Cyclooxygenase-2 (COX-2) is now considered to be the major constitutively expressed COX isozyme in the central nervous system. The present immunocytochemical study details localization of COX-2 immunoreactivity in rat spinal cord along with the expression of prostaglandin E2 receptor subtype EP3. Prominent COX-2 staining was observed in the nuclear envelope of neurons throughout the spinal cord, especially in the superficial dorsal horn laminae and motoneurons of lamina IX, as well as in glial cells of the white matter. Expression of EP3 receptor was strictly confined to afferent terminal areas in the superficial dorsal horns.

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 6h 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.

Prostaglandins are known as mediators in spinal nociceptive processing after peripheral inflammation. Cyclooxygenase isozymes Cox-1 and Cox-2 as enzymes essential for prostaglandin biosynthesis were therefore investigated in rat spinal cord. mRNA and protein of both enzymes was detected in cervical and lumbar sections of the spinal cord of normal animals. Enzyme activity of Cox-1 and Cox-2 could be determined by the use of specific inhibitors. Cox-2-immunoreactivity (IR) was found in the spinal cord of untreated rats in neurons of laminae II-m, motoneurons of lamina IX and in glial cells. Most prominent staining was observed in the nuclear envelope.Under an acute peripheral inflammatory stimulus a transient 2-fold increase in Cox-2 mRNA was noticed bilaterally in the lumbar spinal cord by reverse transcription-polymerase chain reaction. This increase was reflected on a smaller scale at protein levels in Western blot analysis of spinal membrane preparations. In the chronic state of adjuvant-induced arthritis, Cox-2 levels were raised again significantly.Cox-2 might therefore be regarded as the Cox isozyme responsible for increased spinal prostanoid release in nociceptive processing under peripheral stimulation.

Prostaglandins (PG) have been described as mediators in spinal nociceptive processing after peripheral inflammation. Enzymes essential for PG biosynthesis, cyclooxygenase isozymes COX-1 and COX-2, have not yet been investigated in the spinal cord. In two studies on rats with adjuvant-induced peripheral inflammation levels of mRNA expression of both COX isoforms were analyzed in the lumbar section of the spinal cord using reverse transcription-polymerase chain reaction (RT-PCR) technique. We could show that mRNA of both COX isoforms is expressed constitutively in the spinal cord with COX-2 as the predominant isoform. Six hours after induction of peripheral inflammation, levels of COX-2 mRNA expression were raised significantly in respect to untreated control rats and returned to baseline within 3 days after induction of inflammation. COX-2 might therefore be regarded as the COX isozyme responsible for spinal PG release in nociceptive processing under a peripheral inflammatory stimulus.