Figure 9.

Influence of intrathecal 6-hydroxydopamine (6-OHDA) pretreatment on the induction of acute spinal morphine (Mor) tolerance and the effect of low-dose atipamezole on this response in (a) the tail flick test and (b) the paw pressure test. Morphine (15 μg) or saline was administered at 0, 90 and 180 min to groups of animals pretreated with a single injection of 6-OHDA (20 μg) or the vehicle 14 days before testing. Atipamezole (0.08 ng) was administered with morphine to 6-OHDA pretreated animals as a single injection. Nociceptive testing was performed every 30 min post-injection. The data are presented as mean±s.e.mean; n=six to seven animals per treatment group. Significant difference from the action of morphine alone at the corresponding time point in the 6-OHDA-pretreated animals ^*P<0.05, ^***P<0.001.