title: Dopamine receptor mechanism(s) and morphine tolerance in mice.
abstract: Based on our previous demonstration of the involvement of dopamine-2 (D2) dopamine receptors in morphine antinociception, we examined the role of D2 dopamine receptors in the expression and development of tolerance to morphine antinociception in mice. Tolerance to morphine antinociception was assessed by the tail-flick response after the administration of morphine (50 mg/kg) once daily for 3 days. The D2 dopamine receptor agonist, quinpirole (0.01, 0.02 and 0.03 mg/kg), but not the D2 dopamine receptor antagonist, sulpiride (12.5, 25 and 50 mg/kg), increased morphine antinociception in morphine non pre-exposed mice. The response of quinpirole was decreased by the lower doses of sulpiride. Both quinpirole and sulpiride decreased the expression and development of tolerance to antinociception induced by morphine (1.5, 3 and 6 mg/kg). The effect of quinpirole on the expression and development of tolerance, was reduced by a lower and per se non-effective dose of sulpiride. It was concluded that D2 dopaminergic receptors may play a part in the expression and development of tolerance to the antinociceptive effect of morphine.
authors.affiliation: Department of Pharmacology, School of Medicine, Tehran University of Medical Sciences, Iran. Zarinmr@ams.ac.ir
authors.forename: Mohammad-Reza
authors.initials: MR
authors.lastname: Zarrindast
authors.forename: Zahra
authors.initials: Z
authors.lastname: Dinkoub
authors.forename: Houman
authors.initials: H
authors.lastname: Homayoun
authors.forename: Azam
authors.initials: A
authors.lastname: Bakhtiarian
authors.forename: Simin
authors.initials: S
authors.lastname: Khavandgar
mesh_terms: D000818:Animals; D018491:Dopamine Agonists / Q000494:pharmacology; D018492:Dopamine Antagonists / Q000494:pharmacology; D004361:Drug Tolerance; D007279:Injections, Subcutaneous; D008297:Male; D051379:Mice; D008815:Mice, Inbred Strains; D009020:Morphine / Q000494:pharmacology*; D017288:Pain Threshold / Q000187:drug effects* / Q000502:physiology; D019257:Quinpirole / Q000494:pharmacology; D017448:Receptors, Dopamine D2 / Q000187:drug effects* / Q000502:physiology; D013469:Sulpiride / Q000494:pharmacology
chemical_list: D018491:Dopamine Agonists; D018492:Dopamine Antagonists; D017448:Receptors, Dopamine D2; D019257:Quinpirole; D009020:Morphine; D013469:Sulpiride