title: Morphine-nicotine interaction in conditioned place preference in mice after chronic nicotine exposure.
abstract: Previously we found that morphine's effects on locomotor activity and brain dopamine metabolism were enhanced in mice after cessation of 7-week oral nicotine treatment. In the present experiments we show that such chronic nicotine exposure cross-sensitizes NMRI mice to the reinforcing effect of morphine in the conditioned place preference paradigm. The nicotine-treated mice developed conditioned place preference after being conditioned twice with morphine 5 mg/kg s.c. whereas in control mice a higher dose (10 mg/kg) of morphine was required. Since the reinforcing effect of morphine is mediated via micro-opioid receptors we used [3H]DAMGO autoradiography to study whether the number (B(max)) or affinity (K(D)) of mu-opioid receptors in the mouse brain are affected following chronic nicotine exposure. However, no changes were found in the number or affinity of micro-opioid receptors in any of the brain areas studied. Neither did we find alterations in the functional activity of mu-opioid receptors studied by [35S]GTPgammaS-binding. In conclusion, chronic oral nicotine treatment augments the reinforcing effects of morphine in mice, and this cross-sensitization does not seem to be mediated by micro-opioid receptors.
authors.affiliation: Division of Pharmacology and Toxicology, Faculty of Pharmacy, P.O. Box 56 (Viikinkaari 5 E), University of Helsinki, FI-00014, Finland. tanja.vihavainen@helsinki.fi
authors.forename: Tanja
authors.initials: T
authors.lastname: Vihavainen
authors.forename: Marjo
authors.initials: M
authors.lastname: Piltonen
authors.forename: Raimo K
authors.initials: RK
authors.lastname: Tuominen
authors.forename: Esa R
authors.initials: ER
authors.lastname: Korpi
authors.forename: Liisa
authors.initials: L
authors.lastname: Ahtee
mesh_terms: D000701:Analgesics, Opioid / Q000494:pharmacology*; D000818:Animals; D001345:Autoradiography; D003216:Conditioning, Operant / Q000187:drug effects*; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)- / Q000494:pharmacology; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D008297:Male; D051379:Mice; D009020:Morphine / Q000494:pharmacology*; D009271:Naltrexone / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D009538:Nicotine / Q000494:pharmacology*; D018722:Nicotinic Agonists / Q000494:pharmacology*; D017450:Receptors, Opioid, mu / Q000187:drug effects
chemical_list: D000701:Analgesics, Opioid; D009292:Narcotic Antagonists; D018722:Nicotinic Agonists; D017450:Receptors, Opioid, mu; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D009271:Naltrexone; D009538:Nicotine; D009020:Morphine