Anxiolytic-like effects of sinapic acid in mice

Sinapic acid is a phenylpropanoid compound and is found in various herbal materials and high-bran cereals. With the exception of its antioxidant activities, the pharmacological properties of sinapic acid have been rarely reported. The purpose of this study was to characterize the putative anxiolytic-like properties of sinapic acid using an elevated plus-maze (EPM) and hole-board test. Control mice were orally treated with an equal volume of vehicle (10% Tween 80 solution), and positive control mice were treated with diazepam (1 mg/kg, i.p.). Sinapic acid (4 mg/kg, p.o.) significantly increased the percentages of time spent in the open arms of the EPM test (P < 0.05). In the hole-board test, sinapic acid also significantly increased the number of head-dips at 4 mg/kg (P < 0.05). In addition, the anxiolytic-like properties of sinapic acid examined in the EPM test were blocked by flumazenil or bicuculline, which are GABA_A antagonists. Moreover, sinapic acid markedly potentiated GABA current in single cortical neurons in a dose-dependant manner, and reactive I_GABA increased to 1.8 times at 1 μM of sinapic acid. These results suggested that sinapic acid is a prominent anxiolytic agent, and that its anxiolytic-like effects are mediated via GABA_A receptors and potentiating Cl^- currents.