Ontogeny of Adrenergic Receptors in the Rat Amygdala

Chung, Yoon Young; Bae, Choon Sang

Abstract

The mammalian amygdala comprises a heterogeneous complex of cytoarchitectonically, histochemically and connectionally distinct nuclei. To investigate the developmental changes and regional distributions of adrenoceptor binding sites in the adult and postnatal rat amygdala (postnatal days 0, 5, 10, 15, 20, 30), in vitro autoradiography was performed. Binding sites for the alpha1-adrenoceptor ligand [3H]-prazosin, the alpha2-adrenoceptor ligand [3H]-rauwolscine, and the beta-adrenoceptor ligand [125I]-iodocyanopindolol were visualized by the in vitro autoradiography, and anatomically localized by comparing the autoradiograms to Nissl- and acetylcholinesterase-stained sections. On toluidine blue- and acetylcholinesterase-stained sections of the amygdaloid complex of the rat, three major divisions can be distinguished: the cortical-like nuclear group, medial nuclear group, and central nuclear group. The basolateral nuclear group of the cortical-like nuclear group was divided into three subregions, the basal, the basolateral and the basomedial amygdaloid nucleus. Between the medial and the basolateral amygdaloid nucleus, the intercalated nuclei were observed. The highest number of alpha1-adrenoceptor binding sites was detected in the central and the lateral amygdaloid nucleus. The nuclei most strongly labeled by [3H]-rauwolscine were those in the medial part of the amygdaloid complex. The pattern of the beta-adrenoceptor binding was relatively diffuse, the medial amygdaloid nucleus was most strongly labeled among the amygdaloid nuclei. At the postnatal day 0, adrenergic receptor binding sites were only weakly labeled. The expression of a1-adrenoceptor binding was rapidly increased in the central amygdaloid nucleus at the postnatal day 5, and between the postnatal day 10 and 15, the concentration of bindig sites reached the adult levels. The expression of alpha2- and beta-adrenoceptor binding was increased in most amygdaloid nuclei at the postnatal day 10, and higher density was observed at the postnatal day 30. In the adult, the expression of adrenoceptor binding was relatively low in most nuclei when compared to postnatal day 30. These findings may provide evidence that alpha1-adrenoceptor is involved in regulating amygdaloid development and function more specifically than alpha2- and beta-adrenoceptor during postnatal development. These results indicate that the regional distributions of alpha1-, alpha2-, and beta-adrenoceptor show some differences from those of the other mammalian species reported.