In this study two-photon imaging and single cell electrophysiological measurements
were carried out in PV+ hippocampal interneurons to compare the dendritic calcium
dynamics of somatically evoked backpropagating action potentials (BAPs) and in vitro
sharp wave oscillation (SPW) activated BAPs at different distances from the soma.
In the case of 300 mum thick, non-oscillating slices, the BAP-evoked Ca(2+) (BAP-Ca(2+))
influx propagated along the dendritic tree in a non-uniform manner and its amplitude
gradually reduced when measured at more distal regions. In contrast to the evoked
BAP-Ca(2+)s, the spontaneous SPW-induced Ca(2+) influx had only a small distance-dependent
decrement. Our results suggest that similarly to nicotinic acetylcholine receptor
activation, synaptic activity during hippocampal SPWs increases AP backpropagation
into distant dendritic segments. Bath application of Nimodipine, a specific Ca(2+)
channel blocker and tetrodotoxine decreased the amplitude of the somatically evoked
Ca(2+) influx, which suggests that L-type Ca(2+) channels play an important role both
during somatically evoked and SPW-induced BAPs.
