The contribution of NMDA receptors to the visual response in animals that have been partially monocularly deprived

Abstract

Kittens were monocularly deprived to give a partial shift in the ocular dominance histograms from their visual cortices. Responses were measured for the normal and deprived eyes at a variety of contrasts, and curves fitted to give measurements of background activity and peak visual response. The N -methyl- d -aspartate (NMDA) antagonist d -2-amino-5-phosphonovalerate (APV) was then applied, and the effect on the contrast-response curves was measured, and compared in the two eyes. In normal animals, the effect of APV on the contrast-response curve was similar in the two eyes. In monocularly deprived animals, on average, peak visual response was affected similarly in the two eyes, although there was wide variability from cell to cell. When the effect of APV on background activity was measured, there was a difference between the normal and deprived eyes. APV reduced background activity in the normal eye more than it reduced background activity in the deprived eye. In other words, the NMDA contribution to background activity in the deprived eye was reduced compared to the NMDA contribution to background activity in the normal eye. This could represent a reduction of NMDA receptors in the pathway from the deprived eye, like the reduction of acetylcholine receptors associated with the losing input at the neuromuscular junction before the nerve is eliminated.