Common excitatory synaptic inputs to electrically connected cortical fast-spiking cell networks.

Cortical fast-spiking (FS) interneurons are electrically interconnected through gap junctions and form dendritic net structures extending over different functional columns. Here we investigated how pyramidal cells regulate FS cell network activity. Using paired recordings and glutamate puff stimulations, we found that FS cell pairs connected by electrical synapses shared common inputs from surrounding pyramidal cells more frequently than those unconnected or connected only by chemical synapses. Experimental and simulation results suggest that activity spread evoked by common inputs to electrically connected FS cells depends on network state. When cells were in the depolarized state, common inputs to electrically connected cells enhanced spike induction and induced inhibitory effects in surrounding FS cells. By contrast, in the hyperpolarized state, either sub- or suprathreshold inputs produced depolarizing potentials in nearby cells. Our results suggest that globally connected FS cell networks are locally regulated by pyramidal cells in an electrical connection- and network state-dependent manner.