Modified Chaihu Longgu Muli Decoction Improved the Synaptic Plasticity of PFC and Alleviated the Depressive Symptoms in CKD Mice via p38 MAPK Pathway

OBJECTIVE  To study the effect and mechanism of modified Chaihu Longgu Muli Decoction (CLMD) on depressive behavior in chronic kidney disease (CKD) mice.METHODS  Sixty 3-month-old male C57BL/6 mice were divided into control group, model group, fluoxetine group, CLMD low dose group, CLMD medium dose group and CLMD high dose group. Except the control group, the rest 5 groups of mice were intervened by 0.2% adenine diet for 2 weeks, then CLMD low, medium, high groups were gavaged 2.36, 4.725, 9.45 g·kg^-1·d^-1 of CLMD, respectively. Fluoxetine group was given 10 mg·kg^-1·d^-1 fluoxetine by gavage, while the control group and model group were given the same amount of normal saline, for six weeks. Sugar preference test and forced swimming test were used to evaluate the depressive state of mice, Western blot was used to detect the expressions of p38 mitogen-activated protein kinase (p38 MAPK), phosphorylated p38 MAPK (p-p38 MAPK), brain derived neurotrophic factor (BDNF), cAMP-response element binding protein (CREB), phosphorylation CREB (p-CREB), postsynaptic density protein 95 (PSD95), Synapsin (SYN) and growth associated protein 43 (GAP43), Synaptophysin (SYP) proteins in the prefrontal cortex (PFC). The nucleus expression of p-CREB in PFC was detected by immunofluorescence assay, the changes of dendrite spines in PFC were detected by Golgi-Cox staining, and the levels of inflammatory factors in peripheral serum and PFC, and the serum creatinine and urea nitrogen were detected by ELISA assay.RESULTS  The behavior test results showed that, compared with the control group, the immobility time of the model group increased and the percentage of sugar preference level decreased (P < 0.01). Compared with the model group, the immobility time of mice decreased and the percentage of sugar water preference increased after the intervention of CLMD (P < 0.05, P < 0.01), there was no significant difference among the medium dose group, the high dose group and fluoxetine group (P>0.05). Western blot results showed that, compared with the control group, the expressions of p-p38 MAPK/p38 MAPK in PFC of the model group increased (P < 0.01), and the expressions of BDNF, p-CREB/CREB, PSD95, SYN, GAP43 and SYP down-regulated (P < 0.01). Compared with the model group, the relative expressions of p-p38 MAPK/p38 MAPK in medium-dose, high-dose groups and fluoxetine group down-regulated (P < 0.01), and the relative expressions of BDNF, p-CREB/CREB, PSD95, SYN, GAP43 and SYP increased (P < 0.01). Immunofluorescence results showed that, compared with the control group, the nuclear fluorescence level of p-CREB in PFC of the model group significantly decreased (P < 0.01). Compared with the model group, the nuclear fluorescence expression of p-CREB increased in medium-dose, high-dose groups and fluoxetine group (P < 0.05, P < 0.01). The results of Golgi-Cox staining showed that the number of PFC dendritic spines in model group was lower than that in control group (P < 0.01). Compared with the model group, the numbers of PFC dendritic spines increased after medium-dose, high-dose CLMD and fluoxetine intervention (P < 0.01). ELISA results showed that, compared with the control group, the levels of inflammatory factors in both peripheral blood and PFC of model group increased (P < 0.01), the levels of serum urea nitrogen and creatinine increased (P < 0.01). Compared with model group, after medium-dose, high-dose CLMD intervention, the levels of pro-inflammatory factors, serum urea nitrogen and creatinine in PFC and peripheral blood decreased (P < 0.05, P < 0.01).CONCLUSION  CLMD can alleviate the depressive symptoms of CKD mice by regulating the inflammatory state of the central nervous system and affecting the synaptic plasticity of PFC. Meanwhile, CLMD can delay the deterioration of kidney function in CKD model mice by regulating the inflammatory state of the peripheral.