Maturational Effects of Lipopolysaccharide on White-Matter Injury in Fetal Sheep

Abstract

White-matter damage has been associated with the development of cerebral palsy in children born both prematurely and at term, and it has been suggested that intrauterine infection can contribute to the brain injury. However, the relative importance of age on white-matter injury following infectious exposure in utero remains unclear. In this study, fetal sheep were exposed to systemic endotoxemia by administration of Escherichia coli lipopolysaccharide (88.7 ± 7.7 ng/kg) at 65% or 85% of gestation. These gestational ages approximately correspond to human brain development in preterm and near-term infants respectively. White-matter injury was evaluated 3 days after lipopolysaccharide exposure with regard to microglia activation and loss of neurofilament and myelin basic protein. The expression of oligodendrocytes at different maturational stages was demonstrated in preterm and near-term fetuses with the oligodendroglial markers O4 and 2',3'-cyclic nucleotide 3'-phospodiesterase. Forty percent of the fetuses in the preterm group and 22% in the near-term group died within 8 hours of the endotoxin exposure. Three of six preterm and two of seven near-term surviving fetuses demonstrated pathologic changes in the brain with regard to increased microglia activation and loss of neurofilament staining. The number of activated microglia was enhanced in the subcortical white matter in both the preterm lipopolysaccharide-exposed fetuses (lipopolysaccharide: 235 ± 64 cells/mm 2; control: 72 ± 28 cells/mm2; P = .0374) and the near-term fetuses (lipopolysaccharide: 180 ± 40 cells/mm2; control 23 ± 16 cells/mm2; P = .0152). There was a loss of neurofilament staining in both preterm fetuses (lipopolysaccharide: 2.20 ± 0.77 pixel units; control: 0.20 ± 0.10 pixel units; P = .0306) and near-term fetuses (lipopolysaccharide: 1.15 ± 0.48 pixel units; control: 0.06 ± 0.06 pixel units; P = .0285). O4-positive cells were detected at both gestational ages, whereas 2,3-cyclic nucleotide 3-phospodiesterase-positive cells and myelin basic protein staining were mainly detected in the near-term fetuses. In summary, we found white-matter injury in a proportion of both preterm and near-term fetuses after administration of lipopolysaccharide. These results are in agreement with clinical evidence suggesting that both preterm and term infants are at risk of periventricular leukomalacia in association with intrauterine infection. ( J Child Neurol 2005;20:960—964).