Research On Astrocytes' Activity And The Drug Effects On It After Acute Ischemic Brain Injury In Rats

Objective:To investigate different parts of brain astrocytes'(astrocyte, AS) activitiy after acute ischemic brain damage in rats, and the effects after imposing upon the activity of drugs.Methods:Implementation of middle cerebral artery occlusion by using suture embolization method, and reperfusion after 2h, to make the cerebral ischemia-reperfusion model.First experiment, ischemia-reperfusion model rats were treated with different doses of mannitol and were observed the neurological deficit score(mNSS) value at different time points after reperfusion. Determining glial fibrillary acidic protein (glial fibrillary acidic protein, GFAP) positive cells by immnohistochemical staining 72h after ischemia-reperfusion around ischemic lesion and in hippocampal CA1 area of each dose group.Second experiment, rats were randomly divided into control group, sham operation group and ischemia-reperfusion model group, and a minimum effective dose of mannitol was selected by the first experiment's results;the three groups of rats were given and not given mannitol, and then 24h and 72h after reperfusion the rats in groups were sacrificed to observe the number changes of GFAP positive cells around ischemic lesion and in hippocampal CA1 area. Rats in ischemia-reperfusion model group were excised to do some brain TTC (2,3,5-triphenyl tetrazolium chloride) staining, to observe the role of mannitol on the infarct lesion.Results:First experiment, neurological deficit score value (modified neurological severity score, mNSS) of 0 dose group between small, middle and high dose groups had statistical significance P=0.021,P=0.018,P=0.018,while small, middle and high dose group's mNSS score variance results showed no statistical significance, P =0.996.The small, middle and high dose groups' mNSS score at different reperfusion time points were significantly different, all three P=0.000.The number of GFAP-positive cells around ischemic lesion of different dose groups are not identical,P=0.002.Tukey HSD multiple comparison method's result was:0 dose group compared with small dose group, middle dose group and high dose group respectively, P=0.009, P=0.005,P=0.003.Difference among small, middle and high dose groups had no statistical significance by the Student-Newman-Keuls method and the Tukey HSD method test, P=0.899, P= 0.971.The number of GFAP-positive cells in hippocampal CA1 area of different dose groups are not identical, P=0.000.Tukey HSD multiple comparison method's result was:0 dose group compared with small dose group, middle dose group and high dose group respectively, all three P=0.000.Difference among small, middle and high dose groups had no statistical significance by the Student-Newman-Keuls method and the Tukey HSD method test, P=0.899, P=0.971.The Pearson correlation coefficient between the mNSS score values of rats after ischemia-reperfusion for 72h and their corresponding number of GFAP-positive cells around ischemic lesion was-0.528 (P=0.008), it showed a negative correlation between the two.Similarly, the Pearson correlation coefficient between the mNSS score values of rats after ischemia and reperfusion for 72h and their corresponding number of GFAP-positive cells in hippocampal CA1 area was-0.720 (P=0.000), it showed that they also has a negative correlation.Second Experiment, the infarct size difference of the coronary level 8.2mm apart from ear to ear line between used mannitol and didn't use mannitol in model rats was not statistically significant P=0.683,and the infarct size between 24h and 72h after reperfusion also has no statistical significance P=0.773.The operation level, use mannitol or not, the reperfusion time all had statistical significance to affect the number of GFAP-positive cells around the ischemic lesion, P=0.000,P=0.000, P=0.026, the interaction between the operation level and use mannitol or not had statistical significance, P=0.000, the statistical results indicated that there was a synergistic effect between the two.All the differences of GFAP-positive cells around the ischemic lesion between control group and sham operation group, the control group and model group and sham operation group and model group by the Tukey HSD test had statistical significance, all three P=0.000.The operation level, use mannitol or not, the reperfusion time all had statistical significance to affect the number of GFAP-positive cells in hippocampal CA1 area, P =0.000, P=0.000, P=0.028,the interaction between the operation level and use mannitol or not had statistical significance, P=0.000, The statistical results indicated that there was a synergistic effect between the two.All the differences of GFAP-positive cells in hippocampal CA1 area between control group and sham operation group, the control group and model group and sham operation group and model group by the Tukey HSD test had statistical significance, all three P=0.000.Conclusion:This study finds out that, to some extent, it still can not be thought that influence of different doses of mannitol to the activitiy of AS around the ischemic lesion and in hippocampal CA1 area on ischemia-reperfusion model rats are different. Rats mNSS score values and the peripheral ischemic lesion and hippocampal CA1 area were negatively correlated with the number of AS,that is:mNSS score values reduce if the number of AS increase, neurologic behavioral performance gets better. This study demonstrated that AS reactive hyperplasia occur significantly around the ischemic lesion and in hippocampal CA1 area after acute ischemic brain injury in rats. 24h or 72h after using mannitol will both significantly increase the activity of AS reaction in the peripheral ischemic lesion and hippocampal CA1 area in ischemia-reperfusion model rats.It can be inferred that using mannitol after acute ischemic brain injury, may protect ischemic brain tissue and surrounding tissue by increasing the AS reaction activity in peripheral ischemic lesion and hippocampal CA1 area.