Intact female and neonatally castrated male rats were treated with the dopamine agonist/serotonin antagonist lisuride during the early postnatal differentiation period of the brain (Day 2-12) or during the peripuberal maturation period (Day 26-40). It was found that early postnatal as well as peripuberal activation of the dopaminergic system in females resulted in masculinized social play-fighting behaviour, and lisuride application as late as peripuberally resulted in permanent masculinization of sexual behaviour. Comparable trends were found after peripuberal androgen administration. On the other hand, the demasculinized social play fighting as well as the sexual behaviour of neonatally castrated males, which is usually bisexual or even predominantly heterotypical, could be normalized--at least in part-by early postnatal or peripuberal lisuride administration. These findings confirm once more our previous reports that neurotransmitters can act directly as organizers of the brain. This holds true not only for the differentiation period but also for the maturation period.

Lisuride induces in juvenile male and especially in female rats a significant increase of the male-typical initiating activity in tests on social play-fighting behaviour. In neonatally castrated as well as in prenatally stress exposed males, castrated in adulthood, which exhibit under androgen substitution alone bisexual or even predominantly heterotypical sexual behaviour, additional treatment with lisuride resulted in a temporary normalization of sexual orientation in the homotypical male direction, limited to the duration of treatment. In castrated androgen-treated females, lisuride induces a partial conversion of sexual orientation to the heterotypical male direction. When intact newborn females or neonatally castrated males were treated with lisuride during the early postnatal differentiation period of the brain (day 2-12) or, on the other hand, during the peripuberal maturation period (day 26-40), it was found that early postnatal as well as peripuberal activation of the dopaminergic system in females resulted in permanent partial masculinization of sexual orientation. Comparable trends were observed after peripuberal androgen administration in females. In neonatally castrated males, the demasculinized play-fighting as well as the sexual orientation could be normalized--at least in part--by early postnatal or peripuberal lisuride administration. These findings confirm once more our previous reports that neurotransmitters can act directly as organizers of the brain. This holds true not only for the differentiation period but also for the maturation period of the brain.

No abstract