| Chronic cerebral ischemia is chronic cerebrovascular insufficiency for a long time because of all kinds of reasons. It is a common pathological way in the period of many diseases such as vascular dementia, Binswanger disease, Alzheimer disease. Progressive dementia is often a prominently clinical manifestation of chronic cerebral ischemia, in which several aspects of cognitive function are impaired, including learning and memory disorder. In the situation of chronic cerebral ischemia, a series of histopathological changes take place in various brain regions, especially in ischemia-sensitive CA1 of hippocampus. A great deal of neurons degenerate and necrotize, synapses and myelins damage, astrocytes increase and glial fibrillary acid protein (GFAP) as a symbol protein of astrocytes increase too.In recent years, some researches indicate that there is a brain rennin-angiotensin system that is involved in the pathophysiologic process of ischemic cerebrovascular disease besides circulating rennin-angiotensin system. The angiotensin II type 1(AT1) receptor antagonist may penetrate the blood-brain-barrier, competitively block angiotensin II binding to type 1 receptor and effectively protect against neuronal injury. The selective angiotensin II type 1 receptor antagonist valsartan is now widely used incardiovascular system, and its protective effect to brain is being tested by animal experiments.This experiment researches the protective effect of valsartan to chronic cerebral ischemia by observing ultrastructure of brain tissue, GFAP in CAl of hippocampus and cognitive ability to support prevention and therapy of some diseases connected with chronic cerebral ischemia in clinic with angiotensin II type 1 receptor antagonist.Materials and methods1. 39 Wistar rats weighing 300~400g of 11 or 12-month-old were randomly divided into three groups, regardless of male or female, 13 rats each group: control group (sham-operation plus distilled water), only ischemia group (operation plus distilled water), ischemia treatment group (operation plus distilled water plus valsartan). 24h after operation, control group and only ischemia group swallowed distilled water 1.5ml, while ischemia treatment group swallowed the same amount of valsartan (15mg/kg) dissolved by distilled water, once a day.2. Chronic cerebral ischemia rat model was established by permanent occlusion and snip of bilateral common carotid arteries. Rats undergoing permanent bilateral occlusion and snip of the common carotid arteries (2VO) were in only ischemia group and ischemia treatment group. Rats with bilateral common carotid arteries isolated but not ligated and snipped were in control group.3. After all the rats were raised in a usual way for 12 weeks, brain tissue (1×1× 1mm3) in CA1 of hippocampus of 3 rats of every group used to be observed were taken out, put into solution of 4% glutaral, and after a series of treatments, observed under electron microscope. Cognitive ability of the remaining 10 rats of every group was assessed in a Y model maze and shown with the times of electric attack. Then, those assessed rats were anesthetized and perfused with 200ml normal saline and subsequently with 4% polyformaldehyde in 0.1mmol/L phosphylate buffer. Brains were removed, postfixed, embedded, sectioned and processed for HE staining and immunohistochemistry staining.4. All the data were expressed by (x ±s) and analyzed statistically with SPSS 11.5 statistic software. The difference of every two groups was compared with one-way analysis of variance and LSD method. The significant testing standard is a =0.05.Results1. All the rats were in low spirits, reacted slowly, and ate little after operation. The next or third day, control group recovered in spirits, reacted more quickly and ate more, but ischemia groups improved insignificantly.2. The results of cognitive ability. The times of electric attack: control group: 64.7± 4.42, only ischemia group: 95.6 + 5.62, ischemia treatment group: 81.4 ±2.87. The difference between ischemia group and control group about cognitive ability was significant. Ischemia group was significantly lower than control group(P < 0.01), which showed that cognitive impairment appeared in rats with chronic cerebral ischemia. The difference between only ischemia group and ischemia treatment group about cognitive ability was significant too. Ischemia treatment group is significantly higher than only ischemia group(P< 0.01), which indicated that valsartan could improve cognitive impairment in rats with chronic cerebral ischemia.3. The results of pathological section with HE staining. Only a few degenerated and dead neurons were found in control group, while most neurons were normal in morphology. The number of degenerated and dead neurons significantly increased in ischemia group compared with control group. The number of degenerated and dead neurons was less in ischemia treatment group compared with only ischemia group.4. The results of ultrastructure: Nucleus and mitochondrions of neurons, myelins and synapses were normal in control group. But in only ischemia group, cell nucleus were deformed. Mitochondrions were swollen, whose cristae were disordered, and some cristae or membranes of mitochondrions disappeared. The number of synaptic vesicles was significantly lower in only ischemia group than in control group, some synaptic fissures disappeared, but some broadened. Myelins were deformed, cankered and its normal structure was damaged. Nucleus and mitochondrions of neurons, myelins and synapsesinjury in ischemia treatment group were slighter than in only ischemia group.5. The means of GFAP-positive cells in hippocampus CAl of every group: control group: 35.7±4.88, only ischemia group: 60.3±4.08, ischemia treatment group 46.1 ± 3.41. The difference between ischemia group and control group is significant. There was obvious hypertrophy of astrocytes in ischemia group, and the number of GFAP-positive cells was significantly higher than that of control group (P<0.01). The difference between only ischemia group and ischemia treatment group was significant too. The number of GFAP-positive cells in ischemia treatment group was significantly lower than that of only ischemia group (P < 0.01), which showed that astrocytes increased and were hypertrophic in rats with chronic cerebral ischemia. After treatment with vcalsartan, the number of them reduced, and hypertrophy was lightened.Conclusion1. Chronic cerebral ischemia rat model was established by permanent occlusion and snip of bilateral common carotid arteries. 12 weeks after operation, significantly cognitive impairment appeared and a series of histopathological changes took place, neurons degenerated and died. Myelins and synapses damaged, the number of GFAP-positive astrocytes increased, and they were hypertrophic in CAl of hippocampus.2. Valsartan is a selective angiotensin II type 1 receptor antagonist, which can improve cognitive impairment, attenuate neurons, myelin and synapse damage in rats with chronic cerebral ischemia, and lighten proliferation and hypertrophy of astrocytes,3. Valsartan protect significantly brain from chronic cerebral ischemia, which support the use of the angiotensin II type 1 receptor antagonist in some diseases connected with chronic cerebral ischemia in clinic... |
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