title: Alpha-2 agonists decrease expression of morphine-induced conditioned place preference.
abstract: Opioidergic system can interact with different transmission such as dopaminergic and adrenergic system. It has been shown that alpha-adrenergic system is involved in some effects of opioid including reward. In this study, alpha-2 agonists were used before testing on day 6 to evaluate their effects on the expression of morphine-induced conditioned place preference (CPP). Our results showed that intraperitoneal (i.p.) injections of morphine (5 mg/kg) induced CPP. Administration of alpha(2)-agonists clonidine (0.01, 0.02 and 0.04 mg/kg, i.p.), tizanidine (0.1, 0.2 and 0.4 mg/kg, i.p.) and xylazine (2.5, 5 and 10 mg/kg, i.p.) decreases the expression of morphine-induced CPP. Yohimbine (0.5 mg/kg, i.p.) reversed the inhibitory effect of alpha(2)-agonists. The comparison of potency of inhibitory effect of three agonists showed that ID(50) values for clonidine, tizanidine and xylazine were 0.013, 0.32 and 1.86 mg/kg respectively. Therefore, it is concluded that alpha(2)-agonists decrease the morphine-induced CPP in mice and clonidine is more potent than tizanidine and xylazine. The relative potency of clonidine with respect to tizanidine and xylazine was 30 and 180 respectively.
authors.affiliation: Department of Pharmacology, School of Medicine, Medical Sciences/University of Tehran, P.O. Box 13145-784, Tehran, Iran. saminim@yahoo.com
authors.forename: Morteza
authors.initials: M
authors.lastname: Samini
authors.forename: Ayda
authors.initials: A
authors.lastname: Kardan
authors.forename: Shahram Ejtemaei
authors.initials: SE
authors.lastname: Mehr
mesh_terms: D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000701:Analgesics, Opioid / Q000494:pharmacology*; D000818:Animals; D003000:Clonidine / Q000031:analogs & derivatives / Q000494:pharmacology; D003216:Conditioning, Operant / Q000187:drug effects*; D008297:Male; D051379:Mice; D009020:Morphine / Q000494:pharmacology*; D018341:Receptors, Adrenergic, alpha-2 / Q000187:drug effects*; D012201:Reward; D014991:Xylazine / Q000494:pharmacology; D015016:Yohimbine / Q000494:pharmacology
chemical_list: D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D000701:Analgesics, Opioid; D018341:Receptors, Adrenergic, alpha-2; D014991:Xylazine; D015016:Yohimbine; C023754:tizanidine; D009020:Morphine; D003000:Clonidine