title: Pharmacological analysis of the rate-decreasing effects of mu and kappa opioids in pigeons.
abstract: The present study investigated the rate-decreasing effects of several mu (morphine and l-methadone) and kappa (bremazocine, U69,593 and U50,488) opioid agonists in pigeons. Mu and kappa agonists were examined alone, in combination with naltrexone or the mu-selective opioid antagonist, beta-funaltrexamine (beta-FNA), and in pigeons treated chronically with U50,488. Naltrexone was equipotent in shifting the morphine, l-methadone and bremazocine dose-effect curves to the right, but was less potent in shifting the U69,593 dose-effect curve and did not shift the U50,488 dose-effect curve. Beta-FNA shifted the l-methadone dose-effect curve to the right but did not shift the bremazocine, U69,593 or U50,488 dose-effect curves. Pigeons that developed tolerance to U50,488 following daily administration were cross-tolerant to bremazocine but not to l-methadone. Taken together, these experiments indicate that the rate-decreasing effects of morphine and l-methadone are mediated by mu opioid receptors, whereas the rate-decreasing effects of bremazocine, U69,593 and U50,488 in pigeons differ depending on the pharmacological procedures used to assess their effects.
authors.affiliation: Department of Psychology, University of North Carolina at Chapel Hill 27599-3270.
authors.forename: A J
authors.initials: AJ
authors.lastname: Mattox
authors.forename: M J
authors.initials: MJ
authors.lastname: Picker
authors.forename: L A
authors.initials: LA
authors.lastname: Dykstra
mesh_terms: D000818:Animals; D010856:Columbidae; D003216:Conditioning, Operant / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D005260:Female; D009271:Naltrexone / Q000031:analogs & derivatives / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D009294:Narcotics / Q000494:pharmacology*; D017473:Receptors, Opioid, kappa / Q000819:agonists* / Q000037:antagonists & inhibitors; D017450:Receptors, Opioid, mu / Q000819:agonists* / Q000037:antagonists & inhibitors; D012055:Reinforcement Schedule
chemical_list: D009292:Narcotic Antagonists; D009294:Narcotics; D017473:Receptors, Opioid, kappa; D017450:Receptors, Opioid, mu; D009271:Naltrexone; C024524:beta-funaltrexamine