Barrel cortex critical period plasticity is independent of changes in NMDAreceptor subunit composition

The regulation of NMDA receptor (NMDAR) subunit composition and expression during development is thought to control the process of thalamocortical aff erent innervation, segregation, and plasticity. Thalamocortical synaptic pl asticity in the mouse is dependent on NMDARs containing the NR2B subunit, w hich are the dominant form during the "critical period" window for plastici ty. Near the end of the critical period there is a gradual increase in the contribution of NR2A subunits that happens in parallel to changes in NMDAR- mediated current kinetics. However, no extension of the critical period occ urs in NR2A knockout mice, despite the fact that NMDA subunit composition a nd current kinetics remain immature past the end of the critical period. Th ese data suggest that regulation of NMDAR subunit composition is not essent ial for closing the critical period plasticity window in mouse somatosensor y barrel cortex.