Hypoxic pretreatment protects against neuronal damage of the rat hippocampus induced by severe hypoxia

The present study investigates whether under conditions of successive hypoxic exposures pretreatment with mild (15% O-2) or moderate (10% O-2) hypoxia, protects hippocampal neurones against damage induced by severe (3% O-2) hypoxia. The ultrastructural findings were also correlated with regional superoxide dismutase (SOD) activity changes. In unpretreated rats severe hypoxia induced ultrastructural changes consistent with the aspects of delayed neuronal death (DND). However, in preexposed animals hippocampal damage was attenuated in an inversely proportional way with the severity of the hypoxic pretreatment. The ultrastructural hypoxic tolerance findings were also closely related to increased regional SOD activity levels. Thus the activation of the endogenous antioxidant defense by hypoxic preconditioning, protects against hippocampal damage induced by severe hypoxia. The eventual contribution of increased endogenous adenosine and/or reduced excitotoxicity to induce hypoxic tolerance is discussed.