Slow Recovery from Inactivation of Na⁺Channels Underlies the Activity-Dependent Attenuation of Dendritic Action Potentials in Hippocampal CA1 Pyramidal Neurons

TLDR

Na⁺ action potentials invade dendrites of pyramidal neurons, triggering Ca²⁺ influx that likely supports associative synaptic plasticity. The study aimed to uncover why somatic and dendritic action potentials in CA1 pyramidal neurons exhibit different activity dependence. Whole‑cell and cell‑attached patch‑clamp recordings were performed on adult rat CA1 pyramidal neurons to probe the underlying mechanisms. Repeated activation produced a slow, voltage‑dependent reduction of dendritic Na⁺ currents, whereas somatic Na⁺ currents were less affected; K⁺ currents remained constant but were required for dendritic action‑potential attenuation, indicating that regional Na⁺ and K⁺ channel differences underlie the distinct activity dependence of somatic and dendritic action potentials.

Abstract

Na+ action potentials propagate into the dendrites of pyramidal neurons driving an influx of Ca2+ that seems to be important for associative synaptic plasticity. During repetitive (10-50 Hz) firing, dendritic action potentials display a marked and prolonged voltage-dependent decrease in amplitude. Such a decrease is not apparent in somatic action potentials. We investigated the mechanisms of the different activity dependence of somatic and dendritic action potentials in CA1 pyramidal neurons of adult rats using whole-cell and cell-attached patch-clamp methods. There were three main findings. First, dendritic Na+ currents decreased in amplitude when repeatedly activated by brief (2 msec) depolarizations. Recovery was slow and voltage-dependent. Second, Na+ currents decreased much less in somatic than in dendritic patches. Third, although K+ currents remained constant during trains, K+ currents were necessary for dendritic action potential amplitude to decrease in whole-cell experiments. These results suggest that regional differences in Na+ and K+ channels determine the differences in the activity dependence of somatic and dendritic action potential amplitudes.