Influence of androgen on the development of sexual behavior in the rat. II. Time and dosage of androgen administration during the neonatal period and masculine and feminine copulatory behavior in females.

The objective of the present study was to delineate the period of sensitivity to a single androgen exposure during the initial neonatal hours on the development of masculine and feminine copulatory behavior in female rats. Female rats were injected once with either 500, 50, or 5 micrograms testosterone propionate (TP) at either 1 or 24 hr after birth. Following castration in adulthood and TP replacement, the females were tested four times at weekly intervals in prolonged sessions for masculine copulatory behavior. One month following the masculine copulatory tests the females were tested for 3 weeks for feminine copulatory behavior with weekly increasing levels of estradiol benzoate (2.5, 10, and 25 micrograms) and progesterone (200 micrograms). The results demonstrate that a single injection of TP administered at either 1 or 24 hr after birth can significantly increase the capacity of female rats to exhibit ejaculation patterns and that the amount of androgen that is administered is critical in determining the levels of ejaculatory responding. Similarly, the females given high doses (50 and 500 micrograms) of TP at either 1 or 24 hr neonatally were almost completely defeminized. In contrast, however, the females treated with 5 micrograms TP at 1 and 24 hr showed different levels of lordotic performance indicating a greater sensitivity to androgen immediately after birth than at 24 hr in female rats as has been shown in male rats.