ORIGINAL PAPER Enhanced Dendritic Action Potential Backpropagation in Parvalbumin-positive Basket Cells During Sharp Wave Activity Bala ´zs Chiovini • Gergely F. Turi • Gergely Katona • Attila Kasza ´s • Ferenc Erde ´lyi • Ga ´bor Szabo ´ • Hannah Monyer • Attila Csa ´ka ´nyi • E. Sylvester Vizi • Bala ´zs Ro ´zsa Accepted: 30 September 2010 / Published online: 3 November 2010 Ó Springer Science+Business Media, LLC 2010 Abstract 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 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 Nimodi- pine, 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. Keywords Two-photon Á Sharp wave Á Backpropagating action potential Á Parvalbumin-positive basket cell Á Hippocampus Introduction Backpropagating action potentials (BAPs) play a crucial role in neuronal Hebbian plasticity [1] by changing synaptic gains following different time-dependent local dendritic interac- tions with ongoing synaptic activity [2]. Backpropagation has been shown to be cell-type dependent; for example, it is strong in mitral cell dendrites in the olfactory bulb [3] and in stratum radiatum interneurons of the hippocampus [4]. However, backpropagation is weak in dendrites of Purkinje cells [5] and parvalbumin-expressing (PV?) neurons [6], where backpropagation has been shown to become passive due to the distance-dependent decrease of sodium channel density relative to potassium channel density [7]. Fast spiking (FS), PV? basket cells (BCs) as the clock- works for neuronal oscillations are important elements of hippocampal neuronal networks [8]. All types of the PV? interneurons in the CA1 area of the hippocampus, such as axo-axonic, bistratified, oriens-lacunosum moleculare and BCs, have extended dendritic arborization spreading even to the lacunosum moleculare [9]. A strong, distance-dependent decrement of action potential (AP) backpropagation has been demonstrated in cortical and hippocampal PV? cells [6, 7], suggesting that a large part of their dendritic arbori- zation is not reached by BAPs, leaving out these regions from receiving somatic feedback. However, ongoing coin- cident synaptic inputs could slightly modify AP back- propagation as in cortical and hippocampal stratum radiatum interneurons [4, 10, 11]. Synchronous network activity—such as sharp wave oscillations (SPWs)—may be Special Issue: In Honor of Dr. Abel Lajtha. Gergely Katona, E. Sylvester Vizi, Bala ´zs Ro ´zsa, are owners of Femtonics Ltd. B. Chiovini Á G. F. Turi Á G. Katona Á A. Kasza ´s Á F. Erde ´lyi Á G. Szabo ´ Á A. Csa ´ka ´nyi Á E. S. Vizi Á B. Ro ´zsa (&) Institute of Experimental Medicine, Hungarian Academy of Sciences, Szigony str. 43, 1083 Budapest, Hungary e-mail: rozsabal@koki.hu H. Monyer Department of Clinical Neurobiology, University of Heidelberg, Heidelberg, Germany 123 Neurochem Res (2010) 35:2086–2095 DOI 10.1007/s11064-010-0290-4