Distribution of parvalbumin immunoreactivity in the vertebrate retina.

Parvalbumin, a calcium-binding protein thought to buffer intracellular calcium, is expressed in selected neuronal and non-neuronal cell populations. We used a well-characterized antibody directed against parvalbumin to investigate the distribution of parvalbumin in the retina of twelve vertebrate species to evaluate patterns of cellular expression for recurrent functional features. Parvalbumin immunoreactivity was displayed by subpopulations of ganglion, amacrine, bipolar and horizontal cells in different species-specific combinations. In the pigeon retina, subpopulations of amacrine, ganglion and bipolar cells were immunoreactive for parvalbumin. Parvalbumin immunoreactive bipolar cells in this species were mostly confined to the temporal dorsal region of the retina. In the owl, no immunoreactive amacrine cells were found, but many bipolar cells displayed parvalbumin immunoreactivity. In the teleost retina, amacrine and ganglion cells were found to be immunoreactive for parvalbumin. A high degree of species-specific variation was encountered in the mammalian retina. The most consistent finding within this class was that subpopulations of parvalbumin-immunoreactive amacrine cells were consistently observed in every species. In the rabbit, horizontal and ganglion cells displaying parvalbumin immunoreactivity were also seen. In rodents (hamster, ground squirrel), parvalbumin immunoreactivity was displayed by subpopulations of amacrine cells and, in the squirrel, by some ganglion cells as well. In the cat and in the baboon retina, parvalbumin immunoreactivity was found in horizontal cells, ganglion cells and a subpopulation of amacrine cells. The distribution of parvalbumin immunoreactive neurons in the vertebrate retinae studied showed no systematic correlation with phylogenetic proximity. The expression of parvalbumin within the systems of retinal neurons may therefore reflect the functional needs of different visual behaviors.