Fast excitation during sharp-wave ripples

Abstract

Event Abstract Back to Event Fast excitation during sharp-wave ripples Álvaro Tejero-Cantero1*, Nikolaus Maier2, Jochen Winterer2, Genela Morris2, Christian Leibold3 and Dietmar Schmitz2 1 Rutgers University, Newark, Division of Neurobiology, Department of Biology II, Germany 2 University of Munich, Neurowissenschaftliches Forschungszentrum, Germany 3 Bernstein Center for Computational Neuroscience, Germany In freely behaving rodents, the local field potential measured in the hippocampus displays prominent deflections during immobility and sleep. These are called sharp waves, last for about 40 to 60 ms and are jagged with a fast oscillations, or ripples, of about 200Hz. Sharp waves have been shown in rats to co-occur with multi-unit replay and preplay patterns following and preceding a learned spatial experience [1-3]. Patterns are compressed in order to fit within the tight temporal frame offered by the sharp-wave ripple complexes. On a cellular level, it is known that both interneurons and pyramidal cells are significantly phase-locked to the ripple phenomenon.We aim at understanding the coordinated cellular activity that during sharp-wave ripple complexes. To this end, we resort to in vitro simultaneous field potential and single-cell voltage clamp recordings on submerged mouse hippocampal slices, where the phenomenon appears with characteristics known from the in vivo situation [4]. Our results stem from the first direct analysis of sharp-wave associated post synaptic currents (PSCs). These were recorded at different holding potentials representative of different excitation/inhibition mixes (−60 mV vs around −50 mV) as well as under intracellular block of inhibition. The following evidence suggests that the intracellular high frequency oscillations are supported by strong excitatory currents (see also [5]) and complements the present view that high-frequency oscillations during sharp-waves in vivo are mainly mediated by inhibitory interneurons: 1. The kinetics of sharp-wave associated currents were consistent with fast EPSCs.2. The shape of sharp-wave associated PSCs is not compatible with inhibition riding on tonic excitation.3. Intracellular block of inhibition did not affect the absolute ripple-band power nor the frequency of the sharp-wave associated fast PSCs.4. Putative EPSCs showed strong locking to the extracellular ripple and lead the sharp wave peak. Acknowledgements: This work was supported by the Bundensministerium für Bildung und Forschung (BMBF, grant numbers 01GQ0440 and 01GQ0410) and the Deutsche Forschungsgemeinschaft (DFG, grant number LE 2250/2-1).