Anxiolytic-like effect of Shigyakusan extract with low side effects in mice

Shigyakusan is a traditional Japanese herbal (Kampo) medicine used to treat inflammatory conditions such as cholecystitis and gastritis as well as psychiatric disorders. This study examined the anxiolytic-like effect of Shigyakusan extract (SS), and evaluated the activity of the main compound. Three behavioral tests in mice were used to evaluate the activity of SS. Samples were administered orally over a 10-day period. A light and dark box (LDB) test was performed on the 8th day, while an open field (OF) test was done on the 9th day, and an elevated plus maze (EPM) test was performed on the 10th day. Diazepam (DZ), a typical anxiolytic drug, was used as the positive control. Administration of 10 mg/kg DZ resulted in a significant anxiolytic-like effect in the LDB and EPM tests, while administration of 0.3 g/kg SS resulted in a weak anxiolytic-like effect. In the OF test, while DZ caused a significant reduction of locomotor activity, SS did not cause any changes compared to the water controls. This suggests that locomotor activity may be a side effect of DZ, and thus SS, which lacks this response, may be a more useful treatment. Quantitative analysis performed to clarify the activity of the main compound also determined that SS contained 51.4 mg/g naringin, which also has been reported to have anxiolytic-like activity. Since these results suggested that this compound might be responsible for the activity of SS, we subsequently examined the oral administration of a similar dose of naringin. Although we observed a tendency for a weak anxiolytic-like effect, this effect was not greater than that seen for SS.