Spinal cord injury induces long-term upregulation of expression of cell cycle-related proteins. Analysis of expression of cell cycle proteins in intact and injured spinal cord at 4 weeks and 4 months post-injury was performed by Western blotting. (A-B) Representative immunoblots for cell cycle-related proteins (CDK4, cyclin D1 and E, E2F5 and PCNA) and the loading control (GAPDH). (C-D) Expression levels of cell cycle proteins were normalized by GAPDH, as estimated by optical density measurements, and expressed as a percentage of sham spinal cord. Quantitative analysis of Western blots showed significant upregulation of these cell cycle proteins at 4 weeks, which remained elevated for at least 4 months post injury. *p < 0.05 compared with the sham group. n = 4-6 rats per time point.