Humans across the globe are eating their way into some serious health problems, and our apparent addiction to sugar isn’t helping. But what is driving many of us to compulsively overeat? Scientists have known for a long time that it’s not just because sweet snacks taste nice, or because we’re suckers for tempting adverts.
Now, scientists could be closer to understanding these behaviors with the discovery of a brain circuit that controls compulsive sugar consumption in mice. Interestingly, this reward-related network does not govern feeding behaviors necessary for survival, raising hopes that targeting it could provide a means for treating compulsive overeating in humans without impairing healthy eating behaviors.
Much like gambling or drug addiction, compulsive overeating is a reward-seeking behavior. It is for this reason that scientists suspected that a population of brain cells connecting the lateral hypothalamus to the ventral tegmental area could play a role in compulsive overeating since this region has previously been associated with other reward-related behaviors, such as drinking and sex.
To find out whether this might be the case, scientists from MIT enlisted the help of a technique called optogenetics. This method involves inserting genes for light-sensitive proteins into certain cells, allowing scientists to selectively switch on or off distinct populations of brain cells using light, which is delivered through an implanted optical fiber.
As described in Cell, when the researchers activated the projections from the lateral hypothalamus to the ventral tegmental area in well-fed mice, they began to spend significantly more time sticking their nose in an area which delivered a sugary treat. They weren’t even deterred when accessing the reward meant that they had to cross a platform which gave them a small electric shock. Conversely, switching off this population of cells reduced this sugar-seeking behavior, but didn’t affect normal food consumption, suggesting two distinct networks govern these different behaviors.
Interestingly, another recent study, which was also published in Cell, independently identified populations of brain cells involved in both feeding and reward-seeking behavior. Once again using optogenetics, researchers from the University of North Carolina targeted a bunch of cells within the lateral hypothalamus of mice. When the cells were activated, the mice fed more frequently, but when they were switched off, the mice didn’t overeat. Detailed imaging of these cells revealed that distinct populations were active when the mice received food rewards or when they showed interest in food.
From an evolutionary perspective, it makes sense that we have these two separate circuits. Long before the advent of modern transport and refrigerators, many sugary foods would have only been available at certain times of the year, meaning our ancestors would probably binge on these sources of energy whenever they could. However, when food was in overall short supply, such as during winter months, it would be necessary to eat whatever is available, but in sensible amounts in order to ration what little there was.
“We have not yet adapted to a world where there is an overabundance of sugar, so these circuits that drive us to stuff ourselves with sweets are now serving to create a new health problem,” said lead researcher Kay Tye. However, these new discoveries may allow scientists to begin tackling this issue by developing drugs that target these regions.
[Via Cell, Cell, Cell Press and The Scientist]
