title: Effects of naltrindole and nor-binaltorphimine treatment on antinociception induced by sub-acute selective mu opioid receptor blockade.
abstract: When administered repeatedly, in conjunction with hot plate testing, naloxone and naltrexone have the paradoxical effect of producing antinociception in rats and mice. Recently, we have found that the sub-acute selective blockade of mu opioid receptors leads to the development of antinociception and an augmentation of kappa receptor-mediated antinociception. In this study, acute delta/kappa antagonist treatment produced a significant decrease in paw lick latency in rats displaying antinociception induced by sub-acute mu blockade, however, the response level of these animals was still significantly above the baseline. In addition, rats receiving sub-acute combined mu and delta antagonist treatment took longer to develop an antinociceptive response than those treated with a mu antagonist alone. Sub-acute selective blockade of kappa or delta opioid receptors had no overall effect on paw lick latency during the course of 5 days of hot plate testing. The results indicate that delta receptor activity may play a role in the antinociception induced by sub-acute mu blockade. However, while delta antagonist treatment effected the expression, it did not completely attenuate the antinociception induced by sub-acute mu blockade suggesting that there is still a significant non-opioid component to this analgesic response. The results of a final experiment, in which acute delta antagonist treatment had no effect on antinociception induced by repeated systemic injections of naloxone, supported this hypothesis.
authors.affiliation: Addiction Research Foundation, Toronto, Ont., Canada.
authors.forename: M J
authors.initials: MJ
authors.lastname: Walker
authors.forename: A D
authors.initials: AD
authors.lastname: Le
authors.forename: C X
authors.initials: CX
authors.lastname: Poulos
mesh_terms: D000818:Animals; D007211:Indoles / Q000494:pharmacology*; D008297:Male; D009019:Morphinans / Q000494:pharmacology*; D009271:Naltrexone / Q000031:analogs & derivatives* / Q000494:pharmacology; D010146:Pain / Q000503:physiopathology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D017465:Receptors, Opioid, delta / Q000037:antagonists & inhibitors*; D017473:Receptors, Opioid, kappa / Q000037:antagonists & inhibitors; D017450:Receptors, Opioid, mu / Q000037:antagonists & inhibitors*; D012680:Sensitivity and Specificity
chemical_list: D007211:Indoles; D009019:Morphinans; D017465:Receptors, Opioid, delta; D017473:Receptors, Opioid, kappa; D017450:Receptors, Opioid, mu; C051844:norbinaltorphimine; D009271:Naltrexone; C055382:naltrindole