A modified impactor for establishing a graded contusion spinal cord injury model in rats

Background: Given the indispensable role of animal models in preclinical studies of spinal cord injury (SCI) and the current state of available impactors, we designed a modified impactor for establishing contusion SCI in rats. The major improvement is the replacement of the impactor rod with a weight and an impactor tip. Methods: Preoperatively, radiographs of 8-week-old female Wistar rats were taken to establish a protocol for locating the target spinal segment. A total of 72 rats were randomly divided into 4 groups: the sham, 12.5-, 25- and 50-mm groups. Within 35 days postinjury (dpi), the Basso, Beattie, and Bresnahan locomotor rating scale (BBB) was used to evaluate the hindlimb motor function of the rats. At 7 dpi, the rats were sacrificed, and the spinal cord tissue was fixed. Hematoxylin-eosin (HE) staining was used to assess histological changes. Subsequently, immunofluorescence staining was performed to visualize the expression and distribution of GFAP, CD68, MBP, and NeuN. Additionally, rats were sacrificed, and their tissues were extracted for relevant protein assays. At 3 and 7 dpi, electrophysiological function was evaluated by measuring motor evoked potentials (MEPs) and sensory evoked potentials (SEPs). Results: The behavioral results revealed that higher strike heights were associated with lower BBB scores. Over time, the BBB scores of the SCI rats exhibited an improving trend. Quantitative analysis of the lesions indicated that as the impact height increased, the area of histological destruction, GFAP- negative area, CD68-positive cell count, and MBP-positive destruction area increased, and the number of NeuN-positive cells decreased. Western blot analysis further verified relevant protein changes. Electrophysiology confirmed that the MEP and SEP amplitudes decreased as the strike height increased. Conclusions: Thus, these results confirm that this modified impactor can be used to establish a graded SCI model in rats. The model is clinically relevant, reproducible, stable, accessible, and affordable, providing a practical tool with which to elucidate the pathophysiological mechanisms and potential therapies for contusive SCI.