Compulsive overeating and sugar addiction are major threats to human health, but potential treatments face the risk of impairing normal feeding behaviours that are crucial for survival, researchers said.

The study shows a reward-related neural circuit that specifically controls compulsive sugar consumption in mice without preventing feeding necessary for survival.
    
"Although obesity and Type 2 diabetes are major problems in our society, many treatments do not tackle the primary cause: unhealthy eating habits," said senior study author Kay Tye of the Massachusetts Institute of Technology.
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Our findings are exciting because they raise the  possibility that we could develop a treatment that selectively curbs compulsive overeating without altering healthy eating behaviour," said Tye.
    
Tye and her team suspected that a neural pathway from the lateral hypothalamus to the ventral tegmental area might play an important role in compulsive overeating because these brain regions have been implicated in reward-related behaviours such as eating, sexual activity, and drug addiction.

To test this idea, Tye and her team used a technique called optogenetics, which involves genetically modifying specific populations of neurons to express light-sensitive proteins that control neural excitability, and then delivering either blue or yellow light through an optic fibre to activate or inhibit those cells, respectively.
    
Activation of the pathway from the lateral hypothalamus to the ventral tegmental area caused well-fed mice to spend more time feeding and increased the number of times mice poked their nose into a port to receive a sugar reward, even when they had to cross a platform that delivered foot shocks to get to the reward.
    
By contrast, inhibition of the same pathway reduced this compulsive sugar-seeking behaviour without decreasing food consumption in hungry mice, suggesting that different neural circuits control feeding in hungry animals.
    
In an independent study, Garret Stuber of the University of North Carolina School of Medicine and his team similarly used an optogenetic approach in mice to identify neurons in the lateral hypothalamus that control both feeding and reward-seeking behaviour.
    
By imaging the activity of hundreds of individual lateral hypothalamus neurons as the mice freely explored an area with food or worked to obtain a sweet reward, they further uncovered distinct subsets of neurons that either mediate food-seeking behaviour or respond to reward consumption. The research was published in the journal Cell.

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