Effect Of Chronic Stress On The Changes Of Excitatory Amino Acid Levels In The Dentate Gyrus During Spatial Learning Process In Rats

Objective:To observe the changes of excitatory amino acid levels and synaptic plasticity in the hippocampal dentate gyrus(DG)during the spatial learning and memory processes in a rat model of chronic stress,and preliminarily investigate the neurochemical mechanism responsible for effect of chronic stress on spatial learning and memory.Methods:12 month old SD male rats were randomly divided into control group and chronic stress(stress)group.The rats in the stress group randomly received once stimulation every day last for 30 days,and then the corticosterone(CORT)level in the serum of rats was determined by enzyme-linked immunosorbent assay.The spatial learning and memory abilities of rats were detected by Morris water maze(MWM),simultaneously,the concentrations of excitatory amino acids(EAAs,including glutamate and aspartate)in the hippocampal DG were determined by brain microdialysis and HPLC,the amplitudes of field excitatory postsynaptic potential(fEPSP)in the same region were examined by electrophysiological recording.Results:1)The levels of CORT(typical stress hormone)in the serum of the rats in the stress group were significantly higher than the control group(P<0.05).2)In the place navigation trial of MWM test,compared with control group,the escape latencies and total swimming distances were significantly longer in the stress group(P<0.05,respectively).3)In the spatial probe trial on the fifth day of MWM test,the percentage of swimming distance in the target quadrant in the stress group was significantly lower than the control group(P<0.05).4)In the control group,the amplitudes of fEPSP in the DG were significantly increased on the 3rd and the 4th days of MWM test(P<0.05,respectively),in contrast,amplitudes of fEPSP in the DG was not changed during MWM test in the stress group;compared with control group,the fEPSP amplitudes in the stress group were remarkably decreased on the 3rd day of MWM test(P<0.05).5)In the control group,the glutamate(Glu)level in the DG was significantly increased on the 3rd day and aspartate(Asp)levels in the DG were markedly increased on 2nd～4th days during MWM test(P<0.05,respectively).6)In the stress group,levels of Glu and Asp in the DG were not changed during MWM test(P>0.05,respectively),compared with the control group,the Glu levels on the 2nd～4th days and the Asp level on the 3rd day were markedly decreased during MWM test(P<0.05,respectively).Conclusion:Chronic stress impairs the ability of spatial learning and memory,which may be related to the inhibitions of EAAs(including Glu and Asp)increases and synaptic efficiency in the hippocampal DG.