Activity patterns in the prefrontal cortex and hippocampus during and after awakening from etomidate anesthesia

Abstract

Background: The anesthetic properties of etomidate are largely mediated by γ-aminobutyric acid type A receptors. There is evidence for the existence of γ-aminobutyric acid type A receptor subtypes in the brain, which respond to small concentrations of etomidate. After awakening from anesthesia, these subtypes are expected to cause cognitive dysfunction for a yet unknown period of time. The corresponding patterns of brain electrical activity and the molecular identity of γ-aminobutyric acid type A receptors contributing to these actions remain to be elucidated. Methods: Anesthesia was induced in wild-type and β3(N265M) knock-in mice by intravenous injection of 10 mg/kg etomidate. Local field potentials were recorded simultaneously in the prefrontal cortex and hippocampus using chronically implanted electrode arrays. Local field potentials were sampled before, during, and after anesthesia. Results: In the prefrontal cortex and hippocampus of wild-type mice, intravenous bolus injection of etomidate evoked isoelectric baselines and subsequent burst suppression. These effects were largely attenuated by the β3(N265M) mutation. During emergence from anesthesia, power density in the θ band (5-15 Hz) transiently increased in the hippocampus of wild types, but not in the mutants, indicating that this action was caused by the receptors harboring β3 subunits. In both genotypes, etomidate produced a long-lasting (> 1 h after recovery of righting reflexes) decrease in θ-peak frequency. Significant slowing of θ activity was apparent in the hippocampus and prefrontal cortex. Conclusions: Etomidate-induced patterns of brain activity during deep anesthesia mostly involve actions at β3 containing γ-aminobutyric acid type A receptors. During the postanesthesia period, altered θ-band activity indicates ongoing anesthetic action. Copyright © 2010, the American Society of Anesthesiologists, Inc. Lippincott Williams & Wilkins.