Gestational Hypoxia Induces White Matter Damage in Neonatal Rats: A New Model of Periventricular Leukomalacia

Abstract

In the premature infant, periventricular leukomalacia, usually related to hypoxicischemic white matter damage, is the main cause of neurological impairment. We hypothesized that protracted prenatal hypoxia might induce white matter damage during the perinatal period. Pregnant Sprague-Dawley rats were placed in a chamber supplied with hypoxic gas (10% O2-90% N2) from embryonic day 5 (E5) to E20. Neonatal rat brains were investigated by histology, immunocytochemistry, western blotting, in situ hybridization, DNA fragmentation analysis, and in vivo magnetic resonance imaging (MRI). Body weight of pups subjected to prenatal hypoxia was 10 to 30% lower from P0 to P14 than in controls. Specific white matter cysts were detected between P0 and P7 in pups subjected to prenatal hypoxia, in addition to abnormal extra-cellular matrix, increased lipid peroxidation, white matter cell death detected by TUNEL, and increased activated macrophage counts in white matter. Subsequently, gliotic scars and delayed myelination primarily involving immature oligodendrocytes were seen. In vivo MRI with T1, T2, and diffusion sequences disclosed similar findings immediately after birth, showing strong correlations with histological abnormalities. We speculate that protracted prenatal hypoxia in rat induces white matter damage occurring through local inflammatory response and oxidative stress linked to re-oxygenation during the perinatal period.

Vulnerability of white matter towards antenatal hypoxia is linked to a species-dependent regulation of glutamate receptor subunits

“…Among NMDA-receptor subunits, NR2B was markedly down-regulated on P1 in mice, and the subsequent changes in glutamate-receptor expression were consistent with previous data (28). Such transient change may severely impact cortex and white-matter development in the brain challenged by adverse events occurring during perinatal period (1,16). Over the last few years, an increasing number of studies have established that NR2B is involved in various of synaptic signaling events and protein-protein interactions.…”

“…We recently showed that protracted prenatal hypoxia in rats caused dramatic WMD in the pups, with microgial activation and oligodendrocyte death leading to deficient myelination (16). To investigate a potential role for genetic factors, we compared brain damage in mouse and rat pups subjected to similar levels of antenatal hypoxia.…”

Contribution of Diffusion-Weighted Imaging in the Evaluation of Diffuse White Matter Ischemic Lesions in Fetuses: Correlations with Fetopathologic Findings

“…These findings correlate well with the results of Baud's study. 16 Conversely, we could not find any correlation between increased ADC and neuronal or oligodendrocytic modifications and proliferation or congestion of vessels. However, absence of increased neuronal death is not surprising in a case of chronic injury; indeed, a recent study has shown that under chronic ischemic conditions, neuronal death was prevented by increased connexin-43 expression.…”

“…These results are in agreement with what has been reminded above (correlations between DWI and histologic findings) and with Baud's experiments. 16 It is noteworthy that in all cases with increased ADC, abnormalities in signal intensity of the WM were also present, which is not surprising because vasogenic edema also generates changes in signal intensity of the WM. 13 In some cases, abnormalities in WM were marked, whereas in other cases, they were more subtle.…”

“…13 Most experimental studies with animal models are based on an acute external injury and therefore do not reproduce the sequence of events arising in fetuses. In a recently published study, 16 WM lesions were induced in neonatal rats by prolonged exposition under protracted prenatal hypoxia, until the day before delivery. Neonatal rat brains were investigated by in vivo DWI and standard histologic and immunohistochemical evaluations from the day of birth to the twenty-first day.…”