title: Motivational effects of opioids in an animal model of prolonged inflammatory pain: alteration in the effects of kappa- but not of mu-receptor agonists.
abstract: An unbiased preference conditioning procedure was used to characterize and compare the motivational effects of opioids in naive rats and those suffering from the prolonged pain associated with Freund's adjuvant (FA)-induced inflammation of one hind limb. The mu-opioid agonist morphine functioned as a reinforcer in naive animals, producing marked preferences for the drug-paired place. Similarly, rats injected with FA 7 days prior to conditioning exhibited a preference for the morphine place, and the magnitude of this effect did not differ between groups. Administration of the kappa-opioid receptor agonist U-69593 to naive rats produced dose-related place aversions. The aversive effect of this kappa-agonist was, however, abolished in FA-treated rats. Thus, regardless of the dose administered, U-69593 produced conditioning similar to that observed in response to saline. These data suggest that kappa-agonists may lack aversive effects in subjects experiencing prolonged noxious stimulation, and as such may be effective therapeutic agents in the management of chronic pain states.
authors.affiliation: Department of Neuropharmacology, Max-Planck-Institut für Psychiatrie, Am Klopferspitz 18a, 8033 Planegg-Martinsried, F.R.G. Department of Anesthesiology, Ludwig-Maximilians-Universität München, Klinikum Grosshadern, D-8000 Munich 70 F.R.G.
authors.forename: T S
authors.initials: TS
authors.lastname: Shippenberg
authors.forename: C
authors.initials: C
authors.lastname: Stein
authors.forename: A
authors.initials: A
authors.lastname: Huber
authors.forename: M J
authors.initials: MJ
authors.lastname: Millan
authors.forename: A
authors.initials: A
authors.lastname: Herz
mesh_terms: D000818:Animals; D044482:Benzeneacetamides; D007249:Inflammation / Q000150:complications*; D008297:Male; D009020:Morphine / Q000494:pharmacology; D009042:Motivation / Q000187:drug effects*; D009294:Narcotics / Q000494:pharmacology* / Q000627:therapeutic use; D010146:Pain / Q000209:etiology / Q000378:metabolism / Q000523:psychology*; D011759:Pyrrolidines / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D011957:Receptors, Opioid / Q000187:drug effects / Q000502:physiology*; D017473:Receptors, Opioid, kappa; D017450:Receptors, Opioid, mu
chemical_list: D044482:Benzeneacetamides; D009294:Narcotics; D011759:Pyrrolidines; D011957:Receptors, Opioid; D017473:Receptors, Opioid, kappa; D017450:Receptors, Opioid, mu; D009020:Morphine; C045444:U 69593