Calretinin (CR) is a calcium-binding protein, found in a variety of organs and systems such as the central nervous system and the pineal gland. It was first thought to be a specific neuronal marker but this selectivity is now in question since CR has been demonstrated in avian thymus, rat ovary, rat and guinea pig inner ear, rat testis, and chicken and rat pineal gland. To contribute to the knowledge of the presence of CR-positive cells in the pineal parenchyma of rat and other mammalian including man, we performed immunocytochemistry on pineal glands of gerbils, rats, goats, cows, and humans, using a CR anti-serum. To confirm it was actually CR that was demonstrated, we performed Western Blot analyses. Finally, to precisely identify the nature of CR-positive cells we accomplished double-labelling immunofluorescence, using antisera against some nerve cell specific cytosquelettal proteins such as MAP-5, MAP-2, NF-L, NF-M, and NF-H. CR-positive cells were found in all pineal glands studied. These cells all possess a round, oval, or polygonal-shaped perikaryon sending one or more processes of different lengths into the glandular parenchyma. There is a lack of CR immunoreactivity in the nucleus and cell organelles while the cytosol contains a high concentration of this protein. Nevertheless, there are some slight differences between species, especially concerning the number of reactive cells and their relationships with different parenchymal structures such as blood vessels or acervuli. Among the CR-positive cells, only a few were actually nerve cells, contributing probably to an intrinsic innervation of the gland. The remaining CR-reactive cells seem to correspond mostly to pinealocytes in a specific histophysiological state and possibly to neuron-like cells. The significance of the CR-positive cells in the pineal glands remains to be elucidated.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.