MORPHOLOGY OF P-RETINAL AND M-RETINAL GANGLION-CELLS OF THE BUSH-BABY

P/midget ganglion cells mediate red-green color opponency in anthropoi ds. It has been proposed that these cells evolved as a specialization to subserve color vision in primates, If that is correct, they must ha ve evolved about the same time as the long-wavelength ('red') and medi um-wavelength ('green') pigment genes diverged, thirty million years a go. Strepsirhines are another group of primates that diverged from the ancestor of the anthropoids at least 55 million years ago. If P/midge t ganglion cells evolved to subserve color vision, they should be abse nt in strepsirhines. We rested this hypothesis in a nocturnal strepsir hine, the greater bush baby Otolemur. The retinal ganglion cells were labeled with the lipophilic tracer DiI and the results show that bush babies have P/midget and M/parasol cells similar to those found in the peripheral retinas of anthropoids. A number of studies have shown tha t the P and M pathways of bush babies share many similarities with tho se of anthropoids, and our results show that the same is true for thei r retinal ganglion cells. These results support the hypothesis that th e P system evolved prior to the emergence of red-green color opponency . (C) 1998 Elsevier Science I,td. All rights reserved.