Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

How appetite-stimulating brain cells work overtime during fasting

05.01.2007
During periods of fasting, brain cells responsible for stimulating the appetite make sure that you stay hungry. Now, a new study of mice reported in the January issue of the journal Cell Metabolism, published by Cell Press, reveals the complex series of molecular events that keep those neurons active.

The researchers revealed a link between active thyroid hormone in the brain and increases in an "uncoupling" protein (UCP2) that boosts the number of power-generating mitochondria in neurons that drive hunger. The increase in mitochondria, in turn, allows the brain's hunger center to remain active when periods of food scarcity result in a "negative energy balance," said Sabrina Diano of Yale University School of Medicine, who led the study.

Indeed, the researchers found, animals lacking either UCP2 or an enzyme that stimulates thyroid hormone's production ate less than normal after a period of food deprivation.

"This shows the key importance of UCP in the brain and its effect on neuronal activity," Diano said. "It's how neurons 'learn' that food is missing, and it keeps them ready to eat when food is introduced."

The mechanism involved is very similar to the one that regulates core body temperature in peripheral body tissues, Diano added.

Thyroid hormones are known to play major roles during development as well as in adulthood, the researchers said. In adults, the thyroid gland is essential to regulating metabolism. Previous studies had also established a key physiological role for the active thyroid hormone, triiodothyronine (T3), in the regulation of body temperature by heat-generating brown fat.

The molecular underpinning of heat production, or thermogenesis, in brown fat is the activation of mitochondrial uncoupling protein 1 (UCP1) by T3, the researchers said. The UCP1 activation, which is controlled by the sympathetic nervous system, also leads to an increase in the number of mitochondria.

The role of the related protein, UCP2, which is present at high levels in the hypothalamic arcuate nucleus--considered to be the key brain site that responds to changes in peripheral tissue metabolism--had remained less clear. However, scientists did know that that portion of the brain harbors thyroid hormone receptors and has the capacity for local production of T3.

Now, the researchers found that support cells in the hypothalamus producing an enzyme that catalyzes active thyroid hormone production are side by side with appetite-stimulating neurons that express UCP2. In mice that were fasted for 24 hours, the arcuate nucleus showed an increase in the "DII" enzyme's activity and local thyroid production, in parallel with increased UCP2 activity.

This fasting-induced, T3-mediated UCP2 activation resulted in mitochondrial proliferation in the neurons, an event that was critical for the brain cells' increased excitability and consequent rebound feeding by the animals following food deprivation.

"Our results indicate that this mechanism is critical in sustaining an increased firing rate in these [hunger-stimulating] cells so that appetite remains elevated during fasting," Diano's group concluded. "Overall, our study provides strong evidence for an interplay between local T3 production and UCP2 during fasting and reveals a central thermogenic-like mechanism in the regulation of food intake."

While it is as yet unproven, the rise in UCP2 in the brain likely also causes changes in temperature in the same way that UCP1 does in brown fat, Diano said.

"It's possible that heat may act like a neurotransmitter of a sort," Diano said. Neurotransmitters are chemical messengers that relay signals to and from neurons. "Changes in temperature could have a strong effect on brain function."

The findings emphasize the complexity of the feeding circuitry, which once "seemed so simple," wrote Charles Mobbs of Mount Sinai School of Medicine in an accompanying preview article. Researchers had thought that decreased levels of the fat-produced hormone leptin alone signaled the hypothalamus that fat levels have fallen, leading hypothalamic neurons to activate a program, including hunger, to preserve energy and restore fat levels, he said.

Now, "a series of studies, including those reported in this issue of Cell Metabolism by [Diano and colleagues] have elegantly demonstrated that hypothalamic responses to food deprivation involve at least three hormones, two cell types, and an unexpected interlocutor, uncoupling protein 2."

Erin Doonan | EurekAlert!
Further information:
http://www.cellmetabolism.org

More articles from Health and Medicine:

nachricht Cystic fibrosis alters the structure of mucus in airways
28.06.2017 | University of Iowa Health Care

nachricht Mice provide insight into genetics of autism spectrum disorders
28.06.2017 | University of California - Davis

All articles from Health and Medicine >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Can we see monkeys from space? Emerging technologies to map biodiversity

An international team of scientists has proposed a new multi-disciplinary approach in which an array of new technologies will allow us to map biodiversity and the risks that wildlife is facing at the scale of whole landscapes. The findings are published in Nature Ecology and Evolution. This international research is led by the Kunming Institute of Zoology from China, University of East Anglia, University of Leicester and the Leibniz Institute for Zoo and Wildlife Research.

Using a combination of satellite and ground data, the team proposes that it is now possible to map biodiversity with an accuracy that has not been previously...

Im Focus: Climate satellite: Tracking methane with robust laser technology

Heatwaves in the Arctic, longer periods of vegetation in Europe, severe floods in West Africa – starting in 2021, scientists want to explore the emissions of the greenhouse gas methane with the German-French satellite MERLIN. This is made possible by a new robust laser system of the Fraunhofer Institute for Laser Technology ILT in Aachen, which achieves unprecedented measurement accuracy.

Methane is primarily the result of the decomposition of organic matter. The gas has a 25 times greater warming potential than carbon dioxide, but is not as...

Im Focus: How protons move through a fuel cell

Hydrogen is regarded as the energy source of the future: It is produced with solar power and can be used to generate heat and electricity in fuel cells. Empa researchers have now succeeded in decoding the movement of hydrogen ions in crystals – a key step towards more efficient energy conversion in the hydrogen industry of tomorrow.

As charge carriers, electrons and ions play the leading role in electrochemical energy storage devices and converters such as batteries and fuel cells. Proton...

Im Focus: A unique data centre for cosmological simulations

Scientists from the Excellence Cluster Universe at the Ludwig-Maximilians-Universität Munich have establised "Cosmowebportal", a unique data centre for cosmological simulations located at the Leibniz Supercomputing Centre (LRZ) of the Bavarian Academy of Sciences. The complete results of a series of large hydrodynamical cosmological simulations are available, with data volumes typically exceeding several hundred terabytes. Scientists worldwide can interactively explore these complex simulations via a web interface and directly access the results.

With current telescopes, scientists can observe our Universe’s galaxies and galaxy clusters and their distribution along an invisible cosmic web. From the...

Im Focus: Scientists develop molecular thermometer for contactless measurement using infrared light

Temperature measurements possible even on the smallest scale / Molecular ruby for use in material sciences, biology, and medicine

Chemists at Johannes Gutenberg University Mainz (JGU) in cooperation with researchers of the German Federal Institute for Materials Research and Testing (BAM)...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Plants are networkers

19.06.2017 | Event News

Digital Survival Training for Executives

13.06.2017 | Event News

Global Learning Council Summit 2017

13.06.2017 | Event News

 
Latest News

High conductive foils enabling large area lighting

29.06.2017 | Power and Electrical Engineering

Designed proteins to treat muscular dystrophy

29.06.2017 | Life Sciences

Climate Fluctuations & Non-equilibrium Statistical Mechanics: An Interdisciplinary Dialog

29.06.2017 | Seminars Workshops

VideoLinks
B2B-VideoLinks
More VideoLinks >>>