Acute neuronal injury after hypoxia is influenced by the reoxygenation mode in juvenile hippocampal slice cultures

In neonates asphyxia is usually followed by hyperoxia due to resuscitation procedures. In order to study whether hyperoxic reoxygenation might cause additional cell injury we subjected organotypic hippocampal slice cultures of juvenile rats to normoxic or hyperoxic reoxygenation (19 or 85% oxygen, respectively) following hypoxia (3% oxygen) for 30, 60, and 120 min. Cell injury was quantified by lactate dehydrogenase (LDH) release and propidium iodide (PI) fluorescence 1 h after end of the reoxygenation period. In both experimental groups, LDH activity was significantly enhanced by hypoxia as compared to normoxic controls. However, hyperoxic reoxygenation caused a larger increase in LDH activity than normoxic reoxygenation (e.g., by a factor of 1.60 vs. 1.29 following 120 min hypoxia). PI fluorescence increased after hypoxia in all principal cell layers of the hippocampus but again showed a larger enhancement after hyperoxic reoxygenation as compared to normoxic reoxygenation (e.g., by a factor of 3.9 vs. 1.7 for CA1 and 120 min of hypoxia). After normoxic reoxygenation, PI fluorescence intensity was lower in the dentate gyrus as compared to CA1 and CA3, while it reached similar values like CA1 after high oxygen supply. In conclusion, juvenile hippocampal slice cultures subjected to hyperoxic reoxygenation display a greater amount of acute neuronal injury than slice cultures undergoing normoxic reoxygenation.