According to a new study published on the 7th March 2018 in the reputable journal Nature, the past 20 years of research could be called into question in relation to the production of new neurons in adulthood.
Do adults produce new neurons?
First of all, let’s define neurogenesis. According to Wikipedia, neurogenesis is the process by which neurons are generated from neural stem cells.
Up until now, studies on neurogenesis, or the production of neurons, showed that we create new neurons up until we die, but this study, produced by neuroscience researchers from the University of California, San Francisco (UCSF), could prove otherwise.
Arturo Alvarez Buylly, a professor in the department of neurological surgery in UCSF, and his team are responsible for this discovery. Having analysed post-mortem brain tissue and brain tissue in postoperative patients, they observed the presence of new neurons in foetuses, children and adolescents, but not in adults.
The Pasteur Institute remains cautious about the conclusions of this study, as they contradict those of several previous studies showing that adults continue to produce new neurons. According to the results of a study published in 1998 in the journal Nature, Peter Eriksson and Fred H. Gage confirmed that “the human hippocampus maintains its capacity to generate neurons throughout its life”.
In 2000, the same researchers, Peter Eriksson and Fred Gage, produced another study which showed that new neurons could be generated in the dentate gyrus (located in the cerebral cortex, along the hippocampus) up until the age of 72. In 2013, researchers from the Karolinska Institute in Sweden confirmed that in adult humans, 700 new neurons are formed every day in the hippocampus, a rate which reduces slightly with age.
So will 2018 be marked by this new study which contradicts the results obtained by other researchers? The UCSF team collected post-mortem and post-operative samples from the hippocampus of 59 people, including foetuses at 14 weeks gestation up to adults of 77 years of age. The samples were treated with classic antibody markers, responsible for revealing neuronal progenitor cells (future neurons) and young neurons.
In adults, the marked samples did not present with either future or young neurons in the dentate gyrus of the hippocampus, normally thought of as the home of neurogenesis. The researchers established neuronal density per millimeter squared, which varied with age:
- the density of young neurons is around 1618 neurons per millimeter squared at birth
- this drops to 12 per millimeter squared at the age of 7
- and then to 2 young neurons per millimeter squared at 13 years of age.
The researchers found no trace of young neurons in the brain samples of people over 18 years old. None of the 13 people over the age of 11 presented with new cerebral cells.
Although this study contradicts previous research on the matter, its results are similar to those of a study published in 2016 by Greg Sutherland (from the University of Syndey). He analysed human tissue from 23 deceased patients, from 0 to 59 years of age, and he equally concluded that there was a marked decline in the production of neurons with age.
The Pasteur Institute remain cautious about the results of this study published on the 7th March 2018, particularly due to the techniques used: the relevance of the markers and the sampling used.