Effect of mechanical compression on the lumbar nerve root: Localization and changes of intraradicular inflammatory cytokines, nitric oxide, and cyclooxygenase

Study Design. Investigation of intraradicular inflammation induced by mechanical compression. Objective. To investigate the mechanism of nerve root pain, this study used a lumbar nerve root compression model. Summary of Background Data. The manifestation of pain at sites of inflammation has a close relationship with the release of mediators from macrophages. However, the mediators involved in inflammation of nerve roots as a result of mechanical compression remain almost unknown. Methods. In this study, the seventh lumbar nerve root of dogs was compressed with a clip for 3 weeks to observe the changes caused by compression. Immunohistochemistry was performed using the avidin-biotin-peroxidase complex method to observe the changes of T cells (CD45) and macrophages (Mac-1) after compression. Antibodies against as interleukin-1 (IL-1), tumor necrosis factor-alpha (TNF-alpha), inducible nitric oxide synthase (i-NOS), and cyclooxygenase (COX)-1 and 2 were used to examine the localization and changes of these mediators caused by nerve root compression. Results. In control animals, resident T cells were detected, but there were no macrophages. IL-1 beta and COX-2 were positive in the Schwann cells and vascular endothelial cells, while COX-1 was detected in the vascular endothelial cells. However, no cells showed TNF-alpha or i-NOS positively. After nerve root compression, numerous T cells and macrophages appeared among the demyelinized nerve fibers. The macrophages were positive for IL-1 beta, TNF-alpha, i-NOS, and COX-2. Conclusion. Inflammatory cytokines, NO, and COX-2 may be deeply involved in radiculitis caused by mechanical compression, and these mediators seem to be important in the manifestation of root pain.