Active dendritic integrative mechanisms such as regenerative dendritic spikes enrich
the information processing abilities of neurons and fundamentally contribute to behaviorally
relevant computations. Dendritic Ca 2+ spikes are generally thought to produce plateau-like
dendritic depolarization and somatic complex spike burst (CSB) firing, which can initiate
rapid changes in spatial coding properties of hippocampal pyramidal cells (PCs). However,
here we reveal that a morpho-topographically distinguishable subpopulation of rat
and mouse hippocampal CA3PCs exhibits compound apical dendritic Ca 2+ spikes with
unusually short duration that do not support the firing of sustained CSBs. These Ca
2+ spikes are mediated by L-type Ca 2+ channels and their time course is restricted
by A- and M-type K + channels. Cholinergic activation powerfully converts short Ca
2+ spikes to long-duration forms, and facilitates and prolongs CSB firing. We propose
that cholinergic neuromodulation controls the ability of a CA3PC subtype to generate
sustained plateau potentials, providing a state-dependent dendritic mechanism for
memory encoding and retrieval.
