Spatial distribution and functional integration of displaced retinal ganglion cells.

The retina contains distinct types of ganglion cells, which form mosaics with cells of each type at each position of the visual field. Displaced retinal ganglion cells (dRGCs) occur with cell bodies in the inner nuclear layer (INL), and regularly placed RGCs with cell bodies in the ganglion cell layer. An example of mammalian dRGCs are M1-type intrinsically photosensitive ganglion cells (ipRGCs). Little is known, however, about their relationship with regularly placed ipRGCs. We identified mouse ipRGC types M1, M2, and M4/sONɑ by immunohistochemistry and light microscopy. Reconstruction of immunolabeled mosaics from M1 and sONɑ RGCs indicated that dRGCs tiled the retina with their regular RGC partners. Multi-electrode array recordings revealed conventional receptive fields of displaced sONɑ RGCs which fit into the mosaic of their regular counterparts. An RGC distribution analysis showed type-specific dRGC patterns which followed neither the global density distribution of all RGCs nor the local densities of corresponding cell types. The displacement of RGC bodies into the INL occurs in a type-dependent manner, where dRGCs are positioned to form complete mosaics with their regular partners. Our data suggest that dRGCs and regular RGCs serve the same functional role within their corresponding population of RGCs.