IMMUNOCYTOCHEMICAL LOCALIZATION OF TAURINE IN THE PINEAL ORGAN AND RETINA OF AN ANADROMOUS FISH, PLECOGLOSSUS-ALTIVELIS

Light and electron microscopic immuno-localization of taurine, a sulfu r-containing free amino acid, was investigated in the photoneuroendocr ine pineal organ and the retinal photoreceptor and pigment epithelial layer of the ayu Plecoglossus altivelis, an anadromous fish, Intense i mmunostaining was found in the outer segments of pineal photoreceptors and retinal cone-like cells. Moderate but definite immunostaining was found in the cytoplasmic processes of pineal supporting cells, the ou ter segments of retinal rod-like cells, and the apical processes of pi gment epithelial cells. Although the electron microscopic immunogold l abeling was not completely coincident with the results of light micros copic immunostaining, concentrated immunogold particles appeared in th e inner segments of photoreceptor cells, the cytoplasmic processes of pineal supporting cells, and the apical processes of pigment epithelia l cells. These light and electron microscopic findings in taurine immu nolocalization mere discussed in relation to the functions of taurine known mainly from retinal physiology. It was suggested that the abunda nt taurine localization may be involved st least in the protection of photoreceptor outer segments against harmful factors, and in the trans portation of nutrients and metabolites, The immunostaining for taurine is useful for the discrimination of different types of photoreceptor cells in the pineal organ and retina of fish.