ObjectiveTo observe the changes of microstructure of rats'sciatic nerves with non-freezing cold injury after treated with dexamethasone. MethodsTwelve male Wistar rats were randomly divided into cooling group and treating group.Unilateral sciatic nerves of the rats in the cooling group received cooling treatment with 3-5℃ for 2 hours;while unilateral sciatic nerves of the rats in the treating group received cooling treatment with 3-5℃ for 2 hours and underwent the celiac injection with dexamethasone in addition.The other sciatic nerves were exposed,as the control.The bilateral sciatic nerves of rats in each group were harvested after 24 hours.The microstructure of nerves was examined under the light microscope and electron microscope. ResultsLight microscopic examination revealed extensive myelinated fibre degeneration in form of giant empty axons or shrunken dark axons on the first day after cooled.And the endoneurial capillary lumen was narrowed because of swollen endothelial cells.After the treatment,myelinated fibre degeneration was still similar to that before the treatment,but the endoneurial capillary lumen and endothelial cells were normal.By electron microscopy,sciatic nerves showed extensive myelinated fiber degeneration,and swollen endothelial cells.But unmyelinated fibers and tight junction were preserved on the first days after cooled.Aggregated red cells and platelet thrombus were not found.After the treatment,myelinated fibre degeneration was still similar to that before the treatment.Unmyelinated fibers and tight junction were preserved.The endoneurial capillary lumen and endothelial cells were normal. ConclusionAfter the treatment,the damage of endoneurial capillary had improved,but myelinated fiber degeneration was similar to that before the treatment.It suggested that dexamethasone may only improve the vascular system in non-freezing cold injury of sciatic nerve.