Depolarization block of inhibitory neurons impacts neuronal function in epileptic encephalopathy

联系PD/PI：Wengert、Eric Ryan。 项目摘要 SCN8A癫痫性脑病是由SCN8A突变引起的严重婴儿癫痫综合征。 编码电压门控钠通道亚型NaV1.6的基因。NaV1.6不仅在兴奋性 神经元，其中它关键地参与动作电位（AP）的产生和传播，但它也是 在抑制性中间神经元中表达。虽然它们占皮质神经元的少数（~15%），但抑制性神经元的数量仍然很小。 新皮层中的中间神经元通过各种前馈，反馈， 和侧抑制电路基序。先前的研究表明NaV1.6功能障碍与异常兴奋性有关 在兴奋性神经元中主要由持续和复苏的钠电流驱动。但是有 没有研究检测突变体NaV1.6表达对抑制性中间神经元生理学的影响， 这些中间神经元随后对SCN 8A脑病中的行为癫痫发作的贡献。这项建议 试图检验抑制性中间神经元兴奋性在Scn8aD/+小鼠模型中降低的假设， SCN 8A脑病，导致整体网络兴奋性增加。我的初步数据显示 生长抑素阳性抑制性中间神经元（SST）在高放电频率下具有降低的内在兴奋性 由于进入去极化阻滞，并具有异常大的持续钠电流。在目标1中，我将 记录WT和Scn8aD/+，并充分表征电压门控钠电流、内在兴奋性，以及 两个主要中间神经元亚群的突触生理学改变：小清蛋白（PV）-和 生长抑素（SST）阳性抑制性中间神经元。这一目标将阐明功能获得的影响 SCN 8A突变对中间神经元功能和网络兴奋性的影响在目标2中，我将检验以下假设： 使用Cre依赖性shRNA在抑制性中间神经元群体中特异性地基因敲低SCN8A 将挽救中间神经元兴奋性的降低，使异常钠通道生理学正常化， 对Scn8aD/+小鼠的癫痫发作频率和严重程度有影响。总体而言，实现这些目标将 解决了该领域的一个重要问题，即中间神经元如何导致SCN8A脑病， 有望产生新的机制通知的方法，以更好地治疗SCN 8A脑病。

Contact PD/PI: Wengert, Eric Ryan. PROJECT SUMMARY SCN8A epileptic encephalopathy is a severe infantile epilepsy syndrome caused by mutations in the SCN8A gene encoding voltage-gated sodium channel isoform NaV1.6. NaV1.6 is not only expressed in excitatory neurons, where it is critically involved in action potential (AP) generation and propagation, but it is also expressed in inhibitory interneurons. Although they make up the minority (~15%) of cortical neurons, inhibitory interneurons in the neocortex powerfully sculpt network dynamics through various feed-forward, feed-back, and lateral inhibition circuit motifs. Previous work has implicated NaV1.6 dysfunction with abnormal excitability in excitatory neurons driven primarily by persistent and resurgent sodium currents. However, there have been no studies examining the effect of mutant NaV1.6 expression on inhibitory interneuron physiology and the subsequent contribution of these interneurons to behavioral seizures in SCN8A encephalopathy. This proposal seeks to test the hypothesis that inhibitory interneuron excitability is reduced in the Scn8aD/+ mouse model of SCN8A encephalopathy, leading to an increase in overall network excitability. My preliminary data suggest that somatostatin-positive inhibitory interneurons (SST) have reduced intrinsic excitability at high-firing frequencies due to entry into depolarization block, and have aberrantly large persistent sodium currents. In aim 1, I will record WT and Scn8aD/+ and fully characterize the voltage-gated sodium currents, intrinsic excitability, and alterations in synaptic physiology of the two major interneuron subpopulations: parvalbumin (PV) - and somatostatin (SST) -positive inhibitory interneurons. This aim will clarify the impact of a gain-of-function SCN8A mutation on interneuron function and network excitability. In aim 2, I will test the hypothesis that genetic knock-down of SCN8A specifically in inhibitory interneuron populations using a Cre-dependent shRNA will rescue the reduction in interneuron excitability, normalize the aberrant sodium channel physiology and have an impact on seizure frequency and severity in Scn8aD/+ mice. Overall, completion of these aims will resolve an important question in the field regarding how interneurons contribute to SCN8A encephalopathy and hopefully generate novel mechanistically-informed approaches to better treat SCN8A encephalopathy.