Giving strength to the belief that overeating and eating disorders are partially caused by functions in the brain, a team of researchers at the University of North Carolina, Chapel Hill, discovered a neural pathway in the brain that appears to control feeding habits.
The researchers were interested in exploring the connectivity between two regions of the brain: the extended amygdala, which functions in emotional behaviors, and the lateral hypothalamus, which is involved in feeding behaviors, says co-author Garret Stuber, an assistant professor of psychiatry. By manipulating the connection between the two regions, the researchers found they could essentially turn on and turn off a mouse's desire to eat. Their findings will be published Friday in the journal Science.
"It underscores sort of what a lot of people already know, but is forgotten or not thought about, which is obesity and eating disorders clearly have a neurobiological basis to them," Stuber says. "They're not necessarily completely controlled by brain things ... But this is just one of many clear demonstrations where you can manipulate brain circuitry and see changes in eating behavior."
To control the neurons, the team used a technique called optogenetics, in which they made the neurons light-sensitive and could then precisely control their activity with light. As soon as they stimulated the pathway, the mice had a sudden urge to constantly devour food, even when they weren't hungry.
"It was like flipping a light switch," Stuber says. "As soon as we turned the stimulation on, if there was food present they would go over and start eating. And they would continue to eat for the entire duration that they were receiving activation of this pathway."
What was interesting, Stuber says, was that the mice were well-fed and should not have had any desire to overeat. And when given the choice between regular and high-calorie food (which Stuber described as the animal equivalent to junk food) the mice showed a preference for the high-fat, high-calorie chow.
The opposite also proved true: when the researchers inactivated the pathway, the mice stopped eating. In this case, the researchers experimented with mice that were hungry and in close proximity to food. But when the pathway was inactivated, the mice stopped eating.
Although the topic hasn't been researched yet, Stuber says it's possible that this pathway is either over- or under-active in people with eating disorders. Now that researchers know the connection between these two regions of the brain functions in eating habits, Stuber says future research should focus on exploring the genetic makeup of the cells.
"We can go back in and start looking at what makes those cells unique," Stuber says. "That will give us insight into how to try to figure out a rational strategy to design drugs that will regulate the activity of those cells like we're doing with light right now."