Faulty brain wiring triggers overeating
Obesity has become a major health problem across the globe, with two-thirds of adults overweight or obese in the United States alone. And, now, researchers say they have identified an important brain circuit that triggers overeating, according to a study published in the journal Science.
The discovery may offer clues about the cause of obesity, and also lead to treatments for eating disorders such as anorexia nervosa and bulimia, the researchers from the University of North Carolina (UNC) School of Medicine noted.
As they pointed out, it was just 60 years ago when scientists first discovered they could electrically stimulate the brains of mice to make them eat when the mice weren’t hungry – and this newest research is an extension of that discovery, with the UNC team finding that they could use fiber optic cables to stimulate the brains of mice to make them hungry.
Based on the finding that hunger takes over when BNST activated, the researchers for this new study concentrated on one specific cell type in the brain called gaba neurons, which reside in the bed nucleus of the stria terminalis, also referred to as BNST, an area of the brain connected to emotion.
The BNST is also connected to a region of the brain linked to eating, sexual behavior and aggression. As the researchers explained, contained in the gaba neurons is a cell body and a long strand with branched synapses, which are able to transmit electronic signals into the lateral hypothalamus of the brain.
For the study, the UNC researchers set out to stimulate these synapses using fiber optic cables in what they referred to as an "optogenetic technique", which stimulates BNST cells by shining light on the synapses.
Because brain cells usually don’t respond to light, the researchers used genetically engineered proteins from algae that are sensitive to light, transporting them into the brains of mice by injecting genetically engineered viruses.
By using this method, the proteins are only expressed in the BNST cells. In other words, they are expressed in the synapses connected to the hypothalamus of the brain.
This "optogenetic technique” of inserting optic fiber cables into the brains of the mice therefore enabled researchers to shine light through the cables and onto the BNST synapses.
After the BNST synapses were activated by light, a voracious hunger was triggered in the mice, and they exhibited an intense appetite for fat-laden foods, although they had been well fed before the experiment.
"They would essentially eat up to half their daily caloric intake in about 20 minutes," said Garret Stuber, assistant professor in the Department of psychiatry and Department of Cell Biology and Physiology at UNC. "This suggests that this BNST pathway could play a role in food consumption and pathological conditions such as binge eating."
The researchers mentioned that stimulating the BNST also triggered behaviors in the mice associated to reward, suggesting an enhancement of the pleasure of eating when BNST cells are activated.
In contrast, once the light on the BNST was shut off, the mice showed little interest in food, even when they had been deprived of food for some time.
The researchers therefore conclude that faulty brain wiring could lead to obesity and other eating disorders, noting that their findings suggest that if someone has "faulty wiring" within BNST cells, it could potentially interfere with hunger or satiety cues; thus, causing people to eat or avoid food when hungry, or otherwise lead to the development of eating disorders.
"The study underscores that obesity and other eating disorders have a neurological basis,” Prof. Garret Stuber said. “With further study, we could figure out how to regulate the activity of cells in a specific region of the brain and develop treatments."
SOURCE: The Inhibitory Circuit Architecture of the Lateral Hypothalamus Orchestrates Feeding, published in the journal Science, 27 September 2013.