Table 1.
Effect of low dose i.t. atipamezole, idazoxan, mirtazapine and yohimbine on the induction of acute tolerance to morphine
| Acute treatment | Tail flick ED50 (μg; i.t.) (mean±s.e.mean) | Paw pressure ED50 (μg; i.t.) (mean±s.e.mean) |
|---|---|---|
| Saline | 5.5±0.2*** | 5.9±0.1*** |
| Morphine (15 μg) | 27.9±1.9 | 29.0±1.0 |
| Morphine/Atipamezole (0.8 ng) | 3.3±0.1*** | 3.7±0.1*** |
| Morphine/Idazoxan (0.08 ng) | 6.1±0.2*** | 4.5±0.5*** |
| Morphine/Mirtazapine (0.02 ng) | 15.2±0.8*** | 7.2±2.3*** |
| Morphine/Yohimbine (0.02 ng) | 2.8±0.2*** | 3.6±0.2*** |
| Atipamezole (0.8 ng) | 4.8±0.5*** | 8.6±2.1*** |
| Idazoxan (0.08 ng) | 7.2±2.9*** | 2.9±0.2*** |
| Mirtazapine (0.02 ng) | 6.8±0.3*** | 5.1±0.3*** |
| Yohimbine (0.02 ng) | 3.4±0.3*** | 4.6±0.1*** |
The morphine ED50 values were obtained from the cumulative dose–response curves to anti-nociceptive action of the opioid agonist 24 h after termination of drug treatment in the animal groups represented in Figures 4a and b.
The data presented are means ± s.e.mean; n=5–6 animals per treatment group.
Significant difference from the morphine (15 μg) group *** (P<0.001).