Sexual incentive motivation and male and female copulatory behavior in female rats given androgen from postnatal day 20.

Masculinization and feminization of rat sexual behavior has been supposed to occur during a short postnatal period. However, much data have made it evident that these processes may continue until adolescence. In the present study, we evaluated whether androgen treatment of females from postnatal day 20 and onwards could alter sexual motivation and behavior in a male direction. Juveniles were ovariectomized on day 20 and concurrently implanted with Silastic capsules containing either testosterone or dihydrotestosterone. Controls were implanted with an empty capsule. Tests for sexual incentive motivation and male sexual behavior were performed every fifth day when the females were between 50 and 75 days of age. At day 80, a test for female sexual behavior was performed. Females treated with testosterone approached a female sexual incentive far more than a male incentive, showing that sexual motivation had been changed in a male-like direction. Dihydrotestosterone had a similar, albeit smaller, effect. Females implanted with an empty capsule approached both incentives equally. Testosterone produced a high level of mounting behavior, whereas intromission-like behavioral patterns were rare and ejaculation-like behavior was absent. In the test for female sexual behavior, the testosterone-treated animals displayed a relatively high lordosis quotient, far above that displayed in females implanted with dihydrotestosterone or an empty capsule. It is concluded that treatment with an aromatizable androgen during the peripubertal-adolescent period masculinizes sexual motivation and partly sexual behavior. A non-aromatizable androgen weakly masculinize sexual motivation without enhancing male sexual behavior. It appears that simultaneous actions on androgen and estrogen receptors are needed for significant masculinization during the period studied here. Since the testosterone-treated females displayed lordosis, sexual behavior was not defeminized. In sum, these results suggest that sexual differentiation continues well into the peripubertal and adolescent periods.