Thioredoxin-1 expression levels in rat hippocampal neurons in moderate hypobaric hypoxia.

Previous studies have demonstrated that preconditioning (PC) with three sessions of moderate hypoxia significantly increases the expression of the antioxidant protein thioredoxin-1 (Trx-1) in the rat hippocampus by 3 h after subsequent acute severe hypoxia as compared with non-preconditioned animals. However, it remained unclear whether this increase in Trx-1 accumulation during PC is induced before severe hypoxia or is a modification of the response to severe hypoxia. This question was addressed in the present investigation using experiments on 12 adult male Wistar rats with studies of Trx-1 expression after PC without subsequent severe hypoxia. Immunocytochemical studies were performed 3 and 24 h after three episodes of moderate hypobaric hypoxia (three sessions of 2 h at 360 mmHg with 24-h intervals). Immunoreactivity to Trx-1 24 h after the last session was significantly decreased in neurons in all the areas of the hippocampus studied (CA1, CA2, CA3, and the dentate gyrus). Immunoreactivity in CA3 was also decreased 3 h after hypoxia. These results provide evidence that moderate preconditioning hypoxia itself not only does not increase, but even significantly decreases Trx-1 expression. Thus, increases in Trx-1 contents in the hippocampus of preconditioned animals after severe hypoxia are not associated with the accumulation of this protein during PC, but with a PC-induced modification of the reaction to severe hypoxia.

[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.