How Do The Brain And Body Communicate To Maintain Healthy Weight?

How Do The Brain And Body Communicate To Maintain Healthy Weight?31 Oct 2012-nbsp;-nbsp;-nbsp;


A person's brain and body works together to maintain a healthy body weight using energy balance, a correspondence between calories eaten and calories burned. When this balance, which stems from an exchange between the brain's hypothalamus and neurobiological signaling, goes wrong, individuals may develop obesity or anorexia, according to a recent study conducted by researchers at BIDMC (Beth Israel Deaconess Medical Center).

Not much is known about the the workings of this complicated exchange, which is unfavorable considering the seriousness of these disorders. The new study, published in the journal Cell, has revealed new evidence which explains this complicated process.

According to a 2008 study, what we eat may actually alter the regions in the brain that maintain healthy body weight.

The report shows how the GABA neurotransmitter regulates how much energy is expended. It also helps explain how the fat-burning properties of brown fat function in neurocircuits.

Bradford Lowell, Md, PhD, a Professor of Medicine at BIDMC's Division of Endocrinology and Harvard Medical School said:

"Our group has built up a research program with the overall goal of unraveling the 'wiring diagram' by which the brain controls appetite and the burning of calories. To advance our understanding to this level, we need to know the function of specific subsets of neurons, and in addition, the upstream neurons providing input to, and the downstream neurons receiving output from, these functionally defined neurons. Until recently, such knowledge in the hypothalamus has been largely unobtainable."

The hypothalamus, an area in the brain about the size of a pearl which manages a great number of responsibilities in the body, is the control center of energy balance.

Energy balance occurs when the body sends feedback signals, which convey messages regarding the status of fuel stores, to the brain. The brain then combines this information with the input from the outside world, along with a person's emotional condition, in order to alter eating behavior and the output of energy.


During the trial, the investigators looked into a distinct population of neurons found at the bottom of the brain in the arcuate nucleus of the hypothalamus.

Lowell said, "We genetically engineered mice such that they have a specific defect that prevents these neurons from releasing the inhibitory neurotransmitter, GABA. Mice with this defect developed marked obesity and, remarkably, their obesity was entirely due to a defect in burning off calories." He continued that food consumption was completely unchanged.

Next, the experts engineered a different group of mice so that these particular neurons could be turned on when the researchers wanted them to be. Through this, they found that arcuate neurons perform by way of a sequence of neurons heading downstream, in order to prompt energy expenditure in brown fat.

Brown fat has been a topic of interest recently, due to the fact that research has unveiled that brown fat burns energy to produce heat, a process called thermogenesis.

Dong Kong, PhD, an Instructor in Medicine in Lowell's lab, commented: "Energy expenditure mediated by brown adipose tissue is critical in maintaining body weigh and prevents diet-induced obesity. Its brain-based regulatory mechanism, however, is still poorly understood. Our discovery of a hypothalamus-based neurocircuit that ultimately controls thermogenesis is an important advance."

The researchers also determined that when the neurons were activated, energy expenditure was completely reliant on the release of GABA. The findings show that when GABA is released from arcuate neurons, energy expenditure is prompted.

"Our findings have greatly advanced our understanding in the control of energy expenditure and have provided novel insights into the pathogenesis of obesity," continued Kong."

Characteristics of arcuate neurons are significant because they offer a chance to alter energy expenditure by the brain for experimental use. Neurons which receive "GABA-mediated" communication from arcuate neurons are apt to play an important part in managing energy expenditure, not food consumption.

"It is now important to fully delineate the upstream neurons that control these thermogenesis-regulating arcuate neurons, and also the downstream neurons that complete the 'circuit' to brown adipose tissue," concluded Lowell. He and his team have singled out many different kinds of neurons which act downstream of arcuate neurons, but much more evidence is necessary to completely understand this process. The work will pave the way for new opportunities for treatments of obesity and obesity-related conditions, such as heart disease and diabetes.

Written by Christine Kearney
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