The influence of gonadectomy, androgen exposure, or a gonadal graft in the neonatal rat on the volume of the sexually dimorphic nucleus of the preoptic area.

Although the volume of the sexually dimorphic nucleus of the preoptic area (SDN-POA) of the adult rat has been shown to be modified by the hormone environment early in postnatal life, the present study was performed to clarify several fundamental questions related to this process. This study was designed to evaluate the ability of exogenous testosterone propionate (TP), or a gonadal graft, to influence SDN-POA volume in rats which were gonadectomized as neonates. Orchidectomy on day 1 resulted in an approximately 50% decrease in adult SDN-POA volume; however, the influence of the testes on their resulting SDN-POA volume was replaced affectively by the administration of 100 micrograms or 1 mg of TP on postnatal day 2 or by a testicular (but not ovarian) graft on the day of castration. In the female, ovariectomy on postnatal day 1 failed to alter SDN-POA volume relative to that of sham-operated females. Exogenous TP, but neither testicular nor ovarian grafts, resulted in a larger SDN-POA volume when observed in the adult female. Thus, the development of the SDN-POA of the neonatal male is significantly influenced by the hormonal activity of the testes at this time period. While the SDN-POA of the neonatal female is potentially responsive to androgen, the role played by the ovaries in the development of the SDN-POA remains unclear. In addition, the different response of the developing male and female SDN-POA to a testicular graft suggests that the hormonal sensitivity of this nucleus may differ in the two sexes.