Distribution and coverage of beta cells in the cat retina

We have reexamined the retinal distribution and dendritic field dimensions of beta cells in the cat retina. Beta cells were labeled by retrograde transport from the A-layers of the lateral geniculate nucleus and distinguished from alpha cells on the basis of soma size. Dendritic fields of beta cells were visualized by intracellular staining in vitro. The fraction of cat ganglion cells that were beta cells varied with retinal location. Except near the area centralis, beta cells represented about half of all ganglion cells in the nasal hemiretina. They contributed as heavily as the other major ganglion cell classes to the nasal visual streak. In and near the area centralis and in the temporal retina, beta cells represented about two-thirds of all ganglion cells. The areas of beta cell dendritic fields were reciprocally related to beta cell density. For example, they were 3-fold smaller within the visual streak than at matched eccentricities outside it. For many cells, we could estimate both local beta cell density and dendritic field area. Coverage factor (dendritic field area x local density) remained constant at about 4 despite 100-fold variations in beta cell density, and was independent of eccentricity, nasotemporal location, or position relative to the visual streak. Analysis in terms of sampling theory suggests that the beta cell array is matched to X-cell spatial resolution so as to optimize acuity. The beta cell distribution and its systematic reflection in dendritic architecture predict acuity levels that apparently correlate well with actual visual performance across the cat's visual field. (C) 1996 Wiley-Liss, Inc.