• Tamara Timic Stamenic, Simon Feseha, Francesca M Manzella, Damon Wallace, Davis Wilkey, Timothy Corrigan, Hanna Fiedler, Patricia Doerr, Kathiresan Krishnan, Yogendra H Raol, Douglas F Covey, Vesna Jevtovic-Todorovic, and Slobodan M Todorovic.
• Department of Anesthesiology, University of Colorado, Anschutz Medical Campus, Aurora, CO, USA.
• Br J Anaesth. 2021 Jan 1; 126 (1): 245255245-255.

BackgroundThe mechanisms underlying the role of T-type calcium channels (T-channels) in thalamocortical excitability and oscillations in vivo during neurosteroid-induced hypnosis are largely unknown.MethodsWe used patch-clamp electrophysiological recordings from acute brain slices ex vivo, recordings of local field potentials (LFPs) from the central medial thalamic nucleus in vivo, and wild-type (WT) and Cav3.1 knock-out mice to investigate the molecular mechanisms of hypnosis induced by the neurosteroid analogue (3β,5β,17β)-3-hydroxyandrostane-17-carbonitrile (3β-OH).ResultsPatch-clamp recordings showed that 3β-OH inhibited isolated T-currents but had no effect on phasic or tonic γ-aminobutyric acid A currents. Also in acute brain slices, 3β-OH inhibited the spike firing mode more profoundly in WT than in Cav3.1 knockout mice. Furthermore, 3β-OH significantly hyperpolarised neurones, reduced the amplitudes of low threshold spikes, and diminished rebound burst firing only in WT mice. We found that 80 mg kg-1 i.p. injections of 3β-OH induced hypnosis in >60% of WT mice but failed to induce hypnosis in the majority of mutant mice. A subhypnotic dose of 3β-OH (20 mg kg-1 i.p.) accelerated induction of hypnosis by isoflurane only in WT mice, but had similar effects on the maintenance of isoflurane-induced hypnosis in both WT and Cav3.1 knockout mice. In vivo recordings of LFPs showed that a hypnotic dose of 3β-OH increased δ, θ, α, and β oscillations in WT mice in comparison with Cav3.1 knock-out mice.ConclusionsThe Cav3.1 T-channel isoform is critical for diminished thalamocortical excitability and oscillations that underlie neurosteroid-induced hypnosis.Copyright © 2020 The Author(s). Published by Elsevier Ltd.. All rights reserved.

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