Neurosteroid Regulation of Seizures

描述（由申请人提供）：颞叶癫痫（TLE）是一种常见的难治性癫痫，其特征为累及边缘系统结构的复发性无端癫痫发作，通常需要手术治疗。已经提出了多种病理生理机制来解释癫痫发作发生在TLE，其中之一是改变GABAA受体介导的抑制齿状颗粒细胞（DGCs）。我们证明，GABAA受体上的癫痫大鼠的DGCs的神经甾体调制的敏感性远远低于那些对DGCs的控制动物。正在进行的研究表明，在癫痫动物的DGC中，存在与α 4亚基到突触外、突触周和突触膜的异常靶向相关的突触抑制的神经类固醇敏感性降低。此外，有损失的神经甾体敏感性的紧张性抑制与减少贩运的d亚基的表面膜，以及增加的表面表达？2在致痫大鼠大脑中动脉。这些研究表明，在癫痫动物中，在神经类固醇合成减少和癫痫发作发生期间，存在DGC的活性过滤功能的崩溃。我们还提出，减少神经类固醇的紧张性和突触抑制的敏感性，对DGC是因为d亚单位保留在细胞内室和d亚单位含有受体被取代？2个含亚单位的受体。我们建议通过实现四个具体目标来测试我们的假设的预测：第一个目标是表征GABAA受体对癫痫发作易感性和颗粒细胞兴奋性的神经甾体敏感性降低的影响;第二个目标是表征神经甾体敏感性和？2，d，a4，和a5亚单位的具体属性的紧张性GABA能抑制的DGCs;和第三个目的将是确定改变贩运的时间过程中，组装，和针对？GABAA受体α 2、α 4、α 5亚单位在癫痫发作潜伏期和发作后的变化。第四个目标的实验将描述增加的神经元活动和激动剂暴露对d亚基运输、内吞和插入率的影响。这些研究探讨了癫痫动物中与内源性神经类固醇水平下降相关的癫痫发作沉淀的新机制，并将新的GABAA受体定义为癫痫治疗的靶点。公共卫生相关性这些研究试图了解一种常见癫痫形式的机制。他们还试图了解癫痫患者的癫痫发作是如何发生的。这些研究将为开发治疗癫痫的药物寻找新的靶点。

DESCRIPTION (provided by applicant): Temporal lobe epilepsy (TLE) is a common form of medically refractory epilepsy characterized by recurrent unprovoked seizures involving the limbic structures, which often requires surgery. Multiple pathophysiological mechanisms have been proposed to explain seizure occurrence in TLE; among these is an altered GABAA receptor-mediated inhibition of dentate granule cells (DGCs). We demonstrated that GABAA receptors on DGCs of epileptic rats were far less sensitive to neurosteroid modulations than those on DGCs of control animals. Ongoing studies suggest that in DGCs of epileptic animals, there is reduced neurosteroid sensitivity of synaptic inhibition associated with the aberrant targeting of the a4 subunit to extrasynaptic, perisynaptic, and synaptic membrane. Furthermore, there is loss of neurosteroid sensitivity of tonic inhibition associated with diminished trafficking of the d subunit to the surface membrane as well as increased surface expression of the ? 2 in the hippocampi of epileptic rats. These studies suggest the hypotheses that in epileptic animals, there is breakdown of activity filtering function of DGCs during periods of diminished neurosteroid synthesis and seizures occur. We also propose that diminished neurosteroid sensitivity of tonic and synaptic inhibition on DGCs is because the d subunit is retained in intracellular compartment and d subunit-containing receptors are replaced by ?2 subunit-containing receptors. We propose to test the predictions of our hypotheses by accomplishing four specific aims: the first aim is to characterize the impact of diminished neurosteroid sensitivity of GABAA receptors on seizure susceptibility and granule cell excitability; the second aim will be to characterize neurosteroid sensitivity and ?2, d, a4, and a5 subunit-specific properties of tonic GABAergic inhibition of DGCs; and the third aim will be to determine the time course of altered trafficking, assembly, and targeting of ? 2,d, a4, and a5 subunits of GABAA receptors during the latent period and after the onset of recurrent seizures. Experiments in the fourth aim will characterize the effect of increased neuronal activity and agonist exposure on d subunit trafficking, endocytosis, and insertion rates. These studies investigate a novel mechanism of seizure precipitation in epileptic animals related to decline in endogenous neurosteroid levels and define a novel GABAA receptor as target for epilepsy therapy. PUBLIC HEALTH RELEVANCE These studies seek to understand the mechanisms underlying a common form of epilepsy. They also seek to understand how seizures might be precipitated in patients with epilepsy. These studies will seek a new target for developing drugs for the treatment of epilepsy.