The major classes of retina neurons that make synapses in the inner plexiform layer have been identified in rabbit retina: amacrine cells, ganglion cells and now bipolar cells. These cells have been classified morphologically, based on the breadth of their processes, their depth within the inner plexiform layer and the subtle peculiarities in the branching and morphology of their processes. Perhaps the biggest surprise has been the generalization that each of the three cell types is distributed numerically in a rather even way with no particular cell type predominating. This suggests that the rabbit retina has numerous parallel channels, with at least a dozen being given equal weight. Now that the types of cells have been identified, the next problem is to tease apart the multiple parallel microcircuits that exist in the retina. We propose to sort out some of these circuits by looking at cells that interact with directionally selective (DS) ganglion cells. Using combination of techniques that includes microinjection, immunocytochemistry, electron microscopy and photofilling, we propose to study: 1) whether the ON arbor of a DS ganglion cell receives input from multiple bipolar cell types; 2) whether the dendrites of starburst amacrine cells selectively wire with DS ganglion cells on their null, and not on their preferred side; and 3) whether the ON and OFF arbors of the DS ganglion cell receive common input from a single amacrine cell type. This research is important because it is helping to reveal circuits in the retina that contribute to visual processing. By identifying the different circuits that are formed by retinal cells, we may eventually be able to pinpoint the sources of retinal dysfunction.
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