Complete information regarding the neural mechanisms regulating pituitary secretion of luteinizing hormone (LH), follicle stimulating hormone (FSH) and prolactin is still lacking, although it is well established that the central nervous system participates in the regulation of reproductive function in man. Evidence has now accumulated indicating that the hypothalamus contains releasing- and inhibiting-factors which control the rates of synthesis and secretion of pituitary hormones. Of major importance in understanding the relationship between the C.N.S. and pituitary hormone secretion is a clarification of what neurotransmitters are involved in the release of the hypothalamic releasing- or inhibiting-factors. Recent studies suggest that certain amino acids may act as neurotransmitters in the mammalian nervous system. However, the neurally-active amino acids have not been considered as possible candidates in controlling pituitary hormone secretion. Recent preliminary studies from this laboratory have indicated that GABA and glycine can affect pituitary secretion of LH and prolaction in the male rat. The objective of the present study is to $ ascertain more completely the role of neurally-active amino acids in reproductive processes. The study will survey the effects of natural amino acid transmitters in the brain: GABA, glycine, taurine, beta-alanine, lysine, glutamate and aspartate; as well as the effects of amino acid antagonists. Experiments will employ the unrestrained-conscious animal with chronic indwelling cerebro-ventricular and arterial cannulas permitting simultaneous sample infusion and blood withdrawal. Peripheral blood levels of LH, FSH, and prolactin are determined by radioimmunoassay.