Infection in old age can trigger an overly strong immune response that disrupts the hippocampus, an area of the brain critical for remembering new information. This is the conclusion drawn in a series of papers published by a group led by Susan Patterson of Temple University in the United States. The latest study was published on May 28, 2018 in the journal eNeuro.
“With the onset of old age, our memory does not always fade away gradually. It often happens that older people who have recently felt well, having survived a serious [infectious] illness, abruptly lose their ability to think clearly and fall into hallucinations. Even if this attack of delirium passes, such crises significantly increase the likelihood of developing dementia, "says Patterson, quoted by RIA Novosti.
Such conditions are much less well understood than ordinary aging or "classic" pathologies like Alzheimer's and Parkinson's. The researchers decided to close this gap whenever possible.
The experimental animals in the experiment were rats from a genetic line, whose representatives are not prone to pronounced cognitive impairment either in youth or in old age. As specifies the publication Science Daily, scientists infected them with some strains of the common E. coli Escherichia coli. The experiment was carried out on rodents three months and two years old. The last age for rats is old.
Elderly rodents were literally maddened by the infection. They lost the ability to remember where the exit from the maze was, bumped into walls and generally behaved strangely.
This state lasted from 8 to 14 days. The researchers found that it was caused by an overly strong immune response. A complex chain of biochemical reactions led to a decrease in the level of brain neurotrophic factor. This protein plays an important role in the functioning of the nervous system. In particular, the hippocampus needs it to convert short-term memories into long-term ones. The fact is that the lack of this protein interferes with the normal formation of new interneuronal connections.
In young rodents, a decrease in the level of this substance was also observed, but not as strong and more short-term. Within a day, everything was back to normal.
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Although the mental functions of the elderly rats recovered over time, the study revealed irreversible changes in their hippocampus. It is possible that it is this type of transformation that increases the risk of senile dementia in older people who have had an infection.
The authors hope that in the future, their research will help create drugs that block the production of unwanted substances during infection and prevent brain damage.
Anatoly Glyantsev