Activating This Neural Pathway Is Key To Feeling Full, Study Shows
When your stomach is full, how does your brain know to stop eating? It sounds like a simple question, but the answer turns out to be far more complex than scientists originally thought.
For years, researchers assumed the answer lay mainly with neurons, the brain's primary signaling cells. But a new study published in Proceedings of the National Academy of Sciences (PNAS) suggests that another type of brain cell, one long considered mere "support staff," may be playing a far more active role in controlling appetite than anyone realized.
Here's what the research found, and why it could eventually change how we treat obesity and eating disorders.
What the research found
The study, a collaboration between the University of Maryland and the University of Concepción in Chile, identified a previously unknown communication chain in the hypothalamus, the region of the brain responsible for regulating hunger and fullness.
Specialized brain cells called tanycytes detect glucose after you eat, then process the sugar and release a byproduct called lactate. That lactate then reaches neighboring cells called astrocytes, which have specialized receptors (called HCAR1) that detect it. When lactate binds to HCAR1, astrocytes release their own chemical signal, glutamate, which activates the appetite-suppressing neurons in your brain and triggers a feeling of fullness.
In other words: tanycytes "talk" to astrocytes, and then astrocytes "talk" to neurons.
The researchers also noticed a dual effect of the lactate. The hypothalamus contains two opposing populations of neurons: those that promote hunger and those that suppress it. The team found that lactate may work on both simultaneously, activating the fullness neurons through astrocytes while potentially quieting the hunger neurons through a more direct route. It's like hitting the brakes on hunger from two directions at once.
Why this changes how we think about appetite
Astrocytes are among the most abundant cells in the brain. Yet for decades, they've been viewed in terms of supporting neuronal function, not directly influencing behavior.
People tend to immediately think of neurons when they think about how the brain works, but this research overturns that assumption. These communication circuits in our brains use all different types of cells.
One of the study's experiments drove this point home: When researchers delivered glucose directly into a single tanycyte while monitoring surrounding astrocytes, that one cell's activity was enough to trigger responses in multiple neighboring astrocytes.
Even a tiny, localized metabolic event ripples outward throughout the brain's network.
What this could mean for obesity and eating disorder treatments
This study was conducted in animal models, but tanycytes and astrocytes are present in all mammals, including humans. That's what makes this research so promising for future applications.
The team's next steps include investigating whether directly manipulating the HCAR1 receptor in astrocytes can change feeding behavior in animals, a necessary step before this research can progress to clinical applications.
Having this newly discovered mechanism where scientists may be able to target astrocytes, or even specific HCAR1 receptors, could lead to new therapies that improve the lives of many who suffer from obesity and other appetite-related conditions.
The takeaway
If you've ever felt like appetite is complicated, this research validates that instinct. Your brain uses a sophisticated system, with tanycytes, astrocytes, and neurons work together to determine when you've had enough to eat. And, while we're still in the early stages of this research, it opens exciting new doors for future treatments.