Antinociceptive effects of morphine and compound 1 in wild-type C57BL/6 (B6) mice. (A, C) Acute antinociceptive effects of morphine (A) and compound 1 (C) in B6 mice. After detection of basal latencies, each mouse was injected with various dosages of either morphine or compound 1 to detect the radiant heat tail-flick latencies at the indicated time points (30, 60, 90, 120, 150, and 180 min after drug injection), and quantitative results were calculated. *P < 0.01. †P < 0.001 versus vehicle group, two-way ANOVA with appropriate post hoc tests. Data in A and C are based on n = 5 per group. (B, D) Quantitative results from A and C are represented as the area under the curve (AUC). *P < 0.01. †P < 0.001 versus vehicle group, one-way ANOVA with appropriate post hoc tests. Data in B and D are based on n = 5 per group. (E) Mice were injected with vehicle, morphine (4 mg/kg), or compound 1 (20 mg/kg), and then the acute mechanical pain sensitivity to a tail clip was measured. *P < 0.01. †P < 0.001 versus vehicle group. ‡P < 0.01 versus morphine group, one-way ANOVA with appropriate post hoc tests. n = 7 per group. (F) Mice were injected intrathecally with cyprodime, naltrindole, or nor-binaltorphimine (nor-BNI) 5 min before vehicle, morphine (4 mg/kg), or compound 1 (20 mg/kg) injection and were subjected to a tail-flick test 30 min later. †P < 0.001 versus vehicle or morphine group. §P < 0.001 versus vehicle or compound 1 group, one-way ANOVA with appropriate post hoc tests. n = 5 per group. The values indicate the mean ± SD.