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, as compared to 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 sub-class of low-threshold CM responding to gentle mechanical stimulation, and a potential sub-class 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 and multiunit microneurography studies, and in translational animal research into affective touch. Additionally, these differential mechanisms may bepharmacologically targetable for separate modulation of positive and negative affective touch information.
- low-threshold mechanoreceptor
- Copyright © 2016, Journal of Neurophysiology