Maybe it starts off feeling low energy, or maybe you get a little cranky. You may have a headache or difficulty concentrating. Your brain is sending you a message: you are hungry. Find food.
Studies in mice have identified clusters of cells called AgRP neurons near the bottom of the brain that can cause this nasty feeling of hunger. even “hungry”, feeling. They are close to the blood supply to the brain, which gives them access to hormones from the stomach and adipose tissue that indicate energy levels. When energy is low, they act on many other areas of the brain to stimulate nutrition.
By eavesdropping on AgRP neurons in mice, scientists began to understand how these cells turn on and prompt animals to seek food when they lack nutrients, and how they feel it. entry of food into the intestines The researchers also found that the activity of AgRP neurons is impaired in mice with symptoms similar to those of anorexia, and that activation of these neurons can help restore normal eating patterns in these animals.
Understanding and manipulating AgRP neurons could lead to new treatments for both anorexia and binge eating. “If we could control this feeling of hunger, we could have better control over our diet,” says Amber Alhadeff, a neuroscientist at the Monell Chemical Senses Center in Philadelphia.
To eat or not to eat
AgRP neurons appear to play a key role in appetite: their deactivation in adult mice causes the animals to stop eating – they can even starvation. Conversely, when the researchers fire the neurons, the mice jump into the food bowls and overeat.
Experiments in several laboratories in 2015 helped illustrate what AgRP neurons do. The researchers found that when mice ran out of food, AgRP neurons shot more often. But the sight or smell of food alone—especially something savory like peanut butter or Hershey Kiss—was enough to Relax this activity, within a few seconds. From this, the scientists concluded that AgRP neurons make animals look for food. Once food is found, they stop shooting as hard.
One research team, led by neuroscientist Scott Sternson at the Genelia Research Campus in Ashburn, Virginia, also showed that the activity of AgRP neurons appears to make mice feel bad. To demonstrate this, the scientists designed mice so that AgRP neurons would fire when light hit the brain through an optical fiber (the fiber still allowed the mice to move freely). They placed these engineered mice in a box with two distinct areas: one painted black with a plastic slatted bottom, and the other white with a soft tissue paper floor. If the researchers activated the AgRP neurons whenever the mice entered one of the two areas, the mice began to avoid that area.
Sternson, now at UC San Diego, concluded that AgRP activation felt “slightly uncomfortable.” He says this makes sense in nature: every time a mouse leaves its nest, it is at risk from predators, but it must overcome that fear in order to forage and eat. “These AgRP neurons are kind of a push that in a dangerous environment you’re going to look for food to stay alive.”
A 2015 study by Sternson found that while the sight or smell of food quiets the AgRP neurons, it is temporary: activity resumes immediately if the mouse cannot make it to the end and eat the snack. With more experimentation, Alhadeff and colleagues found that something that turns off AgRP neurons is more reliable. Calories enter the intestines.