Researchers from the University of Bonn and University Hospital Bonn announced on Apr. 16 that they have uncovered a key mechanism by which animals learn to avoid food that previously made them sick. The study, conducted in collaboration with Tohoku University in Japan, was published in the journal Neuron.
This research sheds light on a survival strategy known as conditioned taste aversion, where animals and humans learn to steer clear of foods associated with illness. Understanding this process could provide insights into eating behaviors and disorders.
The team used fruit flies (Drosophila) as a model organism to explore how immune responses lead to changes in behavior. According to Prof. Dr. Ilona Grunwald Kadow, head of the Institute for Physiology II at the University of Bonn and University Hospital Bonn, "As this learned food avoidance can be found in all species, we investigated this question in a model organism - the fruit fly Drosophila." In their experiments, flies were given a choice between two food sources: one contaminated with pathogenic bacteria (Pseudomonas entomophila) and another containing a harmless strain.
Grunwald Kadow said that initially flies preferred the harmful food due to its attractive odor but soon learned to avoid it after experiencing negative effects. Yujie Wang, who carried out much of the experimental work during her doctoral thesis, explained that special neurons near the fly's throat detect harmful bacteria through sensors on their surface: "In our experiment, receptors were activated in them that respond to components of the bacterial cell wall." These neurons connect both to the brain and fat stores inside the fly's head.
When these receptors are triggered by pathogens, they cause neurons to release octopamine—a neurotransmitter related to adrenaline—which then stimulates fat cells nearby. Grunwald Kadow said: "The octopamine then triggers the formation of another neurotransmitter, dopamine, in the fat cells... The dopamine, in turn, is transported into the fly's brain where it causes continuous increased activation of neuronal networks that are important for learning and trigger an avoidance response." This process leads flies with prior exposure to spoiled food choosing safer options next time.
The study also suggests adipose tissue plays an important role in this behavioral change; however, Grunwald Kadow said more research is needed: "We still do not have a definitive answer... However, the flies' decision may be linked to their nutritional status." She noted ongoing experiments are exploring whether starving animals produce less dopamine when exposed again—possibly making them more likely to risk eating contaminated food.
These findings may have broader implications for understanding human appetite regulation since human adipose tissue also produces neurotransmitters affecting brain function. Researchers believe disruptions between brain signaling and body organs might contribute to conditions like anorexia or obesity.
