Distal initiation and active propagation of action potentials in interneuron dendrites

Fast and reliable activation of inhibitory interneurons is critical for the stability of cortical neuronal networks. Active conductances in dendrites may facilitate interneuron activation, but direct experimental evidence was unavailable. Patch-clamp recordings from dendrites of hippocampal oriens-a lveus interneurons revealed high densities of voltage-gated sodium and pota ssium ion channels. Simultaneous recordings from dendrites and somata sugge sted that action potential initiation occurs preferentially in the axon wit h long threshold stimuli, but can be shifted to somatodendritic sites when brief stimuli are applied. After initiation, action potentials propagate ov er the somatodendritic domain with constant amplitude, high velocity, and r eliability, even during high-frequency trains.