The Neurobiological Mechanism Underlying The Antidepressant-like Effect Of The Total Flavonoids Extracted From Xiaobuxin-Tang

Background Xiaobuxin-Tang(XBXT),a traditional Chinese herbal decoction,was originally documented in the silk scroll manuscript of Mogao Caves of Dun-huang.The previous studies have demonstrated that the total flavonoids(XBXT-2) isolated from the extract of XBXT possessed potential antidepressant activity.Aim To research the antidepressant-like effect and its possible neurobiological mechanism in XBXT-2.Methods(1)Using multiple animal models of depression,including tail suspension test (TST) in mice,forced swimming test(FST) in mice and rats,learned helplessness(LH) model of rats,chronic mild stress(CMS) model of mice and CMS model of rats to evaluate the antidepressant-like effect in XBXT-2.(2)Using four behavioral and pharmacological models,including 5-HTP-induced mouse head-twitch test, PCPA-induced depletion of serotonin in mouse tail suspension test,yohimbine toxicity potentiation test and antagonism of apomorphine induced hypothermia test to investigate the effect of XBXT-2 on mouse monoaminergic system;applying high performance liquid chromatography with electrochemical detector(HPLC-ECD) to test the level of monoamine and its metabolite in striatum,hypothalamus,hippocampus and prefrontal cortex of CMS rats.(3)Using ELISA to test the serum corticosterone level in HL rats, serum corticosterone and adrenocorticotropic hormone(ACTH) in CMS rats;Using western blot to determine glucocorticoids receptors(GR) expression in CMS rats. (4)Using western blot to determine the expression of brain-derived neurotrophic factor (BDNF),tyrosine kinase receptor B(TrkB) in the hippocampus of CMS mice,and also the expression of BDNF,phosphor-cAMP response element binding protein(pCREB), extracellular signal regulated kinase(ERK1/2) and its phosphated molecular(pERK1/2) in the hippocampus of CMS rats.(5)Using immunohistochemistry method to evaluate the effect of XBXT-2 on hippocampal neurogenesis;performing double immune-fluorescence labeling method to investigate the differentiation of the newly generated cells.(6)Using immunohistochemistry method to evaluate the effect of XBXT-2 on the glial cells of hippocampus and prefrontal cortex in CMS rats.Results Single administration of XBXT-2(50,100mg/kg,ig) significantly decreased the immobility time in TST and FST in mice;Repeated XBXT-2(50,100mg/kg,1,5, 24h before test,ig) administration significantly decreased the immobility time in rat FST; Sub-chronic XBXT-2(25,50mg/kg,2 times everyday for 4 consecutive days,ig) significantly reduced the number of escape failure in LH rats;Chronic XBXT-2((25, 50mg/kg,1 time everyday for 24 or 28 consecutive days,ig) significantly reversed the depressive-like behaviors in CMS mice or CMS rats,including the reduced sucrose preference,deficient activity in Open-field and prolonged latency to novelty-suppressed feeding.The similar effects were found in positive drug FLU or IMI.In addition, XBXT-2(25～100mg/kg,ig) had no effect on locomotor activity.(2) Acute administration of XBXT-2(25,50,100mg/kg,ig) significantly potentiated the mouse head-twitch response induced by 5-HTP(a metabolic precursor to serotonin),and also, decreased the immobility time in mouse tail suspension test,which was completely prevented by PCPA(an inhibitor of serotonin synthesis) pretreatment.However,single treatment with XBXT-2 had no effect on yohimbine toxicity and high dose of apomorphine-induced hypothermia in mice.These results indicated that acute treatment with XBXT-2 produced serotonergic,but not noradrenergic activation.Furthermore, XBXT-2 normalized the neurotransmitter changes,including the decreased serotonin (5-HT) and its metabolite 5-hydroxyindoleacetic acid(5-HIAA) levels in hippocampus and prefrontal cortex in CMS rats.(3)XBXT-2 significantly decreased the serum corticosterone level in LH rats,and also,reduced the serum corticosterone and ACTH level in CMS rats.Moreover,XBXT-2 significantly increased the GR expression in the hippocampus of CMS rats.(4)XBXT-2 significantly increased the expression of BDNF and TrkB in CMS mice,and also,increased the expression of BDNF,pCPEB and pERK1/2 in CMS rats.(5) XBXT-2 significantly up-regulated the hippocampal neurogenesis in CMS rats,while it had no effect on the differentiation of the newly generated cells.(6) Chronic stress caused the reduction and atrophy in glial cell in hippocampus and prefrontal cortex.XBXT-2 restored these changes.Conclusion(1) XBXT-2 possesses excellent antidepressant-like effect in multiple animal models of depression.Meanwhile,the effective doses for behavioral responses have no effect on mouse locomotor activity.(2) The mechanisms underlying the antidepressant-like effect of XBXT-2 may be related to:①XBXT-2 possesses remarkable serotonergic activation in both prefrontal cortex and hippocampus.②XBXT-2 suppresses the hyperaction of the HPA axis during stress.③XBXT-2 up-regulates the activity of BDNF and its related MEK-ERK-CREB signaling pathway.④XBXT-2 up-regulates hippocampal neurogenesis.⑤XBXT-2 reduced the stress-related impairment to glial cell. In conclusion,the beneficial effects of XBXT-2 treatment could then arise from the reversal or amelioration of these dysfunctions,and finally contribute to the maintenance ofhippocampal morphologic and functional plasticity.