Research Division for Clinical Pharmacology, Medical Corporation, Jyuryokai, Kumamoto Kinoh Hospital, Kumamoto, Japan (M.W., N.A.); Research Division for Life Science, Kumamoto Health Science University, Kumamoto, Japan (M.W., N.A.); Research Division of Neurophysiology, Kitamoto Hospital, Koshigaya, Japan (N.K., N.A); and Kogure Medical Clinic, Chouseikai Medical Corporation, Fukaya City, Saitama, Japan (K.K.).
J Pharmacol Exp Ther. 2014 Feb;348(2):246-59. doi: 10.1124/jpet.113.208751. Epub 2013 Nov 20.
Levetiracetam (LEV) is an antiepileptic drug with a unique but as yet not fully resolved mechanism of action. Therefore, by use of a simplified rat-isolated nerve-bouton preparation, we have investigated how LEV modulates glutamatergic transmission from mossy fiber terminals to hippocampal CA3 neurons. Action potential-evoked excitatory postsynaptic currents (eEPSCs) were recorded using a conventional whole-cell patch-clamp recording configuration in voltage-clamp mode. The antiepileptic drug phenytoin decreased glutamatergic eEPSCs in a concentration-dependent fashion by inhibiting voltage-dependent Na⁺ and Ca²⁺ channel currents. In contrast, LEV had no effect on eEPSCs or voltage-dependent Na⁺ or Ca²⁺ channel currents. Activation of presynaptic GABA type A (GABA(A)) receptors by muscimol induced presynaptic inhibition of eEPSCs, resulting from depolarization block. Low concentrations of Zn²⁺, which had no effect on eEPSCs, voltage-dependent Na⁺ or Ca²⁺ channel currents, or glutamate receptor-mediated whole cell currents, reduced the muscimol-induced presynaptic inhibition. LEV applied in the continuous presence of 1 µM muscimol and 1 µM Zn²⁺ reversed this Zn²⁺ modulation on eEPSCs. The antagonizing effect of LEV on Zn²⁺-induced presynaptic GABA(A) receptor inhibition was also observed with the Zn²⁺ chelators Ca-EDTA and RhodZin-3. Our results clearly show that LEV removes the Zn²⁺-induced suppression of GABA(A)-mediated presynaptic inhibition, resulting in a presynaptic decrease in glutamate-mediated excitatory transmission. Our results provide a novel mechanism by which LEV may inhibit neuronal activity.
左乙拉西坦（LEV）是一种抗癫痫药物，其作用机制独特但尚未完全阐明。因此，我们利用简化的大鼠离体神经末梢制备方法，研究了 LEV 如何调节从苔藓纤维末梢到海马 CA3 神经元的谷氨酸能传递。使用传统的全细胞膜片钳记录配置在电压钳模式下记录动作电位诱发的兴奋性突触后电流（eEPSC）。抗癫痫药物苯妥英以浓度依赖的方式减少谷氨酸能 eEPSC，通过抑制电压依赖性 Na⁺ 和 Ca²⁺ 通道电流。相比之下，LEV 对 eEPSC 或电压依赖性 Na⁺ 或 Ca²⁺ 通道电流没有影响。肉毒碱激活突触前 GABA 型 A（GABA(A)）受体诱导 eEPSC 的突触前抑制，这是由于去极化阻断。低浓度的 Zn²⁺ 对 eEPSC、电压依赖性 Na⁺ 或 Ca²⁺ 通道电流或谷氨酸受体介导的全细胞电流没有影响，但降低了肉毒碱诱导的突触前抑制。在 1 µM 肉毒碱和 1 µM Zn²⁺ 的持续存在下应用 LEV 逆转了这种 Zn²⁺ 对 eEPSC 的调制。LEV 对 Zn²⁺诱导的 GABA(A) 受体抑制的拮抗作用也在 Zn²⁺螯合剂 Ca-EDTA 和 RhodZin-3 中观察到。我们的结果清楚地表明，LEV 去除了 Zn²⁺ 诱导的 GABA(A) 介导的突触前抑制，导致谷氨酸能介导的兴奋性传递突触前减少。我们的结果提供了 LEV 抑制神经元活性的新机制。
