Watkins Roger H, Wessberg Johan, Backlund Wasling Helena, Dunham James P, Olausson Håkan, Johnson Richard D, Ackerley Rochelle
Department of Physiology, University of Gothenburg, Gothenburg, Sweden;
School of Physiology and Pharmacology, University of Bristol, Bristol, United Kingdom.
J Neurophysiol. 2017 Apr 1;117(4):1608-1614. doi: 10.1152/jn.00939.2016. Epub 2017 Jan 25.
C-mechanoreceptors in humans comprise a population of unmyelinated afferents exhibiting a wide range of mechanical sensitivities. C-mechanoreceptors are putatively divided into those signaling gentle touch (C-tactile afferents, CTs) and nociception (C-mechanosensitive nociceptors, CMs), giving rise to positive and negative affect, respectively. We sought to distinguish, compare, and contrast the properties of a population of human C-mechanoreceptors to see how fundamental the divisions between these putative subpopulations are. We used microneurography to record from individual afferents in humans and applied electrical and mechanical stimulation to their receptive fields. We show that C-mechanoreceptors can be distinguished unequivocally into two putative populations, comprising CTs and CMs, by electrically evoked spike latency changes (slowing). After both natural mechanical stimulation and repetitive electrical stimulation there was markedly less latency slowing in CTs compared with CMs. Electrical receptive field stimulation, which bypasses the receptor end organ, was most effective in classifying C-mechanoreceptors, as responses to mechanical receptive field stimulation overlapped somewhat, which may lead to misclassification. Furthermore, we report a subclass of low-threshold CM responding to gentle mechanical stimulation and a potential subclass of CT afferent displaying burst firing. We show that substantial differences exist in the mechanisms governing axonal conduction between CTs and CMs. We provide clear electrophysiological "signatures" (extent of latency slowing) that can be used in unequivocally identifying populations of C-mechanoreceptors in single-unit and multiunit microneurography studies and in translational animal research into affective touch. Additionally, these differential mechanisms may be pharmacologically targetable for separate modulation of positive and negative affective touch information. Human skin encodes a plethora of touch interactions, and affective tactile information is primarily signaled by slowly conducting C-mechanoreceptive afferents. We show that electrical stimulation of low-threshold C-tactile afferents produces markedly different patterns of activity compared with high-threshold C-mechanoreceptive nociceptors, although the populations overlap in their responses to mechanical stimulation. This fundamental distinction demonstrates a divergence in affective touch signaling from the first stage of sensory processing, having implications for the processing of interpersonal touch.
人类的C类机械感受器由一群无髓传入神经组成，它们表现出广泛的机械敏感性。C类机械感受器被推测分为两类，一类传递轻柔触觉信号（C类触觉传入神经，CTs），另一类传递伤害性信号（C类机械敏感伤害感受器，CMs），分别产生积极和消极的情感体验。我们试图区分、比较和对比人类C类机械感受器群体的特性，以了解这些推测的亚群之间的划分有多基本。我们使用微神经ography记录人类个体传入神经的活动，并对其感受野施加电刺激和机械刺激。我们表明，通过电诱发的峰潜伏期变化（减慢），C类机械感受器可以明确地分为两个推测的群体，即CTs和CMs。与CMs相比，在自然机械刺激和重复电刺激后，CTs的潜伏期减慢明显较少。绕过感受器终末器官的电感受野刺激在对C类机械感受器进行分类时最为有效，因为对机械感受野刺激的反应有一定程度的重叠，这可能导致错误分类。此外，我们报告了一类对轻柔机械刺激有反应的低阈值CMs亚类，以及一类可能显示爆发性放电的CT传入神经亚类。我们表明，CTs和CMs之间轴突传导的控制机制存在显著差异。我们提供了清晰的电生理“特征”（潜伏期减慢程度），可用于在单单位和多单位微神经ography研究以及情感触觉的转化动物研究中明确识别C类机械感受器群体。此外，这些不同的机制在药理学上可能是可靶向的，用于分别调节积极和消极的情感触觉信息。人类皮肤编码了大量的触觉相互作用，情感触觉信息主要由传导缓慢的C类机械感受传入神经传递。我们表明，与高阈值C类机械敏感伤害感受器相比，低阈值C类触觉传入神经的电刺激产生的活动模式明显不同，尽管这两个群体对机械刺激的反应有重叠。这种基本区别表明，情感触觉信号从感觉处理的第一阶段就存在差异，这对人际触觉的处理有影响。
