The objectives of the present project are to study the potential role of various environmental components, such as lighting schedule, thermal conditions, nutrition and population density in the process of sexual maturation. Current efforts are devoted to studying the effect of different lighting regimes on the 24 hr. endocrine rhythms of male rats during the process of sexual maturation. Special emphasis is being placed on the nocturnal peaks of FSH, prolactin and testosterone. Other studies currently underway are attempting to quantify the impact of low and high ambient temperatures on both male and female sexual maturations. Maturation and development are monitored through serum hormone (gonadotropins, prolactin, gonadal steroids) concentrations and through structural changes (total weight and histological examinations). New studies to be initiated will focus on the effect of nutritional (total caloric intake and protein content) factors and variations in population density and population composition (sex and age) on sexual maturation in both sexes. Modification of the normal endocrine sequences during maturation by any of the above environmental variables will be mimicked by ablation, antibody blocking techniques, or exogenous hormone adminstration. Finally, efforts will be initiated to determine if changes in hormone receptor activity (both at the gonadal and the CNS: pituitary level) play a significant role in the initiation of sexual maturation.