Acute antinociceptive responses in single and combinatorial opioid receptor knockout XXXX : distinct mu, delta and kappa tones.

@entity32981 @entity19 @entity3825 @entity16119 @entity406 @entity10237 @entity158 @entity15320
We have examined responses of @entity19 lacking mu, delta and kappa opioid receptor ( @entity16119 , @entity15320 and @entity32981 , respectively) genes, as well as combinatorial mutants, in @entity158 models. This is the first truly comparative study of all three opioid receptor-deficient @entity19 , with genotypes and gender analysis using @entity19 on the hybrid 50% 129/SV : 50% C57BL/6 genetic background. In the tail-immersion test, only @entity32981 -/- females showed decreased withdrawal latencies. This modification was also found in @entity16119 / @entity32981 and @entity16119 / @entity15320 / @entity32981 , but not @entity16119 / @entity15320 mutants. The hotplate test revealed @entity10237 for @entity16119 -/-, a phenotype which was also observed in double mutants involving the @entity16119 deletion, and in the triple mutants. The tail-pressure test showed increased response for both @entity16119 -/- and @entity15320 -/- mutants, a modification which was enhanced in the triple-mutant @entity19 . In the @entity406 test, @entity16119 -/- and @entity15320 -/- @entity19 showed increased responses in the early and late phases, respectively, while the triple mutant tended to show enhanced nociception in both phases. Finally, the enhanced response of @entity32981 -/- @entity19 in the writhing test, which we have demonstrated previously, was confirmed in double @entity16119 / @entity32981 - and triple-mutant @entity19 . Together, the data support the existence of an antinociceptive opioid tone. Each receptor presents a distinct pattern of activities, with mu receptors influencing responses to mechanical, chemical and thermal nociception at a supraspinal level, kappa receptors involved in spinally mediated thermal nociception and chemical @entity3825 , and delta receptors modulating mechanical nociception and @entity158 . Phenotypes of mutant @entity19 were subtle, suggesting a low endogenous opioid tone in the regulation of physiological @entity158 .
