Protection Of Estrogen On Forebrain Ischemia In Ovariectomized Rats

Objective: The epidemiological studies have shown that pre-menopausal women are at relatively decreased risk of cerebral stroke when compared with men in the same age, and the serious degree of ischemic injury is much lower than the matched men and post-menopausal women in the same age. But the incidence of stroke increased ,when women go into the post-menopausal period. Research shows that the relative risk and motality of stroke decreased in the post-menopausal women who has received estrogen replacement therapy. So people suppose thar estrogen has a cerebral protective function. In the experiment,by making the model of ovariectomized and forebrain ischemia in the female wistar rats, we observe the effects of estradiol benzoate on the morpathological changes in the cerebral frontal cortex and hippocampal CA1 region,thus to make furthur study the neuroprotection of estrogen on the chronic cerebral sichemia.Methods: Fifty female Wistar rats, with good learning and memory abilities ,were selected by Morris water maze ,and then randomized into 4 groups , that is sham-operation , OVX (ovariectomized) , OVX +estrogen replacement and normal control group. 4 weeks of ovariectomy later, all rats, except the normal control group, were subjected to permanent bilateral common carotid artery occlusion(BCCO). The normal control group underwent the same surgical procedures as for the trial group, only the bilateral common carotid arteries were not occluded. After the operation, all rats were kept under the same surrounding for 6 weeks before receiving Morris water maze test to observe the average avoidance latency, then were killed. Brains were removed and coronally sectioned and then were made HE staining,Luxol Fast blue and Cresyl Violet,Immunohistochemical staining. We can calcuated the average distribution of theneurons and capillaries, in the light microscope under 400 times magnification, in the frontal randomly selected sample of non-overlapping five visions, and hippocampal CA1 pyramidal cell layer 3 visions. The results were presented as Means±SD, multiple comparison were analyzed by SNK-q test. Count data was compared by Chi-square test. The difference was statistically significant (P<0.05).Results: After the ischemia , the mortality of sham-OVX+2VO is 40.0%,OVX+ EB+2VO 46.7%, OVX+2VO 60.0% individually , there were no significant differences among the three groups. At the beginning of the experiment, there were no obvious differences among four groups by comparing the escape latency among them. By the end of the experiment, compared with the normal control group, the operated had a longer avoidance latency. the OVX+2VO group had much more time than estrogen-treated group and the sham-operated group. In the light microscope, from Luxol Fast blue and Cresyl Violet, we can observe the OVX+2VO group: the thick of the cortex become thinner, the number of the neuron of cortex and hippocampal CA1 reduced greatly, the arranging irregularly,nerve cells were triangular or round, soma narrowed, the distance between cells increased, nuclear condensation, nuclear fragmentation disappeared, cytoplasm densed, the neurocytes and interstice surrounding were enlarged,cell membrane had a clear boundry, neuron had granulovacuolar degeneration and halo. Nissl bodies decreased; From Luxol Fast blue, the loss of myelin sheath can be seen to some extent. From immunohistochemical staining ,we can see capillary endothelial cells swelled, cell spaces widened, morphology of blood capillary altered, such as distort , twist and spheroidal. Occasionally, capillary endothelial cells even disappeared. However, the neurons of the OVX+EB+2VO group showed lightly ischemia- induced damage , less degeneration and necrosis. soma narrowed, but close tonormal shape; blood capillary proliferated and damage of endothelial cells were not obvious, more cells morphology was flat, like the normal. the soma narrowed, a few neurons is degeneration and necrosis in Hippocampal CA.1 Sham-operated (Sham-OVX+2VO )group had the similar result with the pretreatment with estrogen. But the damage was much milder in the estrogen-treated group and the sham-operated group. The significant differences were found in the number of neuron and blood capillary among ischemia-treated rats and the normal control rats. After the pretreatment with the estrogen,there were significant difference between estradiol benzoate therapy group and ovariectomized group, what's more, the degree of damage lessened, but there was no obvious significance between the estradiol benzoate therapy group and the sham-operated group.Conclusion:1.The combination of ovariectomy and bilateral carotid artery ligation is a better animal model that can intimate clinical postmenopausal women with chronic cerebral ischemia.2.To some extent , there is a correlation between the level of estrogen and the degree of the ischemia-induced damage and the mortality.3. Estrogen do good to the havioral change of the OVX rat with forebrain ischemia.4.Estrogen can exert protection to the neuron and blood capillary of frontal cortex ,and protect the neuron of hippocampal CA1 region, not only the quantity, but also the quality in the cerebral ischemia. So we can conclude estrogen do good to the pathological change induced by ischemia..5. Estrogen cannot lower the mortality of the OVX rats with chronic cerebral ischemia in acute phase.