Capsaicin applied to rat lumbar intervertebral disc causes extravasation in the groin skin: a possible mechanism of referred pain of the intervertebral disc.

Administration of 10 micrograms of capsaicin into the anterior portion of a lumbar intervertebral disc of rats pretreated with Evans blue (i.v.) caused dye extravasation in the groin skin. This phenomenon occurred even when the spinal nerve of the same segment, bilateral sympathetic trunks, and/or the anterior L2 spinal root had been cut; it did not occur in rats with a cut genitofemoral nerve. Infiltration of capsaicin solution directly into the genitofemoral nerve did not cause dye extravasation. These results suggested the presence of dichotomizing sensory C-fibers which innervate both the intervertebral discs and the groin skin in the L2 spinal nerve. If such dichotomizing fibers exist in man, they may contribute to the groin pain sometimes associated with intervertebral disc lesions.