Auswirkungen von Ischämie, Hypoxie und Hyperoxie am unreifen Gehirn der Ratte: Immunhistochemische Untersuchungen und Genexpressionsanalysen

Progress in neonatal care has helped to greatly increase the number of infants surviving extreme preterm birth, and the focus has turned from decreasing mortality to improving morbidity. Periventricular leukomalacia (PVL), retinopathy of prematurity (ROP) and other diseases play an important role in the long-term outcome of these children. White matter damage (loss of myeline basic protein (MBP)) in the periventricular region is typical of PVL in humans and can be simulated in neonatal rat using the Rice-Vannucci-method. In this study neonatal Long-Evans rats underwent unilateral carotid ligation (UCL) inducing ischemic damage on postnatal day 6 (P6). Afterwards they were exposed to hypoxic and/ or hyperoxic conditions. Postmortem analysis of the brains was done on P7, P11 und P21. MBP damage severity was examined on P11 with immunohistochemical methods and a blinded viewer graded the brain slides using the MBP damage score. On P7, P11 and P21 gene expression studies were done on the same tissue for the Epo-R (erythropoetin receptor), HIF-1α (hypoxia inducible factor 1, α subunit), NOS-2 (inducible nitric oxide synthase 2), TNFα (tumor necrosis factor α) and VEGF-A164 (vascular endothelial growth factor-A164) genes. The immunohistochemistry revealed significant damage in the UCL groups under hypoxia on the ipsilateral side as well as the contralateral side. Treatment with hyperoxic conditions also lead to mild bilateral white matter damage. Gene expression analysis showed some mild changes. Epo-R was upregulated in UCL groups under hypoxia on the side of the induced ischemia and then decreased continuously until P21. There was also an upregulation for TNFα in the UCL groups under hypoxia on the ipsilateral side which returned to baseline levels by P21. No significant changes were detected in HIF-1α, NOS-2 and VEGF-A164. In this study, we could show that that ischemia, hypoxia and hyperoxia separately, but especially in combination damage the immature brain, which is in line with other observations made in the field.