Department of Anesthesiology and Intensive Care Medicine, Medical School, Klinikum Rechts der Isar, Technical University Munich, Munich, Germany.
Department of Anesthesiology and Intensive Care Medicine, Experimental Anesthesiology Section, Eberhard Karls University, Tübingen, Germany.
Anesthesiology. 2022 Jun 1;136(6):954-969. doi: 10.1097/ALN.0000000000004202.
Midazolam amplifies synaptic inhibition via different γ-aminobutyric acid type A (GABAA) receptor subtypes defined by the presence of α1-, α2-, α3-, or α5-subunits in the channel complex. Midazolam blocks long-term potentiation and produces postoperative amnesia. The aims of this study were to identify the GABAA receptor subtypes targeted by midazolam responsible for affecting CA1 long-term potentiation and synaptic inhibition in neocortical neurons.
The effects of midazolam on hippocampal CA1 long-term potentiation were studied in acutely prepared brain slices of male and female mice. Positive allosteric modulation on GABAA receptor-mediated miniature inhibitory postsynaptic currents was investigated in organotypic slice cultures of the mouse neocortex. In both experiments, wild-type mice and GABAA receptor knock-in mouse lines were compared in which α1-, α5-, α1/2/3-, α1/3/5- and α2/3/5-GABAA receptor subtypes had been rendered benzodiazepine-insensitive.
Midazolam (10 nM) completely blocked long-term potentiation (mean ± SD, midazolam, 98 ± 11%, n = 14/8 slices/mice vs. control 156 ± 19%, n = 20/12; P < 0.001). Experiments in slices of α1-, α5-, α1/2/3-, α1/3/5-, and α2/3/5-knock-in mice revealed a dominant role for the α1-GABAA receptor subtype in the long-term potentiation suppressing effect. In slices from wild-type mice, midazolam increased (mean ± SD) charge transfer of miniature synaptic events concentration-dependently (50 nM: 172 ± 71% [n = 10/6] vs. 500 nM: 236 ± 54% [n = 6/6]; P = 0.041). In α2/3/5-knock-in mice, charge transfer of miniature synaptic events did not further enhance when applying 500 nM midazolam (50 nM: 171 ± 62% [n = 8/6] vs. 500 nM: 175 ± 62% [n = 6/6]; P = 0.454), indicating two different binding affinities for midazolam to α2/3/5- and α1-subunits.
These results demonstrate a predominant role of α1-GABAA receptors in the actions of midazolam at low nanomolar concentrations. At higher concentrations, midazolam also enhances other GABAA receptor subtypes. α1-GABAA receptors may already contribute at sedative doses to the phenomenon of postoperative amnesia that has been reported after midazolam administration.
咪达唑仑通过不同的γ-氨基丁酸 A 型（GABAA）受体亚型放大突触抑制，这些受体亚型在通道复合物中由α1-、α2-、α3-或α5-亚基定义。咪达唑仑阻断长时程增强并产生术后遗忘。本研究的目的是确定咪达唑仑作用的 GABAA 受体亚型，这些受体亚型负责影响 CA1 长时程增强和新皮层神经元的突触抑制。
在雄性和雌性小鼠急性脑切片中研究了咪达唑仑对海马 CA1 长时程增强的影响。在小鼠新皮层器官型切片培养物中研究了咪达唑仑对 GABAA 受体介导的微小抑制性突触后电流的正变构调制。在这两个实验中，比较了野生型小鼠和 GABAA 受体基因敲入小鼠系，其中α1-、α5-、α1/2/3-、α1/3/5-和α2/3/5-GABAA 受体亚型已被苯二氮䓬类药物失敏。
咪达唑仑（10 nM）完全阻断长时程增强（平均值±标准差，咪达唑仑，98±11%，n=14/8 片/鼠 vs. 对照组 156±19%，n=20/12；P<0.001）。在α1-、α5-、α1/2/3-、α1/3/5-和α2/3/5-基因敲入小鼠的切片实验中，α1-GABAA 受体亚型在长时程增强抑制作用中起主导作用。在野生型小鼠的切片中，咪达唑仑浓度依赖性地增加（平均值±标准差）微小突触事件的电荷传递（50 nM：172±71%[n=10/6] vs. 500 nM：236±54%[n=6/6]；P=0.041）。在α2/3/5-基因敲入小鼠中，当应用 500 nM 咪达唑仑时，微小突触事件的电荷传递没有进一步增强（50 nM：171±62%[n=8/6] vs. 500 nM：175±62%[n=6/6]；P=0.454），表明咪达唑仑与α2/3/5-和α1-亚基的结合亲和力不同。
这些结果表明，α1-GABAA 受体在咪达唑仑在纳摩尔浓度下的作用中起主要作用。在较高浓度下，咪达唑仑还增强了其他 GABAA 受体亚型。α1-GABAA 受体可能已经在镇静剂量下对咪达唑仑给药后报告的术后遗忘现象做出贡献。
