Pre-emptive Effect of Methylprednisolone on the Mechanical Allodynia Development after Peripheral Nerve Injuries in Rats

Abstract

Background: Glucocorticoids have anti-inflammatory effects and have been used to treat many types of nerve injury- associated chronic pain conditions. A randomized double-blind study was performed to determine if methylprednisolone could prevent the development of neuropathic pain after a peripheral nerve injury in rats. Methods: Two groups of rats, one group (n = 50) injected intraperitoneally with methylprednisolone (100 mg/kg/day, for 7 days starting from 3 days prior to the nerve injury) and the other (n = 58) treated with saline with same manner, were compared in tenns of the incidence and intensity of allodynia after a superior caudal trunk transection at the level between the 3trd and 4th sacral spinal nerves. The tail-flick responses to normally innocuous mechanical and thermal stimuli applied to the tail were observed as the behavioral signs of neuropathic pain. Results: The proportions of rats exhibiting tail-flick responses to the mechanical (but not thermal) stimuli 7, 14 and 21 days after the nerve injury were significantly smaller in the methylprednisolone-treated group (2, 3 and 4 of 50 rats, respectively) than in the saline-treated, control group (11, 14 and 15 of 58 rats, respectively) (P = 0.009). However, the pain intensity was similar in mechanical allodynia developed rats of the two groups (P > 0.05), which was estimated based on the frequency and latency of the tail-flick responses after applying mechanical and thermal stimuli, respectively. Conclusions: These results suggest that a pre-emptive treatment with high methylprednisolone doses may be used to prevent the development of mechanical allodynia following peripheral nerve injuries.