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 se vere (3% O-2) hypoxia. The ultrastructural findings were also correlat ed with regional superoxide dismutase (SOD) activity changes. In unpre treated rats severe hypoxia induced ultrastructural changes consistent with the aspects of delayed neuronal death (DND). However, in preexpo sed animals hippocampal damage was attenuated in an inversely proporti onal way with the severity of the hypoxic pretreatment. The ultrastruc tural hypoxic tolerance findings were also closely related to increase d regional SOD activity levels. Thus the activation of the endogenous antioxidant defense by hypoxic preconditioning, protects against hippo campal damage induced by severe hypoxia. The eventual contribution of increased endogenous adenosine and/or reduced excitotoxicity to induce hypoxic tolerance is discussed.