Visceral chemical nociception in mice lacking μ-opioid receptors: Effects of morphine, SNC80 and U-50,488

Writhing responses to intraperitoneal acetic acid administration and their modulation by μ-, κ- and δ-opioid receptor agonists were compared in wild-type and μ-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]) reduced writhing responses in wild-type and knockouts. Morphine and SNC80 [(+)-4-[9-α-R)-α-(2S,5RO-4-allyl-2,5-dimethyl-1-piperazinyl)-3-methoxybenzyl]-N,N-diethylbenzamide] were effective in wild-type mice but ineffective in knockouts. μ-opioid receptors appear to play important roles in responses to this visceral nociceptive stimulus and its modulation by μ- and δ-opioid receptor agonists. Copyright (C) 1999 Elsevier Science B.V.