"A hallmark of drug addiction is that it leads to changes in how the brain's reward system works," Kenny said. "Addiction is a loaded term, but in this case, there is evidence of addiction-like adaptations."
When researchers artificially suppressed the receptor using a virus in the brains of other rats, those rats starting eating junk food compulsively.
"What we think is happening is that, as you become obese over a period of time, the D2 receptors go down, which plays a major role in becoming a compulsive eater," Kenny said, noting there are almost certainly other factors at play as well.
There also could be something in the accumulated fat itself that alters the brain's reward threshold, setting up a "vicious cycle" of overeating yet not feeling satisfied, said Pietro Cottone, an assistant professor in the Laboratory of Addictive Disorders at Boston University School of Medicine.
"The only way to return to normality is probably dieting for a long period of time to lose the body weight and not eating junk food," Cottone said.
This isn't the first study to find commonalities between the brain's reaction to cupcakes and illicit drugs. An earlier study by Cottone and his colleagues suggested that weaning rats off a high-calorie diet might lead to similar, though not identical, effects in the brain as withdrawing from drugs and alcohol.
In that study, researchers gave rats a regular diet for five days and then switched them to a chocolate-flavored food that was high in sugar. When deprived of the sugary food, they showed signs of anxiety and their brains acted as if they were withdrawing from alcohol or drugs. The study was published last November in the Proceedings of the National Academy of Sciences.
In the current study, the rats were r
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