Neonatal Testicular Suppression with a GnRH Agonist in Rhesus Monkeys: Effects on Adult Endocrine Function and Behavior

Abstract

Male rhesus monkeys secrete adult levels of androgen for 3 months postnatally. The role of this neonatal testicular secretion in sexual development was investigated by suppressing luteinizing hormone (LH) and testosterone (T) in neonatal male rhesus ( n = 6)by administering a gonadotropin-releasing hormone agonist (Ag) for the first 4 months of postnatal life. Controls ( n = 4) received vehicle. Six years later, endocrine function and sexual behavior were examined with ovariectomized females ( n = 6) receiving periodic estradiol (E2) treatment during the breeding and nonbreeding seasons. During the breeding season, there were no differences between Ag-treated and control males in levels of LH and T or in frequency of copulatory behavior. However, Ag-treated males masturbated less frequently than controls when the females were not on E2. During the nonbreeding season, Ag-treated males had lower T levels than controls when the females were not receiving E2 and copulated less when the females received E2, even though T levels were comparable. During both E2 and non-E2 treatments, Ag-treated males secreted less T per unit of LH than controls. Neonatal Ag treatment had no effect on social rank. These data demonstrate that neonatal testicular suppression, or the Ag treatment itself, altered systems regulating sexual motivation and neuroendocrine control of these males and suggest that the early neonatal period in male rhesus monkeys is another point when the developing central nervous system is sensitive to the organizing actions of androgens.