Summary

非侵入性评估人类皮质神经元传播的变化

Published: May 24, 2017
doi:

Summary

本研究的目的是评估重复经颅磁刺激后人类皮质类神经元突触的变化。为此目的,引入电生理方法,其允许评估途径特异性皮质脊髓传播, 快速,直接皮质螺旋途径从多突触连接的分化。

Abstract

皮质脊髓通路是连接大脑与肌肉的主要途径,因此对运动控制和运动学习非常重要。存在一些研究该途径的兴奋性和可塑性的无创电生理方法。然而,大多数方法是基于化合物电位的定量,并忽略皮质螺旋途径由许多或多或少直接的不同连接组成。在这里,我们提出一种允许测试皮质脊髓传播的不同部分的兴奋性的方法。这种所谓的H反射调节技术允许评估最快(单突触)和多突触皮质螺旋途径的兴奋性。此外,通过使用两个不同的刺激部位,运动皮层和颈椎管连接处,它不仅允许皮层和脊柱效应之间的分化,还允许评估皮质的传播耳聋突触在这份手稿中,我们描述了这种方法如何用于评估低频重复经颅磁刺激后的皮质类固醇传播,这是先前显示的减少皮层细胞兴奋性的方法。在这里我们证明,不仅皮质细胞受到这种重复刺激的影响,而且在脊髓水平的皮质类神经元突触期间的传播。这一发现对于了解神经可塑性的基本机制和部位很重要。除了基本机制的调查之外,H反射调理技术可以用于测试行为( 例如 ,训练)或治疗干预,病理学或老化后皮质脊髓传播的变化,因此可以更好地理解运动控制和运动的基础的神经过程学习。

Introduction

在灵长类动物中,皮质脊髓束构成控制自愿行为的主要下降途径1 。皮质螺旋途径通过直接的单突触性皮质神经元连接和间接的寡聚和多突触连接2,3将运动皮质区域连接到脊髓α运动神经元。虽然运动皮质可以通过经颅磁刺激(TMS)非常侵入地很容易地被激发,但对这种刺激的诱发肌电图反应通常难以解释。其原因是复合运动诱发电位(MEP)可能受皮质和皮质脊髓神经元,脊髓中间神经元和脊髓α运动神经元4,5,6,7的兴奋性变化的影响。几种无创电生理学cal技术和刺激方案旨在确定皮质脊髓兴奋性和传播的变化是否由皮质或脊髓水平的变化引起。通常,电诱发H反射的振幅的变化被用作运动神经元池的兴奋性改变的“指示性”。然而,之前已经表明,H反射不仅依赖于运动神经元池的兴奋性,而且还受其他因素调节,例如突触前抑制8,9或同源突触后活化抑郁症5,10 。比较MEPs和H反射的另一个限制是检测1112级神经元兴奋性变化的障碍。除了这些缺点,运动神经元可能不同于周围神经刺激而不是wi激活TMS使得运动神经元兴奋性的变化将以与通过皮质脊髓通路13,14,15介导的反应相比以不同的方式影响这些应答。

用于将脊柱与皮质作用分离的另一种方法代表运动皮质16的经颅电刺激(TES)。在低刺激强度下应用,TES被认为不受皮质兴奋性变化的影响。由于TES和TMS都通过皮质螺旋途径激活α运动神经元,所以磁诱发MEPs的比较提供了一种更有吸引力的方法来得出关于MEPs大小变化的皮层性质的结论,而不是H反射之间的比较和MEPs。然而,当刺激强度增加时,TES诱发的MEP也受皮层兴奋性变化的影响sup class =“xref”> 17,18。当电刺激不施加到运动皮质但在颈髓髓结的时候,可以避免这个问题。然而,虽然电刺激可以引起上肢和下肢肌肉的颈动脉运动诱发电位(cMEP),但大多数受试者感觉到脑干(和皮层)的电刺激极其不愉快和痛苦。一个不那么痛苦的替代方案是通过使用磁刺激在宫颈髓核结合处激活皮质脊髓通路19 。通常接受的是,颈动脉磁刺激(CMS)激活许多与运动皮层TMS相同的下降纤维,并且通过将MEP与cMEP 19进行比较可以检测到皮质兴奋性的变化。皮层细胞和皮质神经元细胞的兴奋性增加被认为促进皮层诱发的MEP没有并发改变的宫颈诱发MEP。

然而,在大多数受试者中,不可能在休息20,21的下肢获得磁性诱发的cMEP。克服这个问题的一个方法是通过自愿预先收缩目标肌肉来提高脊柱运动神经元的兴奋性。然而,众所周知,收缩强度的轻微变化影响cMEP的尺寸。因此,难以比较不同的任务。此外,由于预收缩引起的运动神经元兴奋性的变化将影响MEPs和cMEP,但不一定在相同程度上。最后,通过比较化合物MEP和化合物cMEP,一些信息包含在下降的波浪中。通过研究包括通过磁力马达皮层刺激调节比目鱼肌,胫前肌和桡侧肌的H反射的研究揭示了这一点12日 22日 。通过结合外周神经刺激和TMS在运动皮质上具有特异的刺激间期(ISI),可以研究不同下降球对H反射的促进和抑制作用。这种技术受到动物实验中用于确定神经通路传播的空间促进技术的极大启发,可被视为该技术的非侵入性间接版本23 。虽然H反射不仅对于区分皮质脊髓通路的不同部分(快速与较慢的皮质脊髓投射)是重要的,但是也必须以受控和可比较的方式提高脊柱兴奋性。因此,在休息和活动期间,这种刺激技术的组合允许以高时间分辨率评估皮质螺旋途径的不同部分的变化, 在t他最快,可能是单突触性皮质神经元连接和慢性低聚和多突触通路12,22,24,25。最近,这种技术不仅通过运动皮质(M1调节)调节TMS的H反射,而且通过在宫颈髓核结合处(CMS-调节) 26进行额外的调理刺激来延长。通过比较M1-和CMS调节之间的效应,该技术允许具有高时间分辨率的途径特异性分化,并且允许对皮质与脊髓机制进行解释。此外,最重要的是,关于目前的研究,这种技术允许在考虑早期促进时评估皮质转移突触的传播。 H反射的早期促进很可能是由激活引起的对脊柱运动神经元12,26的直接,单突触性皮质转移瘤投射。为了测试最快的皮质脊髓途径,因此,早期促进,H反射必须在TMS之前2至4 ms引出。其原因是与H反射(约34ms;见25 )相比,MEP的等待时间略短(约32ms;见27 )。在应用TMS之前不久就引发H反射,导致脊柱运动神经元水平上升和最快下降兴奋的趋同。当TMS施加在颈髓髓结上时,下降排卵将在脊髓运动神经元游泳池的3〜4毫秒之前比在M1刺激之后达到。对于CMS调理,因此周围神经刺激应在磁脉冲前6 – 8 ms引起。 CMS调节后的早期促进变化表明差异tr在皮质脊髓束和α-运动神经元之间的突触28 。在目前的研究中,最近开发的技术用于区分脊髓与低频重复TMS(rTMS)后的皮层效应。更具体地说,我们假设,如果在rTMS干预之后,如果M1调节的早期促进减少,但CMS调节之后的早期促进不是,其效果应该是纯皮层的起源。相比之下,如果早期促进CMS调理也发生变化,这种改变应该与脊髓水平发生的机制有关。更具体地说,由于H反射的早期促进被认为是由对直接的脊髓运动神经元12,29的直接的皮质类神经元突起的激活引起的,所以在时间上改变了CMS-和M1-调节的H反射早期促进应该指示改变的皮质类神经元传播突触功效28

Protocol

该协议经当地道德委员会批准,实验符合赫尔辛基宣言(1964年)。 主题准备 注意:主题说明 – 在开始实验之前,指导每个受试者了解研究的目的和潜在的危险因素。对于经颅磁刺激(TMS),医疗风险包括任何癫痫发作史 ,眼睛和/或头部精神植入物,心血管系统疾病和怀孕。排除所有确认其中一个风险因素的科目。?…

Representative Results

在M1-和CMS调理之后发生早期促进 在TMS上的H反射调理导致早期促进发生在ISI -3和-4毫秒周围。 CMS调理后的早期促进发生在3毫秒前(分别为ISI -6和-7毫秒)。 图1中显示了一个对象的示例性ISI曲线。在本研究中,早期的促进是在其发生的第一个毫秒内进行评估,同时使用M1-和CMS-调理(参见<strong c…

Discussion

这里描述的H反射调节程序已经专门用于评估在重复激活皮质脊髓通路28之后的皮质类神经元突触的传播的急性变化。在这方面,H反射调理已经突出表明,rTMS不仅影响皮质结构的兴奋性,而且还对皮质类膜转移突触的皮质转移传导有影响。然而,随着运动发育和衰老,运动学习,运动和训练,疲劳,不活动,从损伤恢复,神经生理学和治疗干预,病理学等方面发生皮质螺旋传播?…

Disclosures

The authors have nothing to disclose.

Acknowledgements

这项研究得到瑞士国家科学基金会(316030_128826)的资助。

Materials

Self-adhesive EMG electrodes Blue sensor N, Ambu, Ballerup, Denmark Used to record EMG signals
Electrical stimulator Digitimer DS7A, Hertfordshire, UK Used to elicit the soleus H-reflex
Stimulating electrode Blue sensor N, Ambu, Ballerup, Denmark Used to elicit the soleus H-reflex
Magnetic stimulator no1 Magstim Rapid2 TMS stimulator, Magstim Company Ltd., Whitland, UK Used to elicit contralateral motor evoked potentials in the soleus muscle
Coil no1: 90 mm figure-of-eight coil  Magstim Company Ltd., Whitland, UK Used to elicit contralateral motor evoked potentials in the soleus muscle
            Stimulator no1 and coil no1 were used in the original publication (Taube et al. 2014; Cerebral Cortex)
Magnetic stimulator no2 MagPro X100 with MagOption, MagVenture A/S, Farum, Denmark Used to elicit contralateral motor evoked potentials in the soleus muscle
Coil no2: 95-mm focal “butterfly-shaped” coil (D-B80)  MagVenture A/S, Farum, Denmark
Stimulator no2 and coil no2 were used in the video session
Magnetic stimulator no3 Magstim Company Ltd., Whitland, UK Used to stimulate at the cervicomedullary junction
Coil no3: double-cone magnetic coil Magstim Company Ltd., Whitland, UK Used to stimulate at the cervicomedullary junction
Image-guided TMS navigational system no1 Brainsight 2, Rouge Research, Montreal, Canada Used in the original publication (Taube et al. 2014; Cerebral Cortex) to monitor coil position throughout the experiment
Image-guided TMS navigational system no2 TMS Navigator SW-Version 2.0, LOCALITE GmbH, Sankt Augustin, Germany Used for the video session
Literature: 
Taube et al. 2014 Taube, W., Leukel, C., Nielsen, J. B. & Lundbye-Jensen, J. Repetitive Activation of the Corticospinal Pathway by Means of rTMS may Reduce the Efficiency of Corticomotoneuronal Synapses. Cerebral cortex, doi:10.1093/cercor/bht359 (2014).

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Cite This Article
Taube, W., Leukel, C., Nielsen, J. B., Lundbye-Jensen, J. Non-invasive Assessment of Changes in Corticomotoneuronal Transmission in Humans. J. Vis. Exp. (123), e52663, doi:10.3791/52663 (2017).

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