Spatial patterns of excitation and inhibition evoked by lateral connectivity in layer 2/3 of rat barrel cortex.

In the rat barrel cortex, neurons in layer 4 are topographically arranged in a precise columnar structure, and the excitatory feed-forward input from layer 4 to layer 2/3 projects almost exclusively within the home barrel column. Here we analyzed the lateral connectivity that links neighboring columns in layer 2/3, which is necessary for integrating information across whiskers. We examined the spatial distributions of three different functional types of lateral connections in layer 2/3 of the rat barrel cortex: glutamate receptor-mediated excitatory connections, GABA(A) receptor-mediated inhibitory connections and GABA(B) receptor-mediated inhibitory connections. Synaptic potentials of pyramidal neurons, which are measures of the strength of connections, were evoked by a horizontal array of stimulation electrodes. The synaptic potentials and their decrease with distance from the stimulation site were measured in two types of slices whose planes were parallel to or orthogonal to barrel rows. Excitatory and GABA(B) receptor-mediated inhibitory connections were stronger along barrel rows than across them, whereas GABA(A) receptor-mediated inhibitory connections did not show such a tendency. These results indicate that lateral connectivity in layer 2/3 varies on the basis of not only excitatory polarity but also receptor subtypes.