Topographic nonoverlapping distribution of D1 and D2 dopamine receptors in the amygdaloid nuclear complex of the rat brain

Abstract

The distribution of D1 and D2 dopamine (DA) receptors in the nuclei and subnuclear zones of the rat amygdaloid complex was mapped using quantitative light microscopic autoradiography. [125I]iodosulpiride and [125I]SCH 23982 (in the presence of 50 nM ketanserin) were used to label D2 and D1 DA receptors, respectively. The DA receptor subtypes exhibited a topographic, nonoverlapping distribution which generally conformed to the cytoarchitectonic boundaries of the component nuclei and subnuclear zones of the amygdaloid complex. The highest density of [125I]iodosulpiride binding sites was observed in the main intercalated cell group and the central amygdaloid nucleus where a medial to lateral gradient of binding sites was localized to its subnuclear zones. [125I]SCH 23982 binding sites were localized in the main intercalated cell group and the basolateral amygdaloid nucleus with a uniform low density in the central nucleus. The functional topography of mesoamygdaloid DA neurons may therefore be mediated, in part, at the level of DA receptor subtypes. The pattern of distribution of [125I]iodosulpiride binding sites in subdivisions of the central amygdaloid nucleus and bed nucleus of the stria terminalis suggests that the functions of the "extended amygdala," a major system of the functional organization of the basal forebrain, may be regulated by DA afferents at multiple key sites of D2 receptor action.