Fig. 7. Effects of the subcutaneous administration of morphine (1–16 mg/kg) (A ) and ketoprofen (32–128 mg/kg) (B ) on the referred mechanical hyperalgesia induced by intracolonic administration of capsaicin 0.1% in WT and σ1-KO mice. The drug or its vehicle was injected at 30 min before instillation of capsaicin. The referred mechanical hyperalgesia (evaluated by stimulation of the abdomen with von Frey filaments) was measured at 20 min after the capsaicin instillation. Each point and vertical line represents the mean ± SEM of values obtained in 12 WT or 10 σ1-KO mice per group. The dashed line indicates the 50% threshold in capsaicin solvent-treated WT and σ1-KO mice. Note that the higher doses of morphine increase the mechanical threshold to above the control value (i.e., exert analgesic effects). Statistically significant differences between the values obtained in morphine- and vehicle-injected mice: ##P < 0.01. Statistically significant differences between the values obtained in WT and σ1-KO animals at the same dose of morphine: *P < 0.05; **P < 0.01 (two-way ANOVA followed by Bonferroni test). WT, wild type; σ1-KO, σ1receptor knockout.