GABAA-R α1 subunit knockin mutation leads to abnormal EEG and anesthetic-induced seizure-like activity in mice

Gamma-aminobutyric acid-type A receptors (GABAA-Rs) have been proposed as a target for many general anesthetics. We recently created knockin (KI) mice harboring a point mutation (serine 270 to histidine) in the GABAA-R α1 subunit. This mutation abolishes sensitivity of recombinant GABAA–Rs to isoflurane while maintaining normal sensitivity to halothane and increasing the potency of GABA. KI mice showed abnormalities in the EEG baseline, including occasional spike-wave activity and spindle-like bursts. When anesthetized with isoflurane, the KI mice but not the control mice revealed repetitive 4–5Hz slow wave discharges in the cortical EEG. KI mice did not differ from controls in response to isoflurane or halothane in the standard tail clamp/withdrawal and loss of righting reflex assays. We recorded miniature inhibitory postsynaptic currents (mIPSCs) from hippocampal interneurons and pyramidal cells in brain slices. mIPSCs in neurons from KI mice were of normal amplitude, but decayed more slowly than controls. Hippocampal mIPSCs in control mice were significantly prolonged by 0.4 and 0.9 MAC isoflurane, and by 0.5 MAC halothane. In KI mice, the effect of isoflurane on mIPSC decay was dramatically reduced, while halothane prolonged mIPSCs as for controls. We conclude that the kinetic and pharmacological properties of hippocampal GABAA-Rs in the KI mouse recapitulate many features of mutant α1β2γ2 GABAA-Rs observed in vitro. GABAA-Rs containing α1 subunits do not appear to contribute to the actions of isoflurane in the spinal cord, but both EEG and synaptic recordings provide evidence for effects of isoflurane on these GABAA-R isoforms in cortical structures.