Morphological Differences between the Effects of Different Preconditioning Regimes Correcting Damage to Hippocampal Neurons Due to Exposure to Severe Hypobaric Hypoxia

Studies on five groups of rats (six animals per group) addressed changes in neurons in hippocampal fields CA1 and CA4 seven days after severe hypobaric hypoxia (180 mmHg, 3 h) using different numbers (1, 3, or 6) of sessions of preconditioning (PC) with moderate hypobaric hypoxia (360 mmHg, 2 h, 24 h before severe hypoxia). Single-session PC was found not to prevent damage to neuron structure with neuron death by day 7 after severe hypoxia. At the same time, six and especially three sessions of PC induced protective mechanisms preventing neuron damage. Use of six sessions of PC, in contrast to three, resulted in moderate chromatolysis in hippocampal neurons, which may be a consequence of prolonged hypermetabolic activity of neurons and may be evidence of their functional overloading.