| Objectives: As an chronic and progressive disease, vascular dementia (VD) is an acquired and durative intelligent dysfunction syndrome, resulted from all kinds cerebral vascular disease (CVD). In recent years, with the increasing of the proportion of the elder people and the curing rate of CVD, its morbilty presents an obviously increasing tendency, which gives a heavy threaten to the physical and mental health of the aged people, and a heavy burden of spirit and economy to the families and society. According to the report of study from home and abroad, VD is a stupid illness that may prevent and get hopeful treatment, which can postponement even reversible its progressive if get treatment earlily. Therefore, it is significant to study the pathophysiological mechanism of VD and to find effective treatments of VD.As two advanced functions of human brains, learning and memory are two closely associated with neurobiology procedures despite their differences. Learning is a acquirement of experiences and skills. Memory is conservation and playbacks of experience and skills. It is well known that the hippocampus is correlated with learning and memory. The pathological changes of neurons in the hippocampus have great effects upon the forming and maintance of learning and memory.Subfornical organ (SFO) is located at the area between the lateral ventricle and the third ventricle where the cerebralspinal fluid circulate passing through. As one of the senory circumventricular organs (SCVOs), SFO is an important site in the chemistrical signal transduction in brain because of absentment of blood-brain barrier(BBB). So it has the supervisal function to the immunity molecule. As an effective area of signal exchanging between blood and the central nervous system, which participate in regulating of neuronal secretion, neuronal immunity and signal transduction. SFO has important significance to maintaining the balance of the internal environment.The VD animal model was established through cerebral ischemia- reperfusion repeatly in our study. We observed pathological changes of neuron in VD mice hippocampal CA1 area by transmission electron microscopic (TEM). The characteristics of ependyma in the SFO was investigated by scanning electron microscopic(SEM). The pathogenesis of VD was studed in the cellular biology.Methods: This study was made up of three parts.Part one was to establish VD models. Kunming mice were subjected for three times ischemia-reperfusion through the ligation of the bilateral commom carotid arteries, accompanied by sham-group. The capabilities of learning and memory of mice were evaluated by step-down test and water maze test. The praxiology differences were observed after mice had been bred for 28 days, then we carried out analysis of variance with SPSS 13.0 statistics software, useing t test to compare the differences between the two groups, P<0.05 or P<0.01 mean statistical significance.In part two and three, the mice's cerebral tissue were fixed up via perfusion of 3% paraformaldehyde solution and 1% glutaric dialdehyde solution, and then observed the ultrastructural changes of hippocampal neurons of the CA1 area by TEM and SFO by SEM in two groups.Results:1 The evaluation of behavior of VD model1.1 The test of learning of miceOn day 29 after operation, the learning of mice in every group were tested by step-down test and water maze test respectively. Response time (sec), error times (number/5min) in step-down test, and swimming time (sec) and error times (number/3min) in water maze test were used to evaluate the achivements of learning.The results of step-down test revealed that: (1) The response time in learning phase of VD model group (54.68±26.20)s prolonged distinctly (P<0.01) compared with the response time of sham-operated group (21.94±14.94)s. (2) The error times in learning phase of VD control group (4.05±1.99) increased notably (P<0.05), compared with the error time of sham-operated group (2.79±1.22).The results of water maze test revealed that: (1) The swimming time in learning phase of the VD model group (111.36±26.04)s prolonged significantly (P<0.01), compared with sham-operated group (73.67±19.65)s. (2) The error times in learning phase of the VD model group (7.18±3.22) increased notably (P<0.01), compared with sham-operated group (4.08±1.28). The results suggested that the learning ability of VD group decreased.1.2 The test of memory of miceOn day 30 after operation, the memory of mice in every group were tested by step-down test and water maze test respectively. The results of latency time (sec) and error times (number/5min) in step-down test, swimming time (sec) and error times (number/3min) in water maze test are the memory.The results of step-down test revealed that: (1) The latency time in memory phase of VD model group (79.45±7.96)s shortened remarkably (P<0.01) compared with the latency time of sham-operated group (175.00±49.91)s. (2) The error times in memory phase of VD model group (4.27±2.21) increased notably (P<0.01), compared with the sham-operated group (2.75±1.26).The results of water maze test revealed that: (1) The swimming time in memory phase of the VD model group (104.09±28.38)s prolonged remarkably (P<0.01), compared with sham-operated group (65.17±13.27)s. (2) The error times in memory phase of the VD model group (5.23±2.56) increased notably (p<0.01), compared with sham-operated group (3.42±1.44). These results suggested that the ability of memory of VD mice reduced.2 The observations under electron microscopy2.1 The ultrastructural changes of the hippocampal neurons by TEM(1) In sham-operated group, there were intact neurons and uniform chromain and abundant apparatus in the hippocampal CA1 area. (2) In the model group, there were denatured neuron, reduced apparatus in cytoplast, denatured mitochondria, mitochondrial crista and its membrane were blend and became blurred. Granule were to merge or degranulation on the rough endoplasmic retiulum(RER), slightly reduced polyribosome, nuclear membrane became uneven, its edge blurred and swollen nucleus. These suggested that the hippocampus CA1 area of VD model suffered from the serious damage.2.2 The results of SEM showed that:(1) In the sham-operation group, on entire overview its ependymal surface was on scant of cilia, only seen a few single cilia on its most regions whereas on surrounding regions of SFO. Ependymal cells of SFO were clearly seen as eminence of cobblestone-like each, thus contour of each ependymal cell was clear and size of the cells was different in diameter(3-10um). Surfaces of some of ependymal cells were rather smooth without microvilli whereas the other cellular surfaces were full of microvilli comparatively. On ependymal surface of SFO the supraependymal structures was rather rich, such as the supraepen- dymal neuron-like cells, there two or three processes on it. On ependymal surface secretion granules were also seen in less quantity, the size was different.(2) In the model group, the SFO's surface was uneven, and ependymal cells surface became depressed, and its forming were irregular, the contour of each ependymal cell was various and the boundaries between cells were unclear. There were reduced microvilli on ependymal cells, and the quantity of cilia was decreased even disappear, whereas the number of secretion granules increase. These suggested that the changes of ependyma of SFO might play an important role in pathology of VD.Conclusions:1 This study successfully established the VD mice models, which could imitate the clinical intelligence impairment of VD patients. The animals were confirmed by step-down test and water maze test. The VD model is the reliable animal model and feasible to the further study of VD. 2 In VD mice, neuron of hippocampus CA1 area suffered from the serious damage. These changes of ependyma of SFO indicated that they participated in the pathogenical mechanism of VD.
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