Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, UK.
Wolfson CARD, King's College London, London, UK.
Brain. 2017 Oct 1;140(10):2570-2585. doi: 10.1093/brain/awx201.
See Basbaum (doi:10.1093/brain/awx227) for a scientific commentary on this article. Peripheral neuropathic pain arises as a consequence of injury to sensory neurons; the development of ectopic activity in these neurons is thought to be critical for the induction and maintenance of such pain. Local anaesthetics and anti-epileptic drugs can suppress hyperexcitability; however, these drugs are complicated by unwanted effects on motor, central nervous system and cardiac function, and alternative more selective treatments to suppress hyperexcitability are therefore required. Here we show that a glutamate-gated chloride channel modified to be activated by low doses of ivermectin (but not glutamate) is highly effective in silencing sensory neurons and reversing neuropathic pain-related hypersensitivity. Activation of the glutamate-gated chloride channel expressed in either rodent or human induced pluripotent stem cell-derived sensory neurons in vitro potently inhibited their response to both electrical and algogenic stimuli. We have shown that silencing is achieved both at nerve terminals and the soma and is independent of membrane hyperpolarization and instead likely mediated by lowering of the membrane resistance. Using intrathecal adeno-associated virus serotype 9-based delivery, the glutamate-gated chloride channel was successfully targeted to mouse sensory neurons in vivo, resulting in high level and long-lasting expression of the channel selectively in sensory neurons. This enabled reproducible and reversible modulation of thermal and mechanical pain thresholds in vivo; analgesia was observed for 3 days after a single systemic dose of ivermectin. We did not observe any motor or proprioceptive deficits and noted no reduction in cutaneous afferent innervation or upregulation of the injury marker ATF3 following prolonged glutamate-gated chloride channel expression. Established mechanical and cold pain-related hypersensitivity generated by the spared nerve injury model of neuropathic pain was reversed by ivermectin treatment. The efficacy of ivermectin in ameliorating behavioural hypersensitivity was mirrored at the cellular level by a cessation of ectopic activity in sensory neurons. These findings demonstrate the importance of aberrant afferent input in the maintenance of neuropathic pain and the potential for targeted chemogenetic silencing as a new treatment modality in neuropathic pain.
如需了解本文的科学评论，请参阅 Basbaum（doi:10.1093/brain/awx227）。周围神经性疼痛是由于感觉神经元损伤引起的；这些神经元的异位活动的发展被认为对这种疼痛的诱导和维持至关重要。局部麻醉剂和抗癫痫药物可以抑制过度兴奋；然而，这些药物因对运动、中枢神经系统和心脏功能的不良影响而变得复杂，因此需要替代的更具选择性的抑制过度兴奋的治疗方法。在这里，我们表明，一种被修饰为对低剂量伊维菌素（而不是谷氨酸）激活的谷氨酸门控氯离子通道在沉默感觉神经元和逆转神经性疼痛相关的过敏方面非常有效。在体外，表达在啮齿动物或人诱导多能干细胞衍生的感觉神经元中的谷氨酸门控氯离子通道的激活强烈抑制了它们对电刺激和致痛刺激的反应。我们已经表明，沉默是在神经末梢和胞体中实现的，并且与膜超极化无关，而是可能通过降低膜电阻来介导的。通过鞘内腺相关病毒血清型 9 为基础的传递，谷氨酸门控氯离子通道成功地靶向了小鼠感觉神经元，导致通道在感觉神经元中选择性地高水平和持久表达。这使得在体内可重复和可逆地调节热和机械痛觉阈值；单次全身伊维菌素给药后观察到镇痛作用持续 3 天。我们没有观察到任何运动或本体感觉缺陷，并且在长期表达谷氨酸门控氯离子通道后，没有观察到皮肤传入神经支配减少或损伤标志物 ATF3 的上调。通过 spared 神经损伤模型的神经性疼痛的机械和冷痛相关过敏的建立被伊维菌素治疗所逆转。伊维菌素在改善行为过敏中的疗效在感觉神经元的异位活动停止的细胞水平上得到了反映。这些发现证明了异常传入输入在神经性疼痛维持中的重要性，并且靶向化学遗传沉默作为神经性疼痛的一种新的治疗方式具有潜力。
