Effect of acute exposure to hypobaric hypoxia on learning and memory in adult Sprague-Dawley rats.

The present study aimed to observe the effects of acute exposure to hypobaric hypoxia on learning and memory in adult Sprague-Dawley (SD) rats as well as the changes in N-methyl-D-aspartate receptor (NMDAR) subunits. Learning and memory abilities were evaluated with Morris water maze following simulated hypoxia at 5000 m or 7000 m for 2, 4 or 6 days. The number of red blood cells, the level of hemoglobin, oxidative stress markers, the extent of neuronal damage in the hippocampal CA1, and the expression of NMDAR subunits were all measured. In place navigation test, the escape latency significantly increased only in the 5000 M 6Day (P < 0.05) group than the latency in the plain group on the fourth day. In the spatial probe test, the times of platform passing showed no significant difference between the hypoxia and plain groups. Polycythemia, an increased ratio of superoxide dismutase/malondialdehyde and degeneration of neurons appeared in an elevation-dependent and duration-dependent manner in those hypoxia groups. Furthermore, the protein expression of NR1 increased and the protein expression levels of NR2A, NR2B, and NR3A were all decreased in the 5000M 6Day and 7000M 6Day groups. In summary, the feeble effect of acute exposure to simulated hypobaric hypoxia on learning and memory in adult SD rats may be attributed to increased antioxidative capacities and decreased expression of NR3A. And moreover, differences in the expressions of NMDAR subunits were closely related to the altitude and duration.