Dissociation of analgesic and rewarding effects of endomorphin-1 in rats.
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.
Wilson
A M
AM
Department of Psychology, University of New Orleans, New Orleans, LA 70148, USA.
Soignier
R D
RD
Zadina
J E
JE
Kastin
A J
AJ
Nores
W L
WL
Olson
R D
RD
Olson
G A
GA
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
D000700:Analgesics; D009842:Oligopeptides; C105293:endomorphin 1; C105294:endomorphin 2; D009020:Morphine