Hanaya R, Sasa M, Ujihara H, Ishihara K, Serikawa T, Iida K, Akimitsu T, Arita K, Kurisu K
Department of Neurosurgery, Hiroshima University School of Medicine, Hiroshima, Japan.
Brain Res. 1998 Apr 13;789(2):274-82. doi: 10.1016/s0006-8993(98)00116-4.
Topiramate, a novel antiepileptic drug, inhibits the seizures of spontaneously epileptic rat (SER), a double mutant (zi/zi, tm/tm) which exhibits both tonic convulsion and absence-like seizures from the age of 8-weeks. Hippocampal CA3 pyramidal neurons in SER show a long-lasting depolarization shift with accompanying repetitive firing when a single electrostimulation is delivered to the mossy fibers in vitro. The effects of topiramate on the excitability of CA3 pyramidal neurons in SER were examined to elucidate the mechanism underlying the antiepileptic action. Intracellular recordings were performed in 23 hippocampal slice preparations of 16 SER aged 8-17 weeks. Topiramate (10-100 microM) dose-dependently inhibited the depolarizing shifts with repetitive firing induced by mossy fiber stimulation without affecting the first spike and resting membrane potentials in hippocampal CA3 neurons of SER. Higher dose of topiramate (100 microM) sometimes inhibited the first spike, and decreased excitatory postsynaptic potentials in the SER CA3 neurons. However, topiramate up to 100 microM did not affect the single action potential elicited by the stimulation in the hippocampal CA3 neurons of age-matched Wistar rat devoid of the seizure. Application of topiramate (100 microM) did not significantly affect the firing induced by depolarizing pulse applied in the CA3 neurons of the SER. In addition, topiramate (100 microM) had no effects on the Ca2+ spike induced by intracellularly applied depolarizing pulse in the presence of tetrodotoxin and tetraethylammonium. In contrast, a dose-dependent inhibition of depolarization and repetitive firing induced by bath application of glutamate in CA3 pyramidal neurons was obtained with topiramate (10-100 microM). Furthermore, topiramate (100 microM) decreased the number of miniature postsynaptic potential of CA3 pyramidal neurons of SER. In patch clamp whole cell recording using acutely dissociated hippocampal CA3 neurons from SER aged 8-weeks and age-matched normal Wistar rats, there were no remarkable effects on voltage dependent Ca2+ current with topiramate up to 300 microM in either animal; the current was completely blocked by Cd2+ at a concentration of 1 mM. These findings suggest that topiramate inhibits release of glutamate from the nerve terminals and/or abnormal firing of the CA3 pyramidal neurons of SER by mainly blocking glutamate receptors in the neurons.
托吡酯是一种新型抗癫痫药物，可抑制自发性癫痫大鼠（SER）的癫痫发作。SER是一种双突变体（zi/zi，tm/tm），从8周龄起就表现出强直性惊厥和失神样发作。在体外，当对苔藓纤维进行单次电刺激时，SER海马CA3锥体神经元会出现持续的去极化偏移并伴有重复放电。研究了托吡酯对SER中CA3锥体神经元兴奋性的影响，以阐明其抗癫痫作用的潜在机制。对16只8 - 17周龄SER的23个海马切片标本进行了细胞内记录。托吡酯（10 - 100微摩尔）剂量依赖性地抑制了苔藓纤维刺激诱导的伴有重复放电的去极化偏移，而不影响SER海马CA3神经元的第一个动作电位和静息膜电位。更高剂量的托吡酯（100微摩尔）有时会抑制第一个动作电位，并降低SER CA3神经元中的兴奋性突触后电位。然而，高达100微摩尔的托吡酯对年龄匹配的无癫痫发作的Wistar大鼠海马CA3神经元中刺激引发的单个动作电位没有影响。应用托吡酯（100微摩尔）对SER的CA3神经元中去极化脉冲诱导的放电没有显著影响。此外，在存在河豚毒素和四乙铵的情况下，托吡酯（100微摩尔）对细胞内施加去极化脉冲诱导的Ca2+ 尖峰没有影响。相反，托吡酯（10 - 100微摩尔）剂量依赖性地抑制了CA3锥体神经元中通过浴应用谷氨酸诱导的去极化和重复放电。此外，托吡酯（100微摩尔）减少了SER的CA3锥体神经元的微小突触后电位的数量。在使用8周龄SER和年龄匹配的正常Wistar大鼠急性分离的海马CA3神经元进行的膜片钳全细胞记录中，高达300微摩尔的托吡酯对两种动物的电压依赖性Ca2+ 电流均无显著影响；在浓度为1毫摩尔时，该电流被Cd2+ 完全阻断。这些发现表明，托吡酯主要通过阻断神经元中的谷氨酸受体来抑制SER神经末梢谷氨酸的释放和/或CA3锥体神经元的异常放电。
