The Identification Of Metabolic Disturbances In The Prefrontal Cortex Of The Chronic Restraint Stress Rat Model Of Depression

BackgroundMajor depressive disorder,with a high rate of disability and mortality,is a complex psychiatric disorder characterized by pervasive and persistent low mood.Persistent symptoms of depression are associated with impairments in cognitive and social functioning which has considerable impact on individuals,their partners and families,and wider society.According to the World Health Organization,depression is predicted to be the leading cause of disease burden by 2030.However,the underlying molecular mechanisms of depression remain largely unknown.Recently,more and more studies have indicated chronic stress plays an important role in the development of depression and causes functional and structural changes in the prefrontal cortex(PFC).Data from neuroimaging indicated that decreased activity and gray matter volume in the PFC is an important change in the pathology of depression.Therefore,it is hypothesised that the alterations of functions in the PFC are associated with depression.ObjectiveIn this study,a non-targeted metabolomics approach based on gas chromatography–mass spectrometry(GC–MS)technology was applied to investigate significant metabolic changes in the PFC of chronic restraint stress(CRS)rats,in order to better understand the underlying molecular mechanisms of depression.Methods1.Thirty-five male Sprague-Dawley rats were allowed to acclimatize to the standard conditions for 7 days before the outliers were eliminated from the experiment based on the results of locomotor activity test(LAT)or sucrose preference test(SPT).The remaining rats were randomly assigned to the chronic restraint stress(CRS)group or the non-stressed control(CON)group.CRS was induced in the stress group by restraining rats in a plastic restrainer for 6 h every day.This stress paradigm continued for 21 days.After CRS exposure,the behavioral tests were performed.Based on the SPT,rats in the CRS group were divided into CRS susceptible and CRS resilient subgroups.According to the aim of the study,only susceptible rats were chosen for further research.2.We employed a non-targeted GC-MS-based metabolomic approach to investigate the significant metabolic changes in the PFC of the CRS rat model of depression.Differentially expressed metabolites associated with CRS-treated rats were identified by combining multivariate and univariate statistical analysis and corrected for multiple testing using the Benjamini-Hochberg procedure.A heat map of differential metabolites was constructed using Matlab.3.Bioinformatic analyses were performed for these significantly differential metabolites using Ingenuity Pathways Analysis software,in order to explore the perturbed pathways and biological functions relevant to depression.Results1.Based on the 95% reference interval in the LAT or the 95% percentile interval in the SPT,five outliers were excluded,leaving 20 CRS and 10 CON rats.After CRS exposure,eight rats were defined as CRS susceptible based on the SPT,and the remaining 12 rats were designated as CRS resilient.To keep the quantity balance between the two groups,eight rats in the CON group were randomly selected.Finally,the 16 chosen rats(Susceptible subgroup,n = 8;CON group,n = 8)were used for further analysis.2.Compared with the CON group,the rats in CRS group had a significant decrease in body weight(p < 0.01)and sucrose preference in the SPT(p < 0.05),and an increased in immobility time in the FST(p < 0.05),indicating that depressive-like behavior was being observed.However,no significant effect of CRS was observed in the open field test(OFT)and elevated plus-maze(EPM),suggesting that anxiety-like behavior was not being observed in this study.3.Based on the non-targeted GC-MS-based metabolic profiling of the PFC tissue,a total of 36 differential metabolites between CRS group and CON group were identified by combining multivariate and univariate statistical analysis and corrected for multiple testing using the Benjamini-Hochberg procedure.4.Bioinformatic analyses indicated that these metabolites were identified as potential depression biomarkers related to perturbations in amino acid metabolism,energy metabolism and lipid metabolism.Conclusion1.CRS induces depression-like behaviors and not anxiety-like behaviors.2.Differences between the depressed and control groups were observed in metabolic patterns in the PFC.The CRS disturbed pathways are mainly involved in amino acid metabolism,energy metabolism and lipid metabolism.Consequently,this results provide useful insights into the molecular mechanisms of depression.