Establishment of preventive strategies for nocturnal frontal lobe epilepsy-Elucidation of molecular mechanism to inhibit epileptic seizures

神经型烟碱型乙酰胆碱(ACh)受体α4、SS2或α2亚单位基因突变可引起人类夜间额叶癫痫。与NFLE相关的癫痫发作仅见于睡眠期间，其特点是三种不同的癫痫发作表型：“阵发性觉醒”、“阵发性肌张力障碍”和“阵发性漫游”。我们获得了含有错义突变S284L的转基因大鼠品系，该突变已在NFLE的CHRNA4中被证实。转基因大鼠没有出现生物异常，如中枢神经系统的畸形和行为异常。转基因(突变体chrna 4)的mRNA水平与野生型相似，在脑中没有检测到扭曲的表达。然而，转基因大鼠在慢波睡眠(SWS)中表现出与NFLE相似的癫痫发作表型，表现出三种特征的癫痫发作表型，从而满足人类NFLE的诊断标准。这些大鼠对常规抗癫痫药物的治疗反应也与携带S284L突变的NFLE患者相似。大鼠在神经传递方面表现出两个主要的异常：1)突触和突触外GABA能传递的减弱；2)SWS期间谷氨酸的异常释放。目前可用的基因工程癫痫动物模型仅限于小鼠，因此，我们的转基因大鼠为癫痫研究领域提供了另一个维度。

Mutations of genes encoding α4, ss2 or α2 subunits (CHRNA4, CHRNB2 or CHRNA2, respectively), of neuronal nicotinic acetylcholine (ACh) receptor (nAChR) cause nocturnal frontal lobe epilepsy (NFLE) in human. NFLE-related seizures are seen exclusively during sleep and characterized by three distinct seizure phenotypes ; "paroxysmal arousals", "paroxysmal dystonia" and "episodic wandering". We generated transgenic rat strains that harbor a missense mutation S284L, which had been identified in CHRNA4 in NFLE. The transgenic rats were free of biological abnormalities, such as dysmorphology in the central nervous system, and behavioral abnormalities. The mRNA level of the transgene (mutant Chrna4) was similar to the wild-type and no distorted expression was detected in the brain. However, the transgenic rats showed epileptic seizure phenotypes during slow wave sleep (SWS) similar to those in NFLE exhibiting three characteristic seizure phenotypes and thus fulfilled the diagnostic criteria of human NFLE. The therapeutic response of these rats to conventional antiepileptic drugs also resembled that of NFLE patients with the S284L mutation. The rats exhibited two major abnormalities in neurotransmission ; 1) Attenuation of synaptic and extrasynaptic GABAergic transmission and 2) abnormal glutamate release during SWS. The currently available genetically engineered animal models of epilepsy are limited to mice, thus, our transgenic rats offer another dimension to the epilepsy research field.