A study demonstrates new neurons are formed in the dentate gyrus region throughout adult life. This mechanism, called adult hippocampal neurogenesis, is damaged in patients with Alzheimer’s disease.

Most neurons are already in the brain at the time of birth. However, the formation of new neurons in the adult brain can occur in certain regions, such as the hippocampus. Although previous work has established that this phenomenon occurs in rodents and other vertebrate species, this process in humans has been questioned by recent studies, and scientists haven’t reached to a clear conclusion.

Now, a study led by María Llorens-Martín , a scientist at the Severo Ochoa Molecular Biology Center (CBM-CSIC), shows that a region of the human brain known as dentate gyrus  produces new neurons in humans until the ninth decade of life. The results, from the analysis of tissue samples from 58 human participants, have been published in Nature Medicine.

The authors found that, although there is some decline associated with age, neurogenesis in the hippocampus of the adult human brain can be observed throughout life, at least until 87 years of age. However, they observed that it decreases drastically in patients with Alzheimer’s disease.

“The way in which brain tissue is processed affects in a critical way the detection of immature neurons in the human hippocampus,” explains Llorens-Martín. “There are still many things to know, but we hope to contribute to the advancement of knowledge on this process.”

The birth of new neurons in the adult human brain is of great importance for modern medicine, since this special type of neurons generated in the hippocampus participates in the acquisition of new memories and learning in mice.

“Our study provides data unknown so far on how these cells mature in the human dentate gyrus, both during physiological and pathological aging in Alzheimer’s,” adds the Spanish researcher.

“There is still a long way to be able to apply these results to the treatment of human beings, but the results obtained are encouraging since they show the existence of a dynamic population of cells that in other species of mammals have shown to be important for the regulation of memory,” Llorens-Martín emphasizes.

Application in Alzheimer’s

The study also compares the process of adult hippocampal neurogenesis in a group of 13 healthy individuals and 45 patients with Alzheimer’s disease.

The authors have discovered that the number of new neurons decreases drastically in the initial stages of the disease and continue decreasing progressively as the disease progresses.

“These findings are of great importance in neurodegenerative diseases and, specifically, in Alzheimer’s. In this sense, the early detection of a decrease in the generation of new neurons could be an early marker of the disease,” she says.

“If it were possible to increase the birth and maturation of the new neurons similarly to what is done in laboratory mice, new therapeutic possibilities could be opened that might be useful to alleviate or slow down the progression of this disease,” concludes Llorens-Martin.

Discrepancies with other investigations

This work analyzes in depth the causes of possible contradictory results found by different research groups.

The study shows that the chemical treatments to which it is necessary to submit samples of human brain tissue for further study affect critically the detection of the presence of immature neurons.

The authors point out that the discrepancies may be the result of differences in the methodologies used or in the quality of the tissue samples examined.

This analysis assesses whether factors such as tissue fixation techniques or delays in time between acquisition and tissue processing can affect the quality of histological staining, which is critical for the detection of new neurons.

The researchers showed that, after submitting samples obtained from the same subjects to different chemical treatments, very different cell numbers were observed. In addition, when such treatments were more aggressive or prolonged in time, the signal emitted by the new neurons disappeared completely.

 

Source: SINC