• Vinuta Rau, Sangeetha V Iyer, Irene Oh, Dev Chandra, Neil Harrison, Edmond I Eger, Michael S Fanselow, Gregg E Homanics, and James M Sonner.
• Department of Anesthesia and Perioperative Care, University of California San Francisco, San Francisco, California 94143-0464, USA. rauv@anesthesia.ucsf.edu
• Anesth. Analg. 2009 Dec 1;109(6):1816-22.

BackgroundGeneral anesthesia produces multiple end points including immobility, hypnosis, sedation, and amnesia. Tonic inhibition via gamma-aminobutyric acid type A receptors (GABA(A)-Rs) may play a role in mediating behavioral end points that are suppressed by low concentrations of anesthetics (e.g., hypnosis and amnesia). GABA(A)-Rs containing the alpha4 subunit are highly concentrated in the hippocampus and thalamus, and when combined with delta subunits they mediate tonic inhibition, which is sensitive to low concentrations of isoflurane.MethodsIn this study, we used a GABA(A) alpha4 receptor knockout mouse line to evaluate the contribution of alpha4-containing GABA(A)-Rs to the effects of immobility, hypnosis, and amnesia produced by isoflurane. Knockout mice and their wild-type counterparts were assessed on 3 behavioral tests: conditional fear (to assess amnesia), loss of righting reflex (to assess hypnosis), and the minimum alveolar concentration of inhaled anesthetic necessary to produce immobility in response to noxious stimulation in 50% of subjects (to assess immobility).ResultsGenetic inactivation of the alpha4 subunit reduced the amnestic effect of isoflurane, minimally affected loss of righting reflex, and had no effect on immobility.ConclusionsThese results lend support to the hypothesis that different sites of action mediate different anesthetic end points and suggest that alpha4-containing GABA(A)-Rs are important mediators of the amnestic effect of isoflurane on hippocampal-dependent declarative memory.

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