The Effect Of Voluntary Movement On Long-term Social Defeat Leading To Abnormal Social Behavior And The Regulatory Mechanism Of The Dopamine System

Background:The research and treatment of stress mental disorders have been a hot issue in neuroscience.Human beings or rodents inevitably suffer from chronic,repeated and intense social defeat stress,which seriously affects their physical and mental health.In social interaction,long-term subordination will lead to abnormal social behavior such as persistent social avoidance and defects in social interaction,this problem has not been solved due to the high cost of drug treatment,side-effects and recurrence rate of drug treatment.In recent years,chronic social defeat stress(CSDS)model simulating human bullying has been successfully established,which lays a foundation for related research on mechanism.Exercise has gradually become an important intervention strategy in the treatment of mental illness because of its low cost and no side effects.However,due to lack of enthusiasm for exercise,physical inactivity has become one of the fundamental reasons limiting exercise therapy for mental illness.Therefore,it is urgent to study the neurobiological mechanism underlying regulating voluntary running.In addition,it is not clear whether voluntary running can reverse abnormal in social behavior induced by CSDS?It is found that about 1/3 of individuals do not show susceptibility after CSDS,and whether individuals with different exercise motivations have different susceptibility to CSDS needs further study?Whether individuals choose to exercise actively is related to motivation,and the desire for social interaction is also related to motivation.The midbrain limbic dopamine(DA)system may be very important in motivation and reward,but whether direct activation or inhibition of DA neurons can alter voluntary running levels have not been confirmed by experiments.Dysfunction of DA and its receptors is an important cause of mental illness.But,the brain mechanisms of abnormal social behavior caused by CSDS are inconsistent.Whether voluntary running improves and interferes with abnormal social behavior through midbrain limbic DA system and its neural circuits mechanisms need further study.Purpose:In this study,wild type mice and DAT-Cre mice were used as experimental animals,CSDS was used as modeling animals,voluntary wheel running(VWR)was used as intervention means,Western Blot,immunofluorescence,pharmacology,designer receptors exclusively activated by designer drugs(DREADDs)method,in vivo optical fiber recording and patch-clamp were used to explore involvement of the DA system in the influence of VWR on susceptibility to CSDS.Methods:1.After 10 d of CSDS,the stress model was established,and the CSDS susceptible mice were treated with VWR for 3 w.Three-chambered social test and social interaction test were used to test the influence of 3 w VWR on the sociality,social preference and social interaction of susceptible mice by CSDS;immunofluorescence was used to detect the numbers of tyrosine hydroxylase(TH)positive neurons in the ventral tegmental area(VTA);Western Blot was used to detect the protein expressions of TH in the VTA and DA receptors in the medial prefrontal cortex(mPFC)and nucleus accumbens(NAc),D2 receptor(D2R)antagonist Raclopride was microinjected into the NAc shell to detect role of D2R in regulation of abnormal in social behavior.2.The mice were divided into high voluntary wheel running(HVR)and low voluntary wheel running(LVR)groups by VWR,after 10 d of CSDS,social avoidance test was used to detect the susceptibility and resilience;Western Blot and immunofluorescence were used to detected TH levels in the VTA;the DREADDs method was used to investigate whether activation or inhibition of DA neurons in the VTA can alter levels of VWR and the susceptibility to CSDS.3.In order to further study the mechanism of neural circuits,the DAT-Cre mice were divided HVR and LVR group by VWR.In vivo fiber-optic recording system combined with DA-sensitive fluorescent protein tool virus technology was used to detect the DA signal in the mPFC of HVR and LVR mice while they contacted with wheel running;DAT-Cre mice were injected with DREADDs virus to specifically regulate DA neurons in the VTA-mPFC;patch-clamp and c-Fos were used to detect the activation of CNO in the VTA in vitro and in vivo;the DREADDs method was used to investigate whether activation or inhibition of DA neurons in the VTA-mPFC can alter levels of VWR and the susceptibility to CSDS.Results:1.VWR treatment abnormal in social behavior induced by CSDS:3 w VWR could reverse impairs in social preference and defects in social interaction in mice induced by CSDS;CSDS decreased levels of TH in the VTA and D2R in the nucleus accumbens(NAc)shell and these changes can be recovered by VWR,CSDS produced no significant effect on D1 receptor(D1R)in the NAc core and D1R and D2R in the mPFC;furthermore,we found that the recovery effect of VWR on abnormal in social behaviors in CSDS mice was blocked by the microinjection of D2R antagonist in the NAc shell.2.The effects of different levels of VWR on the susceptibility to social stress in mice:the mice can be successfully divided into HVR and LVR group;LVR mice showed higher susceptibility to CSDS,and HVR mice displayed more resilience to CSDS;LVR mice had low TH levels in the VTA,and the TH levels were obviously suppressed by CSDS,HVR mice had higher TH levels in the VTA,and CSDS did not alter TH levels in HVR mice;the activation of DA neurons in the VTA of LVR mice by DREADDs method increased the levels of VWR and resilience to CSDS,the inhibition of DA neurons in the VTA of HVR mice reduced the levels of VWR and increased susceptibility to CSDS.3.The neural circuits mechanism of different levels of VWR on the susceptibility to social stress in DAT-Cre mice:the DAT-Cre mice can be successfully divided into HVR and LVR mice by VWR;the signal of DA in the mPFC of HVR mice was significantly higher than LVR mice when exposed to VWR;the DREADDs method was used to specifically regulate DA neurons in the VTA-mPFC in DAT-Cre mice,activation this circuit of LVR mice increased the levels of VWR and resilience to CSDS,inhibition this circuit of HVR mice reduced the levels of VWR and increased susceptibility to CSDS.Conclusions:1.VWR can improve abnormal in social behavior caused by CSDS,and its mechanism were related to TH in the VTA and D2R in the NAc shell.2.Different TH levels in the VTA in mice with different levels of VWR may be the reason for the stress susceptibility of mice with low physical activity.3.The activation of DA neurons in the VTA of LVR mice by DREADDs method increased the levels of VWR and resilience to CSDS,the inhibition of DA neurons in the VTA of HVR mice reduced the levels of VWR and increased susceptibility to CSDS.This suggests that DA neurons in the VTA are directly participated in the regulation of levels of voluntary running and susceptibility to stress.4.The difference in DA signals in the mPFC may be the reason for the differences of voluntary running and the susceptibility to stress.5.The activation of DA neurons in the VTA-mPFC of LVR mice by DREADDs method increased the levels of VWR and resilience to CSDS;the inhibition of DA neurons in the VTA-mPFC of HVR mice reduced the levels of VWR and increased susceptibility to CSDS.This suggests that DA neurons in the VTA-mPFC are directly participated in the regulation of levels of voluntary running and susceptibility to stress.To sum up,CSDS can induce impair in social preference and defect in social interaction of mice,and the susceptibility of mice with different physical activity levels after CSDS;voluntary exercise can improve the abnormal in social behavior in mice.These effects were mediated by DA neurons in the VTA,NAc shell and VTA-mPFC.TH in the VTA and D2R in the NAc shell may be the key targets of voluntary exercise to improve CSDS-induced abnormal in social behavior.The DA neurons of VTA-mPFC may be important neural circuits for the difference in susceptibility induced by CSDS with different levels of VWR prediction.