At least in mice, stress appears to have a deleterious influence on movement learning. According to the findings of a recent study. According to the study, following stress, rat neurons lose part of their contacts with other neurons. Motor impairments appeared in the animals as well. The findings could lead to early detection and better treatment of stress-related disorders, including depression. They also show that stress leaves signs in the brain, which may be permanent.
This is the finding of a recent study conducted at the University of Bonn. According to the study, following stress, rat neurons lose part of their contacts with other neurons. Motor impairments appeared in the animals as well. The findings could lead to early detection and better treatment of stress-related disorders, including depression. They also show that stress leaves signs in the brain, which may be permanent. The findings were published in the journal Translational Psychiatry.
People who are chronically stressed frequently have irregularities in their motor skills, such as weaker fine motor control. However, the mechanism by which these symptoms manifest has received little attention thus far. “We addressed this subject in our study,” explains Prof. Dr. Valentin Stein of the University of Bonn’s Institute of Physiology II.
With our technology, we can examine the same neuron at multiple periods in time. As a result, we can see whether and how it changes as a result of stress.
Dr. Anne-Kathrin Gellner
The mice were utilized as experimental animals, with some of them subjected to a stressful condition for a few days. Meanwhile, they photographed the rats’ brains using an unique microscope technique. They concentrated on areas of the cerebral cortex that are involved in motor control and learning new movements.
“With our technology, we can examine the same neuron at multiple periods in time,” explains Dr. Anne-Kathrin Gellner of Bonn University Hospital’s Department of Psychiatry and Psychotherapy. “As a result, we can see whether and how it changes as a result of stress.”
Stressed mice lose synapses
In fact, the researchers discovered an interesting feature: following the stressful experience, the neurons tested lost some of their synapses (contacts with other nerve cells). New synapses are frequently created or existing ones are strengthened during learning processes. The stressed rodents, on the other hand, lost up to 15% of their connections.
Simultaneously, the animals exhibited motor learning deficiencies. They had to, for example, try to capture a food pellet with one paw and bring it into their mouths. Mice in the wild do this with both paws, thus they had to unlearn this ability. After five days, the non-stressed control group had a success rate of 30%. The stressed rodents, however, only managed to take the food in every tenth attempt.
The susceptibility of mice to stress varies. Some of them are considered resilient because they barely acquire any abnormalities after a few days of stress. Surprisingly, these tough animals showed identical difficulties learning to grasp with one hand as their more delicate counterparts. “It is thus feasible that motor tests are particularly suitable for diagnosing stress-related diseases such as depression before other symptoms appear,” Prof. Valentin Stein hopes.
Even resilient animals are not immune
Furthermore, even in resilient animals, the number of synapses dropped following the stress event. The injured neurons, unlike their stress-sensitive counterparts, recovered: after one and a half weeks, the number of synapses was comparable to that before the stress event and comparable to that in non-stressed control animals. “Nevertheless, it may well be that psychological stress also leaves permanent traces on them if it is too long or too frequent,” worries Stein, who is also a member of the Transdisciplinary Research Area (TRA) “Life and Health.”
The researchers have also discovered what causes synaptic loss: Certain immune cells, known as microglia, were activated in the brains of rodents. They are phagocytes and may digest infections or faulty cells, among other things. It is likely that stress “turns them on” and causes them to assault the contact areas.
The researchers also looked at the fluid that circulates around the brain and spinal cord. They discovered proteins that are generally found in neurodegenerative illnesses such as Parkinson’s and Alzheimer’s. “As a result, we believe that stress-related psychiatric illnesses like depression are also associated with neurodegeneration,” Dr. Gellner explains. “As a result, long-term stress – to which youngsters are increasingly exposed – has the potential to cause catastrophic brain damage.”
