Effects of chronic administration of dioscorea on immobility in the forced swim test. Dioscorea (0, 250, 750, or 1 500 mg/kg/day) was given by oral gavage for 27 days and the rats were tested on days 24 and 25. The number of rats in each group is shown in parentheses below each group. * p < 0.05, ** p < 0.01, *** p < 0.001, compared to the data for the first session, paired t-test. ## p < 0.01, compared to sham-operated rats treated with the same dosage. The data are expressed as the mean ± SEM.