[Sexual differentiation of social play and copulatory behavior in prenatally stressed male and female offspring of the rat: the influence of simultaneous treatment by tyrosine during exposure to prenatal stress].

The environmental stress in the late gestational life has been reported to induce impairments of androgen-dependent sex differentiation of the rat brain. This study was performed to investigate the effects of prenatal stress on the features of gender role behavior and copulatory behavior which are masculinized by perinatal androgens. Further, a possible counteraction of tyrosine to the long-term effects of prenatal stress was examined, because the supplementation of amino-acid precursor of catecholamines during the stress is known to maintain the content of catecholamines in the brain, which is considered to contribute to the differentiation of the brain. Time-mated pregnant females were subjected to the forced immobilization stress daily from day 15 of pregnancy to the day of delivery, and they received simultaneous i.p. injections of either tyrosine methylester HCl (200 mg/kg) or saline, less than 60 minutes before stress. Social play in the peripubescent period was observed in the male and female offspring. After maturation, they were castrated and male copulatory behavior under androgen-substitution was tested in the male offspring, and female copulatory behavior under estrogen-substitution was tested in the female offspring. In the male offspring, prenatal stress caused a significant depletion of social play as well as male copulatory behavior, showing the demasculinization of gender role centers and mating centers. In the female offspring exposed to the prenatal stress, a significant increase of social play was observed. And their lordosis quotient did not alter, but a reduced attractivity against male partner was found. These results in the female offspring suggest some extent of masculinization occurred in both centers, probably due to the increase of androgens derived from the adrenal glands when stressed. Tyrosine seemed to reduce the engagement of social play in both sexes, independently of the prenatal stress. On the other hand, tyrosine prevented, at least partially, the long-term effects of prenatal stress in copulatory behavior which were observed in this study. Tyrosine itself had no effect on copulatory behavior. The apparent counteraction of tyrosine in copulatory behavior suggests a positive involvement of catecholamines, especially norepinephrine, in the process of masculinization of the mating centers. The different action of tyrosine to these behaviors may reflect the fact that the different regions of the brain and separate mechanisms are responsible for the sexual differentiation of social play and copulatory behavior.