Short-term Memory Impairment after Isoflurane in Mice Is Prevented by the α5 γ-Aminobutyric Acid Type A Receptor Inverse Agonist L-655,708

Background: Memory blockade is an essential component of the anesthetic state. However, postanesthesia memory deficits represent an undesirable and poorly understood adverse effect. Inhibitory alpha 5 subunit-containing gamma-aminobutyric acid subtype A receptors (alpha 5GABA(A)) are known to play a critical role in memory processes and are highly sensitive to positive modulation by anesthetics. We postulated that inhibiting the activity of alpha 5GABA(A) receptors during isoflurane anesthesia would prevent memory deficits in the early postanesthesia period. Methods: Mice were pretreated with L-655,708, an alpha 5GABA(A) receptor selective inverse agonist, or vehicle. They were then exposed to isoflurane for 1 h (1.3%, or 1 minimum alveolar concentration, or air-oxygen control). Then, either 1 or 24 h later, mice were conditioned in fear-associated contextual and cued learning paradigms. In addition, the effect of L-655,708 on the immobilizing dose of isoflurane was studied. Motor coordination, sedation, anxiety, and the concentration of isoflurane in the brain at 5 min, 1 h, and 24 h after isoflurane were also examined. Results: Motor and sensory function recovered within minutes after termination of isoflurane administration. In contrast, a robust deficit in contextual fear memory persisted for at least 24 h. The alpha 5GABA(A) receptor inverse agonist, L-655,708, completely prevented memory deficits without changing the immobilizing dose of isoflurane. Trace concentrations of isoflurane were measured in the brain 24 h after treatment. Conclusions: Memory deficits occurred long after the sedative, analgesic, and anxiolytic effects of isoflurane subsided. L-655,708 prevented memory deficit, suggesting that an isoflurane interaction at alpha 5GABA(A) receptors contributes to memory impairment during the early postanesthesia period.