Morphological and functional effects of visual deprivation on the rabbit visual system

Abstract

Evidence from studies on the cat suggest that many of the adverse effects of suturing one eyelid are not simply a consequence of reduced visual pattern stimulation, but in large part may be due to unbalanced competitive interaction between projections from the two eyes. The rabbit provides an opportunity for testing the effects of visual deprivation in a system nearly free from binocular synaptic competition. Its visual system has a large monocular projection that includes the central retina. Seven rabbits were reared with monocular lid-suture and trained on brightness, pattern, and form discriminations. They learned these tasks as readily with the deprived eye as with the normal eye. Single-unit recordings were carried out in nine rabbits raised with either monocular or binocular lid-suture. Receptive field properties of cells in the large monocular segment of the visual cortex and in the superior colliculus appeared qualitively normal and the various receptive field types were seen in their normal proportions. Quantitative histological measurements were made on cells in the monocular segment of the dorsal lateral geniculate nuclei of seven rabbits. Monocular lid-suture for 3–5 mo produced no changes in cell size in the dorsal LGN, while deprivation for 10–15 mo produced a small (less than 10%) but statistically significant reduction in size. Monocular enucleation, by contrast, produced a large (26.6%) decrease in cell size and total volume of this nucleus (54.5%). These results, as well as other data available from rabbit and other species with largely crossed visual systems, are discussed in relation to the hypothesis that the principal effects of lid-suture are a consequence of competitive interaction between the two eyes.