Dipyrone into the nucleus raphe magnus inhibits the rat nociceptive tail-flick reflex

Recent studies suggest that non-steroidal anti-inflammatory drugs have central sites of action which contribute to their analgesic efficacy. In the present study microinjections of the non-steroidal anti-inflammatory drug, dipyrone, were made into the medullary nucleus raphe magnus of lightly pentobarbital-anesthetized rats; 25, 50, 100 and 200 micrograms of dipyrone dose-dependently inhibited the nociceptive tail-flick withdrawal reflex. These results suggest that dipyrone modulates bulbospinal neurons in the nucleus raphe magnus to inhibit spinal nociceptive reflexes; thus, new routes of administration and methods of application may be possible for these analgesic agents.