| PrefaceDepression is a kind of syndrome characterized with lasting depressed mood and is one of the most serious mental diseases with high risk of suicide. It is also an important problem of public heath. Depression usually damages the person's general functions, especially social and family functions and influence the life quality. More and more people begin to study the pathogenesis of depression. Stress is a main biological factor, which can change the neuron in central nervous system.Stress can have some impacts on cognition process, such as learning and memory. Stress can also increase the sensitivity of neural apoptosis induced by the changes of metabolism. Apoptosis is a normal physiological process during development wherein excess cells are removed from the brain. In contrast to necrosis, apoptosis is programmed and critically controlled by the levels of pro -apoptoic ( Bax, Bad) and antipoptotic ( Bcl - 2, Bcl - xl) proteins within the cell. In present study, we used the expression of Bcl - xl as the marker of neural injury and protection to explore the neural changes in chronic forced - swimming animal model and the changes of poststress. To study the relation between the expression of Bcl - xl and the structural and functional changes of hippocampus, we try to explore the pathogenesis of depression, and provide basis for etiological treatment and exploitation of new drugs for depression in clinic.Materials1. Experimental animal; Male Wister rats(n =32) weighting about 160 -180g were purchased from the center of experimental animals in China Medical University.2. Experimental reagents: Rabbit anti -bcl -xl and SABC kit( Boster Biotechnology Co. LTD. )3. Experimental instruments: Electrophysiological apparatus, MetaMorph/ Cool Snapfx/Ax70 image analysis system.MethodsAnimal groupingExperimental rats were housed for 7 days to adapt the conditions of the lab. After that, they were divided into 4 groups( C1 C2 E1 E2 n = 8/group) randomly on the basis of their weights and the results of Open - field test. The rats in group E1 and E2 were exposed to forced - swimming stress everyday for consecutive 21 days. (water temperature = 4℃) The control group were housed four per cage with access to food and water. On the 22nd day, the rats in group E1 and C1 were killed. The rats in group E2 and C2 continued to be housed. On the 52nd day all the rats were killed.Anaesthetized with 60mg/kg( i. p. ) of sodiumpentobarbital and perfuse via left ventricle with 200ml Saline followed by 300ml 4% paraformaldhyde. Brains were removed and postfixed for more than 48 h. Then the brains were dehydrated through graded - concentration ethanol and embedded in olefin. And sections were cut coronally.Used immunohistochemistry method to measure the expression of bcl - xl protein in hippocampus. To select two sheets each rat to analyze CA3 and DG zone and calculate the optical density and gray degree of Bcl - xl. To analyze the data with SPSS 10.0 software.Results1. Weight and the results of Open - field testOpen - field measures showed that the stopping time in the center of group E1 increased and weight, ambulation, rearing and grooming decreased compared with group C1. Group E1 and C1 had no difference in defecation. So did the group E2 and group C2.2. Neurons under light microscopeCompared with group C1, the neural distance between CA3 area and DG area increased and the amount of the neurons decreased in group E1. So did the group E2 and group C2.3. Bcl - xl expression in hippocampusBcl - xl expressed obviously in CA3 and DG area of hippocampus in group C1 expressed highly than the group E1. After stress, Bcl - xl expression of group E2 were lower than in group C2, especially in CA3 area. Compared with group E1 ,the expression of Bcl -xl in group E2 increased.DiscussionAn ideal animal model should simulate the clinical manifestation of the disease and has theoretical basis. So far, the animal models include forced swimming model, learned helplessness paradigms, chronic stress, pharmacological model and so on. To establish ideal animal model can not only study the relationship between the symptoms and abnormal changes of some chemical materials in the brain of depressed patients or check the effects of new drugs but also detect the changes in pathogenesis of depression. This study used forced swimming with separate model to make rats depression.The open - field test is used to detect the priming and investigating behaviors, strain level and the vigilance in new environment. The results show that compared with group C1, after 21 days stress, weight, ambulation, rearing and grooming decreased and stopping time in center increased in group E1 and nodifference in defecation. These performances have the most similarity with the depressed patients. So did the group E2 and group C2. That means that after stress the changes are still on.The hippocampus holds an important role in activities of learning, memory, emotion and endocrine and is a vital region regulating the response to the stress. Long - term chronic stress will damage the hippocampal structure and impair its function. Exposure to stress decreases the proliferation of cells in the dentate gy-rus of the hippocampus and inhibits new neural progenitor cells to survive. Repeated stress is reported to cause atrophy of CA3 pyramidal neurons in hippocampus, including a decrease in the number and length of apical dendrites.Apoptosis or programmed cell death is a phenomenon that initially was associated with developmental events and death of cancer cells. Recent studies indicate that cell death in depression may be due to apoptotic mechanisms.The first proteins associated with apoptosis were the members of the Bcl - 2 family . The Bcl - 2 onco - protein has a protective effect against apoptotic and necrotic cell death. Bcl - xl is a more recently discovered member of the Bcl -2 family of proteins. It is located in the mitochondria and endoplasmic reticulum and sometimes associated with the nuclear envelope. Its main function inhibits apoptosis.Recent reports demonstrate that the neural damage in hippocampus induced by stress is via another process called apoptosis. Apoptosis is a normal physiological process during development wherein excess cells are removed from the brain . In the adult brain, however, this process plays an important role in the cell death observed in acute and chronic neurodegenerative diseases. In contrast to necrosis, apoptosis is programmed and critically controlled by the levels of proapoptotic(BAX, BAD) and antiapoptotic (BCL-2 and BCL-xL) proteins within the cell. In response to death - inducing stimuli, these proteins regulate the release of cytochrome c from the mitochondria into the cytoplasm . This process, in turn, sequentially activates cysteine proteases called caspases. Caspases are the main executors of apoptosis, responsible for the morphological and biochemical changes (i. e DNA fragmentation and membrane blebbing) associated with it. Postmortem studies revealed hippocampal apoptosis in limbic... |
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