OBJECTIVE  To study the effect of Xiaoyao Powder (XYP) on anxiety and depression behavior phenotype in vascular dementia (VaD) mice and its possible mechanism.

  METHODS  Three-month-old male C57BL/6 mice were treated with bilateral carotid artey stenosis (BCAS) and chronic restraint stress (CRS) to construct the VaD mice model with anxiety and depression. The model mice were divided into model group, fluoxetine positive drug group and XYP low-dose, medium-dose and high-dose groups. The control group were treated with sham operation and unbound. XYP low, medium and high groups were given XYP water Decoction (5, 10, 20 g·kg^-1·d^-1) by intragastric administration, fluoxetine positive control group was given fluoxetine (10 mg·kg^-1·d^-1) by intragastric administration, control group and model group were given equal volume of normal saline for 4 weeks. And restraint stress was maintained for 6 h·d^-1 during drug intervention. The open field test, forced swimming test, elevated cross maze test and sucrose preference test were used to detect the behavioral phenotypes of anxiety and depression in mice. The fluorescence expression levels of myelin basic protein (MBP) in the prefrontal cortex (mPFC), basolateral amygdala (BLA) and corpus callosum (CC) were detected by immunofluorescence assay. Western blot was used to test the protein expression levels in mPFC and BLA of phosphatidylinositol-3 kinase (PI3K), phosphorylated phosphatidylinositol-3 kinase (p-PI3K), protein kinase B (AKT), phosphorylated protein kinase B (p-AKT), target of rapamycin (mTOR), phosphorylated target of rapamycin (p-mTOR), as well as oligodendrocyte glycoprotein (MOG), myelin associated glycoprotein (MAG) and MBP. The myelin forms of CC in mice were observed by LFB staining.

  RESULTS  Compared with the control group, the percentages of open arm time and open arm entries in open field test and the sucrose preference in sucrose preference test decreased in model group (P < 0.01), and the immobility time of model group increased significantly in forced swimming test (P < 0.01). In open field test, the total distance of movement and the time in the center area significantly decreased (P < 0.01). Compared with model group, the immobility time of mice in XYP high-dose and medium-dose groups decreased (P < 0.05), the percentage of sucrose preference increased (P < 0.01), the percentages of open arm time and open arm entries increased (P < 0.05, P < 0.01). The total distance of movement and the time of movement in the center area significantly increased (P < 0.01). Immunofluorescence results showed that, compared with the control group, the fluorescence intensity of model mice in the brain regions of CC, mPFC and BLA significantly decreased (P < 0.01), and the fluorescence intensity of MBP in XYP medium-dose and high-dose groups and fluoxetine increased to varying degrees(P < 0.05, P < 0.01), among which the XYP high-dose group was the most obvious (P < 0.01). In the LFB staining, compared with the control group, the myelin fibers in CC of the model group loosed arrangement, became lighter in colour and demyelinated. XYP could improve the damage of the myelin structure in the model group. Western blot results showed that, compared with the control group, the expressions of MBP, MOG and MAG in the brain regions of mPFC and BLA in model group decreased (P < 0.01). The above trends were significantly reversed in XYP high-dose and medium-dose groups (P < 0.05, P < 0.01). Fluoxetine had a certain effect on the decreasing trend of MAG (P < 0.05), but had no significant effect on the expressions of MBP and MOG. Compared with the control group, the levels of p-PI3K/PI3K, p-AKT/AKT and p-mTOR/mTOR in model mice significantly decreased (P < 0.01), while the protein expression levels of p-PI3K/PI3K, p-AKT/AKT and p-mTOR/mTOR in model mice significantly increased after XYP and fluoxetine intervention (P < 0.05, P < 0.01).

  CONCLUSION  XYP may alleviate the anxiety and depression phenotype of VaD mice by activating PI3K/AKT/mTOR pathway to promote the regeneration of myelin in the mPFC-BLA neural circuit and increase the structural integrity of myelin.