Figure 1.

Effects of intrathecal administration of α₂-adrenoceptor antagonists, atipamezole (5, 10 μg) yohimbine (30 μg), mirtazapine (2 μg) and idazoxan (10 μg) on the acute antinociceptive action of a maximal dose of the α₂-adrenoceptor agonist clonidine (13 μg) in the tail flick test. The antagonists were administered with clonidine as a single injection. Nociceptive testing was performed every 10 min after the injection for the first hour and every 30 min for the following 2-h test period. The data are expressed as mean±s.e.mean for four to six animals. Significant difference from the action of clonidine alone at the corresponding time point: ^*P<0.05, ^**P<0.01, ^***P<0.001.