Figure 2.

Time course of the effects of ultra-low doses of intrathecal (a) atipamezole (0.08, 0.8 ng), (b) yohimbine (0.2 ng), mirtazapine (0.02 ng) and idazoxan (0.08 ng) on the acute antinociceptive action of a maximal dose of morphine (Mor, 15 μg) in the tail flick test. Each agent was administered with morphine as a single injection. Nociceptive testing was every 10 min post-injected for the first 60 min and every 30 min for the following 2 h period. The data are expressed as mean±s.e.mean for four to seven animals. Significant difference is presented as difference from the action of morphine at the corresponding time point. ^*P<0.05, ^**P<0.01, ^***P<0.001.