Effect Of T₃ On The Expression Of Caspase-3 And MBP And Brain Pathological Lesion After Excitotoxic Brain Injury In The Neonatal Mice

Objectives The study was designed to investigate the effect of T₃ on the expression of caspase-3 and MBP and brain pathological lesion after excitotoxic brain injury in neonatal mice,to explore a new drug treatment for preterm infant white matte damage and provide a theoretical basis.Methods 72 five-days old ICR-type neonatal mice coming from different dams were selected and randomly divided into five groups:PBS control group(PBS,n=18); model group of excitotoxicity(IA,n=18);low-dose(2μg/kg) T₃-treated group (LT,n=12);middle-dose(5μg/kg) T₃-treated group(MT,n=12);and high-dose(10μg/kg) T₃-treated group(HT,n=12).All mice received intracerebral injection at post-natal day 5.The PBS group was injected with PBS,while the excitotoxic model and T₃-treated groups were injected with ibotenic acid.All pups were done intraperitoneal injections at 1,24,48,72 and 96 hours after intracerebral injection respectively.The PBS and excitotoxic model groups received PBS,while the three T₃-treated groups received L-T₃.Blood of six animals of each group were collected after 24h or 120h of intracerebral injection and the total triiodothyronine were detected by ELISA.Six animals of each group were sacrificied at 120h and 30d after intracerebral injection, their brains were taken for cutting and histologcal staining,the size of the brain lesion in each group were calculated through the numbers of the pathological slides with brain injury,And the changes of expression of caspase-3 and MBP were detected by Streptavidin-Peroxidase method(SP)of immunohistochemistry.SPSS 11.5 software was used to analyze the data,P＜0.05 was considered the level of significance.Results 1.The concentration of total triiodothyronine in serum(ng/dl):There were no statistical difference between all groups at 24h and 120h after intracerebral injection(P＞0.05).2.The size of brain pathological lesion(μm):Histologica section of excitotoxic model and all T₃-treated groups could observe brain lesion of right cerebral hemisphere both in white matter(WM) and cortical plate(CP).While there were no white matter lesion except the mechnical injury in saline PBS group mice brain.Compared with the excitotoxic model group(WM:670.0±167.21;CP: 730.0±153.75),the size of white matter(410.0±88.31)and cortical plate(453.33±78.65) lesion in middle-dose T₃-treated group were smaller significantly(P＜0.01);the size of cortical plate lesion(560±90.33) in high-dose T₃-treated group was also smaller significantly(P＜0.05),but the size of white matter lesion(590.0±79.74) was not statistically significant(P＞0.05);the size of both white matter(600.0±84.85) and cortical plate lesion(666.67±90.92) in low-dose T₃-treated group were not statistically significant(P＞0.05) at post-natal day 10.3.the expression of caspase-3(gray level):compared with PBS group(150.92±16.07),the expression of caspase-3 (102.57±10.07) in excitotoxic model group increased significantly(P＜0.001),the caspase-3 staining extent in three T3-treated groups was between the other two groups. compared with the excitotoxic model group,the caspase-3 positive expression (135.87±8.89) in middle-dose and that(126.23±14.87) in high-dose T₃-treated group decreased significantly(P＜0.01) at post-natal day 10,While there was no statistical difference between the low-dose T₃-treated group(106.13±8.53) with the excitotoxic model group(P＞0.05).4.The expression of MBP(gray level):the MBP positive expression(P10:102.31±8.59;P35:91.83±8.45) was strong in PBS group,In excitotoxic model group,the MBP positive expression(P10:140.31±8.67; P35:136.26±13.6) decreased significantly(P＜0.001).Compared with the excitotoxic model group,the MBP positive expression(P10:117.60±12.94;P35:112.31±9.97) in middle-dose and that(P10:124.31±5.63;P35:115.18±12.34) in high-dose T₃-treated group increased significantly(P＜0.05) at P 10 and P35;While there were no statistical difference between the low-dose T₃-treated group(P10:131.33±12.32; P35:124.29±18.70) with excitotoxic model group(P＞0.05) at P 10 and P35.Conclusions 1.Intraperitoneal administration of middle-dose(5μg/kg) and high-dose (10μg/kg) T₃ has a protective effect on excitotoxic brain injury in neonatal mice.The middle-dose(5μg/kg)T₃ do reduce neuronal apoptosis,and promote myelin formation, as well as reduce both the size of white matter and cortical plate lesion in excitotoxic brain injury;high-dose(10μg/kg) T₃ can reduce neuronal apoptosis,promote myelin formation,but reduce neocortical leision size of excitotoxic brain injury alone;2.The low-dose(2μg/kg) T₃ has no effect on neuronal apoptosis and myelin formation and the excitotoxic brain lesion.3.The excitotoxic brain injury does not influence the serum concentration of total triiodothyronine in neonatal mice within 120 hours after intracerebral injection.