Immunocytochemical localization of calretinin containing neurons in retina from rabbit, cat, and dog.

Calcium homeostasis is critical for many neuronal functions, yet the distribution of calcium-binding protein is not always conserved among species, even between closely related species. We decided therefore to study the distribution of one of these calcium-binding proteins calretinin, in retina from rabbit, cat, and dog. Calretinin was localized using antibody immunocytochemistry. Calretinin immunoreactivity was found in numerous cell bodies in the ganglion cell layer in all three animals. These cells had small to medium-sized somas. Large ganglion cells, however, were not labeled using antiserum against calretinin. In the inner nuclear layer, calretinin immunoreactivity was found in many neurons in all three species. The regular distribution of neurons, the inner marginal location of their cell bodies in the inner nuclear layer, and the distinctive bilaminar morphologies of their dendritic arbors in the inner plexiform layer suggested that these calretinin-positive cells were AII amacrine cells. Calretinin immunoreactivity was observed in both A- and B-type horizontal cells in cat and dog retina. However, horizontal cells in the rabbit retina were not labeled by this antibody. Neurons in the photoreceptor cell layer were not labeled by this antibody. The present study suggests that calretinin immunoreactivity is present in several populations in the retina. In particular, calretinin labels AII amacrine cells and a subpopulation of ganglion cells in all three animals. Horizontal cells, however, were not labeled in rabbit.