There is one more reason to not flirt with stress. A team of researchers has found that stress seems to have a negative effect on the learning of movements — at least in mice.
In their study at the University of Bonn, the researchers found that the neurons of rodents lose some of their contact with other neurons after stress. The animals also developed motor deficits. The results may be useful for earlier diagnosis and improved therapy of stress-related diseases such as depression. They also document that stress leaves traces in the brain — possibly permanent ones. The study is published in the journal Translational Psychiatry.
Chronically stressed people often show abnormalities in their motor skills, such as poorer fine motor control. However, how these symptoms occur has hardly been studied so far. "We investigated this question in our study," explained Prof. Dr. Valentin Stein from the Institute of Physiology II at the University of Bonn.
The researchers used mice as experimental animals, some of which they exposed to a stressful situation for a few days. Meanwhile, they used a special microscopy method to take pictures of the rodents' brains. They focused on parts of the cerebral cortex responsible for motor control and learning new movements.
"With our method, it is possible to observe one and the same neuron at different points in time," says Dr. Anne-Kathrin Gellner, a physician at the Department of Psychiatry and Psychotherapy at Bonn University Hospital. "We can therefore see whether and how it changes as a result of
stress."
In fact, the researchers came across a conspicuous feature: after the stressful situation, the neurons studied lost some of their synapses — these are the contacts to other nerve cells. During learning processes, new synapses are usually formed or existing ones are strengthened. Instead, the stressed rodents lost up to 15 percent of their contacts.
At the same time, the animals developed motor learning deficits. For example, they had to try to grasp a food pellet with one paw and transport it into their mouths. In the wild, mice use both paws to do this, so they had to relearn this skill. The non-stressed control group achieved a success rate of 30 percent after five days. The stressed rodents, however, only managed to take the food in every tenth attempt.
Mice vary in their sensitivity to stress. Some of them hardly develop any abnormalities after a few days of stress — they are considered resilient. Surprisingly, these robust animals had similar difficulties as their more sensitive peers in learning to grasp with one hand. "It is, therefore, possible that motor tests are very suitable for detecting stress-related disorders such as depression before other symptoms become apparent," said Prof. Valentin Stein.
The research group also examined the fluid that washes around the brain and spinal cord. They found certain proteins that can normally be detected there in neurodegenerative diseases such as Parkinson's or Alzheimer's. "We, therefore, believe that stress-related psychiatric diseases such as depression are also associated with the degradation of neurons," said Dr. Gellner. "Accordingly, long-term stress — to which children are increasingly exposed — can potentially cause serious damage to the brain."