Effects Of Cation-chloride Cotransporters KCC2/NKCC1 On The Depression-like Behavior Induced By Chronic Social Defeat Stress

Part ? Effects of chronic social defeat stress on the expression of cation-chloride cotransporters KCC2 and NKCC1 protein expressionObjective: GABAergic transmission is impaired in hippocampus of major depression disorder(MDD)patients.Some studies have shown the cation-chloride cotransporters KCC2/NKCC1 are involved in the regulation of GABA-dependent synaptic inhibition.Therefore,we will clarify the changes of KCC2/NKCC1 in depressive mice induced by chronic social defeat stress(CSDS).Methods: Establishing animal models of depression by exposing to CSDS.The depressive behavior was detected by sucrose preference test(SPT)and social interaction test(SIT).Western blotting and immunofluorescence were used to detect the protein expression levels.Results:(1)CSDS induced depressive behavior.Susceptible mice showed social avoidance behavior,and the interaction time ratio of susceptible mice with CD1 significantly decreased(Control: 1.615 ± 0.1083,Susceptible: 0.6274 ± 0.041,p <0.001).The sucrose preference of susceptible mice was significantly lower than control group(Control: 84.18 ± 1.373 %,Susceptible: 51.74 ± 2.390 %,p < 0.001).(2)The expression of KCC2 and NKCC1 were decreased in the dorsal hippocampus of the susceptible mice(KCC2: Control: 100.0 ± 4.858 %,Susceptible: 72.17 ± 3.662 %,p < 0.001;NKCC1: Control: 100.0 ± 3.686 %,Susceptible: 78.78 ± 5.473 %,p <0.01).What's more,KCC2 was also decreased in the ventral hippocampus(Control:100.0 ± 2.055 %,Susceptible: 82.45 ± 3.928 %,p < 0.001)while NKCC1 showed no deference.(3)Compared with the control group,immunofluorescence results showed KCC2 and NKCC1 protein expressions in CA1,CA3 and DG of the dorsal hippocampus of susceptible mice were all decreased.Conclusion: Mice exposed to CSDS showed severe depressive behavior.The protein expression levels of KCC2 and NKCC1 in dorsal hippocampus of depressive susceptible mice were decreased.This change may be involved in the etiology of depression.Part ? Effects of regulation of KCC2/NKCC1 on the depressive-like behavior induced by chronic social defeat stressObjective: To explore the effects of KCC2/NKCC1 on the depression-like behavior induced by CSDS,we enhanced KCC2 function by LV-mediated overexpression or used NKCC1 inhibitor bumetanide to consolidate the GABA-dependent synaptic inhibition.Then we detected the behavior changes of depressive mice.Methods: LV-mediated gene overexpression;drug microinfusion;behavior test:including: social interaction test,sucrose preference test,tail suspension test,open field test.Results:(1)KCC2 overexpression in the dorsal hippocampus of susceptible mice after CSDS reversed the social avoidance of social interaction test,increased the interaction time ratio(CSDS + GFP: 0.4673 ± 0.1016,CSDS + KCC2-OE: 1.470± 0.1657,p < 0.001),increased the sucrose preference ratio(CSDS + GFP: 68.97 ± 2.817 %,CSDS + KCC2-OE: 79.11 ± 2.898 %,p < 0.05),and decreased the immobility time in the tail suspension test(CSDS + GFP: 171.2 ± 10.31 s,CSDS +KCC2-OE: 130.6 ± 7.586 s,p < 0.01),but has little effect on the anxiety-like behavior in the open field test.(2)Mice were injected gradient bumetanide(0.007mg/kg,0.014 mg/kg,0.028 mg/kg,0.056 mg/kg),We found bumetanide(0.028 mg/kg,0.056 mg/kg)groups in acute forced swimming showed a significant decline of the immobility time(0.028 mg/kg: 62.13 ± 13.49 s,p < 0.05;0.056 mg/kg: 48.75 ± 11.42 s,p < 0.05)and the effects can sustain for more than a week.(3)After acute social defeat stress with administration of bumetanide,the interaction time ratio of bumetanide group is higher than the vehicle group in social interaction test(Stress +vehicle: 0.9941 ± 0.1011,Stress + bume: 1.561 ± 0.2322,p < 0.05).Compared with the vehicle group,the sucrose preference rate of the mice in bumetanide group was higher(Stress + vehicle: 67.13 ± 3.075 %,Stress + bume: 76.26 ± 2.111 %,p < 0.05),the immobile time of the tail suspension test was shorter(Stress + vehicle: 164.7 ±4.849 s,Stress + bume: 125.7 ± 3.621 s,p < 0.001),but the open field test exhibited no difference.Conclusion: KCC2 overexpression in dorsal hippocampus plays an antidepressant effect on susceptible mice after CSDS.Bumetanide microinfusion in dorsal hippocampus showed an antidepressant effects in acute forced swimming test.Bumetanide administration in dorsal hippocampus enhanced the resistance of mice against to acute social defeat stress.