Effects of hippocampal sharp wave ripple oscillations on medial entorhinal cortex layer V neurons in vitro
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1
University of Heidelberg, Institute of Physiology and Pathophysiology, Germany
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2
Bernstein Center for Computational Neuroscience (BCCN) Heidelberg/Mannheim, Germany
The mammalian hippocampus displays a variety of state-dependent network oscillations which are believed to organize neuronal activity and synaptic plasticity during memory formation. The peculiar pattern of sharp wave-ripple complexes (SPW-R) entrains neurons into coactive neuronal assemblies within very fast oscillations at ~200 Hz. SPW-R emerge in hippocampal area CA3 and then propagate along the hippocampal "output loop" via CA1 to the entorhinal cortex (EC). The cellular effects of SPW-R in this downstream area are, however, unknown. We therefore investigated the activity of layer V (LV) principal neurons of the medial EC (mEC) during SPW-R oscillations in horizontal mouse brain slices. Intracellular recordings in the mEC were combined with extracellular monitoring of propagating network activity. Ongoing spontaneous SPW-R in CA1 were regularly followed by negative field potential deflections in deep layers of the mEC (5-10 ms delay; ~65 µV amplitude). Entorhinal events carried superimposed fast oscillations which were clearly slower than the original ripples in CA1. Intracellular recordings from mEC LV neurons revealed SPW-R-associated depolarizing synaptic potentials which reached ~2.5 mV and remained sub-threshold at resting potential (-72 ± 5 mV). Amplitude of synaptic potentials correlated positively with amplitude of SPW-R in CA1 while delay time was short for large network events. Synaptic potentials were regularly superimposed by rhythmic activity with leading frequencies below the ripple band in CA1. Conductance analysis revealed that network-associated synaptic input was mostly excitatory. Upon subthreshold membrane depolarization, SPW-R in CA1 regularly triggered spikes in LV neurons. Cross-correlations between entorhinal spikes and field SPW-R in CA1 revealed strong coupling between spikes and sharp waves (delay 10 – 30 ms) but only weak correlation with ripple cycles in CA1. We have recently shown that waveform patterns of SPW-R contain specific signatures of the underlying multicellular assemblies (Reichinnek et al., 2010). We therefore analyzed the correlation between stably recurring SPW-R waveforms in CA1 and corresponding depolarizing synaptic potentials in mEC neurons. Indeed, these downstream synaptic waveform patterns were significantly correlated with the preceding SPW-R, as shown by analysis of information and sparsity of waveform distributions. These correlations were, however, strongly biased by the amplitude of the corresponding SPW-R, indicating dominant effects of convergent synaptic innervation.
Acknowledgements
Supported by BMBF (01GQ1003A, BCCN Heidelberg/Mannheim, B3) and by IB BMBF (RUS 11/015).
Keywords:
Entorhinal Cortex,
Hippocampus,
layer V,
Mouse,
sharp wave-ripple complexes,
slice
Conference:
Bernstein Conference 2012, Munich, Germany, 12 Sep - 14 Sep, 2012.
Presentation Type:
Poster
Topic:
Other
Citation:
Egorov
AV,
Beyer
KM,
Both
M and
Draguhn
A
(2012). Effects of hippocampal sharp wave ripple oscillations on medial entorhinal cortex layer V neurons in vitro.
Front. Comput. Neurosci.
Conference Abstract:
Bernstein Conference 2012.
doi: 10.3389/conf.fncom.2012.55.00249
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Received:
18 Sep 2012;
Published Online:
12 Sep 2012.
*
Correspondence:
Dr. Alexei V Egorov, University of Heidelberg, Institute of Physiology and Pathophysiology, Heidelberg, 69120, Germany, alexei.egorov@urz.uni-heidelberg.de