Fig. 1.

Hyperalgesia in B6 and e/e mice during continuous morphine infusion. Male and female B6 (A, B) and e/e (C, D) mice were implanted with placebo (A, C) or naltrexone (B, D) pellets and assayed for nociception on the tail-withdrawal test 24 h later (Day 0). Mice were then immediately implanted with osmotic pumps providing continuous infusion of a cumulative daily morphine dose of 40.0 mg/kg or vehicle. Nociception was reassessed daily on the subsequent infusion days. Symbols are mean ± SEM withdrawal latencies, with n = 8–10 mice in every group. *Indicates significant difference (in either direction) relative to own baseline (Day 0) latency (Bonferroni corrected P < 0.05).