Collateral sprouting of nociceptive C-fibers after cut or capsaicin treatment of the sciatic nerve in adult rats.

The innervation area of nociceptive C-fibers in the saphenous nerve of adult rats was detected by the Evans blue technique, in which antidromic excitation of the nociceptive C-fibers causes a visible extravasation of dye in the skin it supplied. One month after cutting the sciatic nerve, the nociceptive C-fibers of the intact saphenous nerve had sprouted to the sciatic area. When capsaicin was locally applied to the nerve trunk to destroy C-fibers of the sciatic nerve, there was no sprouting of nociceptive C-fibers from the saphenous nerve. Thus, myelinated fibers and/or the functionally impaired C-fibers of the sciatic nerve are enough to prevent collateral sprouting of nociceptive C-fibers from the saphenous nerve.