Retinal ganglion cells in the albino rat: revised morphological classification

Rat retinal ganglion cells were traditionally classified on the basis of soma size and the morphology of their dendritic fields. However, in the past, techniques used to label ganglion cells (horseradish peroxidase, Golgi, or the neurofibrillar stain) did not always stain the axon and/or the entire dendritic field. In the present study, we have labelled retinal ganglion cells in the adult albino rat with the carbocyanine dye 1,1'-dioctadecyl-3,3,3',3'-tetramethylindo-carbocyanine perchlorate (DiI) or have intracellularly injected them with Neurobiotin. Such procedures enabled us to completely fill these neurons, and our findings prompted us to modify the existing retinal ganglion cell classification in the rat. First, cells were categorised into three groups on the basis of soma and dendritic field size: Group RG(A) cells have large somata and dendritic field diameters, Group RG(B) cells have small somata and dendritic field diameters, whereas Group RG(C) cells have small to medium-sized somata and medium-to-large dendritic field diameters. On the basis of dendritic field morphology and presence across the retina, each Group was then subdivided into subgroups. The significance of our results in terms of retinal ganglion cell function is discussed.