Department of Biology and Biochemistry, University of Houston, Houston, Texas, U.S.A.
Epilepsia. 2014 Feb;55(2):245-55. doi: 10.1111/epi.12487. Epub 2014 Jan 13.
Severe myoclonic epilepsy in infancy (SMEI) or Dravet syndrome is one of the most devastating childhood epilepsies. Children with SMEI have febrile and afebrile seizures (FS and aFS), ataxia, and social and cognitive dysfunctions. SMEI is pharmacologically intractable and can be fatal in 10-20% of patients. It remains to be elucidated how channelopathies that cause SMEI impact synaptic activities in key neural circuits, and there is an ongoing critical need for alternative methods of controlling seizures in SMEI. Using the SCN1A gene knock-in mouse model of SMEI (mSMEI), we studied hippocampal cell and circuit excitability, particularly during hyperthermia, and tested whether an adenosine A1 receptor (A1R) agonist can reliably control hippocampal circuit hyperexcitability.
Using a combination of electrophysiology (extracellular and whole-cell voltage clamp) and fast voltage-sensitive dye imaging (VSDI), we quantified synaptic excitation and inhibition, spatiotemporal characteristics of neural circuit activity, and hyperthermia-induced febrile seizure-like events (FSLEs) in juvenile mouse hippocampal slices. We used hyperthermia to elicit FSLEs in hippocampal slices, while making use of adenosine A1R agonist N6-cyclopentyladenosine (CPA) to control abnormally widespread neural activity and FSLEs.
We discovered a significant excitation/inhibition (E/I) imbalance in mSMEI hippocampi, in which inhibition was decreased and excitation increased. This imbalance was associated with an increased spatial extent of evoked neural circuit activation and a lowered FSLE threshold. We found that a low concentration (50 nm) of CPA blocked FSLEs and reduced the spatial extent of abnormal neural activity spread while preserving basal levels of excitatory synaptic transmission.
Our study reveals significant hippocampal synapse and circuit dysfunctions in mSMEI and demonstrates that the A1R agonist CPA can reliably control hippocampal hyperexcitability and FSLEs in vitro. These findings may warrant further investigations of purinergic agonists as part of the development of new therapeutic approaches for Dravet syndrome.
婴儿严重肌阵挛性癫痫（SMEI）或德拉维特综合征是最具破坏性的儿童癫痫之一。患有 SMEI 的儿童有热性和无热性癫痫发作（FS 和 aFS）、共济失调以及社交和认知功能障碍。SMEI 对药物治疗有抗性，并且在 10-20%的患者中可能致命。目前尚不清楚导致 SMEI 的通道病如何影响关键神经回路中的突触活动，并且迫切需要替代方法来控制 SMEI 中的癫痫发作。使用 SMEI 的 SCN1A 基因敲入小鼠模型（mSMEI），我们研究了海马细胞和回路兴奋性，特别是在体温升高期间，并测试了腺苷 A1 受体（A1R）激动剂是否能可靠地控制海马回路过度兴奋。
我们使用电生理学（细胞外和全细胞电压钳）和快速电压敏感染料成像（VSDI）相结合的方法，量化了突触兴奋和抑制、神经回路活动的时空特征以及幼年小鼠海马切片中的发热性癫痫样发作（FSLEs）。我们利用体温升高来诱发海马切片中的 FSLEs，同时利用腺苷 A1R 激动剂 N6-环戊基腺苷（CPA）来控制异常广泛的神经活动和 FSLEs。
我们发现 mSMEI 海马中的兴奋/抑制（E/I）失衡显著，其中抑制减少而兴奋增加。这种失衡与诱发神经回路激活的空间范围增加和 FSLE 阈值降低有关。我们发现低浓度（50nm）的 CPA 可阻断 FSLEs，并减少异常神经活动传播的空间范围，同时保持基础水平的兴奋性突触传递。
我们的研究揭示了 mSMEI 中海马突触和回路的显著功能障碍，并证明了 A1R 激动剂 CPA 可以可靠地控制海马过度兴奋和 FSLEs 的体外。这些发现可能需要进一步研究嘌呤能激动剂作为开发德拉维特综合征新治疗方法的一部分。
