Mechanism Of Curculigoside Promoting Bdnf Expression To Accelerate Fear Memory Extinction And Improve Depression-like Behaviors

1 Background Post-traumatic stress disorder(PTSD)is a mental disorder caused by fear stress.The main clinical manifestations of PTSD include anxiety,depression,fear,escaping from reality and insomnia.The occurrence of depression and anxiety is closely related to the persistence of fear of traumatic memory.Therefore,accelerating the extinction of fear memory is an important strategy to improve fear and ameliorate neuropsychiatric activities.It is reported that the occurrence of fear and depression and anxiety-like behavior depends on the hippocampus.Brain-derived neurotrophic factor(BDNF)is a member of the neurotrophic factor family,which could regulate extinction of fear memory and the occurrence of depression.Curculigoside(CUR)is the main active ingredient of Cynanchum arundinaceae,which has antioxidant and neuroprotective effects.Previous studies have shown that CUR can improve neuropsychiatric damage caused by electrical stimulation stress.The aim of this study was to further explore the effects of CUR on depression-like behavior in mice with conditioning fear and learned-helpless(LH)depression model and its possible mechanism.This study would provide a reference for the antidepressant mechanism of CUR.2 Objective To investigate the effect of CUR on fear memory extinction and depression-like behavior in learned-helplessness depression model mice,and to elucidate the mechanism of CUR from the perspective of BDNF.3 Method Healthy C57BL/6 mice weighing 20-25 g were included in this study.The study was divided into two sections:(1)CUR increases BDNF expression,promotes fear memory extinction and improves depression-like behavior: Conditioning fear task was established.Before modeling,each group was given corresponding high(40 mg/kg),medium(8 mg/kg),low(1.6 mg/kg)doses of CUR and physiological saline(i.p.7 days),and 7,8-DHF(Trk B agonist)group was intraperitoneally injected with 7,8-DHF(5 mg/kg)30 minutes before re-exposure.To explore the effect of CUR on the extinction of fear memory,we detected the changes of freezing time in mice.Conditioning fear task was followed by tail suspension and forced swimming to observe the effect of CUR on depression-like behaviors in mice.Brain was taken 24 h after the behavioral experiment for biochemical detection.(2)CUR increases BDNF expression and improves depression-like behaviors in learned-helplessness mice: mice were randomly divided into normal control group,LH group,LH + DMSO group,CUR high(40 mg/kg),medium(8 mg/kg),low dose group(1.6 mg/kg)and 7,8-DHF group.The high,medium and low dose groups and DMSO groups were given corresponding dose of DMSO(i.p.14 days)intraperitoneally,and the model group and the normal group were given the same amount of saline.On the 8th day of administration,LH depression model was established.In the 7,8-DHF group,7,8-DHF(5 mg/kg)was injected intraperitoneally 30 minutes before electric shock.Behavioral experiments were conducted after drug administration.Mechanisms: After the behavioral experiments,hippocampal tissues of mice were taken for western blot to detect the expression of BDNF,p-m TOR and p-Akt.The remaining hippocampi were fixed and frozen for immunofluorescence and TUNEL detection.4 Results(1)Curculigoside increases BDNF expression,promotes fear memory extinction and improves depression-like behaviors.During the re-exposure period,there was no significant difference in the freezing time in each group(p>0.05);on the fourth day of the extinction of fear memory,the freezing time in CUR group and 7,8-DHF group was significantly lower than that in FM group(p<0.05);the immobility time of mice in CUR group and 7,8-DHF group in forced swimming and tail suspension test was significantly reduced as compared with FM group(p<0.05);compared with FM group,the expression of hippocampal BDNF in CUR group and 7,8-DHF group was increased.The protein expression of p-m TOR and p-Akt in CUR groups was significantly higher than that of FM group(p<0.05),while the protein expression of p-Erk and PSD95 had no significant difference among the groups(p>0.05).(2)Curculigoside improves depression-like behavior in learned helplessness mice by increasing the expression of BDNF.There was no significant difference in the latency of searching platform in the first four days(p>0.05);in the space exploration experiment,the swimming time in platform quadrant in LH group was significantly lower than that in normal group(p<0.05),and the swimming time in platform quadrant in CUR group was significantly longer than that in LH group(p<0.05);the immobility time in tail suspension and forced swimming in LH group was significantly longer than that in normal group(p<0.05).The immobilization time of mice in CUR group and 7,8-DHF group was significantly decreased compared with that in LH group(p<0.05).TUNEL results showed that apoptosis in DG area of hippocampus was significantly increased in LH mice compared with that in normal group(p<0.05).Apoptosis in DG area of hippocampus in CUR group was significantly decreased compared with that in LH group(p<0.05).Compared with LH group,the expression of BDNF in the hippocampus of CUR group and 7,8-DHF group increased significantly(p<0.05);the expression of p-Akt and p-m TOR in the hippocampus of LH mice decreased significantly(p<0.05);Compared with LH group,the expression of p-Akt and p-m TOR in the hippocampus of CUR group and 7,8-DHF group increased significantly(p<0.05).5 Conclusion(1)CUR increases the expression of BDNF in hippocampus,promotes the extinction of fear memory and improves depression-like behaviors. (2)CUR inhibits apoptosis of hippocampal neurons in LH mice,improves learning and memory and depression-like behaviors.The possible mechanism is related to activation of Akt-m TOR pathway,and promotes the expression of BDNF.