[Brain dopamine receptors. Interactions between D1 and D2 receptors, and dopamine mediated behaviour]

The review begins by a brief presentation of the present state of knowledge on the multiplicity of brain dopamine receptors. The molecular basis of their distinction is reported, as well as the most specific ligands for each receptors type: D1, D2 (their isoforms A and B), D3, the putative D4 and autoreceptors. Then the review focuses on the respective location of D1 receptors (mainly linked positively to an adenylate cyclase) and of so-called D2 (lacking precision for distinguishing D2, D3 or D4), at the cellular level. The theoretical aspects of the functional interactions between these D1 and D2 receptors suggest four possibilities: Antagonism, indifference, additive synergy and potentiation. The effects resulting from the simultaneous administration of either D1 and D2 dopamine agonists or D1 and D2 dopamine antagonists were considered on various behaviours or functions. The four predicted types of interactions were found: D1/D2 antagonism on thermoregulation, D1/D2 indifference on nociception, additive synergy on the traction test, on anorexia or on the latency of the acoustic startle response, and finally potentiation on stereotypies or climbing behaviour. These data are completed by many other reported in an abundant literature about these interactions, which appear as modalities of regulation: their alterations might take part in several pathological states.