Intrathecal opioids block a spinal action of substance P in mice: functional importance of both mu- and delta-receptors.
Inhibition of intrathecal substance P-elicited behavior by mu-, delta- and kappa-opioids was compared. In both the substance P behavioral test and the tail flick antinociceptive test, intrathecal [D-Ala2, Met5]enkephalinamide and [D-Ala2, D-Leu5]enkephalin (DADL) were equipotent, morphine and ethylketazocine were less potent, but nalorphine was inactive. A long-lasting, highly selective, mu-receptor antagonist, beta-funaltrexamine, blocked the inhibition of substance P behaviors by both morphine and ethylketazocine, but did not block the effect of DADL. These results suggest that spinal postsynaptic modulation of nociception is mediated by both delta-type and mu-type opioid agonists.
D000818:Animals; D003496:Cyclazocine / Q000031:analogs & derivatives / Q000494:pharmacology; D004745:Enkephalins / Q000494:pharmacology; D016314:Ethylketocyclazocine; D007278:Injections, Spinal; D008297:Male; D051379:Mice; D009020:Morphine / Q000494:pharmacology; D009294:Narcotics / Q000008:administration & dosage / Q000494:pharmacology*; D011930:Reaction Time / Q000187:drug effects; D011957:Receptors, Opioid / Q000187:drug effects*; D017465:Receptors, Opioid, delta; D017450:Receptors, Opioid, mu; D013116:Spinal Cord / Q000187:drug effects*; D013373:Substance P / Q000037:antagonists & inhibitors*; D009435:Synaptic Transmission / Q000187:drug effects
D004745:Enkephalins; D009294:Narcotics; D011957:Receptors, Opioid; D017465:Receptors, Opioid, delta; D017450:Receptors, Opioid, mu; D013373:Substance P; D016314:Ethylketocyclazocine; D009020:Morphine; D003496:Cyclazocine