The long term goal is to understand the structure and function of the diverse ganglion cell types in human and macaque retina and the cellular mechanisms and circuits that give rise to parallel visual pathways. Our specific goals for the next period are to determine the origin and mechanisms of separate blue/yellow and red/green color opponent pathways. A unique in vitro preparation of the intact macaque monkey retina will be used to record intracellularly form anatomically identified ganglion and amacrine cell types. The proposed research has four specific aims: 1) to determine the locus and cellular mechanisms for blue/yellow spectral oppenency in the small bistratified ganglion cell type. We will test the novel hypothesis that blue-ON/yellow-OFF spectral antagonism derives from combined excitatory ON- and OFF-pathway cone bipolar inputs to the bistratified dendritic tree. 2) To determine the locus and retinal mechanism for red-green spectral opponency in the midget ganglion cell type. We will test the hypothesis that the relative weightings of L- and M-cone input to the excitatory center and inhibitory surround of the midget ganglion cell type determines the presence and degree of red/green opponent signals. 3) To measure the color opponent and non-opponent properties of the newly identified ganglion cell types that project to the lateral geniculate nucleus (LGN). We will characterize in detail the morphology and physiology of novel ganglion cell types that project to the LGN and determine their roles in color-opponent and non-opponent pathways to primary visual cortex. Tracer injection will be made into physiologically identified sites in the LGN and retrogradely labelled ganglion cells will be targeted for intracellular recording and analysis in the in vitro retina. 4) To determine the light responses and functional cone connections of identified amacrine cell types in macaque. We will continue our analysis of primate amacrine cell physiology and test the hypothesis that distinctive small-field cell types contribute to blue/yellow, red/green and non-opponent cone signal pathways. Many aspects of macaque vision and visual pathway organization are comparable to the human counterpart; our results therefore will contribute to the best and most detailed structure-function model of the cell types and functional architecture of the human retina. Primate retinal cell types have traditionally been inaccessible to physiological analysis and their functional significance and relevance to human retinal disease and visual disorders have remain unexplored. Taken together, the proposed projects will contribute to clarifying the retinal origins and circuits for color-opponent pathways, the evolution of color vision in primates, the cellular basis for psychophysical measures of human color vision and mechanisms by which retinal disease affects human color vision.
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