Evolution and humans: brain plasticity ; neurogenesis (Evolution)

by David Turell @, Tuesday, March 26, 2019, 14:30 (1883 days ago) @ David Turell

New evidence, but disputed, that the hippocampus grow new neurons in adults:


"New neurons develop in the brains of healthy adult humans, but neurogenesis is severely diminished in the brains of Alzheimer’s disease patients no matter their age, researchers report today (March 26) in Nature Medicine.

“'This is the first really strong evidence showing that neurogenesis is reduced in human Alzheimer’s disease patients,” Xinyu Zhao, a neurobiologist at the University of Wisconsin-Madison who was not involved in the study, tells The Scientist. Perhaps, the authors suggest, finding a way to promote neurogenesis in these patients could help in treating Alzheimer’s disease.


"The results show that neurogenesis does decrease moderately with age. But the number of immature neurons in healthy people appears to be consistently higher than the number found in patients with Alzheimer’s disease, regardless of their age. These patients typically had tens of thousands fewer immature neurons compared with healthy subjects and the loss of cells progressed with the severity of the disease, the team found.

"Not everyone is convinced by the results. In an email to The Scientist, Shawn Sorrells, a neuroscientist at the University of Pittsburgh and a coauthor of last year’s study finding no evidence of adult human neurogenesis, writes, “accurately identifying newborn neurons is a complicated endeavor requiring multiple lines of evidence to rule out alternative explanations, none of which are presented in this study.” The cells’ appearance and protein profiles, he notes, suggest they are “actually a distinct set of mature hippocampal neurons that have been there since childhood.”

"Zhao disagrees and says the new study is actually the first to provide a clear view of the maturation of newly developing neurons in the human adult brain. In rodent models, scientists have shown that in addition to DCX, developing neurons produce a calcium-binding protein called CR when they are less mature and one called CB when they are a little farther along in their development. In the new study, Llorens-Martín and her colleagues used a labeling technique to identify the cells expressing both DCX and CR and those expressing both DCX and CB and then tracked where they existed in a part of the hippocampus called the subgranular zone. The cells expressing DCX and CR were located at the border of this part of the hippocampus and had smaller cell bodies and were more elongated, characteristic of less mature cells. Cells labeled for DCX and CB were located deeper in the dentate gyrus and had more of an oval shape, indicating they were more mature.

"Tracing the cells this way is important to show for certain that they are maturing into new neurons, Maura Boldrini, a neurobiologist at Columbia University who was not involved in the new study, tells The Scientist. A criticism of past experiments has been that the neurons may be transforming into some other types of cells, but the new work clearly shows the immature cells are becoming actual neurons. Boldrini was a coauthor of the 2018 study providing evidence of neurogenesis in adult humans."

Comment: Evidence seems to be stronger that human adults make new neurons in the memory area of the brain.

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