EXPERIMENTAL DOWN-REGULATION OF THE NMDA CHANNEL ASSOCIATED WITH SYNAPSE PRUNING

The N-methyl-D-aspartate (NMDA) receptor has been implicated in activi ty-dependent synapse stabilization, but its role as a detector of corr elated activity during development is debated. In the amphibian retino tectal system, synaptic sorting and stabilization occur throughout lar val life, and map refinement is dependent on continuous NMDA receptor function. Moreover, tadpole tecta chronically treated with NMDA select ively fail to maintain retinal synapses wherever their activity correl ations are lowest. To determine whether this synapse elimination is as sociated with a specific downregulation of NMDA receptor function, who le cell voltage-clamp recordings were made from single neurons in tect al slices. After chronic NMDA treatment, decreases in the magnitude of NMDA currents were detected in glutamatergic synaptic currents, in ag onist-evoked currents, and in single-channel currents activated by NMD A. The results suggest that the efficacy of NMDA receptors on tectal n eurons determines the amount of correlation required to stabilize sets of tectal inputs during formation of the retinotectal projection.