We manufacture new brain cells throughout life, but less when we are afflicted with Alzheimer's

In a new article in the journal Nature Medicine, it appears that neurogenesis, the process in which new brain cells are created, continues until we are nineteen years old. Reducing this production can be a sign of Alzheimer's disease.

If we find a reduction, we may be able to diagnose Alzheimer's disease earlier than before and more easily identify people at risk. The researchers can then start with different exercises to increase the production of brain cells.

This work is the latest in a field that has shared brain researchers for decades: some believe that the maximum number of brain cells was reached by the end of adolescence, others claim that new brain cells are created for life.

To get closer to the answer, Spanish researchers have launched a series of tests on human brain tissue, with and without Alzheimer's disease. They treated the fabric with new methods so that the quality is better preserved than before. Nerve cells also appear more clearly than in previous tests.

The treatment of the fabric is crucial

María Llorens-Martín is a neurologist at the Autonomous University of Madrid. In collaboration with her research colleagues, she discovered that all brains contained neonatal neurons, but that their numbers gradually decreased with age. They used the brains of 13 donors aged 43 to 87 years.

Between the ages of 40 and 70, the number of newborn neurons in the part of the brain studied decreased from 40,000 to 30,000 neurons per cubic millimeter. Thus, the production of brain cells did not stop as previously thought, but was reduced.

The new cells are born in the part of the brain called dentate gyrus. It is part of the seahorse that plays a central role in learning and memory. The gradual decline of new brain cells seems to go hand in hand with the cognitive disorders that occur during aging.

In the study, the researchers suggest that the reason researchers did not agree on whether the brains of adults were producing healthy neurons was that brain tissue management was crucial for visualizing these brain cells. brain cells.

"In the same brain, we can detect many immature neurons or no immature neurons depending on the treatment of the tissue," says Llorens-Martin in The Guardian online newspaper.

Brain cell formation decreases in Alzheimer's disease

After studying healthy brain tissue, researchers continued to examine the brains of people with Alzheimer's disease before they died. This time, the researchers analyzed the brain tissue of 45 patients aged 52 to 97 years.

Alzheimer's donors have also shown signs of neurogenesis or brain cell formation, but not as much as in the healthy brain. Even at the very beginning of the disease, the brain had only half as many new neurons as healthy ones.

"This is very important for research on Alzheimer's because the number of cells you detect in healthy individuals is always greater than the number detected in patients with the diagnosis of Alzheimer's, regardless of their age," says Llorens-Martín.

There is therefore some independent mechanism, different from body aging, which reduces the formation of brain cells.

Optimal method

Jørgen Sugar is a postdoctoral researcher at the Kavli Institute of Neuroscience at NTNU in Trondheim. He says the results are very interesting.

– There are many studies on cell creation and many studies on Alzheimer's disease. This is the first study that associates a decline in the number of newborn cells to the development of Alzheimer's disease, he told forskning.no.

It highlights the importance of properly treating brain tissue.

– We notice it in the laboratory. Perhaps the most important thing when we do experiments is to treat the tissue properly until we put it under the microscope, he says.

The key to maintaining the quality of the fabric is to repair it or keep it as quickly as possible.

Sugar says that it is often time for a patient to die until his brain is preserved. It is then put in the preservative formalin. The researchers were able to do this faster, so the quality of the tissue was better than before. He added that researchers have avoided freezing the brain, which can go beyond the quality of tissue.

– I'm very familiar with the world of rats and mice, but the process is much simpler. We have the opportunity to quickly put the brain in formalin. Of course, in humans, it's different, he says.

According to Sugar, researchers have therefore found an optimal method for storing and then using the tissue, even in humans. Then they also have the opportunity to see the brain cells clearly and clearly. He says that's why they can detect brain cell formation and a reduction of it just now.

The results are the most important for the future

– The problem of Alzheimer's disease, is that the disease starts well before one presents the symptoms and that one poses the diagnosis. So when you make the diagnosis, it's too late to reverse or fix it, he says.

The researchers therefore want to examine the brain to see if neurogenesis is slowing down so that it can be shown that Alzheimer's disease is on alert.

– They report that a fall in neurogenesis occurs even in young patients with Alzheimer's disease and that she can use it optimally as an early marker. They believe that this may be one of the very first clues we have about a person who will develop Alzheimer's in the future, says Sugar.

The researchers say nothing about how such a brain scanner, intended to detect Alzheimer's disease, should take place.

– I do not see how that would happen today. We currently have no way to analyze the brain to see if newborn cells are formed or not. So, the results will not revolutionize Alzheimer's diagnoses today, but they are hopefully important in the future, if we find the technology to detect it in a living person, says Sugar.

Cause or effect?

If we detect a reduction in neurogenesis, there will surely be a desire to stimulate the production of new brain cells. So, how do we do it, it's not so good to say, says Sugar. The training, socialization and cognitive stimuli can nevertheless be positive.

– How can we understand Alzheimer's disease? Here I have the feeling that this article is accompanied by many I have never thought that the neurogenesis in this part of the brain may be related to the onset of Alzheimer's disease, says- he.

Sugar also says that it's interesting to know if a reduction in brain cell formation is the cause of the diagnosis of Alzheimer's disease or if it's its effect.

– There is nothing said in the article, but it is a question that arises, concludes Sugar.

reference:

María Llorens-Martín et al: The neurogenesis of the hippocampus in adults is abundant in neurologically healthy subjects and decreases significantly in patients with Alzheimer's disease, Nature Medicine, March 25, 2019, doi: https://www.nature.com/articles/s41591-019-0375-9