Antidepressant-like activity of gallic acid in mice subjected to unpredictable chronic mild stress

This study was designed to evaluate antidepressant-like activity of gallic acid in Swiss young male albino mice subjected to unpredictable chronic mild stress and to explore the possible underlying mechanisms for this activity. Gallic acid (5, 10, 20 mg/kg, i.p.) and fluoxetine (10 mg/kg, i.p.) per se were administered daily to unstressed mice and other groups of mice subjected to unpredictable mild stress, 30 min after the injection for 21 successive days. The antidepressant-like activity was evaluated using forced swim test (FST) and sucrose preference test. Stress significantly increased immobility period of mice in FST. Gallic acid (10 and 20 mg/kg, i.p.) and fluoxetine significantly decreased immobility period of unstressed and stressed mice in FST and prevented the stress-induced decrease in sucrose preference, indicating significant antidepressant-like activity. There was no significant effect on locomotor activity of the mice by the drugs. Gallic acid (10 and 20 mg/kg, i.p.) significantly decreased Monoamine oxidase-A (MAO-A) activity, malondialdehyde levels, and catalase activity in unstressed mice; and significantly prevented the stress-induced decrease in reduced glutathione and catalase activity; and also significantly prevented stress-induced increase in MAO-A activity, malondialdehyde levels, plasma nitrite, and corticosterone levels. Thus, gallic acid showed antidepressant-like activity in unstressed and stressed mice probably due to its antioxidant activity and through inhibition of MAO-A activity and decrease in plasma nitrite levels. In addition, gallic acid also showed antidepressant-like activity in stressed mice probably through decrease in plasma corticosterone levels.