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[摘要]：GABA is synthesized by two isoforms of glutamate decarboxylase (GAD), GAD65, and GAD67. However, the relative contributions of GAD65-mediated GABA synthesis to the in vivo actions of anesthetics remain unknown. To address this issue, we used mice deficient in the 65-kDa isoform of GAD and tested the hypothesis that partial reduction of GABA content in GAD65-deficient mice [GAD65(-/-)] would contribute to hypnotic and immobilizing actions of the anesthetics. The open field test, loss of righting reflex (LORR), loss of tail-pinch withdrawal response (LTWR), and locomotor activity were compared between wild-type (WT) mice and GAD65(-/-) mice. Effects of general anesthetics on both phasic and tonic GABAergic currents were examined using the patch-clamp method in frontal cortex pyramidal neurons in brain slices. The duration of propofol (100 mg/kg i.p.)-induced LORR and the duration of propofol (150 mg/kg i.p.)-induced LTWR in GAD65(-/-) mice were significantly reduced compared with WT mice. In contrast, no difference was seen for ketamine. Preinjection of the GABA transporter 1 inhibitor, NO-711 (C21H22N2O3 center dot HCl) (0.75 mg/kg i.p.), reinstated diminished actions of propofol in GAD65(-/-) mice. Cortical pyramidal neurons in GAD65(-/-) mice had smaller tonic conductances, and propofol-induced enhancement of tonic inhibition was smaller than in WT mice, suggesting that genotype differences in GAD65-mediated GABAergic inhibitory tone may be, at least in part, a cellular basis underlying behavioral differences. In conclusion, GAD65(-/-) mice show a diminished response to propofol, but not ketamine, indicating that GAD65-mediated GABA synthesis plays an important role in hypnotic and immobilizing actions of propofol. |
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