title: Comparison between spontaneous and kainate-induced gamma oscillations in the mouse hippocampus in vitro.
abstract: Neuronal synchronization at gamma frequency, implicated in cognition, can be evoked in hippocampal slices by pharmacological activation. We characterized spontaneous small-amplitude gamma oscillations (SgammaO) recorded in area CA3 of mouse hippocampal slices and compared it with kainate-induced gamma oscillations (KgammaO). SgammaO had a lower peak frequency, a more sinusoidal waveform and was spatially less coherent than KgammaO, irrespective of oscillation amplitude. CA3a had the smallest oscillation power, phase-led CA3c by approximately 4 ms and had the highest SgammaO frequency in isolated subslices. During SgammaO CA3c neurons fired at the rebound of inhibitory postsynaptic potentials (IPSPs) that were associated with a current source in stratum lucidum, whereas CA3a neurons often fired from spikelets, 3-4 ms earlier in the cycle, and had smaller IPSPs. Kainate induced faster/larger IPSPs that were associated with an earlier current source in stratum pyramidale. SgammaO and KgammaO power were dependent on alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors, gap junctions and gamma-aminobutyric acid (GABA)(A) receptors. SgammaO was suppressed by elevating extracellular KCl, blocking N-methyl-d-aspartate (NMDA) receptors or muscarinic receptors, or activating GluR5-containing kainate receptors. SgammaO was not affected by blocking metabotropic glutamate receptors or hyperpolarization-activated currents. The adenosine A(1) receptor antagonist 8-cyclopentyl-1,3-dimethoxyxanthine (8-CPT) and the CB1 cannabinoid receptor antagonist N-(piperidin-1-yl)-5-(4-iodophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide (AM251) increased SgammaO power, indicating that endogenous adenosine and/or endocannabinoids suppress or prevent SgammaO in vitro. SgammaO emerges from a similar basic network as KgammaO, but differs in involvement of somatically projecting interneurons and pharmacological modulation profile. These observations advocate the use of SgammaO as a natural model for hippocampal gamma oscillations, particularly during less activated behavioural states.
authors.affiliation: Neuroscience, School of Clinical and Experimental Medicine, University of Birmingham, Birmingham, UK.
authors.forename: Alexander N J
authors.initials: AN
authors.lastname: Pietersen
authors.forename: Nisha
authors.initials: N
authors.lastname: Patel
authors.forename: John G R
authors.initials: JG
authors.lastname: Jefferys
authors.forename: Martin
authors.initials: M
authors.lastname: Vreugdenhil
mesh_terms: D000818:Animals; D001683:Biological Clocks / Q000187:drug effects / Q000502:physiology*; D003344:Cortical Synchronization / Q000379:methods; D006624:Hippocampus / Q000187:drug effects / Q000502:physiology*; D007608:Kainic Acid / Q000494:pharmacology*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology
chemical_list: D007608:Kainic Acid