Table 2.
Effect of low dose atipamezole on the induction of tolerance to chronic antinociceptive effects of i.t. morphine
| Chronic treatment | Tail flick ED50 (μg; i.t.) (mean±s.e.mean) | Paw pressure ED50 (μg; i.t.) (mean±s.e.mean) |
|---|---|---|
| Saline | 5.4±0.1*** | 8.7±1.5*** |
| Morphine (15 μg) | 38.6±0.9 | 42.0±1.4 |
| Morphine+Atipamezole (0.08 ng) | 1.5±0.3*** | 2.5±0.4*** |
| Morphine+Atipamezole (0.8 ng) | 1.8±0.1*** | 2.7±0.2*** |
| Atipamezole (0.8 ng) | 4.2±0.2*** | 7.2±0.2*** |
Chronic i.t. morphine (15 μg) was delivered alone and in combination with atipamezole once daily for 5 days. The morphine ED50 values were obtained from the cumulative dose–response curves for the antinociceptive action of the opioid agonist 24 h after termination of drug treatment in the animal groups represented in Figures 5a and 6a.
The data are presented as mean±s.e.mean; n=4–7 animals per treatment group.
Significant difference from the morphine (15 μg) group ***(P<0.001).