Inflammation reveals inhibition of noxious responses of rat spinal neurones by carbamazepine

The effect of subcutaneously administered carbamazepine, a sodium channel blocker, on the electrically evoked C-fibre (noxious) vs A beta-fibre (innocuous) responses of dorsal horn neurones in non-inflamed and inflamed rats (3 h after plantar injection of carrageenan) was studied. Carbamazepine (0.5-5 mg/kg) significantly reduced the noxious evoked responses of the neurones under inflammatory, but not non-inflamed, conditions. The innocuous evoked responses of the neurones were not sensitive to carbamazepine under any conditions and administration of the vehicle alone did not influence any evoked response of these neurones. We propose that there are changes in the type, or proportion of, sodium channels underlying the transmission of noxious messages following peripheral inflammation which become sensitive to carbamazepine.