Objective
Clinical and experimental evidence indicate that the presence of intrauterine inflammation in pregnancy is not only a cause of preterm birth but is also associated with perinatal brain damage and long-term neurological handicap. In the present study, preterm delivery was induced using a recently developed model in C57BL/6 mice through intrauterine administration of lipopolysaccharide (LPS), and the neuropathological outcome was investigated in surviving pups.
Methods
C57BL/6 mice were subjected to intrauterine infusion (between the amniotic and chorionic membranes) of LPS (250 μg/mouse or 125 μg/mouse) or saline, at a time corresponding to 70% of average gestation (gestational day 15). Fetuses that survived after LPS administration were allowed to deliver and were sacrificed on postnatal 14 days (PND 14) at a time in development when myelination has started. Brain injury was examined in parallel sections stained with H & E, Lectin, microtubule associated protein 2 (MAP2), myelin basic protein (MBP) and glial fibrillary acidic protein (GFAP).
Results
The brain weight of LPS-exposed pups (n=12) were significantly lower than that of saline-exposed pups (n=21) at PND14 (brain weight LPS 0. 278 ± 0.008 g vs. control 0.303 ± 0.005 g, p=0.017). In all LPS-exposed brain sections examined (n=12), 8 displayed various abnormalities that were not observed in any of the saline-exposed animals. Three brains displayed enlarged ventricles as determined in H&E stained sections. Four brains exhibited decreased MBP density in the white matter indicating hypomyelination. Focal cerebral white matter cysts surrounded by activated astrocytes were detected in 5 of the LPS-exposed pups. A focal cortical gray matter lesion was detected by MAP2 immunostaining. The infarct and border zone area was infiltrated with activated microglia and astrocytes. The wedge-like form of the injured area in combination with a vessel located centrally proximal to the lesion suggested a thrombotic infarction. None of these pathologies were detected in sham-treated animals.
Conclusions
LPS impaired brain development and various brain lesions were produced in both the white and gray matter in a clinically relevant model of preterm birth in mice. We suggest that some of this brain damage might be related to LPS-induced perturbation of coagulation. The mechanism by which LPS induces injury in the developing brain needs to be further explored.