The proposed research will determine the pattern of amacrine and bipolar cell synaptic contacts to the dendritic trees of identified retinal ganglion cells in cats. Recent studies of cat retina suggest the existence of ganglion cell types in addition to alpha, beta and gamma cells, but the technical problem of demonstrating the morphology these cells has precluded more detailed studies. This problem was addressed directly by the principal investigator in postdoctoral research with Dr. J. Stone. The morphology of cat retinal ganglion cells was examined by making small, iontophoretic injections of horseradish peroxidase (HRP) directly into the retina. Five ganglion cell types were identified on the basis of soma size, axon diameter, and the size, structure and stratification in the inner plexiform layer of their dendritic trees. The dendritic trees of each type can be divided into two distinct morphological components termed dendritic shafts and dendritic appendages. The proposed research will continue this work with a correlated light and electron microscopic analysis of the synaptic inputs to the dendritic shafts and appendages of each of the five ganglion cell types. Small iontophoretic injections of HRP will be made into the cat's retina. Dendritic appendages and shafts of single, isolated ganglion cells will be identified with the light microscope and subsequently examined with the electron microscope. The number, distribution and density of amacrine and bipolar cell contacts onto single appendages and shafts will be determined for each of the five ganglion cell types. The results will be used to develop a concept of the organization of synaptic inputs to morphologically distinct ganglion cell types.
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