Discharge patterns of human C-fibers induced by itching and burning stimuli.

1. The aim of this investigation was to study the peripheral neural mechanisms of the C-fiber-mediated modalities of burning pain and itch by the use of microneurography of human unmyelinated afferents. 2. Sixteen stable recordings of single C-fibers and 6 multiunit recordings were obtained from the superficial radial nerves of volunteers. All units were excited by stimulating their receptive fields with von Frey bristles (range 10-600 mN), and all but four units were also driven by radiant heat stimulation. 3. Histamine was iontophoretically applied to the receptive fields of these units for 20 or 30 s and was found to provoke itching sensations lasting several minutes, together with wheal and flare responses. Subsequently a solution containing 20 or 30% mustard oil was applied to the receptive field of the respective unit, which provoked a sensation of burning pain. 4. One-half of the units were excited by histamine, and the median discharge rates derived from interspike intervals ranged from approximately 0.1 to 0.8 Hz. Mustard oil-induced activity was observed in all histamine-sensitive units and also in three single units and in one multiunit recording that revealed no histamine response. Median interval-derived discharge rates ranged from 0.2 to 1.2 Hz. 5. Analysis of the interspike interval distribution and of the autocorrelation function derived from the chemically induced discharges of single units provided no evidence for an encoding of itch and burning pain in different discharge patterns of units responding to histamine and to mustard oil.(ABSTRACT TRUNCATED AT 250 WORDS)