A recent study has found that not only the signals sent from the stomach during meals but also the taste of food perceived by the tongue, play a role in regulating appetite.
Researchers at the Kavli Institute for Fundamental Neuroscience at the University of California, San Francisco (UCSF), revealed in a paper published in the international academic journal ‘Nature Metabolism’ on the 23rd of last month, “The taste that attracts us to food activates the eating behavior control circuit in the tail brainstem, controlling the speed and amount of food consumption.”
Appetite is controlled by a ‘new signal’ when eating orally, not from the stomach
The research team studied the activity of ‘Prolactin Releasing Hormone’ (PRLH) neurons and ‘Preproglucagon’ (GCG) neurons, known to play an important role in food intake, in the ‘caudal nucleus of the solitary tract’ (cNTS), a brainstem area where we feel fullness from food.
PRLH neurons have the function of suppressing eating behavior, and GCG neurons produce ‘Glucagon-like peptide-1’ (GLP-1), an appetite-suppressing hormone. GLP-1 is a hormone used in weight loss drugs such as Wegovy, which have swept the world.
The researchers developed a technology that can film while the mice are active and used it to examine the response of neurons when the mice eat food orally and when it is put into the stomach.
As a result, when food was directly put into the mice’s stomach, it was found that PRLH neurons were continuously activated by the nutritional signals sent from the gastrointestinal tract. On the other hand, when eating orally, this signal was absent, and the activation response of PRLH neurons decreased significantly. Instead, a new activity pattern was shown where appetite is controlled by signals coming from the mouth.
Truong Li, the first author of the paper, said, “It is surprising that brainstem cells are activated by perception of taste,” and added, “This shows that there are other components in the appetite control system besides fullness.”
‘Feeling full’ even when air is injected into the stomach
Meanwhile, it was found that neurons that give a ‘feeling of fullness’ are activated not only by food but also when air is injected into the stomach. The research team interpreted this as suggesting that these neurons gauge food consumption through the volume of the stomach.
The research team is considering that the activity of PRLH neurons affects ‘how delicious food is perceived.’ This is similar to the phenomenon where people’s appetite decreases after eating food to the point of feeling full.
In addition, GCG neurons were found to be activated by signals coming from the intestine, tracking the amount of food consumed and maintaining fullness for tens of minutes. Professor Zachary Knight, who led the research, said, “We have discovered a structure in the brainstem that uses signals coming from the mouth and much later, from the intestine, to regulate the speed and amount of eating. This provides a new framework for understanding the mechanism of meal regulation.”
Professor Chen Ran (Neuroscience) of Harvard University told Nature, “The research contains original insights on how taste regulates appetite,” and added, “This neural circuit is also found similarly in humans, so the research results can be applied to humans.”
By. Sung Wook Kim
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