PHOTIC REGULATION OF PINEAL FUNCTION - ANALOGIES BETWEEN RETINAL AND PINEAL PHOTORECEPTION

Light absorbed by a photopigment in a photoreceptor cell causes a phot ochemical reaction converting the 11-cis retinal chromophore into the all-trans configuration. These changes lead to a series of events that causes cGMP hydrolysis, a following decrease of cGMP in the cytoplasm of the photoreceptor outer segment and a closure of cGMP-gated cation ic channels. As a consequence of these processes the membrane hyperpol arizes. In pineal photoreceptor cells of lower vertebrates these proce sses are only partly investigated. Molecules involved in the phototran sduction process and the desensitization, like opsin, vitamin A, alpha -transducin and arrestin, have been immunocytochemically localized in pineal photoreceptors and also electrophysiological studies have shown that phototransduction mechanisms in pineal photoreceptors might be v ery similar to those found in retinal photoreceptors. This review will summarize some of the current knowledge on pineal photoreception and compare it with retinal processes. ((C) Elsevier, Paris).