Antidromic nerve stimulation in monkey does not sensitize unmyelinated nociceptors to heat.

Spread of sensitization of nociceptors has been proposed as the mechanism for the secondary hyperalgesia in the region that surrounds a cutaneous injury. One possibility, tested in this study, is that antidromically propagated action potentials in nociceptors result in the release of substances at their cutaneous arborization which sensitize adjacent nociceptors. Using standard teased-fiber techniques, we recorded from single C-fiber nociceptive afferents innervating hairy skin in the monkey. Heat testing was performed before and after electrical stimulation of the parent nerve at strengths sufficient to activate C-fibers. The heat thresholds and total response to the heat sequences were not changed by the electrical stimulation. We conclude that antidromic stimulation of C-fibers in the monkey does not sensitize C-fiber nociceptors to heat stimuli.