Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Just like us, social stress prompts hamsters to overeat, gain weight

10.05.2006


Put a mouse or a rat under stress and what does it do? It stops eating. Humans should be so lucky. When people suffer nontraumatic stress they often head for the refrigerator, producing unhealthy extra pounds.



When Syrian hamsters, which are normally solitary, are placed in a group-living situation, they also gain weight. So scientists at the Center for Behavioral Neuroscience at Georgia State University are using hamsters as a model for human stress-induced obesity. They want to begin unraveling the complex factors that lead people to eat when under stress and hope that the information can eventually be used to block appetites under this common scenario.

The study, "Social defeat increases food intake, body mass, and adiposity in Syrian hamsters," by Michelle T. Foster, Matia B. Solomon, Kim L. Huhman and Timothy J. Bartness, Georgia State University, Atlanta, appears in the May issue of the American Journal of Physiology-Regulatory, Integrative and Comparative Physiology published by The American Physiological Society.


Hamsters similar to humans

In the study, the researchers look at nontraumatic stress -- the stress we experience in everyday life, such as getting stuck in traffic or trying to complete a major project at work. It is distinct from traumatic stress, such as suffering the death of a loved one. Traumatic stress typically dulls the human appetite, said Bartness, the study’s senior researcher and an authority on obesity.

In the U.S., where food is plentiful and relatively cheap, overeating can be difficult to control. Stress-related overeating is more difficult to control than the overeating that people do just because food tastes good and is available, Bartness said. If scientists could learn how to reduce the urge to eat in the face of stress, it could improve the health of a lot of people. And that was the point of this study.

The researchers used Syrian hamsters, the kind commonly found in pet stores. They set up a situation in which subordinate hamsters would suffer a "social defeat" at the hands of a dominant hamster. The researchers wanted to see if the defeated hamsters would eat more and gain weight under the stress, just like a human. Mice and rats eat less and lose weight when subjected to a similar stress, making them a poor subject for human stress-induced obesity research.

The study asked three questions:

  • Does repeated social defeat increase food intake, weight and fat in hamsters?
  • If so, how many defeats are necessary?
  • Do intermittent (unpredictable) defeats increase fat and food intake more than consecutive (predictable) defeats, as is true in humans?

An uncomfortable situation

To answer these questions, the researchers placed an 11-week-old hamster (the subordinate intruder) into the cage of an older and larger hamster (the dominant resident). The intruder remained in the aggressor’s cage for seven minutes per trial. The situation set up a clear dominant versus subordinate situation between the hamsters, the authors explained.

"Hamster aggression is highly ritualized, with dominance or submission generally established within the first minute and maintained thereafter through social signals and social communication between the opponents," the authors wrote. The intensity of most agonistic encounters was moderate, with some chasing and biting, but with no actual tissue damage.

A trained observer recorded submissive behaviors and also ensured that no harm came to either of the hamsters, which normally live alone. Because the smaller hamster was the intruder, the outcome of the dominance/submissive tussle was a foregone conclusion.

The researchers found that, as a result of the stress of being placed in the home cage of a larger resident, intruder hamsters subsequently:

  • ate significantly more
  • gained significantly more weight
  • gained significantly more fat, including visceral fat

These results occurred when the intruder hamsters were placed in the foreign cage as few as four times, a total of 28 minutes, over the 33-day experiment, Bartness explained. Hamsters that were placed in the situation only once during the experiment did not eat more or gain weight compared to a control group. In addition, the intruder hamsters that were placed in the cage intermittently (at unpredictable times) showed comparable weight and fat gain compared to those placed in a foreign cage consecutively (at regular times).

However, while the intermittent group increased on all measures of fat gain, the consecutive group increased on only two of the fat measures. Still, this was an unexpected result.

"In humans, unpredictable [stress] events are more aversive than predictable events, causing greater alterations in homeostasis and thus increased stress," the authors wrote. "In addition, previous research suggests that unpredictable events cause greater activation in brain regions responsible for fear and anxiety in laboratory rats and reduction in immune function compared with events that are predictable."

Next steps

Syrian hamsters provide a good model for obesity research, not only because they eat more and gain weight, but because, like humans, they add fat to their abdomens -- visceral fat. Visceral fat is particularly unhealthy because it affects the internal organs and is associated with diabetes, cancer and other serious illnesses, Bartness said.

Bartness’ team began a second study to determine whether other stressors, such as a mild foot shock, produce the same effect as the social defeat model; and whether the dominant hamsters gain weight and fat as the result of the intrusion of the submissive hamsters.

Another line of inquiry would be to compare mice and rats to hamsters. Humans and hamsters, which eat more under stress, share the same predominant stress hormone, cortisol, noted Bartness, Rats and mice, which eat less under stress, have a different primary stress hormone, corticosterone. This raises the question of whether stress-induced increases in cortisol play a more important role in the desire to eat and weight gain compared to corticosterone.

Researchers will also want to know if drugs can block stress-induced obesity, for example, by blocking the release of the stress hormone, corticotrophin releasing factor (CRF), or by blocking the body’s CRF receptors, Bartness said. CRF, also sometimes referred to as corticotrophin releasing hormone, produces the body’s "fight or flight" response under stress and helps kick off a cascade of physiological responses.

"There are a whole suite of physiological responses that occur as a result of stress," Bartness said. It will take time to unravel all these physiological responses and to use that knowledge to block stress-induced obesity. It may even turn out that the reactions are too complex to easily block, he said.

Christine Guilfoy | EurekAlert!
Further information:
http://www.the-aps.org

More articles from Studies and Analyses:

nachricht WAKE-UP provides new treatment option for stroke patients | International study led by UKE
17.05.2018 | Universitätsklinikum Hamburg-Eppendorf

nachricht First form of therapy for childhood dementia CLN2 developed
25.04.2018 | Universitätsklinikum Hamburg-Eppendorf

All articles from Studies and Analyses >>>

The most recent press releases about innovation >>>

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

Im Focus: Molecular switch will facilitate the development of pioneering electro-optical devices

A research team led by physicists at the Technical University of Munich (TUM) has developed molecular nanoswitches that can be toggled between two structurally different states using an applied voltage. They can serve as the basis for a pioneering class of devices that could replace silicon-based components with organic molecules.

The development of new electronic technologies drives the incessant reduction of functional component sizes. In the context of an international collaborative...

Im Focus: LZH showcases laser material processing of tomorrow at the LASYS 2018

At the LASYS 2018, from June 5th to 7th, the Laser Zentrum Hannover e.V. (LZH) will be showcasing processes for the laser material processing of tomorrow in hall 4 at stand 4E75. With blown bomb shells the LZH will present first results of a research project on civil security.

At this year's LASYS, the LZH will exhibit light-based processes such as cutting, welding, ablation and structuring as well as additive manufacturing for...

Im Focus: Self-illuminating pixels for a new display generation

There are videos on the internet that can make one marvel at technology. For example, a smartphone is casually bent around the arm or a thin-film display is rolled in all directions and with almost every diameter. From the user's point of view, this looks fantastic. From a professional point of view, however, the question arises: Is that already possible?

At Display Week 2018, scientists from the Fraunhofer Institute for Applied Polymer Research IAP will be demonstrating today’s technological possibilities and...

Im Focus: Explanation for puzzling quantum oscillations has been found

So-called quantum many-body scars allow quantum systems to stay out of equilibrium much longer, explaining experiment | Study published in Nature Physics

Recently, researchers from Harvard and MIT succeeded in trapping a record 53 atoms and individually controlling their quantum state, realizing what is called a...

Im Focus: Dozens of binaries from Milky Way's globular clusters could be detectable by LISA

Next-generation gravitational wave detector in space will complement LIGO on Earth

The historic first detection of gravitational waves from colliding black holes far outside our galaxy opened a new window to understanding the universe. A...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Save the date: Forum European Neuroscience – 07-11 July 2018 in Berlin, Germany

02.05.2018 | Event News

Invitation to the upcoming "Current Topics in Bioinformatics: Big Data in Genomics and Medicine"

13.04.2018 | Event News

Unique scope of UV LED technologies and applications presented in Berlin: ICULTA-2018

12.04.2018 | Event News

 
Latest News

Could a particle accelerator using laser-driven implosion become a reality?

24.05.2018 | Physics and Astronomy

Hot cars can hit deadly temperatures in as little as one hour

24.05.2018 | Health and Medicine

Complementing conventional antibiotics

24.05.2018 | Life Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>