Fig. 5.

Effects of the association of subcutaneous administration of naloxone (1 mg/kg) or its solvent with morphine (0.25 mg/kg), haloperidol (HP, 0.06 mg/kg), haloperidol metabolite II (HP-Met-II, 0.25 mg/kg), and haloperidol metabolite I (HP-Met-I, 64 mg/kg) on mechanical hypersensitivity induced by the intraplantar injection of capsaicin (1 µg) to the mouse hind paw. The results represent the latency to hind-paw withdrawal of the capsaicin-sensitized paw after ipsilateral stimulation with a filament at 0.5 g force (see the “Materials and methods” section for details). Each bar and vertical line represent the mean±SEM of the values obtained in an independent group of animals (n = 8–10 per group). Each group was treated with only one of the drugs under study associated to naloxone or its solvent. Statistically significant differences in values were only found between the morphine-treated and morphine+naloxone-treated groups: **P < 0.01 (nonpaired Student’s t test)