It is proposed to study the fetal and neonatal development of the luteinizing hormone-releasing hormone (LHRH) networks in the guinea pig brain. Evidence for neuroanatomical sexual dimorphism and the possible role of testosterone in development are sought. In the adult guinea pig, the possible roles of sex steroids and gonadotropins in regulating the LHRH neurons will be investigated. Similarly the neuroanatomical connection between LHRH neurons and their fibers and estradiol concentrating neurons will be studied. Characteristics of presumptive LHRH synapses in the suprachiasmatic, arcuate and interpeducular nuclei of the brain will be determined. The differentiation of the magnocellular neurosecretory system will be studied. Correlations of neuron birthdate, onset of neurophysin synthesis and synapse formation will be obtained.