Changes in neurological and pathological outcomes in a modified rat spinal cord injury model with closed canal

Most animal spinal cord injury models involve a laminectomy, such as the weight drop model or the transection model. However, in clinical practice, many patients undergo spinal cord injury while maintaining a relatively complete spinal canal. Thus, open spinal cord injury models often do not simulate real injuries, and few previous studies have investigated whether having a closed spinal canal after a primary spinal cord injury may influence secondary processes. Therefore, we aimed to assess the differences in neurological dysfunction and pathological changes between rat spinal cord injury models with closed and open spinal canals. Sprague-Dawley rats were randomly divided into three groups. In the sham group, the tunnel was expanded only, without inserting a screw into the spinal canal. In the spinal cord injury with open canal group, a screw was inserted into the spinal canal to cause spinal cord injury for 5 minutes, and then the screw was pulled out, leaving a hole in the vertebral plate. In the spinal cord injury with closed canal group, after inserting a screw into the spinal canal for 5 minutes, the screw was pulled out by approximately 1.5 mm and the flat end of the screw remained in the hole in the vertebral plate so that the spinal canal remained closed; this group was the modified model, which used a screw both to compress the spinal cord and to seal the spinal canal. At 7 days post-operation, the Basso-Beattie-Bresnahan scale was used to measure changes in neurological outcomes. Hematoxylin-eosin staining was used to assess histopathology. To evaluate the degree of local secondary hypoxia, immunohistochemical staining and western blot assays were applied to detect the expression of hypoxia-inducible factor 1α (HIF-1α) and vascular endothelial growth factor (VEGF). Compared with the spinal cord injury with open canal group, in the closed canal group the Basso-Beattie-Bresnahan scores were lower, cell morphology was more irregular, the percentage of morphologically normal neurons was lower, the percentages of HIF-1α- and VEGF-immunoreactive cells were higher, and HIF-1α and VEGF protein expression was also higher. In conclusion, we successfully established a rat spinal cord injury model with closed canal. This model could result in more serious neurological dysfunction and histopathological changes than in open canal models. All experimental procedures were approved by the Institutional Animal Care Committee of Shanghai Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, China (approval No. HKDL201810) on January 30, 2018.