Epilepsy: Ion Channels As Antiepileptic Targets

本项目的目的是基于抗癫痫药物与神经元离子通道系统的相互作用，探索合理开发抗癫痫药物的新策略。应用细胞电生理记录技术，研究了神经递质门控和电压激活离子通道在脑片、培养神经元和异种细胞中对离子通道亚单位基因的药物调节作用。相关研究在动物模型中进行。最近的研究主要集中在海藻酸型谷氨酸受体上。我们已经证明，刺激外囊刺激杏仁核基底外侧神经元所引起的兴奋性突触反应的一个组成部分是由含有GluR5亚单位的海人酸受体介导的，我们已经证明这些受体诱导了一种新的突触可塑性，可以介导杏仁核某些类型的癫痫发生。在杏仁核基底外侧主神经元的脑片记录中，我们证明了广泛使用的抗癫痫药物托吡酯选择性和有效地抑制GluR5海人酸受体介导的突触反应。托吡酯拮抗红藻氨酸受体的能力很耐人寻味，因为没有其他临床使用的抗癫痫药物以治疗浓度针对这些受体。为了确定脑片记录中托吡酯对GluR5海人酸受体的抑制作用是否与体内药物的抗惊厥作用有关，我们在小鼠体内测定了托吡酯对静脉注射各种离子型谷氨酸受体激动剂所致癫痫的保护作用。托吡酯(25-100 mg/kg，ip)GluR5海人酸受体选择性激动剂ATPA引起的阵挛发作阈值呈剂量依赖性升高。托吡酯对AMPA和海人藻酸受体的混合激动剂海人酸诱导的阵挛发作的保护作用较差。托吡酯不影响AMPA或NMDA诱导的阵挛发作。相比之下，托吡酯提高了这些不同谷氨酸受体激动剂引起的强直惊厥的阈值。与托吡酯不同，卡马西平提高了AMPA诱导的阵挛发作的阈值，但不能提高ATPA诱导的阵挛发作的阈值。我们的结果与托吡酯对阵挛发作活动的影响可能是由于功能阻断GluR5海人酸受体的可能性是一致的。对强直性癫痫发作的保护作用可能通过药物的其他作用来实现。结合我们的体外细胞电生理结果，目前的观察有力地支持了托吡酯的独特作用机制，其中涉及GluR5海人酸受体。总体而言，我们的研究表明，GluR5海氨酸受体是抗癫痫药物开发的一个有前途的新靶点。

The objective of this project is to explore new strategies for the rational development of antiepileptic drugs based upon their interaction with neuronal ion channel systems. Cellular electrophysiological recording techniques are used to study drug modulation of neurotransmitter-gated and voltage-activated ion channels in brain slices, cultured neurons and heterologous cells transfected with cloned ion channel subunit genes. Correlative studies are carried out in animal models. Recent studies have focused on kainate-type glutamate receptors. We have demonstrated that a component of the excitatory synaptic response evoked in basolateral amygdala neurons by external capsule stimulation is mediated by kainate receptors containing the GluR5 subunit and we have shown that these receptors elicit a novel form of synaptic plasticity that could mediate some types of epileptogenesis in the amygdala. In brain slice recordings from basolateral amygdala principal neurons, we demonstrated that topiramate, a widely used antiepileptic agent, selectively and potently inhibits GluR5 kainate receptor mediated synaptic responses. The ability of topiramate to antagonize kainate receptors is intriguing inasmuch as no other clinically used antiseizure medication targets these receptors at therapeutic concentrations. To determine if the inhibitory action of topiramate on GluR5 kainate receptors as shown in brain slice recordings is relevant to the anticonvulsant effects of the drug in vivo, we determined the protective activity of topiramate against seizures induced by intravenous infusion of various ionotropic glutamate receptor agonists in mice. Topiramate (25-100 mg/kg, i.p.) produced a dose-dependent elevation in the threshold for clonic seizures induced by infusion of ATPA, a selective agonist of GluR5 kainate receptors. Topiramate was less effective in protecting against clonic seizures induced by kainate, a mixed agonist of AMPA and kainate receptors. Topiramate did not affect clonic seizures induced by AMPA or NMDA. In contrast, the thresholds for tonic seizures induced by higher doses of these various glutamate receptor agonists were all elevated by topiramate. Unlike topiramate, carbamazepine elevated the threshold for AMPA- but not ATPA-induced clonic seizures. Our results are consistent with the possibility that the effects of topiramate on clonic seizure activity are due to functional blockade of GluR5 kainate receptors. Protection from tonic seizures may be mediated by other actions of the drug. Together with our in vitro cellular electrophysiological results, the present observations strongly support a unique mechanism of action of topiramate, which involves GluR5 kainate receptors. Overall, our studies indicate that GluR5 kainate receptors represent a promising novel target for antiepileptic drug development.