Effects of neonatal RU486 on adult sexual, parental, and fearful behaviorsin rats

Exposure to gonadal hormones during perinatal life influences later behavio r. The finding that sex differences exist in progestin receptor expression in the perinatal rat brain suggests differential sensitivity of male and fe male brains to progesterone (C. K. Wagner, A. N. Nakayama, & G. J. De Vries , 1998). Because these sex differences are in neural sites that influence s exually differentiated sexual, parental, and fearful behaviors in adults, t his study examined the effects of administering the progestin receptor anta gonist RU486 for the first 10 days after birth on these behaviors in adulth ood. Neonatal RU486 significantly reduced sexual behavior in males but did not impair reproduction in females. Neonatal RU486 did not affect parental responses of virgin rats exposed to pups (sensitization) but reduced fear i n the elevated plus-maze in both sexes. Treatment of pups with RU486 affect ed neither mother-litter interactions nor plasma testosterone levels in mal es during or after treatment. These results suggest that neonatal exposure to progesterone, in addition to androgens and estrogens, influences behavio ral development in rats.