Experimental Anesthesiology Section, Department of Anesthesiology and Intensive Care Medicine, Eberhard-Karls-University, Waldhörnlestrasse 22, 72072 Tübingen, Germany.
Int J Mol Sci. 2020 Oct 7;21(19):7399. doi: 10.3390/ijms21197399.
The neurosteroid allopregnanolone (ALLO) causes unconsciousness by allosteric modulation of γ-aminobutyric acid type A (GABA) receptors, but its actions on the spinal motor networks are unknown. We are therefore testing the hypothesis that ALLO attenuates the action potential firing of spinal interneurons and motoneurons predominantly via enhancing tonic, but not synaptic GABAergic inhibition. We used video microscopy to assess motoneuron-evoked muscle activity in organotypic slice cultures prepared from the spinal cord and muscle tissue. Furthermore, we monitored GABA receptor-mediated currents by performing whole-cell voltage-clamp recordings. We found that ALLO (100 nM) reduced the action potential firing of spinal interneurons by 27% and that of α-motoneurons by 33%. The inhibitory effects of the combination of propofol (1 µM) and ALLO on motoneuron-induced muscle contractions were additive. Moreover, ALLO evoked a tonic, GABA receptor-mediated current (amplitude: 41 pA), without increasing phasic GABAergic transmission. Since we previously showed that at a clinically relevant concentration of 1 µM propofol enhanced phasic, but not tonic GABAergic inhibition, we conclude that ALLO and propofol target distinct subpopulations of GABA receptors. These findings provide first evidence that the combined application of ALLO and propofol may help to reduce intraoperative movements and undesired side effects that are frequently observed under total intravenous anesthesia.
神经甾体化合物别孕烯醇酮（ALLO）通过对γ-氨基丁酸 A 型（GABA）受体的变构调节导致意识丧失，但它对脊髓运动网络的作用尚不清楚。因此，我们正在检验以下假说，即 ALLO 通过增强紧张性而非突触性 GABA 抑制作用，主要减弱脊髓中间神经元和运动神经元的动作电位放电。我们使用视频显微镜评估源自脊髓和肌肉组织的器官型切片培养物中运动神经元诱发的肌肉活动。此外，我们通过进行全细胞膜片钳记录来监测 GABA 受体介导的电流。我们发现，ALLO（100 nM）使脊髓中间神经元的动作电位放电减少 27%，使 α-运动神经元的动作电位放电减少 33%。丙泊酚（1 µM）和 ALLO 联合使用对运动神经元诱发的肌肉收缩的抑制作用具有相加作用。此外，ALLO 诱发紧张性、GABA 受体介导的电流（幅度：41 pA），而不增加相性 GABA 能传递。由于我们之前表明，在 1 µM 的临床相关丙泊酚浓度下增强相性而非紧张性 GABA 抑制作用，我们得出结论，ALLO 和丙泊酚针对 GABA 受体的不同亚群。这些发现首次提供证据表明，ALLO 和丙泊酚的联合应用可能有助于减少全静脉麻醉下经常观察到的术中运动和不良副作用。
