German and British researchers have identified an important control circuit involved in the feeding process.
- Fly larvae have a sort of “stretch receptor” in the esophagus that is triggered whenever the insect swallows something.
- If the larva has swallowed food, the “stretch receptor” instructs the brain to release serotonin, often called the “feel good hormone”, which leads to the larva continuing to eat.
- Researchers assume that humans also have a very similar control circuit.
While the tantalizing smell and delicious taste of food may kick off our meal, it turns out it’s the pleasant feeling we get after swallowing a food that keeps us coming back for more. This was recently revealed by researchers from the University of Bonn (Germany) and the University of Cambridge (United Kingdom) in a study published in the journal Current Biology.
All nerve connections of fly larvae studied
To reach this conclusion, they examined the larvae of the fruit fly Drosophila. As a reminder, this insect has approximately 10,000 to 15,000 nerve cells, which is a reasonable number compared to the 100 billion in the human brain. However, these 15,000 nerve cells already form an extremely complex network. Indeed, each neuron has branches through which it comes into contact with dozens, even hundreds of other nerve cells. As part of the work, the team cut a larva into thousands of very thin slices and photographed it under an electron microscope. Then, she studied the paths of all the nerve fibers of the larvae, but also the connections between the different neurons.
A “stretch receptor” connected to serotonin neurons
At the end of this analysis, the authors discovered a kind of “stretch receptor” in the esophagus. It is connected to a group of six neurons in the larva’s brain that are capable of producing serotonin, a neuromodulator known as the “feel-good hormone.” The latter ensures, for example, that we feel rewarded for certain actions and that we are encouraged to continue them. According to the data, serotonin neurons receive additional information about what the fly has just swallowed. “They can detect whether it is food or not and also assess its quality. They only produce serotonin if they detect good quality food, which ensures that the larva continues to eat.”explained Andreas Schoofswho led the research.
“We do not yet know enough about how the control circuit actually works in humans”
Scientists believe that this mechanism probably also exists in humans. So, if it doesn’t work properly, it could potentially cause eating disorders, such as anorexia or overeating. “But we do not yet know enough about how the control circuit actually works in humans. There are still years of research to be carried out in this area,” concluded Michael Pankratz, co-author of the study.
