Transient up-regulation of spinal cyclooxygenase-2 and neuronal nitric oxide synthase following surgical inflammation

Abstract

Background: Surgery induces pain and hyperalgesia post-operatively. The products of cyclooxygenases and nitric oxide synthase (NOS) have been implicated in the development of inflammatory pain and hyperalgesia experimentally, and the use of drugs clinically that modify cydooxygenase activity has been advocated in the management of perioperative pain. However, regulation of these enzymes following surgery has not been studied. Methods: Adult female sheep (n = 12) undergoing a midline laparotomy for collection of ova were used in this study. Lumbar and cervical spinal cord tissue was collected from animals euthanized day and 6 or 7 days after surgery and processed for cyclooxygenase (cyclooxygenase-1 and cyclooxygenase-2), neuronal NOS mRNA expression using reverse-transcription polymerase chain reaction and in situ hybridization. Tissues were also processed for NADPH-diaphorase staining and cyclooxygenase-1 and cydooxygenase-2 protein expression by immunohistochemistry and Western blotting. Results: No alteration in cyclooxygenase-1 or cyclooxygenase-2 mRNA or protein concentrations were detected in spinal cord by reverse-transcription polymerase chain reaction and Western blotting, respectively, at 1 day or 6 or 7 days after surgery. However, using techniques that localize mRNA and protein expression (in situ hybridization and immunohistochemistry, respectively), increases in cyclooxygenase-2 were identified in lamina V dorsal horn neurons in lumbar spinal cord 1 day after surgery. A significant increase in neuronal NOS mRNA was observed in lumbar spinal cord 1 day after surgery, localized to laminae I-II and lamina V neurons, which returned to baseline concentrations by 6 to 7 days. NADPH-diaphorase staining was significantly increased in laminae I-II in lumbar spinal cord 1 day after surgery but not after 6 to 7 days. Conclusions: Spinal cyclooxygenase and neuronal NOS pathways are differentially altered following surgical inflammation. The early and transient nature of these changes suggests that these enzymes are implicated in postoperative pain and hypersensitivity.