Effects of preconditioning by mild hypobaric hypoxia on the expression of manganese superoxide dismutase in the rat hippocampus

The molecular mechanisms of neuroprotection during hypoxic action involve induction of antioxidants, including manganese superoxide dismutase (Mn-SOD). Previously, we demonstrated that severe hypobaric hypoxia (SHH) resulted in some enhancement of the content of Mn-SOD in rat hippocampal neurons 3 h later. Preconditioning by a 3-time repetitive mild hypobaric hypoxia (MHH) considerably increased the expression of Mn-SOD in the CA2 and CA3 areas of the hippocampus (but not in the CA1 and DG areas) in comparison with unconditioned animals. The mechanism for the enhancement of the increase in Mn-SOD in the preconditioned rats remains unclear. This enhancement could be caused by induction of Mn-SOD expression by MHH prior to SHH, or by modification of the reaction to severe hypoxia itself. It was demonstrated that immunoreactivity to Mn-SOD was increased in CA1 and DG, but not in CA2 and CA3 up to the 24th hour after the three courses of MHH (i.e., until the beginning of SHH). Thus, the effect of preconditioning on Mn-SOD expression after SHH was revealed in those hyppocampal areas in which MSS itself did not result in an increase in the expression of this protein. Thus, the neuroprotective effect of preconditioning on the early stages following severe hypoxia was not associated with Mn-SOD accumulation during preconditioning, but was due to modification of the reaction to SHH itself.