Subcutaneous pretreatment of saline, ketoprofen (1, 2, 4 mg/kg), morphine (0.32, 1 3.2 mg/kg), and U50,488H (0.1, 0.32, 1, 3.2, 10 mg/kg) on intraperitoneal 1% acetic acid (AA)-induced stretching. Data point “saline” represents number of stretches following acid administration after saline pretreatment. Data are expressed as means ± S.E.M. from 6–8 mice. Filled symbols indicate significantly different from saline pretreatment as determined by one-way ANOVA followed by Tukey’s post hoc test (p<0.05).