Ubiquitous Nutrients Suppress Appetite and Promote Movement





Summary: Ingested non-essential amino acids suppress appetite and promote movement in mouse models.

Source: ETH Zürich

In experiments with mice, researchers at ETH Zurich show that non-essential amino acids act as appetite suppressants and promote the urge to move.

Their research is published in Current biology and provides insight into the neural mechanism that controls this behavior.

Protein can suppress appetite, so a high-protein diet can help people lose weight. This is just one of the reasons why this type of diet has become increasingly popular in recent years. Working with mice, researchers at ETH Zurich have now revealed a new mechanism by which protein building blocks, amino acids, curb appetite. More specifically, these are the so-called non-essential amino acids.

Of the 21 amino acids our body needs, there are nine that it is unable to produce on its own. They are called essential amino acids. Because we must get them through our diet, they have long been the focus of nutritional research. The other 12 amino acids are considered non-essential. The body can produce them itself by modifying other molecules.

Shown in mice

It is known that essential and non-essential amino acids can suppress appetite. However, for non-essential amino acids, the mode of action had not yet been demonstrated in living organisms.

Today, a group of researchers led by Denis Burdakov, professor of neuroscience at ETH Zurich, showed for the first time in a living organism that non-essential amino acids influence the brain in ways that curb appetite. and promotes exercise.

The researchers first fed the mice either a mixture of various non-essential amino acids or a sugar solution with the same amount of calories (control group). Both groups of mice were then allowed to drink a milkshake, which they normally like.

While the control group drank large amounts, the mice that had been fed non-essential amino acids avoided their own. Instead, they circled their enclosure in search of alternative livelihoods.

Rooted in evolutionary history

Through additional experiments, the researchers were able to decode the underlying mechanism, in which the brain’s specialized nerve cells, orexin neurons, play the main role. Proteins that mice ingest through food are broken down in the gut into their amino acids, which then enter the bloodstream. From there, the blood carries them to the brain.

Orexin neurons in the hypothalamus have receptors that specifically recognize non-essential amino acids. In response, they initiate a neural circuit that produces the described behavioral changes.

This mechanism is probably rooted in evolutionary history. “Today we have sufficient access to all nutrients and we have plenty of time to eat. In prehistoric times, when this mechanism developed, this was probably not the case,” says Paulius Viskaitis , postdoctoral fellow in Burdakov’s group and lead author of the study.

This shows a diagram of the study
Protein can suppress appetite, so a high-protein diet can help people lose weight. Credit: The Researchers

“At the time, it was advantageous for individuals to spend only a short time on a food source that was composed primarily of non-essential amino acids.” If eating non-essential amino acids promotes the urge to move, the animal will seek out other food sources, which potentially contain more essential nutrients and are more important to the individual.

Viskaitis points out that the results are transferable to humans and other animals, as this mechanism affects a brain region that is very old in terms of evolutionary history and occurs in the same way in all mammals and many other vertebrates. .

Still, for people who want to lose weight, a diet that includes many non-essential amino acids in particular cannot be recommended at all levels, says Viskaitis. Nutritional recommendations should be made on an individual basis, and they should also take health aspects into account.

About this appetite research news

Author: Press office
Source: ETH Zürich
Contact: Press service – ETH Zurich
Picture: Image is in public domain

Original research: Free access.
“Ingested non-essential amino acids recruit orexin brain cells to suppress feeding in mice” by Paulius Viskaitis et al. Current biology


Abstract

See also

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Ingested nonessential amino acids recruit orexin brain cells to suppress feeding in mice

Strong points

  • Ingested non-essential amino acids (nAA) activate orexin cells
  • Optostimulation of nAAs or orexin cells increases exploration and reduces feeding
  • CCK-sensitive vagal afferents are not required for nAA effects
  • Ablation of orexin cells abolishes nAA modulation of feeding and exploration

Summary

Ingested nutrients are proposed to control mammalian behavior by modulating the activity of hypothalamic orexin/hypocretin (HON) neurons. Previous in vitro studies have shown that ubiquitous nutrients in the mammalian diet, such as nonessential amino acids (AA) and glucose, modulate HON in distinct ways. Glucose inhibits HON, while non-essential (but non-essential) AA activates HON. This last effect is particularly interesting because its purpose is unknown.

Here we show that ingestion of a dietary mixture of non-essential AAs activates HON and shifts the behavior from foraging to exploration.

These effects persisted despite the ablation of a key communication pathway between the neural gut and the brain, cholecystokinin-sensitive vagal afferents. The change in behavior induced by ingested non-essential AAs was recapitulated by targeted HON optostimulation and abolished in mice lacking HON.

Moreover, microstructure analysis of licking indicated that non-essential intragastric AA and HON optostimulation each reduce the size, but not the frequency, of eating episodes, thus implicating modulation of food palatability as a mechanism. power removal. Collectively, these results suggest that a key goal of HON activation by ingested nonessential AA is to suppress feeding and reinitiate foraging.

We propose and discuss possible evolutionary benefits of this, such as optimizing the stomach’s limited capacity for ingesting essential nutrients.




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