ObjectiveTo observe the antidepressant effect of Chaihu Shugansan combined with ferulic acid on the rat model of chronic unpredictable mild stress （CUMS） and explore the mechanism from the histomorphology of frontal cortex， expression of key molecules in the brain-derived neurotrophic factor （BDNF）/tyrosine kinase receptor B （TrkB） signaling pathway， and changes in monoamine neurotransmitter levels.MethodsSixty adult male SD rats were randomized into six groups （n=10）： blank control， depression model， Chaihu Shugansan （3.3 g·kg^-1·d^-1）， ferulic acid （50 mg·kg^-1·d^-1）， Chaihu Shugansan （3.3 g·kg^-1·d^-1） + ferulic acid （50 mg·kg^-1·d^-1）， and fluoxetine （2.1 mg·kg^-1·d^-1）. Rats in other groups except the blank control group were subjected to a mild chronic unpredictable stress stimulus every day. Seven stimuli were used， including fasting with free access to water for 24 h， water deprivation with free access to food for 24 h， wetting the bedding with water in the cage， restraint for 3 h， tail clamping for 1 min， swimming in ice water at 4 ℃， and day and night reversal. Each stimulus was used 1 to 3 times， and the modeling lasted for a total of 21 days. At the same time of stimulation， rats in each medication group were treated with corresponding agents by gavage， while those in the blank control group and the depression model group received equal volumes of normal saline by gavage. The open field test， sucrose preference test， and forced swimming test were conducted before and after modeling. The rats were anesthetized by intraperitoneal injection of 3% pentobarbital sodium， and the frontal cortex was isolated on ice. The mRNA and protein levels of BDNF， TrkB， and cyclic adenosine monophosphate-responsive element-binding protein （CREB） in the frontal cortex were determined by Real-time fluorescence quantitative polymerase chain reaction （Real-time PCR） and Western blot， respectively. The levels of monoamine neurotransmitters 5-hydroxytryptamine （5-HT）， dopamine （DA）， and norepinephrine （NE） in the frontal cortex were determined by enzyme-linked immunosorbent assay. Light microscopy was employed to observe the histopathological changes in the frontal cortex.ResultsCompared with the blank control group， the depression model group showed reduced body mass （P<0.05， P<0.01）， decreased number of crossings and rearings in the open field test and sucrose preference （P<0.01）， prolonged time of immobility in the forced swimming test （P<0.01）， reduced neuronal cells， increased necrotic cells， and darkening cell staining in the frontal cortex， down-regulated mRNA and protein levels of BDNF， TrkB， CREB， and lowered levels of 5-HT， NE， and DA in the frontal cortex （P<0.01）. Compared with the depression model group， each intervention group showed improved general state， increased body mass （P<0.05）， increased number of crossings （P<0.05）， shortened immobility time in the forced swimming test （P<0.01）， increased neuronal cells， reduced necrotic cells， and lightened cellular staining in the frontal cortex， up-regulated mRNA and protein levels of BDNF， TrkB and CREB， and elevated levels of 5-HT， NE， and DA in the frontal cortex （P<0.01）. Moreover， the Chaihu Shugansan + ferulic acid group outperformed the Chaihu Shugansan group and the ferulic acid group in increasing the body mass and the 5-HT content in the frontal cortex （P<0.05）. The combination group outperformed the Chaihu Shugansan group regarding the number of rearings and up-regulation in the mRNA level of BDNF in the frontal cortex （P<0.05）， and it was superior to the ferulic acid group in terms of shortening the immobility time in the forced swimming test， up-regulating the mRNA levels of BDNF， TrkB， and CREB and the protein levels of BDNF and CREB in the frontal cortex， and increasing the DA content in the frontal cortex （P<0.05）.ConclusionChaihu Shugansan combined with ferulic acid can exert antidepressant effect on the rat model of CUMS by regulating the BDNF/TrkB signaling pathway and monoamine neurotransmitter content in the frontal cortex. Moreover， the antidepressant effect of Chaihu Shugansan combined with ferulic acid was more significant than that of Chaihu Shugansan and ferulic acid used alone.

Chaihu Shugansan;ferulic acid;depression;brain-derived neutrophic factor （BDNF）/tyrosine kinase receptor B （TrkB） signaling pathway;monoamine neurotransmitters