M&Ms leave the brain craving more
U. MICHIGAN (US) — The same part of the brain usually thought to control movement may also cause people to overeat—especially foods that are extra tasty.
The neostriatum, located near the middle and front of the brain—the part of the brain that is damaged in patients with Parkinson’s disease and Huntington’s disease—has traditionally been thought to control only motor movements.
Yet for several years, it has been known that the neostriatum is active in brains of obese people when viewing or tasting foods and in brains of drug addicts when viewing photos of drug-taking.
Published in the journal Current Biology, a new study shows that an opium-like chemical—enkaphalin—produced naturally in the brain is a mechanism that generates intense motivation to consume pleasant rewards, says Alexandra DiFeliceantonio, a doctoral student in psychology at the University of Michigan and the study’s lead author.
When researchers gave extra morphine-like drug stimulation to the top of the neostriatum in rats, it caused the animals to eat twice the normal amount of sweet fatty foods—in this case, M&M milk chocolate candies.
“The same brain area we tested here is active when obese people see foods and when drug addicts see drug scenes,” DiFeliceantonio says. “So it seems likely that our enkephalin findings in rats mean that this neurotransmitter may drive some forms of overconsumption and addiction in people.”
Researchers measured levels of enkephalin using a painless microdialysis probe while rats were allowed to eat as much chocolate as they wanted. The levels surged dramatically as soon as the rats started to eat—and remained high as long as they ate.
In addition, when researchers gave a painless microinjection of an opioid-stimulating drug in the rats’ neostriatum, the rats ate double the amount of chocolate.
DiFeliceantonio and colleagues mapped where extra drug stimulation of opioid receptors affected eating habits. Overeating was only caused in one region at the front and center part of the neostriatum (called the anterior-medial region of dorsal neostriatum).
“Finding the brain mechanisms for overconsumption is a step towards designing better biological-based treatments for obesity and binge eating disorders,” DiFeliceantonio says.
The study’s other researchers were Omar Mabrouk, a postdoctoral research fellow in pharmacology and chemistry, Robert Kennedy, professor of chemistry and of pharmacology, and Kent Berridge, professor of psychology and neuroscience. NIH grants supported the research.
Source: University of Michigan