Graduate Center, City University of New York, New York, NY, USA.
Center for Developmental Neuroscience, The College of Staten Island, Staten Island, NY, USA.
J Physiol. 2019 Apr;597(8):2201-2223. doi: 10.1113/JP276952. Epub 2019 Feb 21.
Spasticity is a disorder of muscle tone that is associated with lesions of the motor system. This condition involves an overactive spinal reflex loop that resists the passive lengthening of muscles. Previously, we established that application of anodal trans-spinal direct current stimulation (a-tsDCS) for short periods of time to anaesthetized mice sustaining a spinal cord injury leads to an instantaneous reduction of spasticity. However, the long-term effects of repeated a-tsDCS and its mechanism of action remained unknown. In the present study, a-tsDCS was performed for 7 days and this was found to cause long-term reduction in spasticity, increased rate-dependent depression in spinal reflexes, and improved ground and skill locomotion. Pharmacological, molecular and cellular evidence further suggest that a novel mechanism involving Na-K-Cl cotransporter isoform 1 mediates the observed long-term effects of repeated a-tsDCS.
Spasticity can cause pain, fatigue and sleep disturbances; restrict daily activities such as walking, sitting and bathing; and complicate rehabilitation efforts. Thus, spasticity negatively influences an individual's quality of life and novel therapeutic interventions are needed. We previously demonstrated in anaesthetized mice that a short period of trans-spinal subthreshold direct current stimulation (tsDCS) reduces spasticity. In the present study, the long-term effects of repeated tsDCS to attenuate abnormal muscle tone in awake female mice with spinal cord injuries were investigated. A motorized system was used to test velocity-dependent ankle resistance and associated electromyographical activity. Analysis of ground and skill locomotion was also performed, with electrophysiological, molecular and cellular studies being conducted to reveal a potential underlying mechanism of action. A 4 week reduction in spasticity was associated with an increase in rate-dependent depression of spinal reflexes, and ground and skill locomotion were improved following 7 days of anodal-tsDCS (a-tsDCS). Secondary molecular, cellular and pharmacological experiments further demonstrated that the expression of K-Cl co-transporter isoform 2 (KCC2) was not changed in animals with spasticity. However, Na-K-Cl cotransporter isoform 1 (NKCC1) was significantly up-regulated in mice that exhibited spasticity. When mice were treated with a-tsDCS, down regulation of NKCC1 was detected, and this level did not significantly differ from that in the non-injured control mice. Thus, long lasting reduction of spasticity by a-tsDCS via downregulation of NKCC1 may constitute a novel therapy for spasticity following spinal cord injury.
痉挛是一种与运动系统损伤相关的肌肉张力障碍。这种情况涉及到一个过度活跃的脊髓反射环路，它抵抗肌肉的被动伸展。此前，我们已经确定，在麻醉的脊髓损伤小鼠中短时间应用阳极经皮脊髓直流电刺激（a-tsDCS）会导致痉挛即刻减轻。然而，重复 a-tsDCS 的长期效果及其作用机制仍不清楚。在本研究中，进行了为期 7 天的 a-tsDCS，结果发现其导致痉挛的长期减轻、脊髓反射的速率依赖性抑制增加以及地面和技能运动的改善。药理学、分子和细胞证据进一步表明，涉及 Na-K-Cl 共转运蛋白 1 同种型的新机制介导了重复 a-tsDCS 的观察到的长期效应。
痉挛可引起疼痛、疲劳和睡眠障碍；限制步行、坐立和洗澡等日常活动；并使康复工作复杂化。因此，痉挛会对个人的生活质量产生负面影响，需要新的治疗干预措施。我们之前在麻醉小鼠中证明，短时间的经皮脊髓亚阈直流电刺激（tsDCS）可减轻痉挛。在本研究中，我们研究了重复 tsDCS 以减轻患有脊髓损伤的清醒雌性小鼠异常肌肉张力的长期作用。使用电动系统测试速度依赖性踝关节阻力和相关的肌电图活动。还进行了地面和技能运动的分析，并进行了电生理学、分子和细胞研究以揭示潜在的作用机制。在接受 4 周的痉挛减轻治疗后，脊髓反射的速率依赖性抑制增加，并且在接受 7 天的阳极经皮脊髓直流电刺激（a-tsDCS）后，地面和技能运动得到改善。二级分子、细胞和药理学实验进一步表明，在痉挛的动物中，K-Cl 共转运蛋白 2（KCC2）的表达没有改变。然而，Na-K-Cl 共转运蛋白 1（NKCC1）在表现出痉挛的小鼠中显著上调。当用 a-tsDCS 治疗时，检测到 NKCC1 的下调，并且其水平与未受伤的对照组小鼠没有显著差异。因此，通过下调 NKCC1 实现 a-tsDCS 对痉挛的长期减轻可能构成脊髓损伤后痉挛的一种新的治疗方法。
