Abstract Background context The New York University (NYU) impactor and the Infinite Horizon (IH) impactor are used to create spinal cord injury (SCI) models. However, the parameters of these two ...devices that yield equivalent SCI severity remain unclear. Purpose To identify equivalent parameters, rats with SCIs induced by either device set at various parameters were subjected to behavioral and histological analyses. Study design Animal laboratory study. Methods Groups of eight rats acquired SCIs by dropping a 10 g rod from a height of 25 mm or 50 mm by using the NYU device or by delivering a force of 150 kdyn, 175 kdyn, 200 kdyn, or 250 kdyn by using the IH impactor. All injured rats were tested weekly for eight weeks by using the Basso, Beattie, and Bresnahan (BBB) test and the ladder rung test. On the tenth week, the lesion volume of each group was measured by using a 9.4 Tesla magnetic resonance imaging (MRI) and the spinal cords were subjected to histological analysis using anterograde biotinylated dextran amine (BDA) tracing and immunofluorescence staining with an anti-protein kinase C-gamma (PKC-γ) antibody. Results BBB test scores between the 25mm and 200kdyn groups as well as the 50mm and 250kdyn groups were very similar. Although it was not statistically significant, the mean scores of the ladder rung test in the 200kdyn group were higher than the 25mm group at all assessment time points. There was a significantly different cavity volume only between the 50mm and 200kdyn groups. Midline sagittal images of the spinal cord on the MRI revealed that the 25mm group predominantly had dorsal injuries, whereas the 200kdyn group had deeper injuries. Anterograde tracing with BDA showed that in the 200kdyn group, the dorsal corticospinal tract of the caudal area of the lesion was labeled. Similar labeling was not observed in the 25mm group. Immunofluorescence staining of PKC-γ also revealed strong staining of the dorsal corticospinal tract in the 200kdyn group but not in the 25mm group. Conclusions The 25 mm injuries generated by the NYU impactor are generally equivalent to the 200 kdyn injuries generated by using the IH impactor. However, differences in the ladder rung test scores, MRI images, BDA traces, and PKC-γ staining demonstrate that the two devices exert qualitatively different impacts on the spinal cord.
