The Study Of The Different Expression Of β-Amyloid Precursor Protein After Recurrent Forebrain Ischemia And Reperfusion

Objective:To find out the possible reason of histologic changes thevascular dementia and the expression of β-amyloid precursor protein(β-APP) by immunohistochemistry, we use the repeated focal cerebral ischemiaand reperfusion model .By this way,we hope we can provide the base onprevention and therapy of vascular dementia.Methods:1.Male Wistar rats (n=30) were divided at random intosham-operation groups(n=15), cerebral ischemia and reperfusion groups(n=15).Each group was divided into 2w,4w and 6w group by differencereperfusion time. Cerebral ischemic models were made by clamping bilateralcarotid arteries for 15min then reperfuseing for 60min . Subseqently clampagain for 15min then reperfuse for 2w,4w and 6w.Every rat was killed at thespecific time to take brains.Sections were stained with HE for histologicchanges and immunohistochemistry for APP expression.2.Spatial andanamnesis test:We used Morris water maze task to test rats'ability aboutlearning and memory.The water maze pool was a circular water tank,120cmin diameter and 50cm deep. The pool was filled with water at appromixmately20℃to a height of about 20cm,.A platform with top surface being 1cm belowthe surface of water, was located at a constant position in the middle of onequadrant, equidistant from the center and edge of the pool. Powder was throwninto water make it opacity. The pool was placed in a large test room, wherethere were many visal cues external to the maze. There cues were heldconstant throughout the testing period. Each animal was given for trials dailyfor four consecutive days before ischemic model was done. Rats'findingplatform time is qualified within 10s.The test was repeat four times before wekilled animals. The data were analysised by SPSSv12.0 software. Intra-animalcomparisons were done by using H-test, and comparisons between groupswere done by using Q-test. Results: 1. Sham-operation groups'time of finding platform afteropration did not differ from that of before. While time of finding platform ofcerebral ischemia groups was very different between pre-andpostoperative(p<0.05). 2.We observed the pyramidal neurons in hippocampusCA1 in ischemia and reperfusion groups in which express long trail, pyknosiskaryorrhexis and karyolysis. 3.We can found β-APP expression athippocampus, frontal lobe and parietal lobe of Sham-opration groups. And wealso observed β-APP over expression at same sites of cerebral ischemiagroups.There are obvious difference between two grous(p<0.05). Discussion: Ischemia and reperfusion may induce many biochemistrychanges, such as neurotransmitter disturbance, metabolite excessive, activityneuropeptide disturbance, intracellular calcium heighten, excitatory aminoacids increase and suppression amino acids decrease, alteration of cytokine. Inmolecular biology aspect ,it result in some ischemia correlated gene changing.From 1980s, many and many people began to learn and study ischemicalreperfusion injury .Bilateral carotid arteries ligation is widely known as one of successfulmodels which can induce frontal cerebral chronic ischemic. Clamping bilateralcarotid arteries method ,which we used, is more similar to the pathology ofclinical cerebral ischemia. We observed the pyramidal neurons inhippocampus CA1 in ischemia and reperfusion groups in which express longtrail, pyknosis karyorrhexis and karyolysis, which suggested neurons necrosisand prove it caused cerebral ischemia damage by clamping bilateral carotidarteries. APP's transmembran excretion include two hydrolysis pathway. One isnone Aβpathway which produce soluble APPαand C83 fragment. Thepathway is chief pathway in normal conditions. Receptors such as M1,M3,5-HT,IL-1,metabolism glutamic acid receptor and bradykinin receptor canenhance αexcretion enzyme activity by action of protein kinase C andphospholipase C. The other pathway is amyloid pathway. By this way, β-excretion enzyme cut APP at 671st amino acid, and produce β-APP and C99segment, which produce Aβafter γ-excretion enzyme cutting. Now scientistfound that β-excretion enzyme done its best work with acidity surrounding .β-site APP cleaving enzyme (BACE) is the only βexcretion enzyme thatcan be cloned . Aβand β-APP are thought as one of the typical pathology changesAlzheimer's disease. Recent years ,people found that Aβand β-APPdeposition after cerebral ischemia. So, we can suspect that Aβand β-APPmay involved in cerebral ischemia damage and make it more severity. Many kinds of human cells can produce β-APP, which widelydistribute in blood and cerebrospinal fluid. Cerebral β-APP expression iscorrespond to age and the severity of Alzheimer's disease. We observedβ-APP expressed in sham-operation animals'brains at hippocampus,frontallobe and cortex of parietal lobe. It prove thatβ-APP can be expressed bynormal rats. APP physiological function we have known include stabilizing Ca2+passage, anti-blood coagulation and anti intercellular cohere. In normalconditions, sAPPαacts in some aspect, such as nerve nutrien, facilitate nervecell grow, facilitate axon, promote synapse regeneration and nerveconservancy et al. Cell stress and anoxia cause β-APP over expression. The reason ofischemia-reperfusion groups over expression β-APP at hippocampus, frontallobe and parietal lobe perhaps correspond with APPmRNA over expressionand BACE over excrete. The former not only cause cell toxicity and lowglucose utilization but also enlarge damage of excitability toxicity and freeradical, which result in ischemia area cell apotosis. Our experiment confirmation that rats'cortical neuron over expressionβ-APP and Aβafter frontal cerebral ischemia and reperfusion. And β-APPand Aβover expression cause hippocampus ,frontal lobe and parietal lobeneuron necrosis and apoptosis, which destroy rats'memory and prolong rats'finding platform time .Because human's cognition is closely relate tohippocampus , frontal lobe and parietal lobe neuron, we can anticipate thatpeople will become hypophrenia with the areas damage. Conclusion: Clamping bilateral carotid arteries and reperfusion maycause hippocampus , frontal lobe and parietal lobe damage. β-APP mayexpression in normal rats. Recurrent forebrain ischemia-reperfusion causeβ-APP over expression from post-reperfusion 2w to 6w without tendency ofdescent. β-APP over expression induce rats memory damage.