Central plus peripheral stimulation by androgen is necessary for complete restoration of copulatory behavior in the...

Male golden hamsters were castrated and received a unilateral intrahypothalamic implant of either testosterone propionate (TP) or estradiol benzoate (EB). Half the animals from each group also received 5 alpha-dihydrotestosterone (DHT) via subcutaneous silastic capsule implants. The males were tested in a three-part design (intact, castrate, implant) to determine the effectiveness of intracerebral alone versus intracerebral plus systemic hormone regimens in restoring copulatory behavior following castration. All treatment regimens reinstated ectopic and normal mounting behavior to levels comparable to those seen in the intact animals. However, only those animals which received DHT systemically in addition to intracerebral implantation of TP or EB showed intromissions after castration. Both EB and TP groups with systemic DHT had intromission levels comparable to the controls by day 14 after implantation. The results point to a dual mechanism for the regulation of sexual behavior in the male hamster. A central hormone-sensitive mechanism is found in the anterior hypothalamic-preoptic region which is necessary for mounting behavior to be expressed. Androgen can affect stimulation at this level via conversion (aromatization) to estrogen. In addition, a peripheral hormone-sensitive mechanism which is necessary for intromission responses depends on the presence of nonaromatizable androgen for maintenance of its sensory feedback channels. The complete copulatory behavior pattern occurs only when both systems are hormone stimulated.