TABLE I.
The effect of a single i.p. administration of vehicle and SB-277011A on the conditioned place aversion induced by a two-cycle pairing of morphine + naloxone in adult male Sprague-Dawley rats
| Treatment pairings | Drug given p.o. on test day | Time spent in chambers (min)
|
|
|---|---|---|---|
| Paired | Unpaired | ||
| Morphine/Naloxone | Vehiclea | 5.5 ± 0.3b | 9.5 ± 0.3 |
| Vehicle/Naloxone | Vehiclea | 7.1 ± 0.2c | 7.9 ± 0.2 |
| Morphine/Naloxone | SB, 3 mg/kg | 6.3 ± 0.4 | 8.7 ± 0.4 |
| Morphine/Naloxone | SB, 6 mg/kg | 8.8 ± 0.3d | 6.2 ± 0.3 |
| Morphine/Naloxone | SB, 12 mg/kg | 10.0 ± 0.3e | 5.0 ± 0.3 |
| Morphine/Naloxone | SB, 24 mg/kg | 10.3 ± 0.4e | 4.7 ± 0.4 |
Abbreviations: SB: SB-277011A.
The vehicle was 1 ml/kg of distilled water for the pairings. The vehicle used on the test day was 1 ml/kg i.p. of 2% methylcellulose.
Each value represents the mean number of minutes spent in each chamber ± S.E.M. A total of 10 rats were examined for each treatment pairing. All animals received one pairing with 5.6 mg/kg i.p. of morphine followed 4 h later by 0.3 mg/kg s.c. of naloxone followed 24 h later by 1 pairing with vehicle 1 ml/kg i.p. and s.c. of vehicle (deionized, distilled water), and this was repeated once over 4 days. All animals were confined to the appropriate chamber for 20 min during each pairing. On the test day, animals received either 1 ml/kg i.p. vehicle (2% methylcellulose) or SB-277011A (dissolved in 2% methylcellulose) 30 min before being placed into the CPP apparatus. The times spent in paired chamber represents the time spent in the compartment originally paired with morphine + naloxone or vehicle + naloxone.
Significantly greater than Morphine/Naloxone pairings and Vehicle on the test day, P < 0.0001, Student’s unpaired t test.
Significantly greater than Morphine/Naloxone pairings and vehicle on the test day and Morphine/Naloxone pairings and 3 mg/kg of SB-277011A on the test day, P < 0.01, ANOVA and Student-Newman-Keuls test.
Significantly greater than Morphine/Naloxone pairings and Vehicle on the test day (P < 0.01), Morphine/Naloxone pairings and 3 mg/kg of SB-277011A on the test day (P < 0.01) and Morphine/Naloxone pairings and 6 mg/kg of SB-277011A on the test day (P < 0.05), ANOVA and Student-Newman-Keuls test.