| ObjectiveIt is a general opinion now that depression is a polygene disease which is related to hereditary factors and caused by environmental a-gents. A lot of observations suggested that it was not a completely functional mental disorder and the structural impairments of the cerebullar definite regions may be the substance foundation for some patient's depress mood. The stressful life event is the obvious causative factor of depression and concerned with the degree of the depress symptoms. When the organism receives the stressor, the excitability of the Hypothalamus — Pituitary—Adrenal (HPA) axis will be raised and therefore the stress hormone—glucocorticoid (GC) will be highly secreted. With the prolongation of the stress time course, there are hyperf unction in the HPA axis and the concentration of cortisol in blood serum is high. The latter can lead to the atrophy, degeneration and loss of the hippocampal neuron, thus there are a serial of behavioral effects, including the alteration of memory, cognition and behavior.It is well — known that the hippocampus is one of the most important brain regions that regulate the response to the stress and major target which the stress hormone contribute to. Many observations have suggested that stress can lead to the changes of the hippocampus structure and function. The activation of the cyclic adenosine monophosphate — cyclic a-denosine monophosphate response element binding protein (cAMP — CREB) circuit will regulate the express of Brain — derived NeurotrophicFactor (BDNF) and the regeneration of the neurons, while Interleukin— 18 (IL—18) will destroy the long — term potentiation (LTP) and the transmition of the N — methyl — D—aspartate (NMDA) receptor in the hippocampus CAj region. In the present study, we used CREB and IL — 18 respectively as the protective and harmful agents to approach the relationship between the express levels of the 2 substances and the changes of the neurons structure and function. This would help to study the patho-genesis of depression, and would provide basis for the treatment of depression.Materials1. Experimental animals: Male Wistar rats (n=30) weighting about 185'— 255g were purchased from the center of experimental animals in China Medical University.2. Experimental reagents: Rabbit anti — pCREB^anti—IL—18 and SABC kit (Boster Biotechnology co. LTD).3. Experimental instruments: Electrophysiological apparatus, Meta Morph/Cool Snapfx/Ax 70 image analysis system, 1. 5T Magnetic Resonance machine (TOSHIBA Co. LTD).MethodsExperimental rats were housed for 7 days to adapt the conditions of the lab. After that, they were weighted, Open field tested and measured for brain by MR (Tl and T2 weighting in transverse plane, Tl weighting in sagittal plane). All the animals were divided into 2 groups (n=15/ group) randomly.The rats in group C did not receive any stress during 21days. The rats in group T were exposed to various types of stresses every day for consecutive 21 days. On the 22nd day, weighting, open—field tests and brain MR were carried on each rat.All the rats were anaesthetized with 40mg/kg (i. p. ) of sodium pen-tobarbital and perfused via left ventricle with 150ml saline followed by 200~ 250ml 4% paraformaldehyde. Brains were removed and postfixed for more than 48h. Then the brains were dehydrated through graded — concentration ethanol and embedded in paraffin. And sections were cut coronally.Immunohistochemistry method was used to measure the expression of pCREB and IL—18 protein in the brains. 4 pieces of sections of each substance for every rat were analyzed on image analysis system. The lateral cerebral ventricle width and the diameter of midbrain aqueduct for every rat were measured in T2 weighting MRI. One — way ANOVA was used to compare the differences in the expression of pCREB in CA3 region and dentate gyrus (DG) between each group, the difference in the expression of IL—18 in CA1 region and habenular between each group and the difference in the width and the diameter in MRI between each group.Results1. Weight and the result of Open —field test;compared with group C, group T showed less weight, increased stopping time in the center, decreasing rearing and grooming and increased defecation after 21 — day stress (P<0. 01 —0. 05).2. Neurocyte under light microscopy: Compared with group C, the distance between CA3 region pyramidal neurons increased and the amount of the neurons decreased in group T.3. The expression of pCREB in the hippocampus of rats: In CA3 region and DG, pCREB was positive express in both groups, but average optical (AO) in group T decreased by being compared with group C (P0. 05), while the lateral cerebral ventricle width of group T increased after 21—^day stress (P0. 05).Compared with group C, the diameter of midbrain aqueduct had no difference before experiment in group T (P0. 05).Conclusion1. Chronic and comprehensive stress decreased the exploring behaviours, inhibited grooming behaviours and increased defecation of rats.2. The expression of pCREB of the neurons in the rats hippocampus was decreased after the chronic stress.3. The expression of IL—18 of the glial cells in the rats hippocampus and of the neurons in the rats'hgabenular was increased after the chronic stress.4. The MRI of the rats display: the lateral cerebral ventricle width and the diameter of midbrain aqueduct are increased.
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