THE HORMONE-SENSITIVE EARLY POSTNATAL PERIODS FOR SEXUAL-DIFFERENTIATION OF FEMININE BEHAVIOR AND LUTEINIZING-HORMONE SECRETION IN MALE ANDFEMALE RATS

The purpose of this study was to determine the duration of the hormone -sensitive postnatal period during which a single injection of testost erone propionate (TP) influences feminine behavior and luteinizing hor mone (LH) secretion in male and female rats. Male pups were castrated on the day of birth (day 1) between 6 and 12 h postpartum. On postnata l day 3, 4, 5, 6, 7, 8, or 9 female pups and castrated males (fales) w ere injected subcutaneously with testosterone propionate (TP-500 mu g) . The females were laparotomized at 60 days of age, and ovarian tissue was removed for histological analysis. Female behavior was evaluated at 100 days of age. At 150 days of age, the ability of steroids to fac ilitate LH secretion was determined. Tests for lordosis indicated a di minished lordotic quotient (LQ) with both females and fales treated wi th TP on postnatal day 3, 4, 5, 6, or 7. On day 8 or 9, however, the l ordotic response was at control levels. Females in all TP treated grou ps had significantly reduced number of corpora lutea. Females and fale s treated with TP on postnatal day 3, 4, 5, 6, 7, 8, or 9 failed to ex hibit an LH surge as adults. The results indicate that the neural cont rol of feminine behavior (LQ) is hormone-sensitive to a single injecti on of TP up through the 7th day of postnatal life, whereas the neural substrate regulating LH secretion was sensitive in the present study a t least up through day 9 in both fales and females.