Objective: To study the effect of Xiaoyaosan on changes of behavior and plasma monoamine neurotransmitters on chronic unpredictable mild stress (CUMS) model in rats. Method: The stimulus on CUMS model lasted 3 weeks. At the beginning of stimulus

the rats were treated with the decoction of Xiaoyaosan or two positive drugs (fluoxetine and cultural venlafaxine) for 4 weeks. During the experiment

body weight

the percentage of sucrose preference and data of open-field test (including ambulation numbers

rearing numbers

immobility time) were detected

which was to evaluate the anti-depression action of Xiaoyaosan. In the 4th week

all rats were decapitated after the last treatment

then blood was immediately isolated for detecting the concentration of NA and 5-HT by HPLC - fluorescence detection. Result: After 3 weeks of CUMS procedure

body weight

number of activities and percentage of sucrose preference of the rats in model group decreased significantly compare with control group (P<0.01 and P<0.05

respectively). Continually administrated for 4 weeks

the body weight

activity times and percentage of sucrose preference in the model group treated with Xiaoyaosan (92.5 g ·kg-1and 46.3 g ·kg-1) increased significantly (P<0.01 and P<0.05

respectively) compared with model group. Continuous treatment of 92.5

46.3 g ·kg-1and 23.1 g ·kg-1 Xiaoyaosan for 4 weeks could increase the concentration of NA in plasma (P<0.05). Conclusions: It suggested that Xiaoyaosan had the antidepression effect and the anti-depression effect was possibly related to increasing the concentration of NA in plasma.