title: Dissociation of analgesic and rewarding effects of endomorphin-1 in rats.
abstract: The mu-receptor is the primary mediator of the effects of morphine and the endogenous opiates, endomorphin-1 and endomorphin-2. Here we demonstrate a dissociation of the analgesic and rewarding effects of endomorphin-1 in rats. Tail-flick results revealed that endomorphin-1 produced significant analgesic effects within 10-min after injection. However, it failed to show reward properties in the standard 45- min conditioned place preference (CPP) paradigm or in an abbreviated 10-min pairing which paralleled the time frame of the tail-flick findings. Morphine induced both analgesia and reward. Endomorphin-1 therefore is the first mu opiate shown to produce potent analgesia in the absence of reward behavior, and thus may have significant clinical potential.
authors.affiliation: Department of Psychology, University of New Orleans, New Orleans, LA 70148, USA.
authors.forename: A M
authors.initials: AM
authors.lastname: Wilson
authors.forename: R D
authors.initials: RD
authors.lastname: Soignier
authors.forename: J E
authors.initials: JE
authors.lastname: Zadina
authors.forename: A J
authors.initials: AJ
authors.lastname: Kastin
authors.forename: W L
authors.initials: WL
authors.lastname: Nores
authors.forename: R D
authors.initials: RD
authors.lastname: Olson
authors.forename: G A
authors.initials: GA
authors.lastname: Olson
mesh_terms: D000700:Analgesics / Q000494:pharmacology*; D000818:Animals; D008297:Male; D009020:Morphine / Q000494:pharmacology; D009842:Oligopeptides / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012201:Reward; D013997:Time Factors
chemical_list: D000700:Analgesics; D009842:Oligopeptides; C105293:endomorphin 1; C105294:endomorphin 2; D009020:Morphine