[Circadian rhythm, the retina and light]

Abstract

The renewal systems in visual cells, disk-shedding and autophagy, exhibit endogenous circadian rhythms, primarily controlled by an ocular oscillator. Many characteristics of these rhythms have been elucidated, but the actual site and nature of the ocular clock are still unknown. Conceivable regulators of the rhythm are the neurohormone melatonin and the putative retinal neurotransmitter dopamine. Furthermore, dopamine might regulate the sensitivity of the retina to light. It is shown that disk-shedding and autophagy have a circadian sensitivity to light input. The magnitude of the light response was greatest at the beginning of the subjective night, i.e., 12 hours out of phase with the endogenous peak. The latency of the light response was shortest at the beginning of the subjective day, when the endogenous rhythms are at their peak. Additionally, the response to drugs known to modify the metabolism of dopamine was analyzed. The light response of both disk-shedding and autophagy were inhibited by the drugs in the subjective night and stimulated in the subjective day. Thus, light as well as drugs can influence the renewal processes in visual cells.