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

Abstract

Visual pigments in the regressed eye and pineal of the depigmented neotenic urodele, the blind cave salamander (Proteus anguinus anguinus), were studied by immunocytochemistry with anti-opsin antibodies. The study included light- and electron-microscopic investigations of both the eye and the pineal organ. A comparison was made with the black pigmented subspecies Proteus anguinus parkelj (black proteus), which has a normal eye structure. In the retina of the black proteus, we found principal rods, red-sensitive cones and a third photoreceptor type, which might represent a blue- or UV-sensitive cone. Photoreceptors in the regressed eye of the blind cave salamanders from the Planina cave contained degenerate outer segments, consisting of a few whorled discs and irregular clumps of membranes. The great majority of these 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 more pronounced degeneration was observed in the photoreceptors of the animals derived from the Otovec doline, which are completely devoid of an outer segment, most of them not even possessing an inner segment. Even in some of these highly degenerate cells, the presence of rhodopsin could be detected in 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 immunopositive visual pigments indicates the possibility of a retained light sensitivity in the blind cave salamander photoreceptors.

Identification and characterization of visual pigments in caecilians (Amphibia: Gymnophiona), an order of limbless vertebrates with rudimentary eyes

“…One population from the Otovec doline in south-west Slovenia appears to parallel caecilians in the loss of cone opsins while retaining the rod pigment. The eyes of salamanders from this population have regressed and photoreceptors have no discernable outer segments (Kos et al, 2001). This contrasts with another population from the Planina cave which have retained both a long wavelength-sensitive (red) cone opsin and a rod opsin, as determined by immunocytochemistry.…”

“…The cave salamander Proteus anguinus shows a similar morphological diversity and rudimentation of the eye to that in caecilians (Kos et al, 2001). One population from the Otovec doline in south-west Slovenia appears to parallel caecilians in the loss of cone opsins while retaining the rod pigment.…”

Pineal organs in deep demersal fish

“…These findings indicate light levels of about 1×10 12 photons s -1 m -3 (Widder et al 1989) in near surface waters and show a drastic reduction of the frequency of bioluminescent events with increasing depths, with single events occurring only once every other minute in the abyssal domain (Gitel'zon and Levin 1989;Herring et al 2000). Considering the adaptive specialisations of the eyes (apakic spaces, total width of outer segment layer exceeding 100 µm) that are apparently necessary for the visual perception of these stimuli, the general absence of pineal windows in the skull resulting in an effective barrier of solid skin and bone several millimeters thick, on the one hand, and a pineal outer segment length of only about 5 µm, on the other, seems to be counterproductive with respect to allowing photons to reach the visual pigments that can be assumed to be present in the outer segments of pineal photoreceptors (J. Bowmaker, personal communication; Kos et al 2001) and to elicit phototransduction. Therefore, it would appear highly improbable that pineal organs in deep demersal fish perceive bioluminescence in a similar way to the pineal organs that are present in terrestrial vertebrates and that respond to ambient light of considerably higher intensities through the layers of the skull.…”

Non-visual sensory physiology and magnetic orientation in the Blind Cave Salamander, Proteus anguinus (and some other cave-dwelling urodele species). Review and new results on light-sensitivity and non-visual orientation in subterranean urodeles (Amphibia)

“…Th e same was to be noticed on all video-recordings from "cave"-urodeles during this study. (Bulog, 1992 ;Kos and Bulog, 1996 ;Kos et al, 2001 ).…”

“…After rinsing in water, sections were mounted in glycerol for light microscopic observation and photography in a Zeiss Axiophot I photomicroscope, equipped with phase contrast and diff erential interference contrast (Nomarski) optics. To compare immune reactivities of the same receptor cell, light micrographs were taken from identical regions of consecutive sections, exposed to diff erent primary antibodies (Kos et al, 2001 ).…”