Manipulation of neonatal androgen: Effects on sexual responses and penile development in male rats

Male rats castrated at four days of age were given fluoxymesterone (FM) or testosterone (TP) for the next seven days. As adults they were given exogenous testosterone and tested for mating behavior. Most FM animals intromitted frequently but were incapable of ejaculation, whereas all TP animals showed the complete mating sequence. Since phallic development in FM animals was equal to that of TP animals, this behavioral difference was attributed to some difference in development in the central nervous system. After a spinal transection was performed on the same animals, tests for penile reflexes revealed no differences between FM and TP animals, indicating that this differential development was in the brain. In another experiment male rats were castrated at 7 days of age, given exogenous testosterone in adulthood, and tested for mating behavior; about half of these animals were capable of ejaculation. There did not seem to be sufficient differences in phallic development between the ejaculators and nonejaculators to account for the ability or inability to ejaculate. These results and other observations from the two experiments are consistent with the concept that although the neural basis for mounting and intromission behavior in rats may be organized independently of neonatal androgen, the neural substrate controlling ejaculation behavior does require the influence of neonatal gonadal androgen for complete development.