Ganglion cells of a short-wavelength-sensitive cone pathway in New World monkeys: Morphology and physiology

We have studied the morphology and physiology of retinal ganglion cells of a short-wavelength-sensitive cone (SWS-cone) pathway in dichromatic and tri chromatic New World anthropoids, the capuchin monkey (Cebus apella) and tuf ted-ear marmoset (Callithrix jacchus). In Old World anthropoids, in which m ales and females are both trichromats, blue-ON/yellow-OFF retinal ganglion cells have excitatory SWS-cone and inhibitory middle- and long-wavelength-s ensitive (MWS- and LWS-) cone inputs, and have been anatomically identified as small-field bistratified ganglion cells (SB-cells) (Dacey & Lee, 1994). Among retinal ganglion cells of New World monkeys, we find SE-cells which have very similar morphology to such cells in macaque and human; for exampl e, the inner dendritic tree is larger and denser than the outer dendritic t ree. We also find blue-on retinal ganglion cells of the capuchin to have ph ysiological responses strongly resembling such cells of the macaque monkey retina; for example, responses were more sustained, with a gentler low freq uency roll-off than MC-cells, and no evidence of contrast gain control. The re was no difference between dichromatic and trichromatic individuals. The results support the view that SWS-cone pathways are similarly organized in New and Old World primates, consistent with the hypothesis that these pathw ays form a phylogenetically ancient color system.