Scientists talked about the impact of brain injury on stress response
Traumatic brain injury can alter the subsequent brain response to stress. Researchers from Spain and the United States found increased inflammatory processes and behavioral changes in mice after stressful exposure, which was preceded by trauma. How damage can affect the sensitivity of the brain to new loads and what role immune cells play in this is described in the Izvestia article.
How the effects of injury were studied
The study was conducted by an international team led by specialists from the University of Malaga in collaboration with the Ohio State University Wexner Medical Center. The experiments were performed on adult male mice.
14 days after the simulation of traumatic brain injury, the animals were subjected to two hours of acute social stress. It was created in conditions of aggression and social defeat, a situation in which an animal finds itself in a subordinate position when confronted with an aggressive opponent.
The scientists studied changes in the hypothalamus, a small area at the base of the brain that connects the nervous and endocrine systems and is involved in managing the body's stress response.
After a combination of trauma and stress, the researchers identified increased molecular signs of an inflammatory response in the hypothalamus and pituitary gland. At the same time, the shape and complexity of the structure of microglial cells changed. In behavioral tests, injured mice avoided new objects more strongly after stress. The authors describe the reactions found as behaviors resembling anxiety and avoidance.
How immune cells can keep a trace of injury
According to the co-author of the study, Maria Dolores Lopez, a scientist at the University of Malaga, the effects of damage can persist at the cellular and molecular levels and manifest themselves with subsequent stress.
"A previous traumatic brain injury can cause subtle, virtually undetectable changes at the cellular and molecular levels that persist over time and may change behavior in the future when new stressful situations arise," the researcher explained.
The team paid special attention to microglia, the immune cells of the brain involved in inflammation after injury. The researchers suggest that the damage may increase their sensitivity to subsequent impacts. Then the new stress is accompanied by a more pronounced inflammatory reaction.
In the work report, this possible mechanism is described as the acquisition of immune memory. In this case, we are talking about changing the reaction of cells to a new exposure, and not about preserving memories of the event.
"This is reflected in changes in cell morphology and an increase in the production of inflammatory mediators," Lopez said.
At the same time, the authors clarify in the scientific article: the results obtained do not directly prove that trauma causes such a preconfiguration of microglia. They support the assumption of an altered hypothalamic stress response, but the mechanism itself requires further verification.
Why were the brain changes not accompanied by a stronger growth hormone
An increased inflammatory response did not mean an increase in all components of the stress response. In the experiments, the scientists measured corticosterone in the blood, a hormone involved in the stress response of mice.
Ten minutes after the end of the stress exposure, his level increased, but the previous injury did not increase this growth. Thus, cellular and molecular changes in the brain were not accompanied by an additional increase in the measured hormonal response at this moment.
This clarification limits the conclusion: the study does not show that the hormonal response remains the same at all stages. The result refers to a specific measurement time after stress.
What do the results mean for further research?
The work helps to study how trauma can affect the subsequent vulnerability of the brain. The hypothalamus, inflammatory processes and microglial changes, which were accompanied by the peculiarities of animal behavior, became the focus of attention.
However, the results were obtained only in male mice in a specific experimental model. They cannot be directly transferred to humans or considered as proof that an anxiety disorder necessarily develops after any head injury.
The study also did not test ways to treat these changes. For further work, it is important to establish how long they persist, what exactly determines the altered stress response, and whether a comparable mechanism operates in humans.
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