Group I Metabotropic Glutamate Receptors and Epileptogenesis

摘要 创伤性脑损伤(TBI)、中风或癫痫持续状态后癫痫的发展是 这一进程涉及为预防癫痫提供目标的许多机制。一种机制 在癫痫的所有这些原因中，可能重要的是谷氨酸过度释放和激活 代谢性谷氨酸受体(MGluRs)我们还没有开发出预防这种疾病发展的治疗方法。 癫痫，特别是在脑外伤后，我们的建议评估了潜在的预防疗法。的目标是 该计划旨在通过改变mGluR的作用来开发潜在的预防癫痫发生的治疗方法 激活。我们发现选择性激动剂二羟基苯甘氨酸激活I组mGluRs (DHPG)导致自发发生的海马区兴奋性的长期变化 发作间期(发作间期)和发作(发作样)活动。在过去的资助期中，我们展示了 阻断I组mGluRs可以减缓点燃，这是一种癫痫发生的模型。我们的发现创造了新的 研究问题，我们在当前的提案中解决了这些问题。 我们的第一个假设是，激活I组mGluRs优先增加复发 兴奋性突触网络活动与大鼠脑CA3区持续癫痫样活动 海马体。我们的第一组具体目标将解决CA3区突触生理学的变化 在短暂接触DHPG之后。我们将：1)描述自发运动的频率和幅度 DHPG后抑制性突触后电流和兴奋性突触后电流 并将其与对照神经元活动进行比较；2)评估自发发生的EPSCs 在没有突触兴奋的情况下，没有抑制和自发发生的IPSCs；以及3) 确定与DHPG相关的微型IPSC和EPSC频率和幅度的变化 曝光。我们的第二个假设是，由I组mGluRs引起的长期变化是 癫痫发作上调的荷马蛋白1a的产生和I组功能的变化 MGluRs，从而在没有谷氨酸的情况下激活阳离子电流。我们的初步数据显示 荷马1基因敲除(KO)小鼠对DHPG诱导的癫痫样发作具有抵抗力。因此，我们将 确定荷马1KO小鼠是否出现与DHPG暴露相关的膜特性变化和 将确定荷马1KO小鼠与荷马1a的转导是否能重建野生型 表型与DHPG诱导癫痫样活动有关。 我们认为，我们定义的在接触DHPG后发生的变化，模拟了当 高浓度的胞外谷氨酸激活mGluR，它们是治疗的靶点 阻止头部创伤、癫痫持续状态和反复发作后癫痫的发展。这个 我们的实验结果将针对癫痫的新疗法和癫痫的发展，癫痫是一种主要的 经历过脑外伤的退伍军人的发病率。

Summary The development of epilepsy following traumatic brain injury (TBI), stroke, or status epilepticus is a process that involves many mechanisms that provide targets for the prevention of epilepsy. One mechanism that may be important in all of these causes of epilepsy is excessive glutamate release and activation of metabotropic glutamate receptors (mGluRs). We have not yet developed therapies to prevent the development of epilepsy, particularly following TBI, and our proposal evaluates potential prophylactic therapies. The goal of this program is to develop potential treatments to prevent epileptogenesis by altering the effects of mGluR activation. We have found that activation of group I mGluRs with the selective agonist dihydroxyphenylglycine (DHPG) results in long-lasting changes in hippocampal excitability manifest by spontaneously occurring interictal (between-seizures) and ictal (seizure-like) activity. In the past funding period, we have demonstrated that blockade of group I mGluRs can slow kindling, a model of epileptogenesis. Our findings have created new research questions, which we address in the current proposal. Our first hypothesis is that activation of group I mGluRs increases preferentially the recurrent excitatory synaptic network activity and results in persistent epileptiform activity in the CA3 region of the hippocampus. Our first set of specific aims will address changes in synaptic physiology of the CA3 region that follow transient exposure to DHPG. We will: 1) characterize the frequency and amplitude of spontaneously occurring inhibitory postsynaptic currents (IPSCs) and excitatory post synaptic currents (EPSCs) after DHPG exposure and will compare this with control neuronal activity; 2) evaluate spontaneously occurring EPSCs in the absence of inhibition and spontaneously occurring IPSCs in the absence of synaptic excitation; and 3) determine changes in miniature IPSC and EPSC frequency and amplitude that are associated with DHPG exposure. Our second hypothesis is that long-term changes induced by group I mGluRs are the result of production of Homer 1a, a protein up-regulated by seizures, and change in function of group I mGluRs so that a cation current is activated in the absence of glutamate. Our preliminary data indicate that Homer 1 knockout (KO) mice are resistant to the induction of epileptiform by DHPG. We will therefore determine if Homer 1 KO mice develop changes in membrane properties associated with DHPG exposure and will determine if a transduction of the Homer 1 KO mouse with Homer 1a can re-establish the wild type phenotype as relates to the induction of epileptiform activity by DHPG. We argue that the changes we define that occur following DHPG exposure, models what occurs when high concentrations of extracellular glutamate activate mGluRs, and that they represent a therapeutic target to block the development of epilepsy following head trauma, status epilepticus, and recurrent seizures. The results of our experiments will target new therapies for epilepsy and the development of epilepsy, a major morbidity for combat Veterans who have experienced TBI.