OBJECTIVE:To investigate the antidepressant-like effect of active fraction of Polyrhachis vicina Roger (AFPR) in a rat depression model,and to elucidate the underlying mechanism.METHODS:AFPR was extracted with ethanol followed by petroleum ether.Its antidepressant-like effect was investigated in mice by tail suspension test (TST),forced swimming test (FST) and open field test (OPT).A repeated dose of reserpine (0.5 mg/kg,daily for 14 d) was used to establish a rat depression model.Fluoxetine was used as positive control agent.The effect of AFPR on reserpine-induced ptosis,hypothermia and akinesia,the levels of monoamines and their metabolites,and the activity of monoamine oxidase (MAO) in hippocampus and prefrontal cortex were determined.RESULTS:Administration of AFPR by gavage at 160 and 320 mg/kg significantly reduced the duration of immobility in the FST and TST,and did not affect locomotor activity in the OPT.In the reserpine-induced depression model,AFPR attenuated anhedonia,demonstrated by reversing hypothermia,akinesia and sucrose consumption.AFPR significantly increased the concentration of monoamines,including dopamine,serotonin,noradrenaline and acetylcholine.CONCLUSION:AFPR normalized the metabolism rates of noradrenaline,serotonin and dopamine,and the activity of MAO,which were altered by chronic reserpine exposure.The findings suggest that modulation of the monoaminergic neurotransmitter system likely underlies the antidepressant-like effect of AFPR.