Introduction: Pharmacotherapy is a cheap, accessible and non-invasive treatment that can be used in the first hours after the nerve injury. Although using some drugs after nerve injury accelerates the nerve repair process. But their functional outcomes are still not satisfactory. Therefore, the aim of the present study was to evaluate the effects of methylprednisolone (MP) administration on maintaining the regenerative capacity of the distal segment of the transected sciatic nerve in conditions of delayed nerve repair. Methods: The sciatic nerve of male rats (250-300 g) was transected and the animals were interaperitoneally administrated MP succinate (2 mg/kg, n=8) and saline (control group, n=8) for 1 month. In the sham group (Control group, n=5), the sciatic nerve was only exposed. After 1 month, the transected nerve was repaired. Fourteen weeks after surgical repair, morphometric and electron microscopic evaluations were performed on the nerve. Results: In the present study, the mean axonal cross-section area, myelinated fiber diameter, axonal diameter and myelin thickness were significantly higher in the MP distal segment compared to that of the control group (P<0.01). Also, the majority of the fibers in the MP group had a normal myelin sheath and normal Schwann cell nuclei in the electron micrographs. Conclusions: The results of this study showed that, in the situations that immediate nerve repair using surgery is not possible, methylprednisolone administration preserves the axonal regenerative capacity of the distal segment of the transected nerve.

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