Epilepsy: Ion Channels As Antiepileptic Targets

本项目旨在探索基于抗癫痫药物与神经元离子通道系统相互作用的合理开发新策略。利用细胞电生理记录技术研究了药物对脑切片、培养神经元和转染克隆离子通道亚基基因的异源细胞中神经递质门控和电压激活离子通道的调节作用。在动物模型上进行了相关研究。最近的研究主要集中在盐酸盐型谷氨酸受体上。我们已经证明，外部胶囊刺激在杏仁核基底外侧神经元中引起的兴奋性突触反应的一个组成部分是由含有GluR5亚基的海碱盐受体介导的，我们已经证明，这些受体引发了一种新的突触可塑性形式，可以介导杏仁核中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，我们证明了托吡酯，一种广泛使用的抗癫痫药物，选择性地和有效地抑制GluR5盐酸盐受体介导的突触反应。托吡酯拮抗海因酸盐受体的能力令人感兴趣，因为没有其他临床使用的抗癫痫药物以治疗浓度靶向这些受体。为了确定托吡酯对GluR5盐酸盐受体的抑制作用是否与体内药物的抗惊厥作用有关，我们测定了托吡酯对静脉输注各种嗜离子性谷氨酸受体激动剂引起的小鼠癫痫发作的保护活性。托吡酯（25-100 mg/kg, i.p）在输注ATPA （GluR5盐酸盐受体的选择性激动剂）诱导的慢性癫痫发作阈值中产生剂量依赖性升高。托吡酯对由盐酸盐（AMPA和盐酸盐受体的混合激动剂）引起的慢性癫痫发作的保护效果较差。托吡酯对AMPA或NMDA诱导的慢性癫痫发作无影响。相比之下，高剂量的谷氨酸受体激动剂引起的强直性癫痫的阈值都被托吡酯提高了。与托吡酯不同，卡马西平提高了AMPA诱发的慢性癫痫发作的阈值，而不是atpa诱发的。我们的结果与托吡酯对慢性癫痫活动的影响是由于GluR5盐酸盐受体的功能阻断的可能性是一致的。对强直性癫痫发作的保护可能由药物的其他作用介导。结合我们的体外细胞电生理结果，目前的观察结果强烈支持托吡酯的独特作用机制，该机制涉及GluR5盐酸盐受体。总之，我们的研究表明GluR5盐酸盐受体是抗癫痫药物开发的一个有希望的新靶点。

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.