The Role Of Blood Ammonia Abnormality In The Depressive-like Behavior Of Mice And Its Mechanism

Objective:Major depressive disorder?MDD?is the fourth disorder in the world and one of the primary causes of suicide.However,the mechanism of MDD has not been elucidated.In recent years,the investigation of rapid antidepressants such as ketamine,supported the exciting-inhibiting imbalances hypothesis,that:the increase in glutamate release and the hypofunction of Gamma aminobutyric acid?GABA?transmission,may underlie the MDD mechanism.Excess release of glutamate in vivo is often reacted with the cellular metabolite ammonia,which is an important endogenous activator of GABA_AR,to form glutamine.However,whether endogenous ammonia level is involved in the process of depression remains unknown.Our current study mainly explores the relationship between blood ammonia and depressive-like behavior in mice,and the role of blood ammonia change in the depressive-like behavior of mice.Methods:The depressive-like behaviors were induced by chronic social defeat stress?CSDS?model and chronic restraint stress?CRS?model in C57BL/6J mice.The method for evaluating depressive-like behavior in mice include:Sucrose preference test?SPT?,Tail suspension test?TST?,Social interaction test?SIT?,Forced swimming test?FST?.The evaluation of anxiety-like behavior and movement in mice was mainly through open field test?OFT?.The administration methods include intraperitoneal injection?i.p.?,intragastric administration?ig.?,and microinjection in the medial prefrontal cortex?mPFC?.Blood ammonia concentration is detected by ammonia assay kit.The changes of brain-derived neurotrophic factor?BDNF?and Tyrosine Kinase receptor B?TrkB?protein were mainly detected by western blot.Results:1.The blood ammonia in the mice with depressive-like behavior induced by stress significantly lowered than that of control mice:After exposure to CSDS of C57BL/6J mice,the percentage of sucrose preference was significantly decreased?Control:87.2±2.0%,Susceptible:53.6±7.0%,Resilient:86.1±2.2%,n=13–17,P<0.001?;the social interaction ratio was significantly decreased?Control:1.76±0.17,Susceptible:0.67±0.06,Resilient:1.43±0.09,n=13-17,P<0.001?.The blood ammonia of CSDS mice were decreased?Control:1±0.06,Susceptible:0.71±0.08,Resilient:1.34±0.13,n=6-17,P<0.01?.After exposure to CRS,the percentage of sucrose preference in susceptible mice was decreased?Control:90.1±2.9%,CRS:64.4±3.5%,n=9-15,P<0.001?.CRS increased the immobility times in the tail suspension test?Control:131.2±11.0 sec,CRS:174.7±6.7 sec,n=9 or 15,P<0.01?;the blood ammonia in the CRS mice were significantly decreased?Control:1±0.02,CRS:0.70±0.05,n=3 or 5,P<0.05?.2.The blood ammonia increases significantly after intraperitoneal injection of ammonium chloride,and the depressive-like symptoms were alleviated:After intraperitoneal injection of31.25 mg/kg ammonium chloride solution in control mice,the immobility time in forced swimming test were significantly decreased?Veh:50.3±11.8 sec,NH₄Cl:13.3±3.5 sec,n=7or 9,P<0.05?;the blood ammonia of CSDS were significantly increased?Veh:0.71±0.04,NH₄Cl:1.38±0.21,n=8 or 10,P<0.01?;Ammonium chloride increased sucrose preference ratio?Veh:64.9±3.8%,NH₄Cl:76.0±2.8%,n=12 or 13,P<0.05?;and the social contact ratio?Veh:0.69±0.11,NH₄Cl:1.00±0.07,n=15,P<0.05?.The open field experiment had no significant difference.After administration with lactulose,the blood ammonia in mice decreased?Veh:1.0±0.02,Lac:0.82±0.06,n=5 or 6,P<0.05?and the social interaction ratio decreased under SSDS?Veh:1.87±0.24,Lac:1.24±0.17,n=8 or 9,P<0.05?.3.A possible role of low blood ammonia in the development of depressive-like behavior through BDNF-TrkB signaling pathway and GABA_AR:The expression of BDNF was decreased in the mPFC?Veh:1.00±0.03,CSDS:0.86±0.05,n=6 or 7,P<0.05?,and the expression of TrkB decreased?Veh:1.00±0.07,CSDS:0.77±0.05,n=5 or 6,P<0.05?.After intraperitoneal injection of 31.25 mg/kg ammonium chloride,the expression of BDNF increased in the mPFC of CSDS mice?Veh:1.00±0.07,NH₄Cl:1.27±0.08,n=6 or 7,P<0.05?,and the expression of TrkB increased?Veh:1.00±0.05,NH₄Cl:1.13±0.02,n=6 or 7,P<0.05?.And there was no significant change in the expression of BDNF and TrkB in hippocampus of CSDS mice.Microinjection of bicuculline to block GABA_AR in the mPFC,and the social interaction ratio of CSDS mice injected with 31.25 mg/kg ammonium chloride solution was decreased?Veh:1.12±0.18,Bic:0.55±0.15,n=6 or 7,P<0.05?.Conclusion:The blood ammonia in the mice with depressive-like behavior induced by stress significantly lowered than that of control mice.The blood ammonia increases significantly after intraperitoneal injection of ammonium chloride?31.25 mg/kg?,and the depressive-like symptoms were alleviated.The blood ammonia of mice decreased significantly after intragastric administration of lactulose,which also reduced the stress vulnearbility.The expression of BDNF and TrkB protein in the mPFC increased after intraperitoneal injection of ammonium chloride.Bicuculline,an antagonist of gamma-aminobutyric acid type A receptor?GABA_AR?,blocked the anti-depression-like effect of low-concentration ammonium chloride.Our findings indicated blood ammonia homeostasis abnormol may be involved in stress induced GABA_AR function disorders,which is expected to provide new ideas for the treatment or diagnosis of depression.