Effect Of T₃on The Expression Of AIF And PLP After Excitotoxicity Brain Injury In The Neonatal Mice

Objectives:To investigate the effect of T3on the expression of AIT and PLP after excitotoxicity brain injury in neonatal mice and discuss the protective effect of T3on the nerve with excitotoxicity brain injury.Methods:50five-days-old ICR-type neonatal mice coming from different dams were selected and randomly divided into five groups:the PBS control group(PBS, n=10); the model group(IA, n=10); the low-dose T3-treated group(2μg/Kg)(LT, n=10); the middle-dose T3-treated group(5μg/Kg)(MT, n=10); and the high-dose T3-treated group(10μg/Kg)(HT, n=10). All mice received intracerebral injection in postnatal day5(P5), while the PBS was injected with PBS, the others were injected with ibotenate acid(IA) in order to build up a model of excitotoxicity brain injury. All mice received intraperitoneal injection at1h,24h,48h,72h and96h after intracerebral injection respectively. The PBS and the IA received PBS, while the LT, the MT and the HT received L-T3. Five mice of each group were sacrificied at120h(P10) and30d(P35) after intracerebral injection. After being routinely embedded in paraffin, the brains were cut and stained with HE. The expression of AIF and PLP were detected by the Streptavidin-Peroxidase immunohistochemical method. The optical delnsity were analyzed by image analysis system.Results:1.The size of brain lesion(μm):When the P10, the PBS only showed minor injury in the right cerebral hemisphere. The IA and all T3-treated groups can observed that they all had white matter(WM) cystic lesion and cortex lesion in right cerebral hemisphere. To compare the measured size of WM cystic lesion and cortex lesion between the LT and the IA, there was no significant difference (P>0.05). The size of WM cystic lesion and cortex lesion in the MT was smaller than the IA, the difference was statistically significant(P<0.05). The size of cortex lesion in the HT was smaller than the IA, the difference was statistically significant(P<0.05); but compare the size of WM cystic lesion between the HT and the IA, there was no significant difference (P>0.05).2.The expression of AIF(optical delnsity):When the P10, compared with the PBS, the expression of AIF in the IA increased significantly(P<0.05); to compare the expression of AIF in the LT and in the IA, there was no significant difference (P>0.05); compared with the IA, the expression of AIF in the MT and in the HT both decreased significantly(P<0.05).3.The expression of PLP(optical delnsity):(1) When the P10, compared with the PBS, the expression of PLP in the IA decreased significantly(P<0.05); to compare the expression of PLP in the LT and in the IA, there was no significant difference (P>0.05); compared with the IA, the expression of PLP in the MT and in the HT both increased significantly(P<0.05).(2) When the p35, compared with the PBS, the expression of PLP in the IA decreased significantly(P<0.05); to compare the expression of PLP in the LT and in the IA, there was no significant difference (P>0.05); compared with the IA, the expression of PLP in the MT and in the HT both increased significantly(P<0.05).Conclusions:1. T3can exert a protective effect on the nerve with excitotoxicity brain injury in neonatal mice.2. The middle-dose(5μg/Kg) T3can decrease the size of WM cystic lesion and cortex lesion, reduce neuronal apoptosis, and promote myelin formation. The high-dose(10μg/Kg) T3can decrease the size of cortex lesion, reduce neuronal apoptosis, promote myelin formation; but it has no effect on the WM cystic lesion. The low-dose(2μg/Kg) T3has no effect on both neuronal apoptosis, myelin formation, WM cystic lesion and cortex lesion casued by excitotoxicity brain injury in neonatal mice.