Antinociception induced by PAG-microinjected dipyrone (metamizol) in rats:involvement of spinal endogenous opioids

Dipyrone microinjection into the periaqueductal gray matter (PAG) elicits a ntinociception in rats by activating endogenous opioidergic circuits in FAG and the rostral ventromedial medulla. We have now found that endogenous op ioids in the spinal cord are also involved. Responses of dorsal spinal neur ons to noxious stimulation of a hindpaw were diminished (to 38-44%) by dipy rone microinjection (100 mug/0.5 mul) into the FAG. This was abolished by a pplication of naloxone (50 mug/50 mul) to the spinal cord. The fact that di pyrone, a non-opioid analgesic, activates opioidergic circuits may be clini cally important. (C) 7001 Elsevier Science B.V. All rights reserved.