Visceral chemical nociception in mice lacking mu-opioid receptors: effectsof morphine, SNC80 and U-50,488

Writhing responses to intraperitoneal acetic acid administration and their modulation by mu-, kappa- and delta-opioid receptor agonists were compared in wild-type and mu-opioid receptor knockout mice. Unpretreated homozygous knockout mice displayed less writhing than wild-type mice. U-50,488 [trans- 3,4-dichloro-N-methyl-N-[2-(1-pyrolidinyl)cyclohexyl]-benzeneacetamide]) re duced writhing responses in wild-type and knockouts. Morphine and SNC80 [()-4-[9-alpha-R)-alpha-(2S,5RO-4-allyl-2,5-dimethyl-1-piperazinyl)-3-methoxy benzyl]-N, N-diethylbenzamide] were effective in wild-type mice but ineffec tive in knockouts. CL-opioid receptors appear to play important roles in re sponses to this visceral nociceptive stimulus and its modulation by mu- and delta-opioid receptor agonists. (C) 1999 Elsevier Science B.V. All rights reserved.