MORPHOLOGY OF RETINAL GANGLION-CELLS IN A NEW-WORLD MONKEY, THE MARMOSET CALLITHRIX-JACCHUS

We studied the morphology of retinal ganglion cells in a diurnal New W orld primate, the marmoset Callithrix jacchus. This species is of inte rest as a model for primate vision because it has good behavioural vis ual acuity, and the retina and subcortical visual pathways are very si milar to those of Old World monkeys and humans. Ganglion cells were la belled by placing small crystals of the carbocyanin dye DiI into the o ptic fibre layer, or by intracellular injection of neurobiotin. Two ma in classes of ganglion cell were labelled. We call these Group A cells and Group B cells: they are respectively homologous to parasol and mi dget cell classes. Group A and Group B cells show similar patterns of dye coupling, dendritic stratification and dendritic field size as the ir counterparts in Old World monkeys and humans. A third group of cell s, which we call Group C, is morphologically heterogeneous. Examples c orresponding to wide-field ganglion cell types described in Old World primates were encountered. One subgroup of C cells has a morphology ve ry similar to that of the small bistratified (blue-on) cell described in macaque retina, suggesting that this functional pathway is common t o all primates. As for other New World monkeys, the marmoset shows a s ex-linked polymorphism of cone pigment expression, such that all males are dichromats and the majority of females are trichromats. No system atic differences in Group B cells were seen between male and female re tinas, suggesting that trichromacy is not accompanied by specific chan ges in ganglion cell morphology. (C) 1996 Wiley-Liss, Inc.