Evaluation of antihyperalgesic effect of curcumin on formalin-induced orofacial pain in rat

The present study was planned to evaluate the role of curcumin in the formalin-induced orofacial pain in rats that mimics typical human orofacial pain. Adult Wistar rats of either sex received an injection of 50 microL of 5% v/v subcutaneous formalin injection into one vibrissal pad and consequent facial grooming behavior was monitored. Animals exhibited two distinct periods of nocifensive grooming: (a) an acute phase lasting 0-6 min; and (b) a tonic phase lasting 6-45 min. The analgesic response of curcumin was observed at doses of 25, 50, 100, 200, 400 and 600 mg/kg i.p., administered 15 min prior to formalin injection. Another group received subanalgesic dose of diclofenac (0.2 mg/kg) and curcumin 25 mg/kg. Curcumin and diclofenac were administered 15 and 5 min prior to formalin injection respectively. Curcumin produced a dose-dependent inhibition of facial grooming in both acute and tonic phases compared to vehicle and potentiated the subanalgesic dose of diclofenac. The study results for the first time demonstrated the per se antinocifensive effect of curcumin and also exhibited a synergistic interaction with the subanalgesic dose of an NSAID in the facial pain model. More studies are necessary to elucidate the mechanisms of curcumin in this model of pain.