NMDA receptor-mediated currents are prominent in the thalamocortical synaptic response before maturation of inhibition.

1. The N-methyl-D-aspartate subtype of glutamate receptor (NMDAR) is thought to underlie synaptic plasticity in both adult and developing CNS; however, its involvement in the thalamocortical synapse has not yet been directly demonstrated. 2. Whole-cell, thalamus-evoked synaptic currents were recorded from layer IV cells in slices of immature mouse somatosensory cortex. 3. Earlier than postnatal day 9 the majority of responses were monosynaptic and purely excitatory, with both non-NMDAR and NMDAR-mediated glutamatergic components. 4. In older animals, disynaptic inhibitory currents summated with the excitatory ones and lowered the reversal potential of the response to voltages at which the NMDAR conductance is mostly blocked. 5. These findings suggest a cellular basis for the transient plasticity observed in layer IV during early postnatal development.