Role of Melatonin and Dopamine in the Regulation of Retinal Circadian Rhythms

Abstract

Melatonin and dopamine are two important players in the regulation of many physiological functions within the body. These neurohormones are also involved in the regulation of retinal physiology and its pathophysiology. Several studies have shown that melatonin synthesis in the retina primarily occurs during the night, whereas dopamine synthesis occurs during the day. We now know that melatonin and dopamine play opposing roles in the regulation of retinal physiology and visual processing in mammals; dopamine functions as a signal for light adaptation, while melatonin has dark-adaptive effects. This reciprocal feedback loop is believed to be a critical component of the regulation of circadian rhythms in the eye. Melatonin and dopamine exert their infl uence(s) by binding to G-protein-coupled receptors that are expressed by many different cells in the vertebrate retina. Although during the last 20 years we have acquired a substantial knowledge on the role of melatonin and dopamine in many different animal models, a clear role for the melatonin and dopamine systems in human retina is still missing. It is our hope that future genomic studies will be performed on human populations with ocular diseases to determine if polymorphisms in genes encoding enzymes-or receptorsinvolved in the melatonin and dopamine systems are associated with specifi c visual disorders.