Distribution and Function of Gap Junction Coupling in Cortical GABAergic Neurons

Although gap junctions have been observed in GABAergic interneurons of several brain regions, this chapter focuses on the distribution and functions of gap junctions and connexins in inhibitory interneurons of the cerebral cortex and hippocampus. Evidence for interconnections mediated by electrical synapses is reported for at least eight cerebral cortex interneuron types, classified on the basis of morphology, electrophysiology and molecular markers. The main differences in the organization of these interneuronal networks are summarized in terms of homologous and heterologous electrical coupling and mutual chemical inhibition. The role of connexin36 (Cx36) in forming neuronal electrical synapses in interneurons is reviewed by analyzing data derived by techniques such as immunoelectron microscopy, in situ hybridization, immunohistochemistry, reporter gene expression in transgenic mice, and functional and behavioral studies in knockout mice. Possible functional roles of Cx36-based gap junctions in GABAergic interneuronal networks are examined, from the molecular and cellular level to generation of oscillatory activities and synaptic plasticity.