Rats that respond to signals about sugar with the speed and excitement of binge-eaters become less motivated when researchers suppressed certain brain cells.
The findings suggest these neurons, in a largely unstudied region of the brain, are deeply connected to the tendency to overindulge in response to external triggers, a problem faced by people addicted to food, alcohol, or drugs.
“External cues—anything from a glimpse of powder that looks like cocaine or the jingle of an ice cream truck—can trigger a relapse or binge eating,” says Jocelyn M. Richard, a postdoctoral fellow in psychological and brain sciences at Johns Hopkins University. “Our findings show where in the brain this connection between environmental stimuli and the seeking of food or drugs is occurring.”
For the study, published in the journal Neuron, researchers trained rats to realize that if they heard a certain sound, either a siren or staccato beeps, and then pushed a lever, they would get a drink of sugar water. Then, as the rats performed the task, researchers monitored neurons within the ventral pallidum area of the rats’ brains, a subcortical structure near the base of the brain.
When the rats heard the cue linked to their treat, a much larger-than-expected number of neurons vigorously reacted. They also found that when the neuron response was particularly robust, the rats were extra quick to go for the sugar. The researchers were able to predict how fast the rats would move for the sugar just by observing how excited the neurons became at the sound of the cue.
“We were surprised to see such a high number of neurons showing such a big increase in activity as soon as the sound played,” Richard says.
Next, the researchers used optogenetics, a technique that allows the manipulation of cells through targeted beams of light, to temporarily suppress the activity of ventral pallidum neurons while the rats heard the sugar cues.
With those neurons inactive, the rats were less likely to pull the sugar lever; when they did pull it, they were much slower to do so.
That ability to slow and calm the reaction to cues or triggers for binges could, with further research, become important for people trying to moderate addictive behaviors, Richard says.
“We don’t want to make it so that people don’t want rewards. We want to tone down the exaggerated motivation for rewards.”
Other researchers from Johns Hopkins and from Aix-Marseille Université and Le Centre National de la Recherche Scientifique, and the University of California, San Francisco are coauthors of the study, which was supported by the National Institutes of Health and the State of California.
Source: Johns Hopkins University