C-polymodal nociceptors activated bynoxious low temperature inhumanskin

1. Fifty-five C-polymodal nociceptors innervating hairy skin inhumanvolunteers weretested fordiscrete stimulus-response properties through microneurography. 2. Allfifty-five units wereresponsive tomechanical andheatstimuli. Twenty-two (40%)of these exhibited anadditional response tonoxious lowtemperature. Thetwenty-two mechano-heat-cold nociceptors displayed similar receptor responses toheatandmechanical stimuli, andconduction velocity, asthoseofthepuremechano-heat C-polymodal nociceptors. 3. Lowtemperature stimuli between 19and0°Cevoked responses atlowdischarge frequency (04+ 0'22 impulses s-', mean+S.E.M.) inthetwenty-two units sensitive tosuchenergy. These units displayed atendency todecrease their discharge after afewseconds of steady stimulation. 4. Threeunits tested withafreezing stimulus responded withrelatively vigorous discharge, which never exceeded themaximal discharge frequency elicited byeither mechanical orheat stimuli. Oneofthese units became sensitized toheat after thefreezing challenge. 5. Itisconcluded that asubpopulation ofC-polymodal nociceptors issensitive tonoxious low temperature andmaythuscontribute tothedetermination ofcold pain. Thesametypeof primary afferent isprobably onemediator ofthesymptomcold hyperalgesia inperipheral nerve disease.