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.
