Figure 5.

Effects of atipamezole on the induction of tolerance to chronic antinociceptive effects of morphine (Mor) in the tail flick test. (a) Time course of the action of chronic intrathecal morphine (5 μg) delivered in combination with saline or atipamezole (0.08, 0.8 ng) once daily for 5 days. Nociceptive testing was performed 60 min after each injection. The data are expressed as mean±s.e.mean for four to seven animals. ^*P<0.05, ^**P<0.01, ^***P<0.001. (b) Time course of the effect of morphine–saline and morphine–atipamezole combination on day 5 in a subgroup of animals that had received chronic treatment with these drug treatments (panel a). Nociceptive testing was performed every 30 min after the drug injection. The data are expressed as mean±s.e.mean for four to five animals. Significant difference from morphine at the corresponding time point ^***P<0.001.