Establishment Of Controllable Rat Model Of Carotid Artery Stenosis And Study Of Its Cognitive Change

Backgroud and objectives:Cerebral vascular disease (CVD) is a major killer of human health, and most of it is ischemic cerebral vascular disease (ICVD), which has the characteristics of high incidence rate, high disability rate, high fatality rate and high recurrence rate.Carotid artery stenosis is an important risk factor of ICVD. Carotid artery stenosis and ICVD are closely related to the onset, progress and prognosis of ICVD. Carotid artery stenosis may lead to ICVD through embolism and hemodynamic mechanisms. Recently, much attention has been paid to the vital role of carotid artery stenosis in the onset and progress of vascular cognitive impairment (VCI). Carotid artery stenosis has been proposed to relate to cognitive decrease, but the precise mechanisms remain uncertain. Regarding the roles of carotid artery stenosis in ICVD and cognitive changes, the research of carotid artery stenosis has drawn more and more attention. However, previous series of studies on carotid artery stenosis at home or abroad were mostly clinically based and not thorough, and experimental studies relatively rare. Therefore, there are many problems to be elucidated, and it is particularly important to carry out experimental research on carotid artery stenosis. At present, the animal models of carotid artery stenosis are established mainly by percutaneous artery balloon distention, injury from dry gas, and electrostimulation of adventitia plus balloon distention. Although these models possess certain application value, the degree of stenosis defies control. And it will cost a relatively long time to form the stenosis. Thus, current animal models have restricted the animal experiments. Therefore, it is extremely essential for the research of the pathophysiologic changes of carotid artery stenosis to establish ideal models of carotid artery stenosis.Therefore, a Wistar rat model of carotid artery stenosis was to be established first. Then the relations between carotid artery stenosis and cognitive changes in rats were observed using combined methods , such as water maze behaviorial testing , P300electrophysiological detection, neurotransmitter determination and pathologic examination. Possible mechanisms of cognitive changes were investigated in pathological and biochemical (neurotransmitter) ways, thus revealing the relevant mechanisms and substantial basis of cognitive impairment from internal carotid artery stenosis, and also providing theoretical evidence for vascular dementia.Methods.-The models of carotid artery stenosis of various degrees were established by incomplete ligation of bilateral common carotid arteries using needles and thread of different gauges. Qualitative and quantitative studies of artery stenosis were carried out using DSA carotid angiography and the computerized graphic processing system. At the time points of 2 weeks, 1, 2 and 3 months, the rats with severe carotid artery stenosis underwent water maze behaviorial testing, P300 electrophysiological detection, neurotransmitter determination and pathologic examination to assess their cognitive changes. Statistic analysis was performed using SPSS 10 statistical package.Results:1. DSA carotid angiography: The contrast medium passed through the site of stenosis, clearly revealing the existence of stenosis.2. Determination of the degree of stenosis: Determination using the computerized graphic processing system confirmed that there were the models of severe and intermediate stenoses obtained, with the stenosis ratios of 92.87±2.92% and 66.19±5.37% respectively.3. Morris water maze place navigation experiment: After r-test, it showed that there was very significant difference in escape latency between the stenosis and the sham groups at the time points of 2 weeks, 1, 2 or 3 months (P<0 .01), suggesting that the escape latency of the stenosis group was longer than that of the sham group at these four time points. One-way ANOVA of both groups at the four time points revealed that there was no significant difference(P>0.05)in the escape latency between the time points within the same group, indicating that the escape latency did not change apparently with the time of stenosis.4. Morris water maze spatial exploration experiment: There was significant difference (P<0.01)in swim distance percentage in original platform quadrant between the stenosis and sham groups at all the four time points, indicating that the swim distance percentage in original platform quadrant of the stenosis group was significantly lower than that of the shamgroup. One-way ANOVA of both groups at the four time points revealed that there was no significant difference(P>0.05)in the swim distance percentage in the original platform quadrant between the time points within the same group, indicating that the swim distance percentage in the original platform quadrant did not change apparently with the time of stenosis5. P300 detection: There was very significant difference in the latency between the stenosis and the sham groups at the four time points (P<0 .01), suggesting that the P300 latency of the stenosis group was significantly longer than that of the sham group. And the latency of the stenosis group was prolonged with the time of stenosis: The latency at 1, 2 or 3 months was significantly longer than that of 2 weeks(P>0.05). There was no significant difference between 1 and 2 months(P>0.05), while the latency at 3 months prolonged even more apparently, showing very significant difference as compared with that of 1 or 2 months(PO.Ol).6. The changes in cortex and hippocampus neurotransmitters: CD Comparison between the stenosis and the sham groups: Except that there was no significant difference in "DA and 5-TH at 1 month and in DA at 2months between the two groups(P>0.05), there was significant difference in neurotransmitters between the two groups at the four time points(P<0.01), suggesting that the contents of neurotransmitters decreased after carotid artery stenosis. (2) Changes of each neurotransmitter at the four time points. NE: Apparent decrease occurred at 2 weeks. The content of NE increased to 1057 + 29.25 ng/g at 1 month, and then decreased. At 2 months, the content was 846 + 97.22 ng/g, significantly lower than that at 1 month (P<0.01)but still higher than that at 2 weeks. At 3 months, the content was 681 +38.24 ng/g, significantly lower than that at 1 or 2 months (P<0.01)but showing no significant difference as compared with that at 2 weeks (P>0.05).DA: There was no significant difference between the time points (P>0.05), suggesting the content of DA did not change evidently with the time of stenosis. 5-HT: The content of 5-HT decreased evidently at 2 weeks. It decreased at 1 month, but significantly higher than that at 1 months (P<0.05). It showed an decreasing tendency at 2 months and 3 months, but still significantly lower than that at 1 months (P<0.05), but showing no significant difference compared with that at 2 weeks (P>0.05). The general trend was that it decreased at 2 weeks, increased at 1 month and decreased again at 2 and 3 months.7. Pathologic changes: Carotid artery stenosis may lead to ischemic changes of hippocampal and cortical neurons, which was unapparent at 1 month but apparent at 2 weeks, 2 or 3 months.Conclusion:1. The model of carotid stenosis can be established successfully using needles and thread, which can control the degree of stenosis, and showing such advantages as being simple, quick, steady, economic and practical.2. This model can be used for the research of brain injury induced by carotid artery stenosis, for instance, vascular cognitive impairment.3. Carotid artery stenosis may cause cognitive impairment in rats, and the impairment shows an aggravating trend with the time of stenosis.4. Ischemic changes of cortical and hippocampal neurons following carotid artery stenosis may be the morphologic basis for cognitive impairment.5. Decrease of the content of monoamine neurotransmitters in brain tissue following carotid artery stenosis may be the neurobiochemical basis for cognitive impairment.6. P300 can be used to diagnose cognitive impairment sensitively at early stages.