A developmental switch of AMPA receptor subunits in neocortical pyramidal neurons.

AMPA receptors mediate most of the fast excitatory neurotransmission in the brain, and those lacking the glutamate receptor 2 (GluR2) subunit are Ca(2+)-permeable and expressed in cortical structures primarily by inhibitory interneurons. Here we report that synaptic AMPA receptors of excitatory layer 5 pyramidal neurons in the rat neocortex are deficient in GluR2 in early development, approximately before postnatal day 16, as evidenced by their inwardly rectifying current-voltage relationship, blockade of AMPA receptor-mediated EPSCs by external and internal polyamines, permeability to Ca(2+), and GluR2 immunoreactivity. Overall, these results indicate that neocortical pyramidal neurons undergo a developmental switch in the Ca(2+) permeability of their AMPA receptors through an alteration of their subunit composition. This has important implications for plasticity and neurotoxicity.