The role of dopamine in the regulation of melatonin biosynthesis in vertebrate retina.

The vertebrate retina rhythmically synthesizes melatonin, a hormone involved in the regulation of several intraocular processes cued by environmental lighting conditions. The rhythm of retinal melatonin production, with maximal synthesis at night in darkness, is driven by the photoperiodic environment to which animals are exposed, and is generated by an endogenous circadian clock(s). This article reviews data on the role of dopamine, an established retinal neurotransmitter and paracrine factor, as a mediator of acute suppressive and entrainment action of light on the melatonin generating system in the retina. Special emphasis is given to the characterization of dopamine receptor types involved in the control of retinal melatonin formation.