Alpha-2 agonists decrease expression of morphine-induced conditioned place preference.
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.
Samini
Morteza
M
Department of Pharmacology, School of Medicine, Medical Sciences/University of Tehran, P.O. Box 13145-784, Tehran, Iran. saminim@yahoo.com
Kardan
Ayda
A
Mehr
Shahram Ejtemaei
SE
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
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