Department of Anesthesiology, Gunma University Graduate School of Medicine, 3-39-22 Showa-machi, Maebashi City 371-8511, Japan.
Neuropharmacology. 2011 Jul-Aug;61(1-2):172-80. doi: 10.1016/j.neuropharm.2011.03.025. Epub 2011 Apr 7.
Recent studies have suggested that extrasynaptic GABA(A) receptors, which contribute tonic conductance, are important targets for general anesthetics. We tested the hypothesis that manipulations designed to alter ambient GABA concentrations (tonic conductance) would affect hypnotic (as indicated by loss of righting reflex, LORR) and immobilizing (as indicated by loss of tail-pinch withdrawal reflex, LTWR) actions of sevoflurane, propofol, and midazolam. Two manipulations studied were 1) the genetic absence of glutamate decarboxylase (GAD) 65 gene (GAD65-/-), which purportedly reduced ambient GABA concentrations, and 2) the pharmacological manipulation of GABA uptake using GABA transporter inhibitor (NO-711). The influence of these manipulations on cellular and behavioral responses to the anesthetics was studied using behavioral and electrophysiological assays. HPLC revealed that GABA levels in GAD65-/- mice were reduced in the brain (76.7% of WT) and spinal cord (68.5% of WT). GAD65-/- mice showed a significant reduction in the duration of LORR and LTWR produced by propofol and midazolam, but not sevoflurane. NO-711 (3 mg/kg, ip) enhanced the duration of LORR and LTWR by propofol and midazolam, but not sevoflurane. Patch-clamp recordings revealed that sevoflurane (0.23 mM) slightly enhanced the amplitude of tonic GABA current in the frontal cortical neurons; however, these effects were not strong enough to alter discharge properties of cortical neurons. These results demonstrate that ambient GABA concentration is an important determinant of the hypnotic and immobilizing actions of propofol and midazolam in mice, whereas manipulations of ambient GABA concentrations minimally alter cellular and behavioral responses to sevoflurane.
最近的研究表明，突触外 GABA(A) 受体（产生紧张性电导）是全身麻醉的重要靶点。我们检验了以下假说：改变环境 GABA 浓度（紧张性电导）的操作会影响七氟醚、丙泊酚和咪达唑仑的催眠（以翻正反射丧失表示，LORR）和固定（以尾巴夹回缩反射丧失表示，LTWR）作用。研究了两种操作：1）基因敲除谷氨酸脱羧酶 65 基因（GAD65-/-），据称该操作降低了环境 GABA 浓度；2）使用 GABA 转运体抑制剂（NO-711）进行 GABA 摄取的药理学操作。使用行为和电生理测定法研究了这些操作对麻醉剂的细胞和行为反应的影响。HPLC 显示 GAD65-/- 小鼠的大脑（WT 的 76.7%）和脊髓（WT 的 68.5%）中 GABA 水平降低。GAD65-/- 小鼠的丙泊酚和咪达唑仑引起的 LORR 和 LTWR 持续时间显著缩短，但七氟醚则不然。NO-711（3 mg/kg，ip）增强了丙泊酚和咪达唑仑引起的 LORR 和 LTWR 的持续时间，但对七氟醚则不然。膜片钳记录显示，七氟醚（0.23 mM）轻微增强了额皮质神经元的紧张性 GABA 电流幅度；然而，这些作用不够强，无法改变皮质神经元的放电特性。这些结果表明，环境 GABA 浓度是丙泊酚和咪达唑仑在小鼠中产生催眠和固定作用的重要决定因素，而环境 GABA 浓度的操作对七氟醚的细胞和行为反应的影响很小。
