Experimental Brain Research

, Volume 231, Issue 2, pp 139–151 | Cite as

Mechanical allodynia in human glabrous skin mediated by low-threshold cutaneous mechanoreceptors with unmyelinated fibres

  • Saad S. Nagi
  • David A. MahnsEmail author
Research Article


We recently showed that C-tactile fibres (CTs) in human hairy skin (anterior leg) mediate crossover between innocuous touch and noxious touch, i.e. mechanical allodynia. Although there is no evidence for existence of a phenotypically identical class of CTs in human glabrous skin, the ‘qualia’ of affective stimuli are comparable across skin types. In 42 healthy subjects, muscle pain was induced by infusing hypertonic saline (5 %) into flexor carpi ulnaris muscle. Concurrently, sinusoidal vibration (200 Hz–200 μm) was applied to glabrous skin of little finger. The neural substrate of allodynia was determined by employing conduction blocks of myelinated (ulnar nerve compression) and unmyelinated (low-dose intra-dermal anaesthesia) fibres. In order to compare the expression of allodynia across spinal segments and skin types, vibration was also applied to glabrous skin of index finger and hairy skin of dorsal forearm. In addition, high-precision brushing stimuli were applied at speeds of 1.0 and 3.0 cm s−1 to digital glabrous skin with absent myelinated fibres. During muscle pain, vibration caused a significant and reproducible increase in pain (allodynia). This effect persisted during blockade of myelinated fibres, but was abolished by inactivation of unmyelinated cutaneous fibres. The vibration-evoked effects were found to be comparable across spinal segments and skin types. Furthermore, brushing produced a near-identical expression of C-fibre-mediated allodynia. Prior to induction and upon cessation of muscle pain, vibration and brushing were reported as non-painful. Based on these results, we postulate that a functional homologue of the CTs (hairy skin) mediates allodynia in human glabrous skin.


C-tactile fibres Muscle pain Allodynia Hypertonic saline Glabrous skin Rotary tactile stimulator 



C low-threshold mechanoreceptors


C-tactile fibres


Dorsal posterior insular cortex


Dorsal root ganglion


Flexor carpi ulnaris muscle


Hypertonic saline


Intra-neural microstimulation


Meissner corpuscles




Rotary tactile stimulator


Tyrosine hydroxylase


Visual analogue scale


Vesicular glutamate transporter 3


Posterior portion of ventromedial thalamic nucleus



This work was supported by the National Health and Medical Research Council of Australia and the University of Western Sydney. We thank Melia Condon for her assistance in some of the experiments. We also thank Håkan Olausson and Francis McGlone for the loan of the RTS.


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© Springer-Verlag Berlin Heidelberg 2013

Authors and Affiliations

  1. 1.Department of Integrative Physiology, School of MedicineUniversity of Western SydneySydneyAustralia

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