Figure 1.

Tolerance to morphine-mediated antinociception. Mice were surgically implanted with placebo pellet (placebo-P) or 75 mg morphine pellet (morphine-P) without (a) or with (b) supplemental saline (placebo-P+saline) or morphine injections (morphine-P+morphine). Seventy-two hours later, morphine was injected s.c. and tail-withdrawal latencies were obtained 30 min after injection, using the warm water (56°C) tail withdrawal procedure. Each curve represents six mice per dose per group.