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Stress and the Brain

Updated: Apr 20, 2022


Biological stress is created by the brain in response to real or imagined stimuli. the many physiological responses associated with stress help to protect the body and the brain from the dangers that triggered the stress in the first place. But "Stress" in chronic does can have insidious harmful effects as well. Neuroscientists have only begun to understand the relationship between Stress, the Brain, and Brain Damage.

Stress leads to the release of the Steroid Hormone "CORTISOL" from the Adrenal Cortex. Cortisol travels to the brain through the bloodstream and binds to receptors in the Cytoplasm of many Neurons. The activated receptors travel to the cell nucleus, where they stimulate gene transcription and ultimately protein synthesis. One consequence of Cortisol's action is that neurons admit more Ca2+ through voltage-gated ion channels. this may be due to a direct change in the channels, or it may be indirectly caused by changes in the cell's energy metabolism. Whatever the mechanism, presumably in the short term Cortisol makes the brain better able to cope with the stress - perhaps by helping it figure out the way to avoid it!

But What about the effects of chronic, unavoidable stress? We learned that too much Calcium can be a bad thing. If neurons become overloaded with Calcium, they Die! (Excitotoxicity). The question naturally arises: CAN CORTISOL KILL? Bruce McEwen and his colleagues at Standford University have studied this question in the rat brain. They found that daily injections of Cortisosterone (rat cortisol) for several weeks caused dendrites to wither in many neurons with corticosterone receptors. A few weeks later, these cells started to die. A similar result was found when, instead of daily hormone injections, the rat was stressed every day.

Spolsky's studies of baboons in Kenya further reveal the scourges of chronic stress. Baboons in the wild maintain a complex social hierarchy, and subordinate males steer clear of dominant males when they can. During one year when the baboon population boomed, local villagers caged many of the animals to prevent them from destroying their crops. Unable to escape the "top baboons" in the cages, many of subordinate males subsequently died - not from wounds it malnutrition but apparently from severe and sustained stress-induced effects. They had gastric ulcers, colitis, enlarged adrenal glands, and extensive degeneration of neurons in their hippocampus. Subsequent studies suggest that it is the direct effects of cortisol that damage the hippocampus. These effects of cortisol and stress resemble the effects of aging on the brain. Indeed, research has clearly shown that chronic stress causes premature aging of the brain.

In humans, exposure to the horrors of combat, sexual abuse, and other types of extreme violence can lead to Post Traumatic Stress Disorder, with symptoms of heightened anxiety, memory disturbances, and intrusive thoughts. Imaging studies have consistently found degenerative changes in the brains of victims, particularly in the hippocampus.

"NEUROSCIENCE - Exploring the Brain" 4th Edition.

Mark F. BEARn(Ph.D.), Barry W. CONNORS (Ph.D.), Micheal A. PARADISO(Ph.D.)

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