Immunocytochemical localization of cholinergic amacrine cells in the bat retina

The purpose of this study was to localize the cholinergic amacrine cells, one of the key elements of a functional retina, in the retina of a microbat, Rhinolophus ferrumequinum. The presence and localization of choline acetyltransferase-immunoreactive (ChAT-IR) cells in the microbat retina were investigated using immunocytochemistry, confocal microscopy, and quantitative analysis. These ChAT-IR cells were present in the ganglion cell layer (GCL) and inner part of the inner nuclear layer (INL), as previously reported in various animals. However, the bat retina also contained some ChAT-IR cells in the outer part of the INL. The dendrites of these cells extended into the outer plexiform layer, and those of the cells in the inner INL extended within the outer part of the inner plexiform layer (IPL). The dendrites of the ChAT-IR cells in the GCL extended into the middle of the IPL and some fibers ramified up to the outer IPL. The average densities of ChAT-IR cells in the GCL, inner INL, and outer INL were 259 ± 31 cells/mm², 469 ± 48 cells/mm², and 59 ± 8 cells/mm², respectively. The average total density of the ChAT-IR cells was 788 ± 58 cells/mm² (mean ± S.D.; n = 3; 2799 ± 182 cells/retina). We also found that the cholinergic amacrine cells in the bat retina contained calbindin, one of the calcium-binding proteins, but not calretinin or parvalbumin. As the cholinergic amacrine cells play key roles in the direction selectivity and optokinetic eye reflex in the other mammalian retinas, the present study might provide better information of the cytoarchitecture of bat retina and the basic sources for further physiological studies.