• M Grönroos and A Pertovaara.
• Department of Physiology, University of Helsinki, Finland.
• Neurosci. Lett. 1993 Sep 3;159(1-2):215-8.

AbstractThe effect of selective activation of nociceptive primary afferent fibers by capsaicin on a nociceptive lower limb flexion reflex was studied in healthy human subjects. Capsaicin (1%) applied topically to the skin produced a burning spontaneous pain sensation and allodynia in the treated region and in its immediate vicinity. Capsaicin applied to the distal innervation area of the sural or saphenous nerve produced a significant decrease of the threshold for the nociceptive limb flexion reflex induced by electric stimulation of the proximal sural nerve trunk, and this threshold decrease was rapidly attenuated by a cool compress concomitantly with the attenuation of the capsaicin-induced spontaneous pain. The latency of the flexion reflex response was not changed by capsaicin. The non-nociceptive H-reflex was not modified by capsaicin. It is concluded that a selective activation of nociceptive primary afferent fibers of the skin by capsaicin produces a central facilitation of a nociceptive flexion reflex in humans. This facilitation is selective on the nociceptive reflex and depends, at least partly, on the on-going afferent barrage in C-fibers.

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