Pretreatment with pertussis toxin blocks morphine- but not beta-endorphin-induced antinociception in the mouse.

We have previously demonstrated that the antinociception induced by morphine and beta-endorphin given intracerebroventricularly (i.c.v.) is mediated by the stimulation of respective mu- and epsilon-opioid receptors. The effects of i.c.v. pretreatment with pertussis toxin on the antinociception induced by morphine and beta-endorphin given i.c.v. were studied in male ICR mice. Antinociception was assessed by the tail-flick and hot-plate tests. Pretreatment with pertussis toxin (0.5 microgram) given i.c.v. 96 h earlier blocks the antinociception induced by i.c.v. administered morphine in both tail-flick and hot-plate tests. The same pretreatment did not affect the antinociception induced by i.c.v. administered beta-endorphin. Our results indicate that morphine-, but not beta-endorphin-induced antinociception is mediated by pertussis toxin sensitive G-proteins.