Which nerve fibers mediate the axon reflex flare in human skin?

Axon reflex vasodilatation due to transcutaneous electrical stimulation in human skin was measured by laser Doppler imaging. Constant current pulses o f 10 mA, 0.2 ms, delivered at 1 or 10 Hz for 2 min through a probe of 30 mm (2) surface area did not induce a significant flare response, though this s timulus previously has been found supra-maximal for cutaneous polymodal (me chano-heat responsive) C-nociceptors in microneurography experiments. Pulse s of the same strength from a pointed probe yielding a higher current densi ty induced an extended and persistent flare. This type of stimulus previous ly has been proven to recruit mechano-insensitive C-units in microneurograp hy experiments, in contrast to stimuli from the 30 mm(2) probe; It is concl uded that mechano-insensitive C-nociceptors and not polymodal C-units media te the axon reflex flare in human skin. NeuroReport 11:645-648 (C) 2000 Lip pincott Williams & Wilkins.