[Thioredoxin-1 expression level in hippocampal neurons of rats exposed to hypobaric hypoxia]

It was shown recently that preconditioning by 3-time repetitive mild hypoxia significantly augmented expression of thioredoxin-1 (Trx-1) antioxidant protein at 3 h after subsequent acute severe hypoxia in rat hippocampus as compared to the expression of this protein in non-preconditioned rats. However, it was unclear whether this augmentation was due to an accumulation of Trx-1 during the preconditioning before severe hypoxia or by a modification of reaction to severe hypoxia itself. To answer this question, Trx-1 expression level after preconditioning without subsequent severe hypoxia was studied in an experiment on 12 mature male Wistar rats. Trx-1 expression was studied by immunocytochemistry 3 h and 24 h after thrice-repeated mild hypobaric hypoxia (three 2h treatments at 360 Torr spaced by 24 h intervals). 24 h after the last hypoxic treatment, Trx-1 immunoreactivity was significantly decreased in the neurons of all the hippocampal regions studied (CA1, CA2, CA3 and dentate gyrus). In CA3 it was also decreased at 3 h after hypoxia. These findings indicate that mild preconditioning hypoxia, by itself, does not increase, but on the contrary, decreases Trx-1 expression. It may be concluded that the augmentation of Trx-1 content in the preconditioned animals is due to a modified reaction to severe hypoxia, but is not the result of Trx-1 accumulation during preconditioning.