Clinically, eating disorders (obesity, anorexia nervosa, dieting) are associated with subnormal or impaired reproductive function. Recent evidence shows that Neuropeptide Y (NPY), neuropeptide K (NPK) and endogenous opioid peptides (EOP) control food intake as well as reproduction. Although produced in the same neuronal population(s) these neuropeptides are differentially released at specific hypothalamic sites to modulate these two basic functions. Consequently, an understanding of the factors that regulate neuropeptide production in the perikarya and release from remote nerve terminals at the site(s) of action is a new challenge. In this proposal, we plan to address these issues in the control of ovulation, especially in the preovulatory LH surge (PLS). In the rat increased episodic secretion of LH releasing hormone (LHRH) during the critical period on the afternoon of proestrus causes the discharge of PLS. Although it is well known that the neural clock (NC) entrained to the daily photoperiod activates LHRH secretion during the critical period, the origin and route of transmission of neural signals to LHRH neurons have not been delineated. In this context we propose to test the hypothesis that the NC restrains the inhibitory peptidergic circuits leading to activation of excitatory circuits which cause LHRH hypersecretion. Therefore, our focus will be on how the NC and inhibitory circuits, viz. EOP and NPK and the excitatory circuit, viz. NPY and adrenergic systems, operate under the direction of ovarian steroids. The operation of these circuits will be examined locally in the hypothalamus by studying the inter- and intraneuronal secretory events. In addition, the hypothesis that NPK is a potent inhibitory system that mediates the negative feedback effects of gonadal steroids on LH release will be tested. Interneuronal communication will be studied by analyses of peptide release in vivo and in vitro and the intraneuronal events will be assessed by elucidating steroidal effects on Pre-Pro NPY mRNA and peptide levels in microdissected sites. The connections between these circuits will be analyzed by employing pharmacological, surgical and electrolytic lesioning approaches to interrupt the progression of signals. Major techniques are RIA of neuropeptides, LH and ovarian steroids, anterior pituitary dispersed cell cultures, combined autoradiography and immunocytochemistry, neuropeptide output analysis by push-pull cannulae in vivo and hypothalamic perfusion and incubation in vitro. Catecholamines will be measured by HPLC and radioenzymatic assays.
