Abstract: Objective: To explore the effects of chronic restraint stress (CRS) on the abilities of spatial learning and memory and the levels of excitatory amino acids in the hippocampal dentate gyrus (DG) in the old rats,and to investigate the neurochemical mechanism of CRS in affecting the spatial learning and memory abilities. Methods: Sixteen male SD rats (18 months old) were randomly divided into control group (n=8) and CRS group (n=8),and the rats in CRS group received CRS 2 h every day for 30 d.And then the spatial learning and memory abilities of rats were measured by Morris water maze(MWM) test,and the extracellular levels of excitatory amino acids including asparate (Asp) and glutamate (Glu) in the DG were simultaneously determined by in vivo microdialysis and HPLC.The levels of corticosterone (CORT) and epinephrine (EPI) in serum of the rats were examined by ELISA assay. Results: In CRS group,the escape latencies on the 2nd-4th days were significantly increased and the percentage of time spent in target quadrant on the 5th day was markedly decreased in MWM test compared with control group (P<0.05).Compared with before training,the extracelluar level of Asp in the DG in control group was significantly increased on the 2nd day in MWM test;compared with control group,the extracelluar level of Asp in the DG in CRS group was significantly decreased on the 3rd day in MWM test(P<0.05).Compared with before training,the Glu levels in the DG in MWM test in both control and CRS groups were markedly increased (P<0.05),but there was no significant difference between two groups (P>0.05).Compared with control group,the levels of CORT and EPI in the serum of the rats in CRS group were significantly increased (P<0.05). Conclusion: CRS impairs the spatial learning and memory abilities in the old rats,which may be related to the decrease of Asp level in the hippicampal DG of the rats.

Key words: chronic restraint stress, hippocampal dentate gyrus, excitatory amino acids, old rats, spatial learning and memory abilities