People who find themselves rummaging through the refrigerator for a snack shortly after eating a heavy meal might have overactive food-seeking neurons, not an overactive appetite.
Donuts – illustrative photo. Image credit: Pixabay (Free Pixabay license)
UCLA psychologists have discovered a circuit in the brains of mice that makes them want to eat and seek it out, even when they’re not hungry. When stimulated, this cluster of cells causes mice to eat vigorously and prefer fatty, pleasant foods like chocolate over healthier foods like carrots.
People have the same types of cells and, if confirmed in humans, this discovery could offer new ways of understanding eating disorders.
The report, published in the journal Natural Communications, is the first to find dedicated food-seeking cells in a part of the mouse brainstem typically associated with panic, but not eating.
“This region we’re studying is called the periaqueductal gray (PAG), and it’s in the brainstem, which is very old in evolutionary history and because of that, it’s functionally similar between humans and humans. mice,” said the corresponding author. Avishek Adhikari, associate professor of psychology at UCLA. “Although our findings were a surprise, it makes sense that foraging is rooted in such an ancient part of the brain, since foraging is something all animals must do. »
Adhikari studies how fear and anxiety help animals assess risks and minimize exposure to threats. His group made the discovery while trying to understand how this particular location was involved in fear.
“Activation of the entire PAG region causes a dramatic panic response in mice and humans. But when we selectively stimulated only this specific group of PAG neurons called vgat PAG cells, they did not change fear, but instead caused foraging and eating,” Adhikari said.
Researchers injected the brains of mice with a genetically engineered virus to make the brain cells produce a light-sensitive protein. When a laser shines light on cells through a fiber optic implant, the new protein translates that light into electrical neuronal activity in the cells. A miniature microscope, developed at UCLA and attached to the mouse’s head, recorded the neuronal activity of the cells.
When stimulated by laser light, the vgat PAG cells fired and set the mouse in pursuit of live crickets and non-prey foods, even though it had just eaten a large meal. The stimulation also cued the mouse to follow moving objects that weren’t food – like ping pong balls, even though it didn’t try to eat them – and it also cued the mouse to confidently explore everything in its enclosure.
“The results suggest that the following behavior is more related to desire than hunger,” Adhikari said. “Hunger is aversive, meaning mice generally avoid being hungry if they can. But they look for activation of these cells, which suggests that the circuit does not cause hunger. Instead, we believe this circuit causes a craving for highly rewarding, high-calorie foods. These cells can cause mice to eat more high-calorie foods, even in the absence of hunger.
Satiety mice with activated vgat PAG cells craved fatty foods so much that they were willing to endure foot shocks to get them, something satiated mice normally would not do. Conversely, when the researchers injected a virus designed to produce a protein that dampens the activity of cells exposed to light, the mice ate less, even though they were very hungry.
“Mice exhibit compulsive eating in the presence of aversive direct consequences when this circuit is active, and do not seek food even if they are hungry when it is not active. This circuit can bypass normal hunger pressures regarding how, what and when to eat,” said Fernando Reis, a postdoctoral researcher at UCLA who performed most of the experiments described in the paper and came up with the idea for study compulsive eating. “We conduct new experiments based on these results and learn that these cells induce the consumption of fatty and sugary foods, but not vegetables in mice, suggesting that this circuit could increase junk food consumption. »
Like mice, humans also have vgat PAG cells in the brainstem. It could be that if this circuit is overactive in a person, they will feel more rewarded by eating or crave food when they are not hungry. Conversely, if this circuit is not sufficiently active, they might experience less pleasure associated with eating, potentially contributing to anorexia. If discovered in humans, the food-seeking circuit could become a target of treatment for certain types of eating disorders.
The research was supported by the National Institute of Mental Health, the Brain & Behavior Research Foundation, and the National Science Foundation.
Source: UCLA
Originally published in The European Times.
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