title: Morphine self-administration in mu-opioid receptor-deficient mice.
abstract: Morphine-induced place preference was demonstrated recently in wild-type mice, whereas this conditioned behaviour was not observed in mu-opioid receptor-deficient mice. In the present study, we investigated locomotor effects of subcutaneously (s.c.) injected morphine as well as intracerebroventricular (i.c.v.) morphine self-administration in mu-opioid receptor-knockout mice. After s.c. morphine injection, locomotor activity significantly increased in wild-type animals. As expected, in the self-administration test the rate of self-administration constantly increased in wild-type mice reflecting reward effects of morphine. This increase was independent of locomotor/motor activity. In contrast, self-administration rates and locomotor/motor activity significantly decreased in the receptor-deficient animals. It was shown that this aversive effect might partly be due to kappa-opioid receptor interaction.
authors.affiliation: Institute of Pharmacology and Toxicology, Faculty of Medicine, Otto-von-Guericke University, Magdeburg, Germany. axel.becker@medizin.uni-magdeburg.de
authors.forename: A
authors.initials: A
authors.lastname: Becker
authors.forename: G
authors.initials: G
authors.lastname: Grecksch
authors.forename: R
authors.initials: R
authors.lastname: Brödemann
authors.forename: J
authors.initials: J
authors.lastname: Kraus
authors.forename: B
authors.initials: B
authors.lastname: Peters
authors.forename: H
authors.initials: H
authors.lastname: Schroeder
authors.forename: W
authors.initials: W
authors.lastname: Thiemann
authors.forename: H H
authors.initials: HH
authors.lastname: Loh
authors.forename: V
authors.initials: V
authors.lastname: Höllt
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D001345:Autoradiography; D003342:Corpus Striatum / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)- / Q000378:metabolism; D005106:Exploratory Behavior / Q000187:drug effects; D006624:Hippocampus / Q000378:metabolism; D007276:Injections, Intraventricular; D051379:Mice; D018345:Mice, Knockout; D009020:Morphine / Q000008:administration & dosage / Q000494:pharmacology*; D009043:Motor Activity / Q000187:drug effects*; D011869:Radioligand Assay; D011897:Random Allocation; D017473:Receptors, Opioid, kappa / Q000037:antagonists & inhibitors; D017450:Receptors, Opioid, mu / Q000235:genetics / Q000378:metabolism*; D012646:Self Administration
chemical_list: D017473:Receptors, Opioid, kappa; D017450:Receptors, Opioid, mu; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D009020:Morphine