Dopamine receptor localization in the mammalian retina

After a short history of dopamine receptor discovery in the retina and a su rvey on dopamine receptor types and subtypes, the distribution of dopamine receptors in the retinal cells is described and correlated with their possi ble role in cell and retinal physiology. All the retinal cells probably bea r dopamine receptors. For example, the recently discovered D-1B receptor ha s a possible role in modulating phagocytosis by the pigment epithelium and a D-4 receptor is likely to be involved in the inhibition of melatonin synt hesis in photoreceptors. Dopamine uncouples horizontal and amacrine cell-ga p junctions through D-1-like receptors. Dopamine modulates the release of o ther transmitters by subpopulations of amacrine cells, including that of do pamine through a D-2 autoreceptor. Ganglion cells express dopamine receptor s, the role of which is still uncertain. Muller cells also are affected by dopamine. A puzzling action of dopamine is observed in the ciliary retina, in which D-1- and D-2-like receptors are likely to be involved in the cycli c regulation of intraocular pressure. Most of the dopaminergic actions appe ar to be extrasynaptic and the signaling pathways remain uncertain. Further studies are needed to better understand the multiple actions of dopamine i n the retina, especially those that implicate rhythmic regulations.