ABSTRACT
Objective To observe the changes of behavior,blood cortisol level,glucocorticoid receptors (Grs) and mineralocorticoid receptors (MRs) in hippocampus area after four weeks of unpredictable chronic mild stress,and to investigate the probable role of hypothalamus-pituitary-adrenal (HPA) axis in the pathogenesis of depression in aged people.Methods Aged male Wister rats were randomly assigned to control group and model group.The model group received unpredictable mild stress,including food and water deprivation,restrain,tail clipping,forced swimming,white noise,cage titling and cage rotating for 4 weeks,while the control group was undisturbed unless routine feeding and cage changing.After 4 weeks of procedure,the behavior changes were assessed by sucrose intake test,open-field test and state evaluation,serum cortisol level was measured by chemiluminescent assay,the qualitation and quantitation of GRs and MRs in hippocampus area were evaluated by immunohistochemistry and Western blotting respectively.All data were analyzed by using t-test.Results Body weight,the grooming score,activities in openfield test,food intake and sucrose intake were decreased in model group as compared with control group after 2 weeks of chronic mild stress (all P＜0.01),suggesting the stress induced depressive-like behavior effects on aged rats.Serum cortisol level was elevated in model group as compared with control group after 4 weeks of chronic mild stress (P＜0.01).A decrease of the neurons was found in CA3 of hippocampus,but not in DG area.In CA3 area,GR positive neurons were decreased,but no significant decrease was found in MR positive neurons.Conclusions The chronic mild stress leading to depressive-like behavior effects in aged rats induces overall HPA axis dysfunction,elevation of serum cortisol level,impairment of hippocampus neurons and decrease of GR positive neurons.The HPA axis dysfunction induced by chronic mild stress may play an important role in the pathogenesis of depression.