Cortex-restricted disruption of NMDAR1 impairs neuronal patterns in the barrel cortex

In the rodent primary somatosensory cortex, the configuration of whiskers a nd sinus hairs on the snout and of receptor-dense zones on the paws is topo graphically represented as discrete modules of layer IV granule cells (barr els) and thalamocortical afferent terminals(1,2). The role of neural activi ty, particularly activity mediated by NMDARs (N-methyl-D-aspartate receptor s), in patterning of the somatosensory cortex has been a subject of debate( 3-6). We have generated mice in which deletion of the NMDAR1 (NR1) gene is restricted to excitatory cortical neurons, and here we show that sensory pe riphery-related patterns develop normally in the brainstem and thalamic som atosensory relay stations of these mice. In the somatosensory cortex, thala mocortical afferents corresponding to large whiskers form patterns and disp lay critical period plasticity, but their patterning is not as distinct as that seen in the cortex of normal mice. Other thalamocortical patterns corr esponding to sinus hairs and digits are mostly absent. The cellular aggrega tes known as barrels and barrel boundaries do not develop even at sites whe re thalamocortical afferents cluster. Our findings indicate that cortical N MDARs are essential for the aggregation of layer IV cells into barrels and for development of the full complement of thalamocortical patterns.