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M.A. MacNeil, R.F. Dacheux, E. Raviola, R.H. Masland; The Population of Bipolar Cells in a Mammalian Retina . Invest. Ophthalmol. Vis. Sci. 2003;44(13):5161.
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Purpose: Bipolar cells connect photoreceptors in the outer retina with ganglion and amacrine cell dendrites in the inner plexiform layer. In this study, we have identified at least 10 types of bipolar cell in the rabbit retina. Methods: The shape and distribution of bipolar cells were studied in two ways: (1) by measuring the shape and stratification of dendrites and axons after Golgi impregnation, and (2) by randomly "photofilling" DAPI-labeled bipolar cells. The Golgi method revealed cells' morphology and stratification in detail while the photofilling method was quantitative and allowed us to estimate the frequency of the cell types. Results: From a sample of 243 Golgi impregnated bipolar cells and 138 photofilled cells, we identified one type of rod bipolar cell and at least 10 types of cone bipolars. In the various types, the axonal arborizations occupied specific strata of the inner plexiform layer and their morphologies exhibited subtle, but unique differences. In some types, the dendrites also revealed characteristic specializations. All the types were encountered at approximately equal frequencies (~8%); two of the types, however, could be further subdivided. For instance, in a type whose axonal arborization occupied stratum 2 of the inner plexiform layer, the cells fell into two morphologically distinct groups: one with large, horizontal terminal axon swellings and the other with thin and vertically oriented endings. Conclusions: Bipolar cell types are evenly distributed across the retina without any one type predominating. The morphological differences are subtle and types differ primarily in the stratification of their axonal arborizations in the inner plexiform layer. Support: PSC-CUNY 62807-00-31, NIH-MBRS GM08153-26, and NIH-NEI EY-103344.
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