Anxiety and fat-burning may seem entirely unrelated so far as bodily functions go, but scientists have found that a certain molecule appears to connect one with the other. Through experiments on mice, the researchers believe that this shared mechanism may open up new pathways for the development of drugs to help manage anxiety disorders and obesity in humans.

Carried out by scientists at Florida's Scripps Research Institute, the study centers on a molecule called brain-derived neurotrophic factor, or BDNF. This is an important molecule known to promote the growth and function of brain cells and recent research has linked it to schizophrenia, memory and experimental Alzheimer's treatments.

Long-time researcher of obesity at the Scripps Institute, Baoji Xu, uncovered another potential function of BDNF while observing mice engineered to lack the molecule. Just as periods of anxiety and stress can correspond with weight loss in humans, Xu found that these mice displayed anxiety-like tendencies while remaining trim, even though they were fed a diet designed to drive their body weight up.

"Even on a high-fat diet, these mice were really lean," says Xu. "Could the same thing be happening in humans?"

To investigate this, the researchers went on to make adjustments to their experiment to see if they could tease out some useful insights. Because BDNF is known to be necessary to critical functions of the brain, they needed to have it working normally in certain areas of the brain but not in others.

They began by deleting the BDNF gene in the brain's cortex, hippocampus and amygdala regions, and found that the mice continued to develop symptoms of anxiety. Further examination revealed that the lack of BDNF was impairing the activity of a neurotransmitter called GABA, a molecule that slows down brain signaling and promotes relaxation.

In seeking answers to why these nervy rodents with limited BDNF also stayed trim, the team found that they had an elevated basal metabolic rate, meaning they were expending more energy just to keep their anxious bodies in working order. They were also found to produce more brown fat, the type that more readily burns energy to keep the body warm.

While turning this discovery into meaningful drugs that combat anxiety and weight loss, or perhaps both at the same time, will take much more research, the scientists are buoyed by these early results. The discovery of a molecule that is common to both these undesirable biological outcomes offers a promising foundation for the development of drugs that manipulate BDNF to alleviate anxiety or treat obesity.

"We've found a relationship between anxiety and weight loss," says Xu. "This research could guide new therapies for anxiety and help researchers design treatments for obesity."

The research was published in the journal Cell Metabolism.