The long-term goal of this project is to elucidate the mechanisms controlling the occurrence of ovulatory cycles in female mammals. The working hypothesis to be tested is that anovulation during seasonal anestrus in the ewe is due to activation of inhibitory neural systems. Two such systems are proposed: a steroid-sensitive catecholaminergic system and a steroid-insensitive serotonergic system. One major specific aim of this project is to determine the anatomical location of these inhibitory neurons. This will be done using immunohistochemical staining, neurotransmitter receptor localization by in vitro incubation with 3H-ligand and autoradiography, knife cuts of specific neural tracts, and microinjection of neurotransmitter antagonists into specific hypothalamic areas. Experiments in the third specific aim will also make use of the lesioning techniques to test the possibility that one of these inhibitory neural systems activates the other.