Seizure generation and network excitability in Arx related Infantile Spasms

描述(申请人提供)：对婴幼儿癫痫发作和智力残疾的发生机制有广泛的认识空白。 痉挛综合征(ISS)是癫痫的早期脑病之一。婴儿痉挛是一种影响1：2000活产的恶性疾病，导致大多数儿童出现药物抵抗性癫痫发作和严重的发育障碍。婴儿痉挛综合征包括癫痫痉挛、低位节律和发育停滞的脑电模式。这种情况给家庭带来了无数的困难，给孩子造成了终身残疾。目前，还没有真正针对ISS或任何早期癫痫脑病的治疗方法。因此，迫切需要对这些情况的机制进行进一步研究。我们建议阐明一种婴儿痉挛模型的机制。我们的模型是在Arx基因(Arx(GCG)7/Y)中带有聚丙氨酸扩展突变的转基因小鼠，是ARX相关ISS儿童中最常见的突变，并概括了临床观察到的大部分癫痫发作和行为表型。这是唯一一个模仿已知的人类侮辱的模型。这些研究验证了我们的假设，即Arx在发育过程中的变化改变了神经元间的发育和功能，导致了过度兴奋的局部网络和随着小鼠发育而变化的癫痫发作。我们的初步数据显示，DG和CA3的过度兴奋性，以及对CA1锥体细胞的抑制消失。为了扩大这些发现并阐明婴儿痉挛的机制，我们提出了三个系列的实验。首先，将使用电压敏感染料(VSD)成像和多电极记录(MEA)对婴儿和年轻成年Arx(GCG)7/Y小鼠在不同年龄确定局部网络功能障碍。随着我们的初步数据证实海马区DG和CA3区的活性增加，我们将尝试通过将GABA激动剂直接应用到CA3区和DG区来局部挽救表型。接下来，我们将通过膜片钳记录锥体细胞和中间神经元，并量化Arx(GCG)7/Y和对照组小鼠之间基线和诱发活动的变化，来确定Aim 1中发现的网络变化背后的机制。最后，我们将通过研究Arx(GCG)7/Y和对照组小鼠的丘脑皮质回路来确定海马区外是否存在局部网络变化。指导拟议实验的基本原理是，通过定义在已定义的ISS模型中产生癫痫发作的机制，可以开发针对这些机制的特定治疗方法。因此，从拟议的研究中获得的知识将成为为这些破坏性疾病设计新疗法的转化性研究的基础。

DESCRIPTION (provided by applicant): There is an extensive gap in the knowledge of the mechanisms involved in generating seizures and intellectual disabilities in children with infantile spasms syndrome (ISS), one of the early epileptic encephalopathies. Infantile spasms, a malignant disorder affecting 1:2000 live births, results in the majority of children developing medication resistant seizures and severe developmental disabilities. Infantile spasms syndrome consists of epileptic spasms, an EEG pattern of hypsarrhythmia and developmental stagnation. This condition results in innumerable hardships to the families and life long disabilities to the child. Currently, there is no treatment truly specific for ISS or any early epileptic encephalopathies. Consequently, there is a pressing need for further research into the mechanisms of these conditions. We are proposing to elucidate the mechanisms of one model of infantile spasms. Our model, a transgenic mouse with a polyalanine expansion mutation in the Arx gene (Arx(GCG)7/Y), is the most common mutation in children with ARX related ISS and recapitulates much of the clinically observed seizure and behavioral phenotype. This is the only model that mimics a known human insult. The studies proposed test our hypothesis that changes in Arx during development alter both interneuron development and function resulting in hyperexcitable local networks and seizures that change as the mouse develops. Our preliminary data demonstrates hyperexcitability in the DG and CA3, and loss of inhibition onto CA1 pyramidal cells. To extend these findings and elucidate the mechanisms of infantile spasms, three series of experiments are proposed. First local network dysfunction will be determined at different ages using voltage sensitive dye (VSD) imaging and multielectrode recordings (MEA) of infantile and young adult Arx(GCG)7/Y mice. As our preliminary data establishes increased activity in the DG and CA3 regions of the hippocampus, we will attempt to locally rescue the phenotype by application of GABA agonists directly into CA3 and the DG. Next, we will determine the mechanisms behind the network changes found in Aim 1 by patch clamp recording both pyramidal cells and interneurons and quantifying the alterations in baseline and evoked activity between the Arx(GCG)7/Y and control mice. Finally, we will determine if there are local network changes outside the hippocampus by studying the thalamocortical circuitry in the Arx(GCG)7/Y and control mice. The rationale guiding the proposed experiments is by defining the mechanisms involved in generating seizures in a defined model of ISS, specific therapies can be developed to target these mechanisms. Hence, the knowledge obtained from the proposed studies will be the foundation for the translational studies that design novel therapeutics for these devastating conditions.