Antagonism of swim-stress-induced antinociception by the delta-opioid receptor antagonist naltrindole in adult and young rats.
1. The availability of the non-peptide delta-opioid receptor antagonist naltrindole has provided the possibility for in vivo studies on the function of delta-opioid receptors. We have studied the effects of naltrindole on swim-stress-induced antinociception in adult and neonatal rats. 2. Adult, 25 and 20 day old rats were stressed by warm water (20 degrees C) swimming for 3 min periods and antinociception was assessed by the tail immersion test (50 degrees C). 3. Naltrindole (0.5 and 1 mg kg-1) antagonized swim-stress-induced antinociception in adult and 25 day old rats but in 20 day old rats naltrindole (1 mg kg-1) was without effect. 4. Antinociception induced by the highly mu-opioid receptor selective agonist alfentanil was completely antagonized by naloxone (1 mg kg-1) but virtually unaffected by naltrindole (1 mg kg-1). 5. Neither naloxone nor naltrindole (1 mg kg-1) antagonized swim-stress-induced rises in plasma corticosterone in adult rats at the time of peak antinociception. 6. In conclusion, naltrindole shows in vivo antagonism of opioid-mediated responses. Swim-stress-induced antinociception is mediated through the delta-opioid receptor in 25 day old and adult rats and through the mu-opioid site in 20 day old animals.
Kitchen
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Department of Biochemistry, University of Surrey, Guildford.
Pinker
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SR
D000375:Aging / Q000502:physiology; D000818:Animals; D000831:Animals, Newborn / Q000502:physiology; D003345:Corticosterone / Q000378:metabolism; D007211:Indoles / Q000494:pharmacology*; D008297:Male; D009019:Morphinans / Q000494:pharmacology*; D009271:Naltrexone / Q000031:analogs & derivatives*; D009292:Narcotic Antagonists / Q000494:pharmacology*; D009619:Nociceptors / Q000187:drug effects* / Q000502:physiology; D005082:Physical Exertion; D051381:Rats; D011919:Rats, Inbred Strains; D011957:Receptors, Opioid / Q000502:physiology; D017465:Receptors, Opioid, delta; D013315:Stress, Psychological / Q000503:physiopathology*
D007211:Indoles; D009019:Morphinans; D009292:Narcotic Antagonists; D011957:Receptors, Opioid; D017465:Receptors, Opioid, delta; D009271:Naltrexone; C055382:naltrindole; D003345:Corticosterone