Problem statement: Diabetes mellitus occurs mainly with chronic polyneuropathy, and oxidative stress plays an important role in emergence of most neurologic and behavioral changes in diabetic patients. Many studies have focused on the beneficial effects of various antioxidants such as melatonin on diabetic neuropathy. The aim of this study is to evaluate the effect of melatonin in prevention of neuropathy in Streptozotocin-induced diabetic rats. After prescribing Streptozotocin (STZ), treatment rats received melatonin (10 mg kg day-1) or DMSO for a period of 6 weeks. Approach: At the end of the sixth week, non diabetic control group, diabetic control group (sham) and treated rats were examined by thermal pain response tests (hot plate and tail flick). The horizontal and vertical activities of rats were measured in an open field test. After that, Motor Nerve Conduction Velocity (MNCV) of sciatic-tibial nerve recorded. Also, to study morphological alterations resulting from diabetic neuropathy of sciatic nerve, Myelinated Fiber Diameter (MFD), Axon Diameter (AD) and Myelin Sheath Diameter (MSD) were evaluated by light microscope. Results: According to hot plate results, response time to thermal pain at the end of sixth week in sham group showed a significant decrease in comparison with the control group (p<0.01). In hot plate test, although melatonin approximated to the response time to control group, the significant difference was not observed among melatonin receivers and other groups. In the open field test, Total Distance Moved (TDM) and mobility duration showed significant decrease in sham and DMSO groups in comparison to the control and melatonin groups. Diabetic rats treated with melatonin showed significant increase in MNCV compared to sham and DMSO groups (p<0.05). In morphological study, pretreatment with Melatonin significantly reversed sciatic nerve diameters (MFD, AD, and MSD) reduction in diabetic rats. Electron microscopy showed myelin splitting and myelin sheath infolding in diabetic control group compare to non diabetic group. Conclusion: This study showed that melatonin can decrease the destructive progress of diabetes and causes neuroprotection against damages resulting from STZinduced hyperglycemia.
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