Table 2.
The effects of ultralow doses of opioid receptor antagonists on the reversal of tolerance to intrathecal morphine
|
Chronic treatment (10 days) |
ED50 (mean±s.e.m.) (mg) |
||
|---|---|---|---|
| Days 1–5 | Days 6–10 | Tail flick | Paw pressure |
| Saline | Saline | 5.1±0.3 | 6.4±0.3 |
| Morphine (15 μg) | Morphine (15 μg) | 43.5±1.2a | 57.9±1.2a |
| Morphine (15 μg) | Morphine/CTAP (0.001 ng) | 4.9±0.2 | 8.8±1.6 |
| Morphine (15 μg) | Morphine/naltrindole (0.01 ng) | 3.7±0.1 | 5.6±0.5 |
| Morphine (15 μg) | Saline | 7.3±0.3 | 18.1±3.9 |
| Morphine (15 μg) | CTAP (0.001 ng) | 6.8±0.6 | 6.7±0.8 |
| Morphine (15 μg) | Naltrindole (0.01 ng) | 5.2±0.8 | 10.0±0.7 |
Following the end of the 10-day chronic treatment period, cumulative dose–response curves to acute morphine were generated on day 11, and ED50 values for morphine were derived from these curves.
a
Significant differences from saline group (P<0.001).