Dopamine induces a biphasic modulation of hypothalamic ANF neurons:: a ligand concentration-dependent effect involving D5 and D2 receptor interaction

Increasing evidence now suggests that more than one subtype of dopamine receptors is co-expressed in some of the central neurons, The neurobiological effects on the host cells when these receptors are concurrently activated by their common physiological ligand, dopamine, however, remains elusive. Among the members of the family of dopamine receptors, coupling of D-1-like dopamine receptors to Gs and D-2-like receptors to Gi proteins are known to augment or suppress cellular functions respectively, through modulation of adenylyl cyclase activity and consequently cAMP generation, Simultaneous activation of D-1 and D-2 receptors in transfected cell lines expressing the two cloned receptors, however, produced antagonistic effects, This is in contrast to in vivo studies, in which concurrent activation of D-1-like and D-2-like receptors by their respective agonists may induce synergistic or antagonistic effects or both, We report here that in long-term rat hypothalamic cell cultures, activation of both D-1-like (D-1 and D-5) and D-2 receptors on atrial natriuretic factor-producing neurons by dopamine yields a biphasic response. The response is ligand concentration-dependent and involves type II adenylyl cyclases, This process is mediated primarily through antagonistic and synergistic interactions of D-5 and D-2 receptors as the event is mimicked by the concurrent activation of these two receptors co-transfected in CHO cells, Our present findings suggest a novel action of dopamine, and the biochemical processes involved may underlie some of the pharmacological actions of atypical anti-psychotic drugs.