Functionally distinct NMDA receptors mediate horizontal connectivity within layer 4 of mouse barrel cortex

In sensory areas of neocortex, thalamocortical afferents project primarily onto the spiny stellate neurons of Layer 4. Anatomical evidence indicates t hat these cells receive most of their excitatory input from other cortical neurons, including other spiny stellate cells. Although this local network must play an important role in sensory processing, little is known about th e properties of the neurons and synapses involved. We have produced a slice preparation of mouse barrel cortex that isolates Layer 4. We report that e xcitatory interaction between spiny stellate neurons is largely via N-methy l-D-aspartate receptors (NMDARs) and that a given neuron contains more than one type of NMDAR, as distinguished by voltage dependence. Thus, spiny ste llate cells act as effective integrators of powerful and persistent NMDAR-m ediated recurrent excitation.