Once daily administration of various doses of melatonin had a limited or no effect on thermal hyperalgesia in each group of WKY rats treated with 30, 60 or 120 mg/kg melatonin as compared with the baseline in the same group. Only the highest dose (120 mg/kg) had an effect (P< 0.05, Fig. 3a). The vehicle treatment did not change thermal hyperalgesia (P> 0.05, Fig. 3a). Mechanical allodynia was not improved by all three doses of melatonin (P> 0.05, Fig. 3b). Mel30, 60 and 120mg: melatonin 30, 60 and 120mg/kg, respectively; Bas, Baseline; CCI1w, 1 week after CCI; T1W, 1 week after CCI followed by 1-week treatment with vehicle or DM. *, P<0.05 as compared with baseline in the same group.