The brain cells that control the speed at which mice eat and when they stop eating have been identified. Researchers say these findings could lead to a better understanding of human appetite.
Discovery of Brain Cells That Affect Eating Speed
Cells in the gut, called vagal nerves, have been found that sense the amount of food the mice have consumed and the nutrients they have ingested. The vagal nerves use electrical signals to transmit this information to a small area in the brainstem believed to influence when mice and humans stop eating. This area, known as the nucleus of the solitary tract, contains prolactin-releasing hormone (PRLH) cells and GCG cells. However, until now, studies had involved filling the stomachs of anesthetized mice with liquid food, making it unclear how these cells regulate appetite when the mice are awake.
Researchers’ Experiment to Understand Appetite Regulation
To answer this question, physiologist Zachary Knight at the University of California, San Francisco, and his colleagues implanted a light sensor in the brains of genetically modified mice such that PRLH cells emit a light signal when activated by electrical signals transmitted from other parts of the body. Knight and his team then injected a liquid food called Ensure – which contains a mixture of fats, proteins, sugars, vitamins, and minerals – into the intestines of these mice. Over a ten-minute period, the activation of the cells increased gradually with the amount of injected food. This activity peaked a few minutes after the injection stopped. Conversely, PRLH cells were not activated when the team injected saline into the mice’s intestines.
Impact of Signals from the Mouth and Gut on Appetite
When the team allowed the mice to freely consume the liquid food, PRLH cells activated within seconds of the animals starting to lick the food, but they stopped being active when the licking stopped. This indicates that PRLH cells respond differently depending on whether signals come from the mouth or the gut, and Knight points out that signals from the mouth dominate those from the gut.
Effect of Taste on Appetite
Using lasers to activate PRLH cells in mice that were eating freely, researchers were able to reduce the speed at which the mice consumed food. Further experiments showed that PRLH cells were not activated during feeding in mice that lacked most of their ability to taste sweetness, suggesting that taste activates the cells.
Impact of Gut Signals on Appetite
Researchers also found that GCG cells are activated by signals from the gut, controlling when mice stop eating. Knight says, “Signals from the mouth control the speed of eating, and signals from the gut control the amount of food.”
Neuroscientist Chen Ran at Harvard University in Boston, Massachusetts, says, “I am very impressed with this paper.” He states that the work provides original insights into how taste regulates appetite. Ran adds that the findings may also apply to humans, as these neural circuits tend to be well-preserved across species.
References:
– Ly, T. et al. Nature https://doi.org/10.1038/s41586-023-06758-2 (2023).
– Alcantara, I. C. et al. Nature Metab. 4, 836–847 (2022).
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