Effects of Dioscorea villosa (DV) on the acetic acid-induced writhing test in mice. Vehicle (control, per os or p.o.), morphine (MOR 3 mg/Kg, i.p) and DV (100, 200 and 400 mg⁄kg, per os or p.o.) were administered 1,0 hr before acetic acid injection. Each column represents mean ± S.E.M. (n = 6). ***p < 0.0001 versus control (ANOVA followed by Tukey’s test).