Testosterone effects on staining density and autoradiographic investigations of the alpha 2-adrenergic receptor in the medial preoptic nucleus of the Japanese quail: relationship to the activation of reproductive behavior.

The effects of gonadectomy combined or not with testosterone (T) therapy on the sexual behavior, cloacal gland area, staining density and alpha 2-adrenergic receptors in the medial preoptic nucleus (POM) were studied in male and female Japanese quail. In castrated males, T increased the cloacal gland size and activated copulatory behavior. In agreement with previous reports, these effects were sexually differentiated: under the influence of T, cloacal gland growth was smaller and this treatment did not activate masculine sexual behavior in females. The optical density of the medial preoptic nucleus stained with thionein blue (Nissl stain) was decreased by castration and increased by T in both males and females. This suggests that T has a profound effect on the synthesis of proteins in the POM and, since POM is a critical site in the activation by T of masculine sexual behavior, these induced proteins are, in all probability, a part of the causal chain of biochemical events giving rise to copulatory behavior. The treatment with T had, by contrast, no clear effect on the number of binding sites and on the affinity of the alpha 2-adrenergic receptors in the POM. Therefore, if the noradrenergic transmission is involved in the induction by T of copulatory behavior, it is probably acting either through the alteration of another adrenergic receptor subtype or through the modulation of the baseline levels or turnover of the transmitter itself.