Characterization of the Binding of 3H-2-Amino-6,7-dihydroxy-tetrahydronaphthalene (ADTN) to Rat Striatal Membranes: Similarities and Discrepancies between D1 and D3 as well as D2 and D4 Dopamine Receptors

Abstract

Recently, the original distinction of brain DA receptors into D1 and D2 subtypes (Kebabian and Calne 1979) has been extended to a D1–D4 classification, based on the affinities of various ligands and displacers in binding studies (Seeman 1980). D3 and D4 binding sites both have high affinities for DA agonists but can be distinguished on the basis of their differing affinities for butyrophenones. However, the functional relevance of these binding sites is not yet clear. It has been suggested that the D3 and D4 sites might correspond to putative high agonist affinity states of the D1 and D2 receptors (Bacopoulos, 1983). This assumption was mainly based on correlations between the potencies of antagonists in inhibiting DA-stimulated adenylate cyclase or the binding of 3H-Spiperone to D2 receptors on one hand, and the binding of 3H-DA to D3 and D4 sites on the other hand. We have tested this hypothesis by using various agonists and antagonists with known selectivities for the D1 and D2 receptors.