Abstract
Activities of cortical pyramidal cells are regulated by GABAergic nonpyramidal cells. Recently several dynamic properties of cortical circuitry have been revealed, but the precise intracortical wiring by each nonpyramidal cell subtype remains largely unknown. We investigated synaptic connections made by double bouquet cells, a subtype of nonpyramidal cells, in rat frontal cortex. Non-pyramidal cells were identified in isolated slices of frontal cortex from 18-22 days postnatal rats by whole cell, current-clamp recording, followed by intracellular injection of biocytin. After overnight fixation, the slices were histochemically stained with DAB and embedded in Epon. The postsynaptic structures were reconstructed three-dimensionally from serial ultra-thin sections of the intracellulary-stained axon terminals. Double bouquet cells innervated dendritic shafts, spine heads, spine necks, and rarely somata. About half of the dendrites contacted by double bouquet cell axons received numerous asymmetrical synapses on their dendritic shafts, which indicated these postsynaptic targets were nonpyramidal cells. The rest of the target dendrites were proximal dendrites and distal dendrites of pyramidal and nonpyramidal cells. The target spines usually had an asymmetrical input, which may indicate that double bouquet cell specifically inhibits the excitatory input. These observations indicate the double bouquet cells have a several specific synaptic targets and may have a specific role in a regulation of cortical activity. [Jpn J Physiol 54 Suppl:S49 (2004)]
