Diversity of opsin immunoreactivities in the extraretinal tissues of four anuran amphibians

The pineal complex, deep brain, and skin have been known to function as ext raretinal photoreceptors in non-mammalian vertebrates. To see the diversity of localization of extraretinal photoreceptors in lower vertebrates having different habitats, we analyzed the opsin-like immunoreactivities in anura n amphibians, Xenopus laevis, Rana catesbeiana, Rana: nigromaculata, and Bu fo japonicus. An antiserum (toad Rh-AS) was raised against rhodopsin purifi ed from the retinas of Japanese toad, B. japonicus. In the retina of all th e anurans examined, the outer segments of rods were immunopositive to toad Rh-AS. The outer segments of most pinealocytes were immunopositive in R. ca tesbeiana, R. nigromaculata, and B. japonicus. The outer segments of photor eceptor-like cells within the frontal organ of R. nigromaculata were immuno stained. Interestingly, toad Rh-AS immunostained many secretory cells of mu cous glands in the head skin of B. japonicus, implying the presence of a no vel photoreceptive molecule. Within the hypothalamus, toad Rh-AS immunostai ned many cells in the magnocellular preoptic nucleus of R. catesbeiana and B. japonicus. Toad Rh-AS also labeled cerebrospinal fluid (CSF)-contacting cells in the anterior preoptic nucleus of R. nigromaculata and those adjace nt to the lateral ventricle within the septum of R. catesbeiana. Thus the d istribution patterns of the rhodopsin-like immunoreactivities among the anu rans were highly diverged, and there was no relationship between the distri bution patterns and their habitats. (C) 2000 Wiley-Liss, Inc.