Effect of melatonin on sciatic nerve regeneration in different injury models: Ultrastructural and biochemical analyses

Several kinds of injury models, such as crush, cut and graft repair have been well studied in terms of neuroprotective effect of melotonin. However, definitive experimental studies are lacking on neuroprotective effect of melatonin (50 mg/kg/day) in both cut and crush injuries. In the present study, our aim was to study the effect of melatonin on recovery of the sciatic nerve after cut or crush injuries. A total number of 90 Wistar rats were used for this purpose and divided into six groups (Group 1: Control, Group 2: Sham-operated, Group 3: Cut, Group 4: Cut + melatonin, Group 5: Crush, Group 6: Crush+ melatonin). After operation, melatonin administration was performed from the first to the end of the sixth postoperative week between 16:00-17:00. Sciatic nerve regeneration was evaluated by walking track analysis, pinch test, light and electron microscopy and antioxidant effect of melatonin was evaluated by biochemical analysis. In the preoperative day, SFI values of the experimental group showed no significant deference (p>0.05) compared with the control group. However there was statistical significance between group 3, 4 and group 5, 6 in the 3rd and 4th postoperative weeks (p<0.05). In control and sham-operated groups withdrawal responses to pinch were full (Grade 3). The onset day of full withdrawal response (Grade 3) to pinch stimulation was in the 3rd postoperative week. At the same week, number of the animals of group 5 showing withdrawal was higher than those in group 6. In spite of that group 3 had no full response in the 3rd postoperative week. Electron microscopic analysis revealed more less phagocytic cells and lamellar separation of the myelin sheaths in animals administered Melatonin than those of sciatic nerve injury performed. As a result of electrophysiologic analysis revealed that components P1, N1, P2 and N2 were significantly (p<0.001) increased in group 3 an 5 compared with the Sham group and these components were also prolonged in the Group 4 and Group 6 with respect to the group 3 and 5 (p<0.001). Biochemical analysis showed that treatment with melatonin in both crush and cut injury groups induced a significant increase in tissue MDA levels, but a decrease in tissue SOD, CAT, GPx activities (p<0.001).