Immuocytochemical analysis of spatial organization of photoreceptors and amacrine and ganglion cells in the tiger salamander retina

Abstract

In the present study, using double- or triple-label immunocytochemistry in conjunction with confocal microscopy, we aimed to examine the population and distribution of photoreceptors, GABAergic and glycinergic amacrine cells, and ganglion cells, which are basic but important parameters for studying the structure-function relationship of the salamander retina. We found that the outer nuclear layer (ONL) contained 82,019 +/- 3203 photoreceptors, of which 52% were rods and 48% were cones. The density of photoreceptors peaked at approximately 8000 cells/mm2 in the ventral and dropped to approximately 4000 cells/mm2 in the dorsal retina. In addition, the rod/cone ratio was less than 1 in the central retina but larger than I in the periphery. Moreover, in the proximal region of the inner nuclear layer (INL3), the total number of cells was 50,576 +/- 8400. GABAergic and glycinergic amacrine cells made up approximately 78% of all cells in this layer, including 43% GABAergic, 32% glycinergic, and 3% GABA/glycine colocalized amacrine cells. The density of these amacrine cells was approximately 6500 cells/mm2 in the ventral and approximately 3200 cells/mm2 in the dorsal area. The ratio of GABAergic to glycinergic amacrine cells was larger than 1. Furthermore, in the ganglion cell layer (GCL), among a total of 36,007 +/- 2010 cells, ganglion cells accounted for 65.7 +/- 1.5% of the total cells, whereas displaced GABAergic and glycinergic amacrine cells comprised about 4% of the cells in this layer. The ganglion cell density was approximately 1800 cells/mm2 in the ventral and approximately 600 cells/mm2 in the dorsal retina. Our data demonstrate that all three major cell types are not uniformly distributed across the salamander retina. Instead, they exhibit a higher density in the ventral than in the dorsal retina and their spatial arrangement is associated with the retinal topography. These findings provide a basic anatomical reference for the electrophysiological study of this species.