Effect of neonatal gonadectomy and administration of testosterone on coital masculinization in the ferret.

Male ferrets castrated on postnatal day 5 displayed significantly lower levels of neck gripping, mounting, and pelvic thrusting behavior than groups of males castrated on postnatal days 20 or 35 when tested in adulthood after treatment with testosterone (T). Administering a high dosage of T via sc Silastic capsules to ovariectomized female ferrets over postnatal days 5-20 caused a significant enhancement of all three parameters of masculine coital behavior and ossification of clitorides, in comparison with control females that received no exogenous hormone neonatally. A lower dosage of T given to other ovariectomized females over the same neonatal period caused only slight coital masculinization even though the plasma concentrations of T achieved in females with this particular implant were somewhat higher than the levels normally present in gonadally intact male ferrets at any time between postnatal days 5 and 40. Administration of high and low dosages of T to ovariectomized females over days 20-35 failed to cause any coital or genital masculinization. The results suggest that T acts in the male ferret brain between postnatal days 5 and 20 to cause coital masculinization. The sensitivity of the male brain to T during this period may, however, normally be enhanced by the action of T or some other hormone before day 5.