It is proposed to study the development of the magnocellular and parvicellular neurosecretory systems in the guinea pig by means of light microscopic immunocytochemical demonstration of neurophysin and vasopressin, and luteinizing-hormone releasing hormone (LH-RH) respectively. These experiments are designed to detail the morphological and biochemical events in the embryo, neonate, and prepubertal animal which result in maturity of the hypothalamo-pituitary axis. In addition, lesion experience will be carried out to determine the locus of origin of LH-RH positive axons which are out sides of the hypothalamus. Experiments to localize LH-RH in the brain of the adult rhesus monkey will also be conducted. Electron microscopic immunocytochemical localization of LHRH in both guinea pig and mouse brain will establish: (1) the ultrastructural characteristics of LH-RH producing neurons under different physiological states and (2) the possible nature of LH-RH synapses in various brain regions. BIBLIOGRAPHIC REFERENCES: Silverman, A.J. and Desnoyers, P. The hypothalamic magnocellular neurosecretory system of the guinea pig. III. Ultrastructure of the fetal neural lobe. Am. J. Anat. 145:499-516, 1976a. Silverman, A.J. Distribution of luteinizing hormone-releasing hormone (LH-RH) in the guinea pig brain. Endocrinology 99:30-41, 1976a.