Neuromodulatory role of melatonin in retinal information processing

Sep 19, 2012Progress in retinal and eye research

Melatonin’s role in adjusting how the eye processes visual information

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Circadian Biology on OpenScience ↗PubMed ↗DOI ↗

Abstract

Melatonin, produced mainly in photoreceptors of the retina, modulates neuronal activities through different receptor subtypes.

Melatonin is synthesized and released primarily from retinal photoreceptors.
Different subtypes of melatonin receptors are present on various types of retinal neurons, with expression varying by species and neuron subtype.
In the outer retina, melatonin regulates photoreceptor activity and alters the responsiveness of horizontal cells and bipolar cells.
In the inner retina, melatonin enhances signals from glycinergic amacrine cells to ganglion cells in rats.
The effects of melatonin on retinal neurons are mediated by distinct intracellular signaling pathways associated with different melatonin receptor subtypes.

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The neurohormone melatonin is implicated in a variety of physiological processes. In the retina, a major source for melatonin production, melatonin is involved in modulation of neuronal activities. In this article we review recent advances in this research field, which is preceded by a concise account of general information about melatonin, melatonin receptors and intracellular signaling pathways for melatonin actions. Melatonin is mainly synthesized in and released from photoreceptors in the retina. Different subtypes of melatonin receptors are present on major types of retinal neurons, and the expression of these receptors is highly species- and neuron subtype-dependent. By activating different melatonin receptor subtypes, melatonin modulates activities of retinal neurons. In the outer retina, melatonin regulates the activity of photoreceptors. In addition, melatonin reduces the light responsiveness of cone-driven horizontal cells, but potentiates rod signal to rod-dominant ON type bipolar cells in teleost fish or inhibits the TEA-sensitive potassium channel of rod-driven ON type bipolar cells in rats. In the inner retina, melatonin potentiates inputs from glycinergic amacrine cells to ganglion cells in rats. These actions of melatonin on retinal neurons are mediated by distinct intracellular signaling pathways via different subtypes of melatonin receptors and all serve to improve visual performance in a world of changing ambient illumination. The topics, concerning allosteric action of melatonin, interplay between melatonin and dopamine systems, and potential interaction between melatonin and melanopsin systems, are also discussed. An in-depth discussion of future directions in this research field is presented.

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Neuromodulatory role of melatonin in retinal information processing

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