Cyclooxygenase-2 expression in Schwann cells and macrophages in the sciatic nerve after single spinal nerve injury in rats.

Recent evidence suggested that cyclooxygenase-2 (COX-2) expression in the peripheral nerve early after nerve injury might be involved in the development of neuropathic pain. Although previous investigators have demonstrated that COX-2 is expressed in peripheral nerve at a late phase (2-4 weeks) after nerve injury, COX-2 up-regulation at an early phase after nerve injury has not been determined. Using immunohistochemistry, we observed biphasic increases of COX-2 expression after L5 single spinal nerve injury. The first increment of COX-2 positive cells was noted 1 day after nerve injury and these cells co-expressed the Schwann cell marker S-100. A second increment was noted after 7-14 days and these cells co-expressed the macrophage marker ED-1. These results suggested that the cellular sources of COX-2 expression might be different between the early and late phases after nerve injury.