy and steroid replacement. Specific hypothalamic nuclei will be analyzed for changes in the concentrations of NPY and LHRH using RIA, and CAs using HPLC-EC. 6. The effects of these steroid manipulations on the sensitivity of the hypothalamus and pituitary to NPY administration (as described in aims 3 and 4 above) and on the density of NPY receptors in these tissues will be examined.