A Comparison of the Effects of Single and Triple Exposures to Moderate Hypobaric Hypoxia on the Expression of Cu, Zn-superoxide Dismutase in the Rat Hippocampus

It was shown that preconditioning by three-time moderate hypobaric hypoxia improves and accelerates the expression of Cu, Zn-superoxide dismutase (SOD) in response to subsequent severe hypoxia in neurons of the rat hippocampus. However, preconditioning per se in the absence of subsequent exposure to severe hypoxia does not increase but even decreases Cu, Zn-SOD expression in some regions of the hippocampus. In the present study, we compared our previous immunocytochemical data on Cu, Zn-SOD expression 3 and 24 h after the last of three exposures to moderate hypobaric hypoxia with the data on the expression at the same time points after a single exposure to moderate hypobaric hypoxia. We found that a single exposure to hypoxia has similar effects on Cu, Zn-SOD expression as triple hypoxia. When we compared four time points during preconditioning, i.e., 3 and 24 h after single and triple exposures to hypoxia, respectively, we revealed wave-like changes in the levels of Cu, Zn-SOD expression, which may play an important role in modification of the response to subsequent severe hypoxia and, thus, in the mechanism of the formation of the tolerance of hippocampal neurons to hypoxia.