Evidence for degeneration of retinal W cells following early visual cortical removal in cats.

Size and distribution of ganglion cells surviving unilateral visual cortical removal at 5-7 days of age were examined in domestic cats. Such lesions were expected to result in a substantial loss of X cells in ipsilateral temporal and contralateral nasal retina, leaving ipsilateral nasal and contralateral temporal retina to serve as intact controls. A computer model of normal retinal ganglion cell topography was used to make qualitative predictions of the distribution of surviving ganglion cells. Contrary to expectations, a visual streak was no more prominent in the distribution of surviving cells than in the distribution of the normal ganglion cell population. The magnitude of ganglion cell loss, furthermore, was at least twice as great in nasal retina as in temporal retina. In nasal retina, the cell loss extended well into the small-medium size range, while in temporal retina, cell loss was restricted to the large-medium size range. Taken together, the differential magnitude of cell loss in nasal and temporal retina and the greater loss of small-medium cells in nasal retina cannot be explained by the exclusive degeneration of X cells and suggest that many of the degenerated ganglion cells were medium-sized W or gamma cells. These cells, therefore, share the susceptibility of retinal X cells to early cortical ablation. Surviving gamma cells in both nasal and temporal retina appeared to increase in soma size which may explain why their decreased numbers were not detected in previous physiological studies. Alpha cells, at least in nasal retina, decreased in some size.