title: Involvement of mu-opioid receptors in potentiation of apomorphine-induced climbing behavior by morphine: studies using mu-opioid receptor gene knockout mice.
abstract: The present study examined the hypothesis that mu-opioid receptors contribute to a behavioral stimulation produced by stimulation of dopamine receptors by comparing responses in mu-opioid receptor knockout and wild type mice. Apomorphine-induced climbing behavior was augmented by 65%, in wild type mice, but not in mu-knockout, following subcutaneous administration of morphine (15 mg/kg). Moreover, pretreatment with either naloxone (an opioid receptor antagonist) or haloperidol (a mixed D(1)/D(2) receptor antagonist) eliminated the enhancement by morphine of climbing behavior in wild type mice. These results indicate that expression of mu-opioid receptors plays an important role in the enhancement of climbing behavior induced by the dopamine receptor agonist, apomorphine. Furthermore, this augmentation is mediated by interaction between dopamine and mu-opioid receptors.
authors.affiliation: Department of Pharmacology and Toxicology, University of Mississippi Medical Center, 2500 North State Street, Jackson, MS 39216-4505, USA.
authors.forename: C
authors.initials: C
authors.lastname: Jang
authors.forename: Y
authors.initials: Y
authors.lastname: Park
authors.forename: S
authors.initials: S
authors.lastname: Tanaka
authors.forename: T
authors.initials: T
authors.lastname: Ma
authors.forename: H H
authors.initials: HH
authors.lastname: Loh
authors.forename: I K
authors.initials: IK
authors.lastname: Ho
mesh_terms: D000701:Analgesics, Opioid / Q000494:pharmacology*; D000818:Animals; D001058:Apomorphine / Q000494:pharmacology*; D001923:Brain Chemistry / Q000187:drug effects / Q000502:physiology; D018491:Dopamine Agonists / Q000494:pharmacology*; D018492:Dopamine Antagonists / Q000494:pharmacology; D004357:Drug Synergism; D006220:Haloperidol / Q000494:pharmacology; D051379:Mice; D018345:Mice, Knockout; D009020:Morphine / Q000494:pharmacology*; D009043:Motor Activity / Q000187:drug effects* / Q000502:physiology; D009270:Naloxone / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D017450:Receptors, Opioid, mu / Q000235:genetics*
chemical_list: D000701:Analgesics, Opioid; D018491:Dopamine Agonists; D018492:Dopamine Antagonists; D009292:Narcotic Antagonists; D017450:Receptors, Opioid, mu; D009270:Naloxone; D009020:Morphine; D006220:Haloperidol; D001058:Apomorphine