Objective： To determine the mechanisms underlying the anti-depressant effects of Kaixin JieyuDecoction （开心解郁汤, KJD） by investigating the effects of KJD on behavior, monoamine neurotransmitterlevels, and serotonin （5-HT） receptor subtype expression in the brain in a rat model of depression. Methods：The rat depression model was established using chronic unpredictable mild stress （CUMS）. Forty-eight SpragueDawley rats were randomly divided into control, depression model （CUMS）, CUMS＋KJD （7.7 g/kgl-d1 ofcrude drug）, and CUMS＋fluoxetine （2.4 mg/kgl.d1） groups （n=12 in each group）, and the treatments lastedfor 21 days. We regularly evaluated body weight, sucrose consumption, and horizontal and vertical activityscores in open-field tests. The content of the monoamine neurotransmitters 5-HT, norepinephrine （NE）, anddopamine （DA） and the DA metabolite homovanillic acid in the cerebral cortex, and 5-HT1A and 5-HT2A receptormRNA in the cerebral cortex and the hippocampus, were determined respectively by high-performance liquidchromatography-coularray electrochemical detector and real-time polymerase chain reaction. Results： Comparedwith the control group, CUMS rats showed a variety of depression-like behavioral changes, including a significantreduction in body weight, sucrose consumption, and horizontal and vertical activity scores in open-field tests（P〈0.05 or ,P〈0.01）, and a significant decrease in 5-HT and NE levels and 5-HT2A receptor mRNA expression.In contrast, they showed a significant increase in 5-HT1A receptor mRNA expression in the cerebral cortex. Inthe hippocampus, 5-HT1A receptor mRNA expression was lower whereas 5-HT2A receptor mRNA expressionwas higher than in the control group （P〈0.05 or P〈0.01）. Treatment with KJD or fluoxetine partially attenuatedthese changes （,P〈0.05 or ,P〈0.01）. Conclusion： KJD could normalize the levels of 5-HT and NE and adjust thebalance of 5-HT2A and 5-HT2A receptor expression in rat cerebrum, and thi
