But with increasing age, the production of new neurons in the hippocampus decreases – in Alzheimer's patients more than in neurologically healthy people
Position of the hippocampus (red) in the human brain
© Center for Life Sciences Database, (CC BY-SA 2.1 JP), https://creativecommons.org/licenses/by-sa/2.1/jp/deed.en
Adults form new brain cells only in certain regions of the brain, such as the hippocampus, which is important for memory. Although the ability of neurogenesis to decrease with age, it remains intact throughout life, report researchers in the journal Nature Medicine. Their results are more reliable than the previous results, partially contradictory, because the processing of their tissue samples was performed immediately after removal and very smoothly. It has been found that Alzheimer's patients may still form new neurons, but to a much lesser extent than people of the same age without dementia. Therefore, accelerated neurogenesis may play an important role in the development of dementia. This could lead to new approaches to therapy.
"Even in neurologically healthy people over 80, we have identified thousands of immature neurons in the dentate gyrus, a part of the hippocampus," write the researchers around María Llorens-Martín of Severo Ochoa Molecular Biology Center in Madrid. In addition, there is evidence that disturbed neurogenesis could be a cause of memory impairment in Alzheimer's dementia. The scientists looked at brain tissue samples from 45 Alzheimer's patients who died between the ages of 52 and 97. Brains samples from 13 non-demented people aged 43 to 87 served as a comparison.
The researchers determined the number of immature neurons in the dentate gyrus as a measure of the development of new brain cells from adult stem cells. Specific cell characteristics, such as the protein duplacortin (DCX), which is produced only in progenitor cells and can no longer be detected in mature neurons, were used for this purpose. It was discovered that immature cells of different stages of development were present in all tissue samples. Their number was smaller, the oldest was the deceased. Compared with non-demented people, the rate at which the number of immature neurons decreased due to age was very accelerated in Alzheimer's patients. Fewer new cells developed or more cells died during maturation.
In previous studies, some groups of researchers in adult humans could show no or only weak neurogenesis. The cause of this discrepancy is probably methodological differences in tissue preparation, the authors explain. For example, the quality of staining used to identify immature neurons depends on pre-treatment of tissue samples and the speed with which they are processed after collection. From their findings, the researchers concluded that neurogenesis declines in the early stages of Alzheimer's disease – even before the typical plaques of the disease developed. If it were possible to reignite the production of new neurons, this could stop the progressive course of dementia.