ROLES OF N-METHYL-D-ASPARTATE RECEPTORS IN OCULAR DOMINANCE PLASTICITY IN DEVELOPING VISUAL-CORTEX - REEVALUATION

We have re-examined whether N-methyl-D-aspartate receptors play a spec ific role in experience-dependent plasticity in kitten visual cortex. A specific antagonist of this glutamate receptor subtype, D,L-2-amino- 5-phosphonovaleric acid, was directly and continuously infused into ki tten striate cortex for one week concurrently with monocular lid sutur e. In the hemisphere infused with 50 mM antagonist, we found the usual shift in ocular dominance toward the open eye with only a few binocul ar cells remaining. The changes were accompanied by an extremely high incidence (38%) of abnormal cells lacking orientation selectivity acro ss different ocular dominance groups. In kitten cortex infused with 10 mM antagonist concurrently with monocular deprivation for a week, rec ording from a drug-affected region near the infusion centre, we again found the U-shaped ocular dominance distribution with the high inciden ce of non-selective cells. In antagonist-infused, otherwise normal str iate cortex of adult cats, we found that the proportion of binocular c ells decreased by one-half in two cellular populations: one recorded d uring the continuous infusion of 10 mM antagonist under general anaest hesia and paralysis, and the other about two days after stopping the i nfusion. We also established that in vivo concentrations of chronicall y infused 10 mM antagonist decreased, not near-exponentially, but line arly with increasing distance from the infusion site. Thus, the effect s of a directly and continuously infused, concentrated antagonist of N -methyl-D-aspartate receptors on receptive-field properties of visuoco rtical cells are complex. The present findings strongly suggest that t he antagonist effects in the developing cortex may be due primarily to blockade of normal synaptic transmission rather than specific disrupt ion of an experience-dependent mechanism underlying ocular dominance p lasticity. (C) 1997 IBRO. Published by Elsevier Science Ltd.