Researchers have identified surprising ways that encountering food—even before eating it—affects hunger signals in mouse brains. These are insights that pertain to the mental processes disrupted in some people with eating disorders.

In a paper published February 26th in Cell, a team led by 2013 NARSAD Young Investigator Grantee Zachary A. Knight, Ph.D., of the University of California, San Francisco, reported on experiments involving mice that had been deprived of and then exposed to food. After the fasting mice discovered food, neuron clusters linked with feeding behavior in the brain “reset” their status. It was as if the mice already had eaten—yet this was before the mice had actually consumed a morsel of food.

Those clusters of brain cells contain two types of neurons. One type is known as AgRP neurons, named for agouti-related protein, a chemical signal expressed by these cells. The other type is called POMC neurons, named for a chemical called proopiomelanocortin they express. Both neuron types are found in the hypothalamus, a structure deep in the brain that directs the pursuit and consumption of food, among many other functions. Within the hypothalamus, AgRP neurons are activated when the body sends signals that it needs energy; when active, these neurons promote feeding behaviors. In contrast, POMC neurons respond when signals indicate the body is satiated; when POMC neurons are active, feeding behavior diminishes.

In Dr. Knight’s study, the presentation of chow pellets to fasting mice stalled activity in AgRP neurons, reducing the signals that would tell the mice to seek food, and activated POMC neurons, telling the mice to halt their search. These “stop-seeking-food” signals were even more pronounced when mice were presented with peanut butter, a tastier option than the chow pellet. But the signals were less pronounced when the presented food was packaged in containers that allowed the mice to see and smell but not touch (or eat) the food. All of this suggests that AgRP and POMC neurons track specific information about food in the environment: how appetizing it is, and how likely it is to end up in the stomach.

Coupled with the finding that quickly removing presented food resets the hunger signals a second time, and drives the mice to look for food once again, these findings paint a picture of AgRP and POMC neurons as integrating information about a possible meal to help mice decide whether or not to seek food and then to eat. This processing involves associations between sensory information about food—how it looks and smells—and the food’s nutritional content.

These associations are sometimes disrupted in people with eating disorders, meaning that fully understanding the role of AgRP and POMC neurons in hunger and eating may prove useful for finding new ways to treat such conditions.

Read the abstract.