Alpha ganglion cells in the rabbit retina.

In the rabbit retina a distinctive morphological class of large ganglion cells was demonstrated by a combination of intracellular staining with Lucifer Yellow and the quantification of reduced silver-stained preparations. The class is called alpha because of the qualitative and quantitative resemblance to the alpha cells of the cat's retina. Rabbit alpha cells change their size with location on the retina. In the high ganglion cell density region of the visual streak, their somata are about 15 micron in diameter, and their dendritic fields have diameters as small as 180-220 micron. The largest alpha cells in the inferior periphery have soma diameters of 30 micron and dendritic field diameters of 960 micron. There is a considerable scatter of sizes at any retinal location. Alpha cell density changes from about 55/mm2 in the streak to about 3/mm2 in far periphery, and the cells make up 1-1.4% of the ganglion cell population. Dendritic trees stratify in either an inner or an outer sublamina of the inner plexiform layer, suggesting an on/off dichotomy in the response to light. Each of the inner and outer branching subtypes is distributed in a regular mosaic, and the dendritic trees cover the retina completely and economically. The possibility is discussed that the alpha cells are the brisk transient/Y cells of physiology.