Figure 2.

Pain scores of formalin-induced nociceptive behaviours (mean ±S.E.M. of 8–10 mice per group) following injection of saline (10 ml/kg) or morphine (A1-A3) measured every 3 minutes for a total 60 minutes (A) and bar chart for different doses of morphine 1.5, 3, and 6 mg/kg in the formalin test and control site (B1-B3). Columns represent the mean nociceptive score in each phase: phase 1 (minutes 1–7), inter phase (minutes 8–14), and phase 2 (minutes 15–60) (B1-B3). The mice received morphine 30 minutes before formalin injection in the right hind paw. Recording of the nociceptive behaviors began immediately after formalin injection (time 0) and continued for 60 minutes. For clarity, each dose of morphine was plotted in separate graphs, with the same control group in each.

*P < 0.05; ***P < 0.001 compared with saline