Prolonged latency to CNS-O₂ toxicity induced by heat acclimation in rats is associated with increased antioxidative defenses and metabolic energy preservation

We have previously shown that heat acclimation provides protection against central nervous system oxygen toxicity (CNS-OT). This was well correlated with increased levels of heat shock protein 72 (HSP72). We now examine other antioxidative defenses against CNS-OT that are correlated with heat acclimation. Two groups of male Sprague-Dawley rats were used. The heat-acclimated group (HA) was exposed for 4 wk to 32°C, and the control group (C) was maintained at 24°C. At the end of the acclimation period, rats were exposed to oxygen at 608 kPa. EEG was recorded continuously until appearance of the first electrical discharge. Brain samples were taken from each group after exposure to pressure. Levels of the antioxidant enzymes CuZnSOD, MnSOD, catalase, and glutathione peroxidase, as well as levels of HSP72, were quantified by Western blot. Comparative proteome analysis of the brains of HA and C rats was carried out using two-dimensional electrophoresis and mass spectrometry to define protein spot alterations. Levels of HSP72 and CuZnSOD were higher in HA rats. Levels of the other antioxidant enzymes were not affected significantly by heat acclimation. Differences in the levels of four protein spots identified as α-synuclein, valosin-containing protein, adenylate kinase 1 (AK1), and the mitochondrial H+-ATP synthase α subunit were found between HA and C rats. We conclude that elevation of HSP72, CuZnSOD, AK1, and the mitochondrial H+-ATP synthase α subunit and possible phosphorylation of α-synuclein - all proteins involved in oxidative stress or energy conservation - might contribute to the prolongation of latency to CNS-OT induced by heat acclimation.