Epilepsy: Ion Channels As Antiepileptic Targets

本项目的目的是探索基于与神经元离子通道系统相互作用的抗癫痫药物的合理开发新策略。细胞电生理记录技术被用来研究药物调制的神经递质门控和电压激活的离子通道在脑切片，培养的神经元和异源细胞转染克隆的离子通道亚基基因。在动物模型中进行了相关研究。最近的研究集中在红藻氨酸型谷氨酸受体。我们已经证明，兴奋性突触反应的一个组成部分引起的基底外侧杏仁核神经元的外囊刺激是由红藻氨酸受体介导的含有GluR 5亚基，我们已经表明，这些受体引起一种新形式的突触可塑性，可以介导某些类型的癫痫发生在杏仁核。在基底外侧杏仁核主神经元的脑切片记录中，我们证明了托吡酯，一种广泛使用的抗癫痫药，选择性地和有效地抑制GluR 5红藻氨酸受体介导的突触反应。托吡酯拮抗红藻氨酸受体的能力是令人感兴趣的，因为没有其他临床使用的抗癫痫药物在治疗浓度下靶向这些受体。为了确定托吡酯对GluR 5红藻氨酸受体的抑制作用是否与药物在体内的抗惊厥作用有关，我们测定了托吡酯对小鼠静脉输注各种离子型谷氨酸受体激动剂诱导的癫痫发作的保护活性。托吡酯（25-100 mg/kg，i. p.）产生了剂量依赖性的升高，由ATPA，GluR 5红藻氨酸受体的选择性激动剂输注诱导的阵挛性癫痫发作的阈值。托吡酯对红藻氨酸（AMPA和红藻氨酸受体的混合激动剂）诱导的阵挛性癫痫发作的保护效果较差。托吡酯不影响AMPA或NMDA诱发的阵挛性发作。与此相反，托吡酯升高了高剂量这些不同谷氨酸受体激动剂诱导的强直性癫痫发作的阈值。与托吡酯不同，卡马西平提高了AMPA诱导的阵挛性癫痫发作的阈值，但对ATPA诱导的阵挛性癫痫发作没有影响。我们的研究结果与托吡酯对阵挛性癫痫发作活动的影响是由于GluR 5红藻氨酸受体的功能性阻断的可能性是一致的。对强直性癫痫发作的保护作用可能由药物的其他作用介导。连同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，其中涉及GluR 5红藻氨酸受体。总体而言，我们的研究表明，GluR 5红藻氨酸受体代表了一个有前途的新的抗癫痫药物开发的目标。

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.