Involvement of GABA-mediated inhibitory neuronal processes in seizure activity in rat hippocampal slices

本研究的主要目的是阐明γ-氨基丁酸(GABA)介导的抑制癫痫发作活动的机制。我们使用了一种体外癫痫模型，在该模型中，重复向大鼠海马片CA1区辐射层施加高频刺激(1秒，100赫兹)，可发育地诱导出发作性活动样节律性后放电(ADS)。我们已经报道了GABA_A受体拮抗剂荷包牡丹碱抑制AD的产生，提示GABA_A介导的抑制机制的激活可能是癫痫发作所必需的。为了验证该模型是否可以作为颞叶癫痫的体外癫痫模型，我们观察了抗癫痫药物对该模型的影响。苯妥英钠和卡马西平在临床上对与颞叶癫痫相关的癫痫发作是有效的，它们在临床相关浓度下抑制了AD的产生。乙琥胺在临床上对失神发作有效，但对颞叶癫痫无效，但在临床相关浓度下对AD的产生没有影响。这些发现表明，我们的实验模型可以成为颞叶癫痫的实验性癫痫模型。此外，我们还记录了CA1区锥体神经元的细胞内电位。重复高频刺激CA1层辐射后，单次刺激诱导的GABA_A介导的抑制性突触后电位的幅度随着AD产生的增强而增加。因此，我们得出结论，激活GABA_A介导的抑制过程是诱导颞叶癫痫发作所必需的，并对癫痫发生的简单去抑制假说提出了修正。

The main purpose of our study is to clarify the involvement of γ-aminobutric acid (GABA)-mediated inhibitory mechanism in generation of seizure activity of epilepsy. We used an in vitro seizure model, in which ictal activity-like rhythmic afterdischarges (Ads) are developmentally induced following repetitive application of high-frequency stimuli (1 sec, 100 Hz) to the stratum radiatum of the CA1 region in rat hippocampal slices. We have previously reported that the GABA_A receptor antagonist bicuculline suppresses AD generation, suggesting that activation of GABA_A-mediated inhibitory mechanism may be necessary for ictal activity.In order to test whether this model can serve as an in vitro seizure model for temporal lobe epilepsy, we examined the effects of antiepileptic drugs on this model. Bath application of phenytoin and carbamazepine, which are clinically effective against seizures associated with temporal lobe epilepsy, suppressed AD generation at their clinically relevant concentrations. On the other hand, ethosuximide which is clinically effective against absence seizure but not against temporal lobe epilepsy had no effect on AD generation at its clinically relevant concentration. These findings suggest that our experimental model can become an experimental seizure model for temporal lobe epilepsy. In addition, we recorded intracellular potentials of pyramidal neurons in the CA1 region. Following repetitive high-frequency stimulation to the CA1 stratum radiatum, the amplitude of GABA_A-mediated inhibitory postsynaptic potentials induced by single stimuli increased in conjunction with enhancement in AD generation. Therefore we conclude that activation of GABA_A-mediated inhibitory processes is necessary for seizure induction of temporal lobe epilepsy, and propose a modification to the simple disinhibition hypothesis for epileptogenesis.