去极化诱导的分流抑制对海马CA3区神经元兴奋性和癫痫性抽搐的调控作用及其机制

Epilepsy is a major chronic neurologic disorder characterized by repetitive, unprovoked seizures. However, the underlying mechanisms of the self-termination of epileptiform discharges in the brain remain undetermined. In particular, in the early phase of life epilepsy occurs at its higher incidence and pharmacoresistance, for which one of the major reasons is believed to be the depolarizing action of GABA receptor in the immature neuron. Our preliminary data showed that, in the immature mice hippocampal CA3 region, after sustained depolarization the responses of GABA, glycine, glutamate receptors were attenuated in contrast to the increment of membrane conductance tested at depolarizing voltage, indicating that the depolarizing response of ligand-gated ion channel was suppressed via depolarization-induced shunting inhibition (DShI, currently termed). We reasonably hypothesize that DShI plays an important role in maintaining the balance of excitation and inhibition of immature neuron, and participates in the self-termination of epileptiform discharges in the brain. Thus, in order to elucidate the detailed mechanism and the physiological and pathophysiological relevance of DShI so as to try to reach new inside of epileptic seizures and novel therapeutic target for the treatment of epilepsy, we propose to go further to uncover the molecular pathway mediating DShI, whether DShI influence neuronal excitability and whether DShI leads to self-termination of epileptiform discharges in the brain and epileptic seizure.

癫痫是神经系统最常见的疾病之一，以反复发作性抽搐为临床特征，但脑内发作性癫痫样放电的自发性中止的机理仍不明确。癫痫的发病率和耐药率在发育早期较高，主要的原因被认为是未成熟神经元GABA受体活动产生去极化作用。我们预实验发现，新生小鼠海马CA3区锥体神经元被持续去极化后，GABA、甘氨酸、谷氨酸受体反应性下降并伴随去极化膜电导增加，表明去极化诱导的分流抑制（Depolarization-induced shunting inhibition，DShI-暂定术语）是这些配体门控离子通道的反应性下降的原因。我们假设DShI对未成熟神经元维持兴奋性和抑制性之间的平衡起重要作用、并参与脑内发作性癫痫样放电的自发性中止。因此，我们拟深入研究以探明介导DShI的分子途径、DShI是否影响神经元的兴奋性、是否促成脑内发作性癫痫样放电和癫痫性抽搐的自发性中止，为癫痫性抽搐提出新的病理机制和发现新的治疗靶点。

神经兴奋与抑制之间的稳态平衡受突触和神经元内在活动的调控，是脑实现正常功能的基本条件。在生理或病理情况下，神经元过度兴奋是否会诱发神经元内在的抑制性增强以恢复稳态平衡，目前还不清楚。通过该课题的研究，我们发现海马CA3区神经元在抽搐样的持续去极化后会出现膜分流导致的短时程抑制。这种持续去极化诱导的分流抑制（DShI）是非突触的、细胞内在的短时程抑制，能抑制运作电位的产生和离子通道型受体的反应。DShI可被串联孔域钾通道敏感的阻断剂阻断，属于该类型的TRESK通道对DShI的诱导有重要作用。TRESK基因敲除后DShI明显减弱，癫痫模型小鼠的癫痫性抽搐加重，而TRESK过表达则显著减轻癫痫性抽搐。这些结果不仅发现了一种新的、在细胞内在水平的稳态可塑性及其机制，也揭示TRESK可能是癫痫治疗的新靶点。