Involvement of spinal kappa opioid receptors in a type of footshock induced analgesia in mice.
We have studied the effects of several opioid antagonists on a type of footshock stress-induced analgesia (FSIA) measured by the tail-flick test in male mice. Naloxone injected either subcutaneously (0.1-10 mg/kg) or intrathecally (1-20 micrograms) antagonized FSIA at higher doses than those that blocked a similar degree of analgesia induced by morphine. Intracerebroventricular (i.c.v.) naloxone (1-20 micrograms) did not modify the FSIA while antagonizing the i.c.v. morphine-induced analgesia. As a consequence, the antagonism of the FSIA by naloxone probably occurs at the level of the spinal cord and through receptors different than mu. The delta selective antagonist naltrindole (0.1-3 mg/kg s.c.) did not antagonize the analgesic effects of the stress. Nor-binaltorphimine, a kappa selective antagonist, blocked the FSIA when administered systemically (1-4 mg/kg i.p.) or locally (0.1-1 microgram i.t.). These results strongly suggest that spinal kappa opioid receptors are responsible for this type of endogenous analgesia.
Departamento de Medicina, Facultad de Medicina, Universidad de Oviedo, Spain.
L
L
Menendez
F
F
Andres-Trelles
A
A
Hidalgo
A
A
Baamonde
D000698:Analgesia; D000818:Animals; D002552:Cerebral Ventricles / Q000187:drug effects / Q000502:physiology*; D004597:Electroshock; D007276:Injections, Intraventricular; D007278:Injections, Spinal; D008297:Male; D051379:Mice; D008815:Mice, Inbred Strains; D009020:Morphine / Q000008:administration & dosage / Q000494:pharmacology; D009270:Naloxone / Q000008:administration & dosage / Q000494:pharmacology*; D009271:Naltrexone / Q000008:administration & dosage / Q000031:analogs & derivatives / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000008:administration & dosage / Q000494:pharmacology*; D010146:Pain / Q000503:physiopathology; D017473:Receptors, Opioid, kappa / Q000187:drug effects / Q000502:physiology*; D013116:Spinal Cord / Q000187:drug effects / Q000502:physiology* / Q000503:physiopathology; D013315:Stress, Psychological / Q000503:physiopathology*
D009292:Narcotic Antagonists; D017473:Receptors, Opioid, kappa; D009270:Naloxone; C051844:norbinaltorphimine; D009271:Naltrexone; D009020:Morphine; C055382:naltrindole