Axo-axonal coupling: A novel mechanism for ultrafast neuronal communication

We provide physiological, pharmacological, and structural evidence that axo ns of hippocampal principal cells are electrically coupled, with prepotenti als or spikelets forming the physiological substrate of electrical coupling as observed in cell somata. Antidromic activation of neighboring axons ind uced somatic spikelet potentials in neurons of CA3, CA1, and dentate gyrus areas of rat hippocampal slices. Somatic invasion by these spikelets was de pendent on the activation of fast Na+ channels in the postjunctional neuron . Antidromically elicited spikelets; were suppressed by gap junction blocke rs and low intracellular pH. Paired axo-somatic and somato-dendritic record ings revealed that the coupling potentials appeared in the axon before inva ding the soma and the dendrite. Using confocal laser scanning microscopy we found that putative axons of principal cells were dye coupled. Our data th us suggest that hippocampal neurons are coupled by axo-axonal junctions, pr oviding a novel mechanism for very fast electrical communication.