Neurons are brain cells and they are similar to the other cells of the body in most every way, except that they reach for each other and pass little messages between themselves. It all happens through tiny connections, and the messages themselves are individually simple, but they are traded on such a massively numerous scale, that together they somehow create the very core of your being. These circuits are the Genesis of the syrupy flavor on your waffles. They are the chocolatey goodness of your, well, chocolate. And they motivate you to search for another mouthful.
How this all happens—the ingredients of this mental Chop Suey—are not well understood. But a new tour de force of a study in Nature by Deniz Atasoy and colleagues brings us a little closer to knowing the recipe.
The group based at Janelia Farms in Virginia analyzed the connectivity between neurons within the hypothalamus, specifically within the arcuate nucleus, which are activated in normal behavior by the feeding hormone ghrelin, evoke voracious binge eating when stimulated, and lead to starvation when they are killed. It’s pretty clear that they are critical to regulating feeding behavior. These cells are called AGRP neurons because they express a poorly understood gene called AGouti Related Protein. The brilliant strategy of the researchers was to reverse engineer the connectivity of the AGRP neurons in order to determine the underlying circuits that drive AGRPs to ring the dinner bell.
The surprising answer was that AGRP neurons evoke eating, at least in part, by suppressing oxytocin neurons in the nearby paraventricular hypothalamus. Oxytocin is known as the “love hormone”, and so the result brings a whole new meaning to the term “comfort food” since the results suggest that you can only feel truly touchy feely when your hunger is sated.