Bieber Matthias, Schwerin Stefan, Kreuzer Matthias, Klug Claudia, Henzler Marie, Schneider Gerhard, Haseneder Rainer, Kratzer Stephan
Department of Anesthesiology and Intensive Care Medicine, School of Medicine, Technical University Munich, Munich, Germany.
Front Syst Neurosci. 2022 Dec 22;16:1044536. doi: 10.3389/fnsys.2022.1044536. eCollection 2022.
Despite ongoing research efforts and routine clinical use, the neuronal mechanisms underlying the anesthesia-induced loss of consciousness are still under debate. Unlike most anesthetics, ketamine increases thalamic and cortical activity. Ketamine is considered to act a NMDA-receptor antagonism-mediated reduction of inhibition, i.e., disinhibition. Intact interactions between the thalamus and cortex constitute a prerequisite for the maintenance of consciousness and are thus a promising target for anesthetics to induce loss of consciousness. In this study, we aim to characterize the influence of s-ketamine on the thalamocortical network using acute brain-slice preparation. We performed whole-cell patch-clamp recordings from pyramidal neurons in cortical lamina IV and thalamocortical relay neurons in acute brain slices from CB57BL/6N mice. Excitatory postsynaptic potentials (EPSPs) were obtained electrical stimulation of the cortex with a bipolar electrode that was positioned to lamina II/III (electrically induced EPSPs, eEPSPs) or optogenetic activation of thalamocortical relay neurons (optogenetically induced EPSPs, oEPSPs). Intrinsic neuronal properties (like resting membrane potential, membrane threshold for action potential generation, input resistance, and tonic action potential frequency), as well as NMDA-receptor-dependent and independent spontaneous GABA-receptor-mediated inhibitory postsynaptic currents (sIPSCs) were evaluated. Wilcoxon signed-rank test (level of significance < 0.05) served as a statistical test and Cohen's U3_1 was used to determine the actual effect size. Within 20 min, s-ketamine (5 μM) significantly increased both intracortical eEPSPs as well as thalamocortical oEPSPs. NMDA-receptor-mediated intracortical eEPSPs were significantly reduced. Intrinsic neuronal properties of cortical pyramidal neurons from lamina IV and thalamocortical relay neurons in the ventrobasal thalamic complex were not substantially affected. Neither a significant effect on NMDA-receptor-dependent GABA sIPSCs (thought to underly a disinhibitory effect) nor a reduction of NMDA-receptor independent GABA sIPSCs was observed. Both thalamocortical and intracortical AMPA-receptor-mediated EPSPs were significantly increased.In conclusion, our findings show no evidence for a NMDA-receptor antagonism-based disinhibition, but rather suggest an enhanced thalamocortical and intracortical synaptic transmission, which appears to be driven increased AMPA-receptor-mediated transmission.
尽管一直在进行研究并在临床中常规使用，但麻醉诱导意识丧失背后的神经元机制仍存在争议。与大多数麻醉药不同，氯胺酮会增加丘脑和皮质的活动。氯胺酮被认为是通过NMDA受体拮抗介导的抑制作用减弱，即去抑制作用来发挥作用的。丘脑和皮质之间完整的相互作用是维持意识的先决条件，因此是麻醉药诱导意识丧失的一个有前景的靶点。在本研究中，我们旨在使用急性脑片制备来表征S-氯胺酮对丘脑皮质网络的影响。我们对C57BL/6N小鼠急性脑片中皮质第IV层的锥体神经元和丘脑皮质中继神经元进行了全细胞膜片钳记录。通过将双极电极置于第II/III层对皮质进行电刺激（电诱导兴奋性突触后电位，eEPSP）或对丘脑皮质中继神经元进行光遗传学激活（光遗传学诱导兴奋性突触后电位，oEPSP）来获得兴奋性突触后电位（EPSP）。评估了神经元的内在特性（如静息膜电位、动作电位产生的膜阈值、输入电阻和强直动作电位频率），以及NMDA受体依赖性和非依赖性的自发GABA受体介导的抑制性突触后电流（sIPSC）。采用Wilcoxon符号秩检验（显著性水平<0.05）作为统计检验，并使用Cohen's U3_1来确定实际效应大小。在20分钟内，S-氯胺酮（5μM）显著增加了皮质内eEPSP以及丘脑皮质oEPSP。NMDA受体介导的皮质内eEPSP显著降低。来自第IV层的皮质锥体神经元和腹侧基底丘脑复合体中的丘脑皮质中继神经元的内在神经元特性没有受到实质性影响。未观察到对NMDA受体依赖性GABA sIPSC（被认为是去抑制作用的基础）有显著影响，也未观察到NMDA受体非依赖性GABA sIPSC减少。丘脑皮质和皮质内AMPA受体介导的EPSP均显著增加。总之，我们的研究结果没有证据支持基于NMDA受体拮抗的去抑制作用，而是表明丘脑皮质和皮质内突触传递增强，这似乎是由AMPA受体介导的传递增加所驱动的。
