i.c.v. bolus doses of oxycodone, morphine, or saline (control rats) administered to naive, oxycodone-tolerant, and morphine-tolerant adult male DA rats2-a
| Treatment Period 1: Naive Rats | Treatment Period 2: Tolerant Rats | Treatment Period 3: Tolerant Rats |
|---|---|---|
| Oxycodone i.v. infusion 2.5 mg/24 h for 60 h | i.c.v. bolus dose of morphine | i.c.v. bolus dose of oxycodone |
| 18 nmol (n = 5) | 44 nmol (n = 5) | |
| 34 nmol (n = 5) | 78 nmol (n = 5) | |
| 55 nmol (n = 5) | 132 nmol (n = 5) | |
| 150 nmol (n = 5) | 300 nmol (n = 5) | |
| Morphine i.v. infusion 10 mg/24 h for 60 h | i.c.v. bolus dose of oxycodone | i.c.v. bolus dose of morphine |
| 44 nmol (n = 5) | 18 nmol (n = 5) | |
| 78 nmol (n = 5) | 34 nmol (n = 5) | |
| 132 nmol (n = 5) | 55 nmol (n = 5) | |
| 300 nmol (n = 5) | 150 nmol (n = 5) | |
| 225 nmol (n = 4) | ||
| i.c.v. bolus dose of oxycodone | ||
| 22 nmol (n = 4) | ||
| 44 nmol (n= 5) | ||
| 78 nmol (n = 6) | ||
| 132 nmol (n = 5) | ||
| i.c.v. bolus dose of morphine | ||
| 18 nmol (n = 5) | ||
| 34 nmol (n = 5) | ||
| 55 nmol (n = 5) | ||
| 150 nmol (n = 4) | ||
| i.c.v. bolus dose of saline (n = 4) |
↵2-a Each treatment period was followed by a 12-h washout period with saline.