Studies have shown that stress increases the death of specific brain cells, especially those concerned with memory and orientation, the very ones affected by Alzheimer's disease.465 To a large degree this is due to the fact that prolonged stress of any kind dramatically increases free-radical generation and lipid peroxidation in the brain.
Two hormones, adrenaline and Cortisol, appear to be responsible for most of the destructive effects. When we experience stress, both hormones are released in large concentrations and as we age, Cortisol release is more prolonged. The physiological events that occur with stress are called allostasis; unrelieved stress is known as an allostatic load.
Dr. Bruce McEwen, director of the Laboratory of Neuroendocrinology at Rockefeller University, has demonstrated through a series of experiments conducted on animals the importance of the brain's response to the allostatic load. He found that unrelieved stress could destroy stem cells in a portion of the hippocampus of the brain, which is vital to memory storage and which contains more Cortisol receptors than any other part of the brain.466 In addition, stress destroyed synaptic connections and dendrites as well.
Further, he found the process was reversible if stress was eventually stopped. With his experimental animals, the limit was twenty-eight days. After that, permanent changes took place. In fact, Dr. Robert Sapolsky of Stanford University found that stress beyond this period actually killed brain cells. The mechanism of brain-cell destruction involves oxidation of these hormones, as well as interaction with the excitotoxin glutamate.
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