CALRETININ IMMUNOREACTIVITY IN PINEAL-GLAND OF DIFFERENT MAMMALS INCLUDING MAN

Calretinin (CR) is a calcium-binding protein, found in a variety of or gans and systems such as the central nervous system and the pineal gla nd. It was first thought to be a specific neuronal marker but this sel ectivity is now in question since CR has been demonstrated in avian th ymus, 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 mammali an including man, we performed immunocytochemistry on pineal glands of gerbils, rats, goats, cows, and humans, using a CR anti-serum. To con firm it was actually CR that was demonstrated, we performed Western Bl ot analyses. Finally, to precisely identify the nature of CR-positive cells we accomplished double-labelling immunofluorescence, using antis era against some nerve cell specific cytosquelettal proteins such as M AP-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 poly gonal-shaped perikaryon sending one or more processes of different len gths into the glandular parenchyma. There is a lack of CR immunoreacti vity in the nucleus and cell organelles while the cytosol contains a h igh concentration of this protein. Nevertheless, there are some slight differences between species, especially concerning the number of reac tive cells and their relationships with different parenchymal structur es such as blood vessels or acervuli. Among the CR-positive cells, onl y a few were actually nerve cells, contributing probably to an intrins ic innervation of the gland. The remaining CR-reactive cells seem to c orrespond mostly to pinealocytes in a specific histophysiological stat e and possibly to neuron-like cells. The significance of the CR-positi ve cells in the pineal glands remains to be elucidated.