Mechano-insensitive nociceptors encode pain evoked by tonic pressure to human skin

Neuroscience. 2000;98(4):793-800. doi: 10.1016/s0306-4522(00)00189-5.

Abstract

Single unmyelinated axons in the superficial branch of the peroneal nerve of human subjects were recorded (microneurography) and the response patterns during tonic pressure stimulation (14N at 30 mm(2); 120 s) were assessed using the previously described "marking technique". It was found that tonic pressure stimuli induced augmenting pain responses which were matched by the discharges of initially mechano-insensitive ("silent") C-units, whereas mechano- and heat-responsive "polymodal" C-nociceptors showed a response pattern incompatible with the stimulus-induced perceptions, namely strong initial excitation, followed by adaptation. Eighteen mechano- and heat-responsive "polymodal" C-fibers and 11 mechano-insensitive units were studied. The former had von Frey thresholds <160 mN, the latter were not excited by a von Frey filament of 750 mN (six of them responded to radiant heat stimulation). However, in the course of pressure stimulation, nine of the 11 mechano-insensitive units were activated after more than 20s. A second, identical pressure stimulus induced a stronger response in mechano-insensitive and a weaker response in mechano-responsive units. The stronger response, indicating sensitization, matched the more intense pain perception during the second pressure stimulus. It is concluded that mechano-insensitive C-nociceptors encode pressure-induced pain in human hairy skin and that they play an important role in static mechanical hyperalgesia.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Female
  • Humans
  • Male
  • Mechanoreceptors / physiology*
  • Nociceptors / physiology*
  • Pain Measurement / methods*
  • Pain Measurement / psychology
  • Peroneal Nerve / physiology
  • Physical Stimulation / methods
  • Pressure
  • Reaction Time / physiology*
  • Skin Physiological Phenomena*
  • Statistics, Nonparametric