Alouatta trichromatic color vision – single–unit recording from retinal ganglion cells and microspectrophotometry.

Abstract

Abstract: : Purpose. ERG recordings have shown that the retina of both male and female howler monkeys have three cone photopigments. However, the retinal organization underlying colour vision in these animals is not well understood. Since the M and L opsin genes each have a locus control region, there is a possibility that the howler monkey retina co–expresses M and L opsins in one cone. The purpose of this work was to test this possibility. Methods. One adult male Alouatta caraja was used. Extracellular recordings were obtained from parafoveal retinal ganglion cells. We used three different stimuli: luminance or chromatic flashes to classify the cell in transient or sustained; narrow–band heterochromatic stimuli modulated with different relative phases or in counterphase at different contrasts at six different temporal frequencies to study cells’ spectral sensitivity. Post–mortem microspectrophotometry (MSP) was performed on the same retina to obtain rod and cone spectral sensitivities. Results. The temporal properties of Alouatta ganglion cells were similar to those of another New–World primate, the Cebus apella (Lee et al., 2000). P–cell responses showed strong opponency, resembling those of trichromatic female Cebus. The MSP data are consistent with only a single opsin being expressed in each cone. Conclusions. These results argue against the hypothesis that in the howler monkey two different opsins are expressed in the same cone. It appears that this primate expresses full trichromacy, and has a very similar retinal organization to Old–World monkeys. Cone–specific opsin expression in the presence of a locus control region for each opsin may call into question the hypothesis that this region controls opsin expression.

Keywords: ganglion cells • color pigments and opsins • color vision