Intrathecal administration of a cylcooxygenase-1, but not a cyclooxygenase-2 inhibitor, reverses the effects of laparotomy on exploratory activity in rats.

Studies of hypersensitivity to mechanical stimuli after incisional surgery suggest that cyclooxygenase (COX)-1, but not COX-2, in the spinal cord participates in postoperative pain. In the current study, we sought to determine the role of COX isoenzymes after laparotomy, examining spontaneous exploratory behavior rather than withdrawal reflexes. Adult male Sprague-Dawley rats underwent subcostal laparotomy surgery under isoflurane anesthesia or received anesthesia without surgery. Exploratory locomotor activity was measured on the first postoperative day after intrathecal injection of dimethyl sulfoxide (vehicle) or COX-1 (SC-560) or COX-2 (NS-398) inhibitors. Laparotomy reduced ambulation, rearing, and rapid small movements (stereotypy) similarly in animals without intrathecal catheters and those receiving intrathecal vehicle control. SC-560 produced a dose-related return to normal exploratory behavior with complete return at doses of 20 mug and larger. In contrast, NS-398 in doses up to 50 mug failed to increase exploratory behavior. These data with exploratory behavior and laparotomy agree with studies with reflexive withdrawal responses after incisional surgery and indicate that COX-1 inhibition reduces pain responses after surgery. Spinal COX-1 inhibition completely restores exploratory activity, including rearing behavior that stretches the abdominal muscles. These data suggest that targeting COX-1 in the spinal cord may produce postoperative analgesia.