Department of Cellular and Integrative Physiology, University of Texas Health San Antonio, San Antonio, Texas.
Hippocampus. 2020 May;30(5):435-455. doi: 10.1002/hipo.23163. Epub 2019 Oct 17.
M-type (KCNQ2/3) K channels play dominant roles in regulation of active and passive neuronal discharge properties such as resting membrane potential, spike-frequency adaptation, and hyper-excitatory states. However, plasticity of M-channel expression and function in nongenetic forms of epileptogenesis are still not well understood. Using transgenic mice with an EGFP reporter to detect expression maps of KCNQ2 mRNA, we assayed hyperexcitability-induced alterations in KCNQ2 transcription across subregions of the hippocampus. Pilocarpine and pentylenetetrazol chemoconvulsant models of seizure induction were used, and brain tissue examined 48 hr later. We observed increases in KCNQ2 mRNA in CA1 and CA3 pyramidal neurons after chemoconvulsant-induced hyperexcitability at 48 hr, but no significant change was observed in dentate gyrus (DG) granule cells. Using chromogenic in situ hybridization assays, changes to KCNQ3 transcription were not detected after hyper-excitation challenge, but the results for KCNQ2 paralleled those using the KCNQ2-mRNA reporter mice. In mice 7 days after pilocarpine challenge, levels of KCNQ2 mRNA were similar in all regions to those from control mice. In brain-slice electrophysiology recordings, CA1 pyramidal neurons demonstrated increased M-current amplitudes 48 hr after hyperexcitability; however, there were no significant changes to DG granule cell M-current amplitude. Traumatic brain injury induced significantly greater KCNQ2 expression in the hippocampal hemisphere that was ipsilateral to the trauma. In vivo, after a secondary challenge with subconvulsant dose of pentylenetetrazole, control mice were susceptible to tonic-clonic seizures, whereas mice administered the M-channel opener retigabine were protected from such seizures. This study demonstrates that increased excitatory activity promotes KCNQ2 upregulation in the hippocampus in a cell-type specific manner. Such novel ion channel expressional plasticity may serve as a compensatory mechanism after a hyperexcitable event, at least in the short term. The upregulation described could be potentially leveraged in anticonvulsant enhancement of KCNQ2 channels as therapeutic target for preventing onset of epileptogenic seizures.
M 型(KCNQ2/3)钾通道在调节神经元的主动和被动放电特性方面发挥着重要作用,如静息膜电位、频率适应性和超兴奋性状态。然而,在非遗传性癫痫发生形式中,M 通道表达和功能的可塑性仍不清楚。我们使用带有 EGFP 报告基因的转基因小鼠来检测 KCNQ2 mRNA 的表达图谱,以检测海马体亚区的过度兴奋诱导的 KCNQ2 转录变化。使用匹罗卡品和戊四氮化学惊厥模型诱导癫痫发作,并在 48 小时后检查脑组织。我们观察到,在化学惊厥诱导的过度兴奋后 48 小时,CA1 和 CA3 锥体神经元中的 KCNQ2 mRNA 增加,但在齿状回(DG)颗粒细胞中没有观察到显著变化。使用显色原位杂交测定法,在超兴奋挑战后未检测到 KCNQ3 转录的变化,但 KCNQ2 的结果与使用 KCNQ2-mRNA 报告小鼠的结果相似。在匹罗卡品挑战后 7 天的小鼠中,所有区域的 KCNQ2 mRNA 水平与对照小鼠相似。在脑片电生理学记录中,CA1 锥体神经元在过度兴奋后 48 小时表现出 M 电流幅度增加;然而,DG 颗粒细胞的 M 电流幅度没有显著变化。创伤性脑损伤导致对侧海马半球的 KCNQ2 表达显著增加。在体内,用亚惊厥剂量的戊四氮进行二次挑战后,对照小鼠易发生强直阵挛性发作,而给予 M 通道 opener retigabine 的小鼠则免受此类发作的影响。这项研究表明,兴奋性增加以细胞类型特异性的方式促进海马体中的 KCNQ2 上调。这种新型离子通道表达可塑性可能是过度兴奋事件后的一种代偿机制,至少在短期内是如此。所描述的上调可能作为 KCNQ2 通道的抗惊厥增强的治疗靶点,用于预防致痫性发作的发生。