Oxygen-challenge MR study on the dynamic evolution of ischemic penumbra in rats with middle cerebral artery occlusion / 中华放射学杂志

ABSTRACT

Objective:To investigate the application value of oxygen-challenge MRI in the identification of ischemic penumbra in acute middle cerebral artery occlusion (MCAO) model in rats.Methods:Fifty-eight SD rats were received MCAO processing. Ten MCAO rats were randomly selected. MRI scanning was performed and modified neurological severity score mNSS was evaluated before and after oxygen stimulation at the 1st, 3rd, 6th and 12th hour after MCAO model preparation. The scanning data before and after oxygen stimulation were recorded as air group and oxygen group respectively. T 1 values and T 1 change rate of different brain regions were measured. Twenty-four MCAO rats were selected for oxygen stimulation according to the above four time points. At each time point, 3 MCAO rats were randomly selected for HE staining and recorded as oxygen stimulation group 1 ( n=12). Meanwhile, 3 MCAO rats were randomly selected for immunohistochemical examination at each time points to determine the expression of protein kinase C receptor (RACK1), recorded as oxygen stimulation group 2 ( n = 12). Another 24 MCAO rats were selected without oxygen stimulation. Among them, three MCAO rats were randomly selected at each time point for HE staining, recorded as non-oxygen stimulation group 1 ( n=12); and three MCAO rats were randomly selected at each time point for immunohistochemistry to detect the expression of RACK1, recorded as non-oxygen stimulation group 2 ( n=12). Independent sample t-test was used for the comparison between the two groups. One way ANOVA was used for the comparison in T 1 change rate between different brain regions, and repeated measurement ANOVA was used for the comparison of T 1 change rate in the same brain region at different time points. The correlation between the expression of RACK1 protein in oxygen group 2 and non-oxygen group 2, as well as T 1 values in air group and oxygen group was analyzed by Spearman analysis. Results:At the same time point, the difference of mNSS scores between air group and oxygen group was statistically significant ( P<0.05). At different time points, the difference of mNSS between the two groups was also found statistically significant ( P<0.05). There were significant differences in T 1 values and T 1 change rate between air group and oxygen group in ischemic core area, mismatched area and contralateral normal area, among which the difference was statistically significant (all P<0.05). At different time points, the cellular edema or vacuolation in the cerebral ischemic area of 24 MCAO rats in the oxygen challenge group 1 and the non-oxygen challenge group 1 showed an aggravating trend, and the degree of cellular edema or vacuolation in the cerebral ischemic area of the non oxygen challenge group 1 was slightly less degree than that of the non-oxygen challenge group 1. The expression of RACK1 protein in the cerebral ischemia area of 24 MCAO rats in the oxygen challenge group 2 and the non-oxygen challenge group 2 decreased at different time points, and the expression of RACK1 protein in the non-oxygen challenge group 2 was higher than that in the oxygen challenge group 2 ( P<0.05). Conclusions:Oxygen challenge MRI can be used to determine the oxygen metabolism in the brain infarction tissue of MCAO rats. The oxygen challenge MRI T 1 value and T 1 change rate can help to identify the ischemic penumbra of MCAO rats. Oxygen stimulation may delay the development of cerebral ischemia. The expression of RACK1 plays a protective role in acute cerebral ischemia and is related to the development of hypoxia in brain tissue.