Abstract
In CA1 pyramidal neurons, correlated inputs trigger dendritic plateau potentials that drive neuronal plasticity and firing rate modulation. Given the strong electrotonic coupling between soma and axon, the >25 mV depolarization associated with the plateau could propagate through the axon to influence action potential initiation, propagation, and neurotransmitter release. We examined this issue in brain slices, awake mice, and a computational model. Despite profoundly inactivating somatic and proximal axon Na+ channels, plateaus evoked action potentials that recovered to full amplitude in the distal axon (>150 mm) and triggered neurotransmitter release similar to regular spiking. This effect was due to strong attenuation of plateau depolarizations by axonal K+ channels, allowing full axon repolarization and Na+ channel deinactivation. High-pass filtering of dendritic plateaus by axonal K+ channels should thus enable accurate transmission of gain-modulated firing rates, allowing neuronal firing to be efficiently read out by downstream regions as a simple rate code.