Androgen increases formation of behaviourally effective oestrogen in dove brain

Abstract

Oestradiol-17β (E₂) formed from testosterone in the brain is thought to be involved in the hormonal control of male sexual behaviour in some mammal species^1–3;. In the male dove, Streptopelia risoria, the aromatase system in the preoptic area (POA) is very active in converting testosterone to E₂ (ref. 4), This oestrogenic metabolite has specific effects on male nest-orientated courtship patterns, which are mediated by an oestrogen-sensitive system in the preoptic-anterior hypothalamic area of the brain⁵. The preoptic aromatase system is likely to be important in the regulation of androgen action on male courtship behaviour, as no circulating oestrogen can be detected in the blood plasma of the male⁶. We report here that the level of aromatase activity in the POA depends on androgenic stimulation. Conversion of testosterone to E₂ is markedly increased in castrated males injected intramuscularly (i.m.) with testosterone propionate (TP). Increased aromatase activity seems to be due to induction of the enzyme and is specific to the POA These findings indicate that the formation of behaviourally effective oestrogen in a specific brain target area is under hormonal control and suggest a role for this regulatory mechanism in the integration of courtship behaviour in the male dove.