Activity-Dependent Action Potential Invasion and Calcium Influx into Hippocampal CA1 Dendrites

TLDR

The study used simultaneous somatic and dendritic patch‑pipette recordings combined with calcium imaging to map the temporal and spatial dynamics of membrane potential and intracellular calcium in CA1 pyramidal neuron dendrites. Backpropagating action potentials in CA1 pyramidal neurons propagate actively into dendrites only during the early phase of a spike train, with later spikes failing to invade distal dendrites—especially at branch points—leading to attenuated calcium transients during trains, so that neighboring dendritic regions experience distinct voltage and calcium signals that modulate synaptic integration and plasticity depending on dendritic branching and firing patterns.

Abstract

The temporal and spatial profile of activity-evoked changes in membrane potential and intracellular calcium concentration in the dendrites of hippocampal CA1 pyramidal neurons was examined with simultaneous somatic and dendritic patch-pipette recording and calcium imaging experiments. Action potentials are initiated close to the soma of these neurons and backpropagate into the dendrites in an activity-dependent manner; those occurring early in a train propagate actively, whereas those occurring later fail to actively invade the distal dendrites. Consistent with this finding, dendritic calcium transients evoked by single action potentials do not significantly attenuate with distance from the soma, whereas those evoked by trains attenuate substantially. Failure of action potential propagation into the distal dendrites often occurs at branch points. Consequently, neighboring regions of the dendritic tree can experience different voltage and calcium signals during repetitive action potential firing. The influence of backpropagating action potentials on synaptic integration and plasticity will therefore depend on both the extent of dendritic branching and the pattern of neuronal activity.