REDUCTION OF FUNCTIONAL GABA_A RECEPTOR EXPRESSION IN THE NEOCORTEX OF EL MICE

大量证据表明γ-氨基丁酸在癫痫的发生中起着至关重要的作用。EL(癫痫样)小鼠是从ddy小鼠发展而来的癫痫模型，非常容易发作。研究发现，EL小鼠表现出GABA介导的抑制减少。然而，以前的研究仍然是关于GABA受体功能和癫痫发生之间的关系的核心。在本研究中，我们研究了未受刺激的EL小鼠和ddy对照组(18-20周龄)小鼠大脑皮层GABAA受体基因的表达和功能。1)Northern印迹分析显示，EL小鼠GABAA受体α1亚单位信使核糖核酸水平比Ddy小鼠降低了30%。另一方面，β-2和γ-2亚单位基因表达水平无显著差异。2)利用非洲爪哇卵母细胞表达系统检测GABAA受体的功能。注射EL小鼠新皮质mRNA的卵母细胞的最大GABA诱导电流明显小于注射ddy MICE基因的卵母细胞。3)单脉冲配置的新皮质脑片细胞外记录显示，GABA_A受体拮抗剂(荷包牡丹碱：BMI和印防己毒素：PTX)引起的视野变化在EL(-)小鼠的BMI和PTX诱导的场电位变化中显著降低。这些结果表明，在EL(-)小鼠的新皮质，GABA_A受体的表达减少和反复的GABA能抑制，这可能与EL株的致痫作用有关。

There is extensive evidence indicating a crucial role for γ-aminobutyric acid (GABA) in epileptogenesis. The El (epilepsy-like) mouse is an epilepsy model developed from the ddY mouse and is very susceptible to seizure. El mice have been found to exhibit a decrease in GABA-mediated inhibition. However, previous studies remained nuclear about relationship between the GABA receptor function and epileptogenesis. In the present study, we investigated the GABA_A receptor gene expression and function in the neocortex of unstimulated El mice and ddY control mice (18-20 weeks old).1) Northern blot analysis showed 30% decrease in GABA_A receptor α1 subunit messenger RNA (mRNA) level in El mice, compared to ddY mice. On the other hand, β2 and γ2 subunit mRNA levels did not show any significant differences.2) GABA_A receptor functions were analyzed by the measurement of GABA-induced currents using Xenopus oocytes expression system. The maximal GABA-induced currents obtained from oocytes injected with neocortex mRNA of El mice, were significantly smaller than those obtained from oocytes injected with mRNA of ddY mice.3) Extracellular recordings from the neocortex slices using single-pulse configuration showed significant difference in the GABA_A receptor antagonist (bicuculline: BMI and picrotoxin:PTX)-induced changes of field significant decrease in the BMI and PTX-induced changes of the amplitude of field potentials in El(-) mice.These results suggest that, in the neocortex of El(-) mice, there is a decrease in GABA_A receptor expression and recurrent GABAergic inhibition, which may be related to the epileptogenesis in the El strain.