Antidepressant Effects And Mechanisms Of Xiaochaihutang In Depression Animal Models Induced By Chronic Social Isolation Stress

Xiaochaihutang(XCHT)was recorded as a classic prescription in traditional Chinese medicine in "ShangHan Lun" written by Zhang Zhongjing in the Chinese Eastern Han Dynasty to treat Shaoyang syndrome.Our previous studies have used behavioral despair models and drug-induced depression models to screen the efficacy of XCHT and further systematically evaluated the antidepressant effects of XCHT using chronic unpredictable mild stress(CUMS)model,corticorsterone(CORT)-induced depression model and ovariectomized mice model.The mechanisms of XCHT for treating depression might be related to maintenance of neurotransmitter homeostasis,remodeling the function of HPA axis,improving the neurotrophic factors and regulating of female hormones levels and the activity of downstream signalling pathway.It has been known that chronic social isolation stress is considered particularly important since it closely mimics the pathogenesis of depression due to lacking social interaction rather than physical stress.Therefore,we established two kinds of depression models induced by chronic social isolation stress to further investigate the antidepressant effects and mechanisms of XCHT using various technologies including behavior,immunofluorescence,western immunoblotting,in vivo microdialysis and high performance liquid chromatography-tandem mass spectrometry(HPLC-MS/MS).Firstly,we used chronic social isolation(SI)-reared mice model of depression/anxiety to investigate XCHT's antidepressant-like effects and mechanism of action.Our results showed that chronic social isolation stress for 6 weeks induced series of depressive/anxiety-like behaviors.Oral administration of XCHT(0.8,2.3,and 7.0 g/kg)for 6 weeks significantly attenuated the increase of immobility time in tail suspension test(TST)and forced swimming tset(FST),weaken the hyper-motility in open field test(OFT)and alleviated the decreased duration spent in open arms in elevated-plus maze test(EPM)and improved aggressive behaviors.By in vivo microdialysis technology based on HPLC-MS/MS platform,we found that XCHT significantly reversed the decreased levels of monoamine neurotransmitters(5-HT,DA,NE)and inhibited 5-HT turnover(5-HIAA/5-HT)in hippocampal microdialysates of SI-reared mice.By western immunoblotting method,we found XCHT significantly reversed the decrease of tyrosine hydroxylase(TH)and tryptophan hydroxylase 2(TPH2)expressions,reversed the increase of serotonin transporter(SERT)and monoamine oxidase A(MAOA)expression without changing the protein levels of noradrenaline transporter(NET),dopamine transporter(DAT)and monoamine oxidase B(MAOB)in the hippocampus of SI-reared mice.We further used immunofluorescence technology to study the effects of XCHT on neurogenesis and neurotrophin expressions and found that XCHT significantly prevented impairments of hippocampal neurogenesis(Ki-67,DCX and BrdU positive cells)and improved BDNF expression in hippocampus of SI-reared mice.These results suggested that monoaminergic system,neurogenesis and neurotrophin might contribute to the neurobiological mechanisms underlying depressive/anxiety-like behaviors induced by post-weaning social isolation stress.We then used socially isolated adult rats model to access the antidepressant-like effects of XCHT.The results showed that chronic social isolation stress(CSIS)for 5 weeks induced depressive/anxiety-like behaviors of adult rats.Oral administration of XCHT(0.6,1.7,5.0 g/kg)for 5 weeks significantly increased sucrose preference,decreased immobility time in FST,shortened the latency to feed and increased food consumption in novelty-suppressed feeding test(NSFT)and attunuated isolation-induced aggressive behaviors.XCHT significantly inhibited the increase of ACTH and CORT levels in plasma of socially isolated adult rats exposed to forced swimming stress.XCHT also significantly reversed CSIS-induced decrease of 5-HT,NE,DA,DOPAC and HVA levels in cerebrospinal fluid(CSF)and promoted hippocampal neurogenesis.Additionally,XCHT reversed CSIS-induced decrease of 5-HT1A receptor expression,promoted the phosphorylation of 5-HT1A receptor-regulated ERK/AKT protein and promoted the expression of p-CREB and BDNF in the hippocampus.Taken together,our results suggest that XCHT could significantly regulate the depressive/anxiety-like behaviors of socially isolated adult rats,which are likely attributed to the promotion of hippocampal neurogenesis and neurotrophin expressions through the activation of serotonergic system and regulation of HPA axis for secreting hormone.In summary,we found that XCHT exerted significant antidepressant effect in SI-reared mice and socially isolated adult rats.The possible molecular and cellular mechanism of XCHT might be related to improving monoaminergic function,regulating the function of HPA axis for secreting hormone under stress,promoting hippocampal neurogenesis and neurotrophin expressions through the activation of the serotonergic system.This study provides new evidence for the therapeutic effect of XCHT against different kinds of depression and suggests that XCHT needs to be further investigated as a potential antidepressant therapeutic.