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Neuron creation in brain’s memory centre stops after childhood

neuron brain neurogenesis hippocampus dentate gyrus

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#1 APBT

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Posted 10 March 2018 - 02:34 AM


https://www.nature.c...586-018-02812-6

 

 

Every day, the human hippocampus, a brain region involved in learning and memory, creates hundreds of new nerve cells — or so scientists thought. Now, results from a study could upend this long-standing idea. A team of researchers has found that the birth of neurons in this region seems to stop once we become adults.

A few years ago, the group looked at a well-preserved adult brain sample and spotted a few young neurons in several regions, but none in the hippocampus. So they decided to analyse hippocampus samples from dozens of donors, ranging from fetuses to people in their 60s and 70s. They concluded that the number of new hippocampal neurons starts to dwindle after birth and drops to near zero in adulthood. The results1, published in Nature on 7 March, are already raising controversy.

If confirmed, the findings would be a “huge blow” not only to scientists in the field, but also to people with certain brain disorders, says Ludwig Aigner, a neuroscientist at Paracelsus Medical University in Salzburg, Austria. This is because researchers had hoped to harness the brain’s ability to generate new neurons to treat neurodegenerative diseases such as Alzheimer’s and Parkinson’s, he says.

Preservation problems

But Aigner and other neuroscientists are not fully persuaded by the findings, which contradict multiple lines of evidence that the hippocampus keeps producing neurons throughout a person’s life. “I wouldn’t close the books on [that],” says neuroscientist Heather Cameron of the US National Institute of Mental Health in Bethesda, Maryland.

Over the past 20 years, scientists have found that neuron creation in the hippocampi of people and animals such as rodents tends to decrease with age, but a few newborn nerve cells are present even in the oldest individuals2.

However, when a team of neuroscientists led by Arturo Alvarez-Buylla at the University of California, San Francisco, looked at thin hippocampus sections from 37 donors of different ages who had died in various ways, they spotted young neurons only in fetuses and children. The oldest sample in which the researchers still saw a few immature nerve cells belonged to a 13-year-old. “In the 18-year-old’s sample, we just don’t find any,” Alvarez-Buylla says.

But the findings are not so clear-cut, warns Gerd Kempermann, a neuroscientist at the Technical University of Dresden in Germany. Just because the scientists don’t see new neurons doesn’t mean they aren’t there, he says. Alvarez-Buylla and his colleagues used marker molecules to tag immature in brain samples that had been collected and prepared for analysis within 48 hours after an individual died. Whether these markers can reliably tag young neurons depends a lot on the quality of the tissue, which is influenced by how soon after death the samples are treated to keep them from decaying, Kempermann says.

The chemicals used to preserve and stabilize the tissue samples might also further prevent the markers from binding to their target cells, says neuroscientist Paul Lucassen at the University of Amsterdam. “It’s very hard to get these markers to work in these conditions.”

Making waves

Although Alvarez-Buylla acknowledges the limitations of the study, he stands by its results. “We have done our homework and studied many samples of different ages,” he says. His team also analysed hippocampi from 22 patients treated for epilepsy, who had had parts of their brains removed and prepared for analysis on the spot. In those cases, the researchers didn’t find any young hippocampal neurons in people older than 11.

Some neuroscientists also caution that the physical and mental states of those who donated their brain for the analysis is important. “How much exercise did they have? Were they bedridden? Were they depressed because of the disease they had?” asks Fred Gage, a neuroscientist at the Salk Institute for Biological Studies in La Jolla, California. This is relevant, he says, because factors such as exercise, stress and disease influence the number of new hippocampal neurons generated3.

Despite these concerns, the study is likely to have some immediate effects on the field, says Sandrine Thuret, a neuroscientist at King’s College London. It could encourage others in the field to look for young neurons in the adult hippocampus, and push researchers to develop better markers for tracking the formation of neurons in living organisms, she says. At the very least, Thuret adds, the study’s conclusions are set to stir up debate.

 

 

 

Abstract

New neurons continue to be generated in the subgranular zone of the dentate gyrus of the adult mammalian hippocampus1,2,3,4,5. This process has been linked to learning and memory, stress and exercise, and is thought to be altered in neurological disease6,7,8,9,10. In humans, some studies have suggested that hundreds of new neurons are added to the adult dentate gyrus every day11, whereas other studies find many fewer putative new neurons12,13,14. Despite these discrepancies, it is generally believed that the adult human hippocampus continues to generate new neurons. Here we show that a defined population of progenitor cells does not coalesce in the subgranular zone during human fetal or postnatal development. We also find that the number of proliferating progenitors and young neurons in the dentate gyrus declines sharply during the first year of life and only a few isolated young neurons are observed by 7 and 13 years of age. In adult patients with epilepsy and healthy adults (18–77 years; n = 17 post-mortem samples from controls; n = 12 surgical resection samples from patients with epilepsy), young neurons were not detected in the dentate gyrus. In the monkey (Macaca mulatta) hippocampus, proliferation of neurons in the subgranular zone was found in early postnatal life, but this diminished during juvenile development as neurogenesis decreased. We conclude that recruitment of young neurons to the primate hippocampus decreases rapidly during the first years of life, and that neurogenesis in the dentate gyrus does not continue, or is extremely rare, in adult humans. The early decline in hippocampal neurogenesis raises questions about how the function of the dentate gyrus differs between humans and other species in which adult hippocampal neurogenesis is preserved.

https://www.nature.c...les/nature25975

 



#2 recon

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Posted 11 March 2018 - 12:35 AM

I read this the other day. This is quite a disappointing news.
  • Agree x 1

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#3 Daniel Cooper

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Posted 11 March 2018 - 06:17 PM

Aren't some anti-depressants alleged to stimulate hippocampal neurogensis?  

 

What evidence was used to make that claim?

 

If I'm not mistaken you can see hippocampal volume increase on MRIs after dosing various anti-depressants (Trazodone being one I looked at a study of just the other day).

 

 

 

 


Edited by Daniel Cooper, 11 March 2018 - 06:21 PM.

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#4 Turnbuckle

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Posted 12 March 2018 - 01:28 PM

Aren't some anti-depressants alleged to stimulate hippocampal neurogensis?  

 

What evidence was used to make that claim?

 

If I'm not mistaken you can see hippocampal volume increase on MRIs after dosing various anti-depressants (Trazodone being one I looked at a study of just the other day).

 

Precisely--

 

Adult hippocampal neurogenesis: Is it the alpha and omega of antidepressant action?

It is now well established that all clinically available antidepressants share a common aptitude: they increase the production of adult-generated neurons in the dentate gyrus of the hippocampus. This was first observed in animal models and subsequently in human populations, highlighting the clinical relevance of this finding.

https://www.ncbi.nlm.../?term=28800956

 


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#5 Rocket

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Posted 12 March 2018 - 02:06 PM

Hasn't this been known for decades???



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#6 Daniel Cooper

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Posted 12 March 2018 - 06:16 PM

Hasn't this been known for decades???

 

 

I believe so.  But perhaps that study shows that in the absence of antidepressants hippocampal neurogenisis does not occur, though I find that a little hard to believe.  In fact, I find it hard to believe that if those autopsies were done in the Western world that at least some of those people weren't on ADs unless they specifically excluded them.







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