Scientists identified the brain neurons responsible for the insatiable need to snack.
Negative emotions associated with hunger can make dieting and losing weight miserable, but these new findings reveal the evolutionary reason behind these nagging hunger pangs, Howard Hughes Medical Institute reported. The findings linked the urge to snack to hunger-sensitive neurons in the brain called AGRP neurons.
Early humans (and animals in the wild) required some type of biological encouragement to venture into risky areas to find food and water.
"We suspect that what these neurons are doing is imposing a cost on not dealing with your physiological needs," said Scott Sternson, a group leader at Janelia Research Campus.
AGRP neurons do not directly prompt one to eat, but rather teaches them to respond to sensory cues that indicate the presence of delicious food.
"We suspect that these neurons are a very old motivational system to force an animal to satisfy its physiological needs. Part of the motivation for seeking food is to shut these neurons off," Sternson said.
Hunger influences almost every cell in the body, and a number of neurons work to make sure animals eat when necessary. These new findings provide insight into why these feelings of hunger are so unpleasant or even painful. Past findings have shown neurons promoted eating through positive feelings, leaving the mechanisms behind the uncomfortable feeling of hunger a mystery.
"There was an early prediction that there would be neurons that make you feel bad when you were hungry or thirsty. This made sense from an intuitive point of view, but all of the neurons that had been looked at seemed to have the opposite effect," Sternson said.
To solve this mystery, researchers conducted a series of behavioral experiments. In the firs the team offered well-fed mice a choice between a strawberry or orange flavored gel, neither of which contained any nutrients. The scientists manipulated the hunger signals in the rodents' brains by switching AGRP neurons while either flavor was consumed. Following this manipulation the bees tended to avoid the flavor linked to the false hunger signals.
In a second experiment, the researchers switched AGRP neurons off while hungry animals ate a specific flavor. These animals showed a preference for the flavor associated with the silencing of the AGRP neurons, suggesting they these signals were unpleasant. A third experiment showed mice also look for an environment in which AGRP neurons had been silenced in the past.
The team used mobile microscopes to look at the mice's brains, and found AGRP neurons switched off as the rodents saw food, as opposed to when they actually ate it.
"There's a similar motivational quality to hunger and thirst," Sternson said. "You want them to end."
The findings were published in a recent edition of the journal Nature.
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