DEVELOPMENTAL EXPRESSION PATTERN OF PHOTOTRANSDUCTION COMPONENTS IN MAMMALIAN PINEAL IMPLIES A LIGHT-SENSING FUNCTION

Whereas the pineal organs of lower vertebrates have been shown to be p hotosensitive, photic regulation of pineal function in adult mammals i s thought be mediated entirely by retinal photoreceptors. Extraretinal regulation of pineal function has been reported in neonatal rodents, although both the site and molecular basis of extraretinal photorecept ion have remained obscure. In this study we examine the developmental expression pattern of all of the principal components of retinal photo transduction in rat pineal via cRNA in situ hybridization. All of the components needed to reconstitute a functional phototransduction pathw ay are expressed in the majority of neonatal pinealocytes, although th e expression levels of many of these genes decline dramatically during development. These findings strongly support the theory that the neon atal rat pineal itself is photosensitive. In addition, we observe in n eonatal pinealocytes the expression of both rod-specific and cone-spec ific phototransduction components, implying the existence of functiona lly different subtypes of pinealocytes that express varying combinatio ns of phototransduction enzymes.