Cortical inhibitory but not excitatory synaptic transmission and circuit refinement are altered after the deletion of NMDA receptors during early development.

Neurons in the cerebral cortex form excitatory and inhibitory circuits with specific laminar locations. The mechanisms underlying the development of these spatially specific circuits is not fully understood. To test if postsynaptic N-methyl-D-aspartate (NMDA) receptors on excitatory neurons are required for the development of specific circuits to these neurons, we genetically ablated NMDA receptors from a subset of excitatory neurons in the temporal association cortex (TeA) through in utero electroporation and assessed the intracortical circuits connecting to L5 neurons through in vitro whole-cell patch clamp recordings coupled with laser-scanning photostimulation (LSPS). In NMDAR knockout neurons, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor-mediated connections were largely intact. In contrast both LSPS and mini-IPSC recordings revealed that γ-aminobutyric acid type A (GABA A ) receptor-mediated connections were impaired in NMDAR knockout neurons. These results suggest that postsynaptic NMDA receptors are important for the development of GABAergic circuits.