Contrast sensitivity in rats with increased or decreased numbers of retinal ganglion cells.

Contrast thresholds were measured electrophysiologically on striate cortex in normal rats and in rats in which either the superior colliculi were removed bilaterally or unilaterally at 5 days of age, or one eye was removed on the day of birth. Despite the fact that the collicular ablation leads to the degeneration of more than half the retinal ganglion cells, contrast sensitivity was normal in this group, with the possible exception of sensitivity at very low spatial frequencies below 0.1 c/deg. The result is strong evidence that retinal ganglion cells which project to thalamus as well as to mid-brain escape the degenerative effects of neonatal mid-brain lesions. The contrast sensitivity of neonatally operated one-eyed rats was significantly and substantially better than that of normal rats tested monocularly. The increased sensitivity was greatest in the cortex ipsilateral to the remaining eye. This supernormal sensitivity is presumably related to the increase in the number of ganglion cells in the remaining eye, especially those projecting ipsilaterally from the temporal retina and which show a five-fold expansion of their terminal zone in the thalamus.