Distribution of α₂-adrenergic receptors in the brain of the Japanese quail as determined by quantitative autoradiography: implications for the control of sexually dimorphic reproductive processes

With the use of [³H]p-aminoclonidine (PAC), α₂-adrenergic binding sites were mapped in the brain of the Japanese quail (Coturnix coturnix japonica). The sites were labeled with the use of in vitro quantitative autoradiography. Special attention was given to areas implicated in the control of sexually dimorphic reproductive processes including sexual behavior. Preliminary competition experiments found that [³H]PAC binding on tissue sections exhibited a pharmacology appropriate to the α₂ receptor. Binding sites were found to be heterogenously distributed throughout the brain. Some of the highest levels of specific binding were found in several areas regulating reproductive function such as the preoptic area, the infundibulum, and the medial mammillary nucleus of the infundibulum. [³H]PAC labeled precisely the morphologically dimorphic preoptic medial nucleus but no sexual dimorphism in density of receptor binding was identified. However, dimorphism in density of receptor binding was identified in two areas: the medial mammillary nucleus and the mesencephalic intercollicular nucleus. The former area appears to be involved in the regulation of gonadotrophin secretion and the latter area has been implicated in the control of vocal behavior. These neurochemical dimorphisms may contribute to the regulation of two sexually dimorphic reproductive processes, gonadotropin secretion and courtship vocalizations.