Immunocytochemical demonstration of visual pigments in the degenerate retinal and pineal photoreceptors of the blind cave salamander (Proteus anguinus)

Visual pigments in the regressed eye and pineal of the depigmented neotenic urodele, the blind cave salamander (Proteus anguinus anguinus), were studi ed by immunocytochemistry with anti-opsin antibodies. The study included li ght- and electron-microscopic investigations of both the eye and the pineal organ. A comparison was made with the black pigmented subspecies Proteus a nguinus parkelj (black proteus), which has a normal eye structure. In the r etina of the black proteus, we found principal rods, red-sensitive cones an d a third photoreceptor type, which might represent a blue- or UV-sensitive cone. Photoreceptors in the regressed eye of the blind cave salamanders fr om the Planina cave contained degenerate outer segments, consisting of a fe w whorled discs and irregular clumps of membranes. The great majority of th ese outer segments showed immunolabelling for the red-sensitive cone opsin and only a few of them were found to be positive for rhodopsin. An even mor e pronounced degeneration was observed in the photoreceptors of the animals derived from the Otovec doline, which are completely devoid of an outer se gment, most of them not even possessing an inner segment. Even in some of t hese highly degenerate cells, the presence of rhodopsin could be detected i n the plasma membrane; however, immunoreactions with antibodies recognizing cone visual pigment were negative. In the pineals of all studied animals, the degenerate photoreceptor outer segments were recognized exclusively by the antibody against the red-sensitive cone opsin. The presence of immunopo sitive visual pigments indicates the possibility of a retained light sensit ivity in the blind cave salamander photoreceptors.