title: Opioid inhibition of kainic acid-induced scratching: mediation by mu and sigma but not delta and kappa receptors.
abstract: Scratching induced by intrathecal (IT) administration of kainic acid (0.5 nmol) to rats was inhibited by IT pretreatment with the selective mu agonists levorphanol (30 and 90 nmol), [D-Ala2,N-Met-Phe4,Gly5-ol]-enkephalin (DAGO, 0.4 and 1.1 nmol), or morphine (90 nmol), the mixed mu-delta agonist [D-Ala2,D-Leu5]-enkephalinamide (DADLE, 10 and 30 nmol), or the sigma/phenycyclidine (PCP) agonists dextrorphan (90 nmol) or (+)-N-allyl-N-normetazocine ([+]-NAM, 90 nmol). The kappa agonists dynorphin (1.1 nmol) and ethylketocyclazocine (EKC, 90 nmol) had no significant effect, nor did the selective delta agonist [D-Pen2,D-Pen5]-enkephalinamide (DPDPE, 90 nmol). The nonopioids (+)-3-(3-hydroxyphenyl)-N-(1-propyl)piperidine ([+]-3-PPP, 90 nmol) and PCP (90 nmol), selective for sigma and PCP sites, respectively, both antagonized kainic-induced scratching. Levorphanol- and DADLE-induced attenuation of scratching was partially antagonized by naltrexone. These findings suggest that opioid inhibition of kainic acid-induced scratching is mediated by classical mu receptors as well as sigma and PCP sites.
authors.affiliation: Department of Physiology, Medical College of Virginia, Virginia Commonwealth University, Richmond 23298.
authors.forename: D E
authors.initials: DE
authors.lastname: Kellstein
authors.forename: R C
authors.initials: RC
authors.lastname: Coghill
authors.forename: H
authors.initials: H
authors.lastname: Frenk
authors.forename: D F
authors.initials: DF
authors.lastname: Bossut
authors.forename: D J
authors.initials: DJ
authors.lastname: Mayer
mesh_terms: D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects*; D002408:Catheters, Indwelling; D007278:Injections, Spinal; D007608:Kainic Acid / Q000008:administration & dosage / Q000037:antagonists & inhibitors*; D008297:Male; D009271:Naltrexone / Q000494:pharmacology; D009294:Narcotics / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D011957:Receptors, Opioid / Q000187:drug effects / Q000502:physiology*; D017465:Receptors, Opioid, delta; D017473:Receptors, Opioid, kappa; D017450:Receptors, Opioid, mu; D017480:Receptors, sigma
chemical_list: D009294:Narcotics; D011957:Receptors, Opioid; D017465:Receptors, Opioid, delta; D017473:Receptors, Opioid, kappa; D017450:Receptors, Opioid, mu; D017480:Receptors, sigma; D009271:Naltrexone; D007608:Kainic Acid