Effects of Methylprednisolone on Nerve Regeneration after Delayed Repair in Wistar Rats

Functional recovery after delayed nerve repair is poor due to nerve degeneration and muscle atrophy. It is well known that the inflammationplays a pivotal role in the degeneration process. The aim of this study was to investigate the effects of methylprednisolone (MP) as an anti-inflammatory agent on nerve regeneration after delayed repair in rats. Materials and Methods: The sciatic nerve of male Wistar rats was transected at the mid-thigh and the operated animals were administrated a low dose of methylprednisolone succinate (2 mg/kg/day, i.p.) for a period of 2 weeks. The control animals underwent the same procedure without treatment. After a period of 4-weeks, the transected nerve was re-exposed, refreshed and the nerve gap was repaired by a 6 mm allograft from the sciatic nerve of normal donors. Nineteen weeks after surgical repair, histomorphometric analyses were performed in both graft and distal part of repaired nerves to determine the number of mast cells, nerve fiber density and diameter of axons. Results: Although there was no remarkable difference in the fiber density between the two groups, the mean diameter of axons in the distal stump of MP group was approximately 1.7 times of control. Interestingly, in the MP group, the density of mast cells in the graft was about 2 fold higher than that of the control group. Conclusion: Following nerve transaction, a 2 week systemic administration of MP resulted in an increase in axonal diameter. This finding shows that, in situations that immediate nerverepair using surgical intervention is not available, methylprednisolone administration may keep the regenerative capacity in the distal stump of transected nerve. On the other hand, the increased density of mast cells in the graft is in contrast to immunosuppressant effects of MP in the transplantational approches and needs to further studies