THE OPIOID ANTAGONIST NALOXONE DOES NOT ALTER DISCHARGES OF NOCICEPTIVE AFFERENTS FROM THE ACUTELY INFLAMED KNEE-JOINT OF THE CAT

Recent studies have shown peripheral antinociceptive effects of opiate s in inflamed tissue. To test whether the afferent activity during an acute inflammation may also be suppressed by endogenous opioids, we st udied whether the application of the opioid antagonist naloxone would alter the afferent discharges from the cat knee joint inflamed by kaol in and carrageenin. After i.a. bolus administration of naloxone (3 mu g/kg and 1 mg/kg) close to the joint, neither the ongoing activity nor the responses to noxious and innocuous movements significantly change d in group In or group IV units. Since naloxone did not unmask opioide rgic activity under these conditions, we conclude that the development of increased activity in joint afferents during an acute kaolin/carra geenin-induced inflammation is not tonically suppressed by endogenous opioids.