The excitation of cutaneous nerve endings in a neuroma by capsaicin.

Spontaneous electrophysiological activity and excitation by capsaicin of regenerating sensory fibers has been studied using 1 to 20-week-old neuromas induced in rats by ligating and transecting the saphenous nerve. Overall, spontaneous activity occurred in 12% of fibers, and capsaicin at concentrations up to 1.0 microM excited 3.8% of all the A delta-plus C-fibers examined. There was a slight increase in the incidence of spontaneous activity, but not excitation by capsaicin, with increasing age of the neuromas. The responses to capsaicin were similar to those seen with normal saphenous nerve endings, including bursting discharges and desensitization with repeated applications. The results are considered in the context of the requirements for reexpression of normal sensory capacities on regenerating sensory nerve endings.