Sport helped to get rid of traumatic and intrusive memories
The mice that ran in the wheel formed new nerve cells and rearranged neural circuits in the hippocampus, the area of the brain where memories are formed. This allowed the animals to forget the fear they had experienced and to stop being dependent on drugs.
Post-traumatic stress disorder (PTSD) is a mental illness that can occur in people who have experienced a traumatic event, such as a natural disaster, car accident, or assault. This disorder is associated with vivid and sometimes intrusive memories that cause a person to avoid places and people that are associated with difficult moments in the past. PTSD is commonly treated with psychotherapy and medication, including antidepressants, but not all people can cope with these methods.
Researchers from Kyushu University (Japan), the University of Toronto (Canada) and the Hospital for Children (Canada) conducted an experiment, the results of which may become the basis for a new method of treating PTSD and drug addiction. They found out that sports activities trigger the formation of new neurons in the brain and subsequent reorganisation of neuronal circuits. This helps to forget traumatic or addiction-related experiences. The corresponding scientific paper was published by the journal Nature.
"Neurogenesis (formation of new neurons. - Editor's note) is important not only for the formation of memories, but also for getting rid of them. We believe this is because when new neurons integrate into neural circuits, new connections are formed. And old connections are lost, impairing the ability to recover memories," the study authors explained.
As part of the experiment, the scientists subjected the mice to two strong electric shocks. One shock was in a brightly lit white box, the second - in a dark box. After the second shock, the mice showed behaviour resembling symptoms of PTSD. It persisted a month later: the animals could not enter the dark chamber where they had encountered the electric shock, and also avoided similar dark spaces.
Next, the mice that had experienced two electric shocks were divided into two groups. One group was given a treadmill wheel and allowed to use it freely. Four weeks later, the hippocampus of the mice that exercised on the wheel had more new neurons. At the same time, the behaviours characteristic of PTSD were not as pronounced as in the animals without exercise. "Training" on the wheel before the second shock also affected the condition of the mice: some behaviours resembling PTSD symptoms did not develop.
To understand whether the positive effect of exercise is really due to increased neurogenesis and rearrangement of neuronal circuits in the hippocampus rather than other factors, the researchers tried to influence the formation of new nerve cells in the hippocampus by two genetic methods. In both cases, the mice had reduced PTSD-like symptoms and it took the animals less time to forget the fear. However, the effect was weaker than after treadmill exercise, and anxiety levels did not decrease.
The scientists also investigated whether enhanced neurogenesis and subsequent hippocampal remodelling can help with substance use disorders. Memory plays an important role in combating these, as memories of places and environments in which a person used the drug can trigger strong cravings for the substance.
The mice were placed in a cage with two "rooms". In one of them, the animals were given saline solution, and in the second, cocaine. When the mice were allowed to freely choose which part of the cage to be in, they spent more time in the "room" with cocaine.
The researchers again used exercise and genetic techniques to enhance the formation of new neurons and rearrange the hippocampus. As a result, the mice stopped choosing the room with cocaine. This means that the connection between a certain part of the cell and the drug was erased in the animals' memory.
In the future, scientists plan to develop a drug to stimulate neurogenesis or hippocampal rearrangement. Such a drug could be a potential remedy for PTSD and drug addiction. But the research team considers the most important result to be the finding that exercise is highly effective in combating these diseases.