Distribution of oxytocin- and vasopressin-binding sites in the rat extended amygdala: a histoautoradiographic study.

Radioligand receptor autoradiography has shown that oxytocin- and vasopressin-binding sites exist in numerous rat brain regions, among which the amygdala and the bed nucleus of the stria terminalis (BST) are especially prominent. However, these descriptions did not take into account the numerous subdivisions of the amygdala and the BST. Thus, we have reinvestigated the distribution of these sites in the rat extended amygdala, which is formed by a continuum of structures stretching from the BST to the centromedial amygdala, including parts of the accumbens nucleus, substantia innominata, and transition areas between the amygdala and the striatum. For this purpose, histoautoradiography was used to detect binding sites at the cellular level, and anatomical boundaries were defined on the basis of acetylcholinesterase histochemistry and tyrosine-hydroxylase immunohistochemistry. Oxytocin- and vasopressin-binding sites were detected in well-defined subdivisions of both medial and central parts of the extended amygdala, but they almost never coexisted in the same region. Compared with previously reported distributions, our reinvestigation describes novel oxytocin- and vasopressin-binding sites in the lateral and supracapsular BST, in the sublenticular extended amygdala, in the interstitial nucleus of the posterior limb of the anterior commissure, in the marginal zone, in the central amygdaloid nucleus, and in the anterior amygdaloid area. These results indicate that oxytocin- and vasopressin-binding sites represent an important feature of the extended amygdala and may participate in the large variety of functions that characterize this area, including reproductive and ingestive behaviors, conditioned fear and autonomic regulation.