Dopamine receptors: Novel insights from biochemical and genetic studies

Dopamine receptors are targets for drugs with antipsychotic potency, and they are also the primary target in the treatment of Parkinson's disease. Molecular cloning has identified five genes that code for dopamine receptors. These receptors belong in two functionally distinct classes of G-protein-coupled receptors, known as the D-1 class of receptors (D-1 and D-5) and the D-2 class of receptors (D-2, D-3, and D-4). The diversity of dopamine receptor subtypes that belong to the same functional class, their high degree of structural similarity, and the lack of antagonists with selectivity for each of the individual subtypes have challenged studies on the function of the individual receptor subtypes. This review focuses on the recent progress made with studies on the expression and function of D-1, D-2, and D-3 receptors. It summarizes results of studies that suggest that these receptor proteins are expressed in monomeric and oligomeric forms and reviews results of a growing number of gene-targeting studies that begin to illustrate major differences in the phenotypes of D-1-, D-2-, and D-3-mutant mice.