Aromatization of testosterone in the preoptic area and control of male sexual behavior in the Japanese quail

Sexual behavior in Japanese quail is activated by testosterone and the POA is one major site of action of the hormone. We review here the anatomical and neurochemical mechanisms which underlie the activation of copulatory behavior by testosterone. The POA contains a sexually dimorphic nucleus (the medial preoptic nucleus or POM) which is testosterone sensitive. Stereotaxic implantation of testosterone in but not around the POM activates copulation in castrated males. This nucleus also contains high levels of aromatase activity and most of its cells contain estrogen receptors. The aromatase activity in the POM is higher in males than in females and is androgen-dependent. The induction by testosterone of aromatase activity in the POA is correlated with the activation of sexual behavior by the steroid. If the induction of the aromatase is blocked by specific inhibitors, the activation of the behavior is suppressed or at least delayed which shows the key role played by this enzymatic transformation in the activation of behavior. The noradrenergic transmission seems to be very important in the POM and probably participates in the mechanisms which control copulatory behavior. The POM contains high concentrations of norepinephrine and is specifically labeled by noradrenergic receptors. A partial dener-vation produced by the specific noradrenergic neurotoxin DSP4 enhances the effects of testosterone on both behavior and aromatase. This suggests that under physiological conditions, the noradrenergic system inhibits the effects of testosterone in the POA. Research is now in progress to identify the adrenergic receptor subtypes which are implicated in these responses and what their relevance is to the control of the reproduction in intact animals.