BACKGROUND: Studies have shown that the combined use of sufentanil and neural stem cell (NSC) transplantation can increase the number of newborn nerve fibers.OBJECTIVE: To investigate the effect of sufentanil on the hind limb function of rats with spinal cord injury after neural stem cell transplantation.METHODS: (1) Eighty adult female Sprague-Dawley rats were used to build spine cord injury model according to the modified Allen's method and divided into model group, sufentanil group, NSCs transplantation group and sufentanil combined with NSCs transplantation group (combined group). Extra 20 adult female Sprague-Dawley rats were not conducted any treatment as normal control group. (2) After 6 days of modeling, the model rats were subjected to subarachnoid injection of 10 μL of NSC culture medium and intraperitoneal injection of 100 μL of saline in the model group; subarachnoid injection of 10 μL of NSC culture medium and intraperitoneal injection of 100 μL of sufentanil (150 μg/kg) in the sufentanil group; subarachnoid injection of 10 μL of 1×1010/L NSCs suspension and intraperitoneal injection of 100 μL of saline in the NSCs transplantation group; and subarachnoid injection of 10 μL of 1×1010/L NSCs suspension and intraperitoneal injection of 100 μL of sufentanil (150 μg/kg) in the combined group. (3) After 72 hours of modeling, the AQP4 and MMP9 gene expression levels were detected by RT-PCR, and the cell apoptosis changes around the spine cord injury area were determined with TUNEL staining method. (4) The motor functions of rats were tested by Basso, Beattie and Bresnahan score and inclined plane test after 1, 3 days and 1, 2, 3 and 4 weeks of modeling. (5) After 4 weeks of modeling, the histopatholgical changes in the area of spine cord injury were observed by hematoxylin-eosin staining method. The survival changes of NSCs labeled by CM-Dil were determined by fluorescence microscope. The regenerations and distributions of spinal nerve fibers were observed by fluorescein gold retrograde tagging.RESULTS AND CONCLUSION: (1) After 72 hours of modeling, the AQP4 and MMP9 gene expression levels as well as the cell apoptotic rate in the combined group were significantly lower than those in the model, sufentanil and NSCs transplantation groups (P < 0.05). (2) After 2 weeks of modeling, the combined treatment significantly improved the hind limb motor functions of rats compared with the sufentanil and NSCs transplantation groups (P < 0.05), and the recovery of motor function was better in the sufentanil and NSCs transplantation groups than in the model group (P < 0.05). (3) After 4 weeks of modeling, the results of hematoxylin-eosin staining manifested that the spinal cord tissues lost and the magnified syringomyelias occurred in the model group. The syringomyelias in the sufentanil and NSCs transplantation groups were significantly smaller than that in the model group, and the syringomyelias almost disappeared in the combined group. (4) The number of positive cells was the most in the combined group, more in the NSCs transplantation group, but there were no positive cells labeled by CM-Dil in the sufentanil and negative control groups. (5) The number of positive neural fibers in the combined group was the highest followed by the sufentanil and NSCs transplantation groups, and the number of positive neural fibers in negative control group was the lowest. To conclude, sufentanil can improve the recovery of hind limb motor function by reducing the AQP4 and MMP9 expression levels in the injury area, promoting the survival of transplanted NSCs, and decreasing the local NSCs apoptosis after spinal cord injury.