Circadian Signaling in the Retina
The neurohormone, melatonin, is a primary output signal of the circadian clock in the retina and pineal gland. Melatonin enhances the susceptibility of rat photoreceptors to light-induced cell death. It also appears to enhance the sensitivity of the retina and central visual system to light. Thus melatonin, synthesized at night, may act as a paracrine hormone, and bind to receptors in the retina and brain to increase the sensitivity of the visual system to facilitate dark adaptation and other diurnal events that occur in the retina. Because one function of melatonin may be to increase the sensitivity of the retina to light as part of a dark-adaptation mechanism, an undesirable consequence of this may be an increased sensitivity by the photoreceptors to the damaging effects of light.
KeywordsRetinal Pigment Epithelium Amacrine Cell Horizontal Cell Melatonin Receptor Inner Nuclear Layer
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