Background: The memory-blocking properties of general anesthetics have recently received considerable attention because of concerns related to intraoperative awareness and postoperative cognitive dysfunction. The goal of this study was to identify the mechanisms by which gamma-aminobutyric acid subtype A receptors that contain the alpha5 subunit (alpha5GABAARs) induce memory-blockade by etomidate and a pharmacologic strategy to reverse this impairment.
Methods: The effects of etomidate and the alpha5GABAAR-preferring inverse agonist L-655,708 on the plasticity of glutamatergic excitatory transmission in hippocampal slices and behavioral memory for spatial navigational and fear-associated memory tasks were studied in wild-type and null mutant mice for the gene that encodes the alpha5 subunit (Gabra5-/- mice). Long-term potentiation of field excitatory postsynaptic potentials was induced in CA1 pyramidal neurons following high-frequency stimulation of Schaffer collaterals. Memory performance was studied in contextual, cued, and trace fear conditioning assays and the Morris water maze.
Results: Robust synaptic plasticity induced by high-frequency stimulation and memory performance for contextual fear and spatial navigational memory were not influenced by a decrease in the function of alpha5GABAARs. Nevertheless, etomidate, via an increase in alpha5GABAAR activity, completely blocked long-term potentiation and impaired memory performance, and these effects were reversed by pretreatment with L-655,708.
Conclusions: The results provide the first proof of concept that memory blockade by a general anesthetic can be reversed by inhibiting the function of alpha5GABAARs. The findings suggest a mechanism and model for awareness during anesthesia.