C nociceptor activity in human nerve during painful and non painful skin stimulation.
Percutaneous recordings from more than one hundred single C fibres have been performed in the radial nerve of conscious human subjects. All these fibres belong to the poly-modal C nociceptor group, being excited by mechanical and thermal and also by chemical stimulation. Conduction velocities showed a monophasic distribution with a mean value of 0.86 m/s (SD: 0.17). The mechanical threshold, measured with von Frey hairs, varied between 2.3 and 13.1 g. The receptive field was circular or elliptical; for 33 units the mean axes were 6 mm and 7 mm. Mechanically evoked C fibre discharge even up to more than 10 spikes/s was not necessarily accompanied by pain sensation. Nettle sting evoked an irregular C fibre discharge (maximum 10 spikes/s) accompanied by a pricking and burning sensation; the sensation of itch which was sometimes reported, was not correlated with the discharge frequency. C fibre activation by a chemical irritant (paint remover) also evoked an irregular discharge (maximum 3 to 6 spikes/s), accompanied by pricking and burning pain sensation. The C threshold for radiant heat usually lay below the subject's pain threshold. Increasing skin temperature produced increasing neural firing rate. The mean spike frequency rarely exceeded two spikes/s even with stimuli evoking strong heat pain. The occurrence of subjective heat pain response could be as well predicted from th C fibre spike frequency as from the skin temperature. It is concluded that nociceptive C input provoked by thermal or chemical stimuli correlates well with pain sensation. However, similar C input provided by mechanical stimulation which activates also A beta mechanoreceptors, did not necessarily produce pain sensation.
D000328:Adult; D006632:Histamine / Q000494:pharmacology; D006358:Hot Temperature; D006801:Humans; D008752:Methylene Chloride / Q000494:pharmacology; D009412:Nerve Fibers / Q000502:physiology*; D009431:Neural Conduction; D009619:Nociceptors / Q000502:physiology*; D010146:Pain / Q000503:physiopathology*; D010812:Physical Stimulation; D012867:Skin / Q000294:innervation*; D013268:Stimulation, Chemical
D008752:Methylene Chloride; D006632:Histamine