Neurosteroid Regulation of Seizures

描述（由申请人提供）：颞叶癫痫（TLE）是医学上难治性癫痫的一种常见形式，其特征是反复无端发作，涉及边缘结构，通常需要手术治疗。已经提出了多种病理生理机制来解释TLE发作的发生；其中包括GABAA受体介导的齿状颗粒细胞（DGCs）抑制的改变。我们证明癫痫大鼠DGCs上的GABAA受体对神经类固醇调节的敏感性远低于对照动物DGCs上的GABAA受体。正在进行的研究表明，在癫痫动物的DGCs中，神经类固醇对突触抑制的敏感性降低，这与a4亚基异常靶向突触外、突触周围和突触膜有关。此外，神经类固醇对强直抑制的敏感性丧失与d亚基到表面膜的运输减少以及表面表达增加有关。2个在癫痫大鼠的海马中。这些研究提出了一种假设，即在癫痫动物中，在神经类固醇合成减少和癫痫发作期间，DGCs的活性过滤功能被破坏。我们还提出，强直性和突触抑制对DGCs的神经类固醇敏感性降低是因为d亚基保留在细胞内腔室中，而含d亚基的受体被？2个含亚基受体。我们提出通过实现四个具体目标来测试我们假设的预测：第一个目标是表征GABAA受体的神经类固醇敏感性降低对癫痫易感性和颗粒细胞兴奋性的影响；第二个目标将是表征神经类固醇敏感性和？2、d、a4和a5亚基特异性gaba能强直性抑制DGCs；第三个目标将是确定改变贩运、集结和锁定目标的时间进程。2、d、a4和a5亚基GABAA受体在潜伏期和复发性癫痫发作后的变化。第四个目标的实验将描述神经元活动增加和激动剂暴露对亚基运输、内吞作用和插入率的影响。这些研究探讨了一种与内源性神经类固醇水平下降有关的癫痫动物癫痫发作沉淀的新机制，并确定了一种新的GABAA受体作为癫痫治疗的靶点。这些研究旨在了解一种常见癫痫的发病机制。他们还试图了解癫痫患者是如何诱发癫痫发作的。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.