Figure 7.

Effect of low-dose atipamezole (0.8 ng) on the antinociceptive effect and the morphine (Mor) potency in animals tolerant to the opioid agonist in the tail flick (a) and paw pressure test (b). Time course for the effects of atipamezole on the morphine-induced antinociception in the opioid-tolerant animals. Tolerance was induced by a single daily injection of morphine (15 μg) from day 1 to 5. On day 6, morphine was administered alone or in combination with atipamezole as a single injection until day 10. Nociceptive testing was performed after 60 min after each injection. The data are expressed as mean±s.e.mean of six to seven animals. Significant difference from the morphine alone (10 days). ^*P<0.05, ^**P<0.01, ^***P<0.001.