Effects of lipopolysaccharide on myelination of early neonatal rat at different maturity levels and the changes of tumor necrosis factor-α expression

Objective To monitor the function of infection on myelination in white matter damage,neonatal Wistar rats of postnatal day 2 (P2) and postnatal day 7 (P7) were injected intraperitoneally with the same doses of lipopolysaccharides (LPS),and 2',3 '-cyclic nucleotide phosphodiesterase (CNPase) and myelin basic protein (MBP) were labeled in immature oligodendrocytes and mature oligodendrocytes.To investigate the function of tumor necrosis factor(TNF)-α according to test the change of TNF-α expression in the brain.Methods Ninty-six neonatal Wistar rats were randomly divided into four groups (each group 24 rats):group A:LPS (5.0 mg/kg) was injected intraperitoneally on P2 ; group B:LPS (5.0 mg/kg) was injected intraperitoneally on P7 ;group C1 and C2 were control groups in which equal amount of normal saline was injected intraperitoneally on P2 or P7.The expression of CNPase at 24 h after injection and MBP at P14 in brain tissue of each group were measured by immunohistochemistry and express of TNF-α mRNA at 4 h after the injection was measured by RT-PCR.Results Punctate hemorrhage in the corpus callosum,external capsule and intraventricular hemorrhage were seen in group A.Periventricular leukomalacia appeared in the corpus callosum and glial cells hyperplasia could be seen periventricular in P14 rat brains,but not found in the group B and any of the saline-injected rat brains.Compared with group C1 and C2 respectively,CNPase-positive cells showed obvious decrease in the area of white matter in periventricular in group A(106.93 ± 2.62 vs 113.67 ± 2.69,P ＜ 0.01) and group B (96.37 ± 1.82 vs 101.65 ± 2.01,P ＜ 0.01).Following LPS treatment in group A,the protein expression of MBP in neonatal brain decreased evidently compared with group C1 at P14 (128.21 ± 2.99 v s 134.81 ± 2.98,P ＜ 0.01),while no significant change was found between group B and group C2(134.77 ±3.68 vs 134.81 ±2.98,P ＞0.05).After 4h of the LPS treatment,the level of TNF-α mRNA was greatly increased in group A,it was significantly higher than that in group B (1.79 ± 0.04 vs 1.18 ± 0.04,P ＜ 0.01).Conclusion Intraperitoneal injection of LPS to the development neonatal rats can lead to dysmyelination and white matter damage.The expression of TNF-oα mRNA increased significantly in these immature neonatal rats,while only myelination delay occurred in those of mature neonatal rats without dysmyelination. Key words: Lipopolysaccharide;  Myelination;  White matter damage;  Tumor necrosis factor-α ;  Rat, newborn