Female rats were intracerebrally implanted with testosterone propionate (TP) or 5 alpha-dihydrotestosterone (DHT) on the 3rd day of life. After both treatments, prepuberal social play behaviour was significantly enhanced as compared to control females and did not differ from that recorded in males. In contrast, intracerebral implantation of oestradiol benzoate (OB) at the same day of age had no effect on the frequency with which females engaged in social play. DHT, which is not aromatizable to oestrogen, showed a significant male-type organizational effect also on sexual orientation but not on the organization of gonadotrophin secretion pattern and hence on ovarian weight. On the other hand, OB displayed in a dose-dependent manner a significant male-type organizational effect on gonadotrophin secretion resulting in an anovulatory syndrome with significantly decreased ovarian weights due to failure of corpus luteum formation as well as on male-type sexual orientation. The results suggest that different sex hormones (oestrogens and/or androgens) are responsible for the sex-specific brain differentiation of gonadotrophin secretion, sexual orientation and gender role behaviour.

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.

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