Local Postsynaptic Voltage-Gated Sodium Channel Activation in Dendritic Spines of Olfactory Bulb Granule Cells

Neuronal dendritic spines have been speculated to function as independent computational units, yet evidence for active electrical computation in spines is scarce. Here we show that strictly local voltage-gated sodium channel (Nav) activation can occur during excitatory postsynaptic potentials in the spines of olfactory bulb granule cells, which we mimic and detect via combined two-photon uncaging of glutamate and calcium imaging in conjunction with whole-cell recordings. We find that local Nav activation boosts calcium entry into spines through high-voltage-activated calcium channels and accelerates postsynaptic somatic depolarization, without affecting NMDA receptor-mediated signaling. Hence, Nav-mediated boosting promotes rapid output from the reciprocal granule cell spine onto the lateral mitral cell dendrite and thus can speed up recurrent inhibition. This striking example of electrical compartmentalization both adds to the understanding of olfactory network processing and broadens the general view of spine function. •First report of postsynaptic activation of Nav channels within spines•Local Na+ spike opens high-voltage-activated Ca2+ channels•Spine Nav accelerates somatic postsynaptic potentials•NMDA receptor activation does not require active boosting Bywalez et al. provide functional evidence that synapses activate voltage-dependent sodium and calcium conductances exclusively within the spines of olfactory bulb granule cells, confirming the theoretical prediction of active computation in spines.