Stress-induced analgesia in mu-opioid receptor knockout mice reveals normal function of the delta-opioid receptor system.
Stress-induced analgesia (SIA) was examined in wildtype and mu-opioid receptor knockout mice. We used thermal paw withdrawal (TPW) latency following a continuous 3-min swim in 20 degrees C water, and found a significant increase in TPW latency in both wild-type and knockout mice. Pre-treatment prior to the swim with naltrindole, a selective delta-opioid receptor antagonist, blocked the increase in TPW latency in knockout mice. These results demonstrate an intact delta-receptor-mediated function of a physiologically-released endogenous agonist in the mu-opioid receptor knockout mouse. The present findings are in contrast with previous reports that analgesia induced by exogenous delta agonists is reduced in the knockout mice.
LaBuda
C J
CJ
Department of Psychology, University of Texas at Arlington, Box 19528, Arlington, TX 76019, USA. labuda@imaginemail.com
Sora
I
I
Uhl
G R
GR
Fuchs
P N
PN
D000698:Analgesia; D000818:Animals; D003080:Cold Temperature / Q000009:adverse effects; D051379:Mice; D018345:Mice, Knockout; D009271:Naltrexone / Q000031:analogs & derivatives / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D010147:Pain Measurement; D011930:Reaction Time / Q000502:physiology; D017465:Receptors, Opioid, delta / Q000378:metabolism*; D017450:Receptors, Opioid, mu / Q000172:deficiency* / Q000235:genetics; D013312:Stress, Physiological / Q000503:physiopathology*; D013550:Swimming / Q000502:physiology; D013997:Time Factors
D009292:Narcotic Antagonists; D017465:Receptors, Opioid, delta; D017450:Receptors, Opioid, mu; D009271:Naltrexone; C055382:naltrindole