Amygdala Circuit Mechanism For The Alleviative Effect Of Environmental Enrichment On Chronic Stress-induced Anxiety Disorder

With the rapid development of economy and society,people’s life and work pressure are increasing day by day,and the prevalence of anxiety disorder is also increasing year by year,which has become a global public health problem that can not be ignored.Brain dysfunction caused by long-term stress exposure(chronic stress)is one of the key causes of anxiety disorder.A large number of studies have shown that the structural and functional remodeling of amygdala,especially basolateral amygdala(BLA)induced by chronic stress is closely related to the occurrence of mental diseases such as anxiety disorder.As a preclinical non drug auxiliary intervention,environmental enrichment(EE)has been widely used in the rehabilitation of many diseases,but it is still unclear whether its role is related to amygdala and its specific mechanism.In this study,we used the paradigm of chronic restraint stress(CRS)to construct the anxiety disorder model of mice,and set up two kinds of rearing environments,namely,home cage rearing and enriched environment rearing.The mice were divided into Control group and CRS group,Control+EE group and CRS+EE group.Through a series of testing methods such as behavior,electrophysiology and morphology,we explore the role and mechanism of environmental enrichment in alleviating anxiety disorder caused by chronic stress.The main results are as follows:(1)In order to determine whether the environmental enrichment can alleviate the anxiety disorder caused by chronic stress,we used the open field test and elevated plus maze test to detect the anxiety-like behaviors of mice in each group.The results showed that after experiencing chronic stress,anxiety like behaviors of the mice in CRS group increased obviously compared with Control group,while CRS+EE mice showed significantly less anxiety-like behavior than CRS mice,and there was no significant difference between CRS+EE mice and Control+EE mice,indicating that environmental enrichment could significantly alleviate the anxiety-like behavior of mice induced by chronic stress.(2)To explore whether enriching the environment to relieve anxiety caused by chronic stress is related to synaptic transmission changes of BLA neurons,we recorded the mini excitatory postsynaptic current(mEPSC)of BLA neurons through electrophysiological experiments.The results showed that after chronic stress,the mEPSC frequency of BLA neurons in CRS group was significantly higher than that in Control group,while the mEPSC frequency of BLA neurons in CRS+EE group was significantly lower than that in CRS group,and there was no significant between CRS+EE group and Control+EE group.The results suggest that environmental enrichment may alleviate the anxiety disorder caused by chronic stress by reducing the excitatory synaptic transmission efficiency of BLA neurons.(3)In order to explore whether the improvement effect of environmental enrichment on the synaptic function of BLA neurons has circuit selectivity,we further recorded the mEPSC of BLA neurons in different circuits.The results showed that the mEPSC frequency of BLA→vHPC PNs in CRS group was significantly higher than that in Control group,while the mEPSC frequency of BLA→vHPC PNs in CRS + EE group was significantly lower than that in CRS group,and there was no significant difference between CRS+EE group and Control+EE group.However,for BLA→NAc PNs,there was no significant difference in the frequency and amplitude of mEPSC in each group of mice.The results suggest that environmental enrichment may improve the synaptic function damage caused by chronic stress by selectively regulating the synaptic transmission of BLA→vHPC PNs.(4)In order to further clarify whether the synaptic transmission efficiency of BLA neurons in different circuits regulated by environmental enrichment is related to the structural remodeling of neurons,we labeled the above different projection neurons by sparse virus labeling technique,and then carried out structural remodeling and morphological analysis.Consistent with the change trend of mEPSC,the dendritic length,branch number and dendritic spine density of BLA→vHPC PNs in CRS group were significantly higher than those in Control group,while these structural indexes in CRS + EE group were significantly lower than those in CRS group,and there was no significant difference between CRS+EE group and Control+EE group.The morphological analysis of BLA→NAc PNs showed that there was no obvious change in the structural indexes of each group of mice.These results suggest that environmental enrichment may selectively affect the synaptic structure of BLA→vHPC PNs,and then affect the synaptic transmission efficiency of this group of neurons.To sum up,in this study,through a series of experiments such as behavior,electrophysiology and morphology,we proved that environmental enrichment may selectively affect the abnormal morphological structure and synaptic transmission efficiency of BLA→vHPC PNs caused by chronic stress,and then alleviate the anxiety-like behavior of mice.