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 lm thick, non-oscillating slices, the
BAP-evoked Ca2? (BAP-Ca2?) 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-Ca2?s, the spontaneous SPWinduced
Ca2? 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 Ca2? channel blocker and tetrodotoxine
decreased the amplitude of the somatically evoked Ca2?
influx, which suggests that L-type Ca2? channels play
an important role both during somatically evoked and
SPW-induced BAPs