RETINAL CIRCUITS AND SYNAPSES FOR PRIMATE COLOR VISION

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Human trichromatic color vision arises from 'blue-yellow' and 'red-green' cone-driven channels. The blue-yellow channel compares the quantal catch of short- (S) with long- (L) and middle- (M) wavelength-sensitive photoreceptor types, and the red-green channel compares the quantal catch of L and M cones. Color vision begins in the complex retinal circuitry and in the projection to the parvocellular layers of the lateral geniculate nucleus (LGN) and, subsequently, to visual cortex. In the primate retina, two ganglion cell classes have been studied for their roles in blue-yellow and red-green color vision: the small bistratified and midget cell, respectively. However, several key questions remain unanswered about the roles of excitatory and inhibitory synaptic input in color-coding, as experimental approaches in the primate retina have been limited. For the proposed project, we will use our well-established in vitro retina preparation from the macaque monkey, an ideal model for understanding human vision, to determine the roles of excitatory and inhibitory neurotransmission in blue-yellow and red-green chromatic coding. To achieve these goals, small bistratified and midget ganglion cells will be targeted using loose-patch and whole-cell patch-clamp recording combined with pharmacological manipulation of excitatory and inhibitory receptors, conductance analysis, and short- (S), middle- (M), and long- (L) wavelength cone-selective stimuli to determine the roles of S-, L-, and M-cone-driven excitation and inhibition to a ganglion cell. A series of experiments have been designed to characterize the roles of ionotropic glutamate receptors (AMPA- and NMDA-type) in chromatic contrast sensitivity. Previous work has demonstrated complementary roles for AMPA and NMDA receptors in achromatic coding and our preliminary data suggests that these receptors are also important for color-coding. Direct testing of the roles of two types of inner retinal inhibition, feedforward and crossover, in color-coding will be performed.