"Don't Eat More When Full"…Discovered Appetite-Suppressing Signal Neurons

KAIST Research Team Identifies Animal Appetite Regulation System Through Fruit Flies

[Asia Economy Reporter Kim Bong-su] Animals, including humans, stop eating once they have consumed an adequate amount of food, no matter how hungry they are. Why is that? A Korean research team has discovered through experiments using Drosophila (fruit flies) that there are specific neurons that suppress overeating. This finding could provide clues to addressing eating disorders and obesity.

The Korea Advanced Institute of Science and Technology (KAIST) announced on the 15th that Professor Seongbae Seo's research team from the Department of Biological Sciences, in collaboration with Dr. Yangkyun Oh's team at New York University (NYU), has for the first time identified two independent overeating suppression systems specifically found in fruit flies that have consumed sufficient food.

The research results were published in the online edition of the international neuroscience journal Neuron on the 19th of last month.

Within the brains of animals, there exist nutrient-sensing neurons that predate the development of taste neurons. In a 2015 paper published by Professor Seongbae Seo and postdoctoral researcher Dr. Monica Dus during their time at NYU, it was discovered that in situations where fruit flies require nutrients, a specific group of neurons secreting the diuretic hormone (DH44) peptide (DH44+ neurons) detect the concentration of sugars in the body, triggering behavioral changes that lead the flies to select nutritious food. While nutrient-sensing neurons that regulate their own activity have been reported in mammalian brains, this study was the first to reveal the biological function of these nutrient-sensing neurons.

Following the publication on the biological function of DH44 neurons, the research team conducted further studies and discovered a higher-level regulatory signal that specifically inhibits DH44 neurons when the fruit fly's body is rich in nutrients. First, the team demonstrated using an automated fruit fly feeding behavior measurement device that the biological function of DH44 neurons is not limited to regulating food choice behavior but actively increases feeding behavior toward nutritionally valuable carbohydrates when nutrients are needed. In other words, activation of DH44 neurons increases the fruit fly's food intake, and an inhibitory signal that is specifically activated when the fly is full prevents overeating caused by DH44 activation.

Next, the team experimentally confirmed that the inhibitory signal to DH44 neurons originates from peripheral organs outside the fruit fly brain. To identify which terminal organs send the DH44 inhibitory signal, the researchers sequentially removed various terminal organs connected to the fruit fly brain to trace the source of the inhibitory signal. As a result, they confirmed that the DH44 inhibitory signals originate from the crop, the organ corresponding to the fruit fly's stomach, and the ventral nerve cord (VNC), which corresponds to the spinal cord.

Continuing their research, the team found that DH44 neurons extend nerve branches to the fruit fly's crop and can detect physical expansion signals caused by food intake through the Piezo channel. The Piezo channel is a sensor that detects physical expansion applied to specific cells or tissues and plays an important role in mammalian respiration and blood pressure regulation. In fruit flies, it induces appetite suppression by sensing physical expansion of the digestive organs. This study revealed that after the Piezo channel senses the physical expansion of the fruit fly's crop caused by food intake, it specifically inhibits the function of DH44 neurons, preventing further carbohydrate consumption and thereby protecting the internal organs from excessive physical expansion.

Additionally, the 'Hugin' neurons located in the ventral nerve cord, which corresponds to the fruit fly's spinal cord, detect high concentrations of circulating nutrients and suppress the neural activity of DH44 cells expressing Hugin receptors. Through this mechanism, the team experimentally confirmed that additional feeding behavior, which could burden the digestive organs when the body's energy levels are already high, can be effectively blocked.

Through these experiments, the research team confirmed that the Piezo channel, activated by sensing physical pressure on the fruit fly's internal organs, and the Hugin neurons, activated when circulating nutrients are abundant, independently and complementarily suppress overeating caused by DH44 neuron activation by detecting different physical and chemical signals.

Professor Seongbae Seo stated, "This research is the first case demonstrating that the feeding-inducing function of nutrient-sensing neurons in the animal brain can be specifically inhibited by higher-level signaling systems. The suppression of overeating involves systematically integrating independently perceived physical and chemical measures, highlighting how crucial this process is for animal survival."

This content was produced with the assistance of AI translation services.