Branch-Specific Ca 2+ Influx from Na + -Dependent Dendritic Spikes in Olfactory Granule Cells

Two-photon laser scanning microscopy was used to correlate electrical events detected with whole-cell somatic recordings to Ca 2+ transients in dendrites of olfactory bulb granule cells. A subset of spontaneous subthreshold depolarizing events recorded at the soma were shown to correspond to suprathreshold dendritic, Na-dependent action potentials [APs; dendritic spikes (D-spikes)]. These potentials were blocked by intracellular QX-314 (lidocaine N -ethyl bromide), hyperpolarizing current injection at the soma, and by partial inhibition of AMPA/kainate receptors with 0.75 μ m DNQX. They were affected only slightly by 100 μ m NiCl 2 . The majority of D-spikes recorded at the soma had a time to peak of 5–6 ms. Generation of a D-spike in a particular dendrite