Activity coregulates quantal AMPA and NMDA currents at neocortical synapses

AMPA and NMDA receptors are coexpressed at many central synapses, but the f actors that control the ratio of these two receptors are not well understoo d. We recorded mixed miniature or evoked synaptic currents arising from coa ctivation of AMPA and NMDA receptors and found that long-lasting changes in activity scaled both currents up and down proportionally through changes i n the number of postsynaptic receptors. The ratio of NMDA to AMPA current w as similar at different synapses onto the same neuron, and this relationshi p was preserved following activity-dependent synaptic scaling. These data s how that AMPA and NMDA receptors are tightly coregulated by activity at syn apses at which they are both expressed and suggest that a mechanism exists to actively maintain a constant receptor ratio across a neuron's synapses.