Large-scale Morophological Survey of Rat Retinal Ganglion Cells

Ganglion cells in an isolated wholemount preparation of the rat retina were labeled using the "DiOlistic" labeling method (Gan et al., 2000) and were classified according to their morphological properties. Tungsten particles coated with a lipophilic dye (DiI) were propelled into the wholemount retina using a gene gun. When a dye-coated particle contacted the cell membrane, the entire cell was labeled. The ganglion cells were classified into four types based on their soma size, dendritic-field size, branching pattern, and level of stratification. Broadly monostratified cells were classified into three types: RG(A) cells (large soma, large dendritic field); RG(B) cells (small- to medium-sized soma, small- to medium-sized dendritic field); and RG(C) cells (small- to medium-sized soma, medium-to-large dendritic field). Bistratified cells were classified as RG(D). Several subtypes were identified within each ganglion cell group. A number of new subtypes were discovered and added into the existing catalog, among them were two types of bistratified cells. This study therefore represents the most complete morphological classification of rat retinal ganglion cells available to date.