Disrupted dentate granule cell chloride regulation enhances synaptic excitability during development of temporal lobe epilepsy
Disrupted dentate granule cell chloride regulation enhances synaptic excitability during development of temporal lobe epilepsy
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DOI：
10.1523/jneurosci.4390-07.2007
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发表时间：
2007-12-19
影响因子：
5.3
通讯作者：
Coulter, Douglas A.
中科院分区：
文献类型：
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作者：
Pathak, Hemal R.;Weissinger, Florian;Coulter, Douglas A.
GABA(A)受体介导的抑制依赖于细胞内氯离子浓度([Cl-](In))维持在低水平。在发育中的中枢神经系统神经元中，[Cl-](In)升高，E-GABA去极化，因此GABA是兴奋性的。去极化GABA能突触反应可在包括癫痫在内的各种神经病理条件下重现。在本研究中，用Granicidin穿孔贴片技术记录了致痫后不同时间(1-60d)的大鼠海马齿状回颗粒细胞。在正常的非癫痫动物中，这些强烈抑制的齿状颗粒细胞充当门，调节海马区的兴奋，控制癫痫的启动和/或传播。STEP后2周，颗粒细胞内E-GABA阳性移位。E-GABA的这种变化改变了突触整合，增加了颗粒细胞的兴奋性，并导致齿状回的“门”功能受损。当动物发生癫痫后，E-GABA在较长的潜伏期(2-8周)后恢复到控制值。在E-GABA移位期间，氯-挤出K-/Cl-共转运蛋白KCC2的表达降低。应用KCC2阻滞剂速尿来控制神经元，模拟颗粒细胞在步进后明显的E-GABA移动。此外，后台阶效应和速尿效应对颗粒细胞中的E-GABA和齿状回的把关功能都有阻塞性作用。这暗示了一种共享的机制，减少了KCC2的功能。这些结果表明，KCC2的表达减少在致痫损伤后持续数周，从而降低了抑制效果，并增强了齿状颗粒细胞的兴奋性。这一病理生理过程可能构成了将损伤与随后的癫痫发展联系起来的一个重要机制。
GABA(A) receptor-mediated inhibition depends on the maintenance of intracellular Cl- concentration ([Cl-](in)) at low levels. In neurons in the developing CNS, [Cl-](in) is elevated, E-GABA is depolarizing, and GABA consequently is excitatory. Depolarizing GABAergic synaptic responses may be recapitulated in various neuropathological conditions, including epilepsy. In the present study, rat hippocampal dentate granule cells were recorded using gramicidin perforated patch techniques at varying times (1-60 d) after an epileptogenic injury, pilocarpine-induced status epilepticus (STEP). In normal, non-epileptic animals, these strongly inhibited dentate granule cells act as a gate, regulating hippocampal excitation, controlling seizure initiation and/or propagation. For 2 weeks after STEP, we found that E-GABA was positively shifted in granule cells. This shift in E-GABA altered synaptic integration, increased granule cell excitability, and resulted in compromised "gate" function of the dentate gyrus. E-GABA recovered to control values at longer latencies post-STEP (2-8 weeks), when animals had developed epilepsy. During this period of shifted E-GABA, expression of the Cl- extruding K-/Cl- cotransporter, KCC2 was decreased. Application of the KCC2 blocker, furosemide, to control neurons mimicked E-GABA shifts evident in granule cells post-STEP. Furthermore, post-STEP and furosemide effects interacted occlusively, both on E-GABA in granule cells, and on gatekeeper function of the dentate gyrus. This suggests a shared mechanism, reduced KCC2 function. These findings demonstrate that decreased expression of KCC2 persists for weeks after an epileptogenic injury, reducing inhibitory efficacy and enhancing dentate granule cell excitability. This pathophysiological process may constitute a significant mechanism linking injury to the subsequent development of epilepsy.