Molecular and chemical neuropharmacology of dopamine receptor subtypes

In the fields of psychiatry and neurology, the dopaminergic system is one of the most important neurotransmitter systems in the brain. Whereas pharmacological and biochemical studies had initially indicated two subclasses of dopamine receptors (DA-R), recent progress in molecular biology techniques has led to the identification of five distinct genes of DA-Rs (D1-R-D5-R) and splice variants. The gene products are classified into the D1-R family (D1-R and D5-R) and D2-R family (D2-R, D3-R and D4-R) based on their structure and pharmacological features. This review summarizes the structure, localization, function and pharmacology of DA-R subtypes on the basis of knowledge obtained during the past few years. The genes encoding the D1-R family have no intron and the D2-R family genes have introns. The distributions of mRNAs encoding these five DA-R subtypes in the brain were different from their respective receptors. The localization of DA-R subtypes to particular brain regions and specific pharmacological profiles of DA-R subtypes allow new insights to be made into the mechanism of action of DA in the control of psychiatric and motor functions. The availability of detailed information about DA-R subtypes will not only clarify their roles in the brain, but will probably also lead to the development of new therapeutic drugs with more specific actions.