Expression of cyclooxygenase isoforms in the rat spinal cord and their regulation during adjuvant-induced arthritis

Objective and Design: Spinal regulation of cyclooxygenase (COX) isoforms was investigated in the animal model of peripheral inflammation induced by injection of complete Freund's-type adjuvant (CFA) in the rat hindpaw. Subjects and Treatment: Peripheral inflammation was induced by intraplantar injection of CFA in one hind footpad of male Sprague Dawley rats (n = 3 per time point). Methods: Spinal cord was removed after different times (3 h to 22 d). mRNA and protein were isolated and analyzed by comparative reverse transcriptase-polymerase chain reaction (RT-PCR) and Western blot analysis, respectively. Results: Under the acute inflammatory stimulus 6 h after CFA application, RT-PCR revealed a twofold increase in COX-2 mRNA that reached baseline again at day 3. This transient increase occurred in the lumbar spinal cord, but changes in COX-2 mRNA expression were also registered in RNA preparations from cervical sections, spinal COX-2 induction thus not being a spatially confirmed phenomenon. Western blot analysis of spinal membrane preparations reflected the transient COX-2 mRNA induction at protein levels. During the chronic phase of arthritis at day 22, COX-2 levels were again raised significantly (1.6 fold) over baseline. Spinal levels of COX-1 were not altered at any time point of the peripheral inflammation. Conclusion: These data imply a regulatory role for COX-2 but not COX-1 in the spinal modulation under acute and chronic peripheral inflammation.