Patchouli Alcohol Protects Against CUMS-induced Depressant-like Behaviour Through Activating MTOR Signaling Pathway

ObjectiveDepression,a psychiatric disease associated with serious mood disorder,was known to the word for its significant morbidity and mortality and poses a substantial health threat to the modern society.Although antidepressants have developed well over the past 50 years,antidepressants still has various side effects,such as sexual dysfunction,dry mouth,nausea,tremor and insomnia.In addition,the treatment of depression exhibited the disadvantages of low efficiency,slow onset of action,incomplete symptom relief,long-term medication and high recurrence rate.Therefore,it is necessary to find a novel,effective and low-side effect antidepressant.Pogostemon cablin Benth,one of "Top Ten South Medicines",is the dry aerial part of Pogostemon cablin(Blanco)Benth of the Labiatae plant.Pogostemon cablin Benth has a variety of beneficial therapeutic effects,such as anti-inflammatory,relieve depression,stress,calm nerves,control appetite,improve sexual interest and antidepressant.Patchouli oil,the main medicinal ingredient of Pogostemon cablin Benth,is used to improve sexual interest and to relieve depression and stress in aromatherapy.Patchouli alcohol(PA)is the main component of patchouli oil,and its content can account for up to 57%in patchouli oil.Study shown that the dichloromethane extract of Valeriana wallichii patchouli alcohol chemotype exerted antidepressant effect,which contains patchouli alcohol.Moreover,previous studies have shown that patchouli alcohol had neuroprotective effects and had protective effects on scopolamine-induced cognitive and memory impairment in mice.These studies indicate that patchouli alcohol is likely to have antidepressant effects.In addition,toxicity experiments showed that patchouli alcohol had a low toxicity.If patchouli alcohol exerts antidepressant effects,it is likely to be a safe and effective antidepressant.Therefore,this study aimed to investigate the antidepressant-like effect of patchouli alcohol and its underlying mechanism via chronic unpredictable mild stress model.Methods1.Male SD rats(180?220g)were randomly divided into six groups:Normal(Vehicle)group,CUMS+Vehicle group,CUMS+fluoxetine 20mg/kg group,CUMS+PA 10mg/kg group,CUMS+PA 20mg/kg group,and CUMS+PA 40mg/kg group.2.The normal(Vehicle)group received no stimulation,and the remaining SD rats were kept in a single cage with the following stimulation:food or water deprivation for 24 h,exposure to a soiled cage for 24 h,inversion of light/dark cycle every 2 h,5min of cold swim at 4?,5 min of heat swim at 420 C,2 min of tail pinch,and 45° cage tilt for 24 h.To prevent habituation and to ensure the unpredictability of the stressors,all stressors were randomly scheduled over a one-week period and were repeated throughout the 8 weeks experiment.3.In the last 4 weeks of 8 weeks,pure water or fluoxetine or different concentrations of PA were given to the rats once a day for intragastric administration for 4 weeks.4.After administration,behavioral tests were conducted in each group,including open-field test,forced swimming test and sucrose preference test,and data were collected.5.The expression of phosphorylated mTOR,p70S6K and 4E-BP-1,and LC3-II and p62 in the hippocampus of GUMS rats were detected by western blot.6.The levels of PSD-95 and SYN-I in the hippocampus of CUMS rats were detected by enzyme-linked immunosorbent assay.7.Rapamycin(autophagy inducer and mTOR pathway inhibitor)and chloroquine(autophagy flux inhibitor)were used to investigate the antidepressant mechanism of PA via blocking.Result1.PA significantly attenuated CUMS-induced depression-like behaviorPA effectively increased the number of crossing and rearing of CUMS rats.Compared with CUMS rats,PA significantly enhanced the sucrose preference of CUMS rats and reduced the immobility time of CUMS rats.2.PA inhibited autophagy and increased autophagic flux via mTOR signaling pathway.PA markedly attenuated CUMS-induced phosphorylated mTOR and p70S6K reduction.Compared with Vehicle rats,CUMS effectively increase the expression of LC3-II and p62.However,this effect was reversed by PA.3.PA increased the formation of synaptic proteins by activating mTOR signaling pathway.Compared with CUMS rats,PA significantly increased the levels of p-p70s6k and p-4E-BP-1 in the hippocampus.ELISA results showed that PA effectively reduced the decreased levels of PSD-95 and SYN-I induced by CUMS in the hippocampus.4.Both rapamycin and chloroquine all reversed the antidepressant effect of PA.Behavioral test results showed that PA effectively improved the number of crossing and rearing,increased the sucrose preference,and reduced the immobility time of CUMS rats.However,this effect was reversed by rapamycin and chloroquine.ConclusionPA exerted the antidepressant-like effect in CUMS rats via activating mTOR signaling pathway to inhibit autophagy,repair synapse and increase autophagy flux.