Scientists eavesdrop on communication between fat and brain

Scientists eavesdrop on communication between fat and brain

What did the fat say to the brain? For years, it was assumed that hormones passively floating through the blood were the way that a person’s fat — called adipose tissue — could send information related to stress and metabolism to the brain. Now, Scripps Research scientists report in Nature that newly identified sensory neurons carry a stream of messages from adipose tissue to the brain.

“The discovery of these neurons suggests for the first time that your brain is actively surveying your fat, rather than just passively receiving messages about it,” says co-senior author Li Ye, PhD, the Abide-Vividion Chair in Chemistry and Chemical Biology and an associate professor of neuroscience at Scripps Research. “The implications of this finding are profound.”

“This is yet another example of how important sensory neurons are to health and disease in the human body,” says co-senior author and professor Ardem Patapoutian, PhD, who is also a Nobel laureate and a Howard Hughes Medical Institute investigator.

In mammals, adipose tissue stores energy in the form of fat cells and, when the body needs energy, releases those stores. It also controls a host of hormones and signaling molecules related to hunger and metabolism. In diseases including diabetes, fatty liver disease, atherosclerosis and obesity, that energy storage and signaling often goes awry.

Researchers have long known that nerves extend into adipose tissue, but suspected they weren’t sensory neurons that carry data to the brain. Instead, most hypothesized that the nerves in fat belonged mostly to the sympathetic nervous system — the network responsible for our fight-or-flight response, which switches on fat-burning pathways during times of stress and physical activity. Attempts to clarify the types and functions of these neurons have been difficult; methods used to study neurons closer to the surface of the body or in the brain don’t work well deep in adipose tissue, where nerves are hard to see or to stimulate.

Ye and colleagues developed two new methods that enable them to overcome these challenges. First, an imaging approach called HYBRiD turned mouse tissues transparent and allowed the team to better track the paths of neurons as they snaked into adipose tissue. The researchers discovered that nearly half of these neurons didn’t connect to the sympathetic nervous system, but instead to dorsal root ganglia — an area of the brain where all sensory neurons originate.

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