A mouse catching a whiff of food doesn't just feel hunger—its brain is already preparing the body for the meal to come, releasing insulin before a single bite. Now scientists have discovered the molecular engine powering this anticipatory response, opening a new window into how the brain controls metabolism and what goes wrong in obesity.
The finding, published in Nature Metabolism, centers on a hidden fuel source inside POMC neurons, a group of brain cells in the hypothalamus that regulate hunger and satiety. Researchers led by Marc Schneeberger Pane, an assistant professor in cellular and molecular physiology, and Marc Claret of the Institut d'Investigacions Biomèdiques August Pi i Sunyer found that these neurons store energy in the form of glycogen—the same molecule that powers muscles and the liver. When we merely see or smell food, this neuronal glycogen kicks into gear, triggering the brain to prime the body for digestion.
The discovery matters because obesity, despite its physical manifestations, is fundamentally a brain disorder. "Obesity is a dysregulation of the feeding circuitry at the level of the brain—it's more of a disease of the brain than a disease of the body," Schneeberger Pane explains. Understanding precisely how POMC neurons function in healthy metabolism is the essential first step toward developing better treatments.
The researchers began by exposing mice to food they could see and smell but not eat, presented behind a wire mesh. They then traced which molecular signatures activated in the neurons. What emerged was striking: the sensory perception of food triggered glycogen synthase, the molecular machinery that builds and stores glycogen. This finding prompted a crucial question—what role does this neural glycogen actually play in the feeding response?
To answer it, the team engineered mice lacking glycogen synthase in their POMC neurons. When exposed to food, these mice barely responded. They showed little interest in approaching the food, spent less time eating, and critically, failed to produce the anticipatory insulin release that normally primes the body for incoming glucose. To rule out developmental complications, the researchers took a second approach: they injected normal adult mice with a virus that stripped away glycogen synthase. These mice displayed the same non-responsive behavior, confirming that glycogen itself was the key.
The team also pinpointed which sensory channel matters most. POMC neurons connect with brain regions that process smell, but surprisingly, not those that process vision. This suggests that aroma—not the sight of food—drives the anticipatory metabolic response.
Perhaps most intriguing is what this discovery challenges. Neuroscientists long believed that glycogen in the brain resided almost exclusively in astrocytes, support cells that nourish neurons. This study suggests glycogen plays a far larger and more direct role in neural function than previously recognized, with implications reaching far beyond appetite control.
The findings offer a concrete biological target for obesity research. When the sensory anticipation of food goes awry, the body loses its ability to properly prepare for incoming nutrition—a dysregulation that accumulates over time. By understanding how neuronal glycogen fuels this priming response, scientists now have a clearer map for intervention, potentially opening new pathways toward metabolic health.