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 Study relating to materials testing Detecting damages in non-magnetic steel through magnetism
23.07.2018 | Technische Universität Kaiserslautern

nachricht Innovative genetic tests for children with developmental disorders and epilepsy
11.07.2018 | Christian-Albrechts-Universität zu Kiel

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: Unraveling the nature of 'whistlers' from space in the lab

A new study sheds light on how ultralow frequency radio waves and plasmas interact

Scientists at the University of California, Los Angeles present new research on a curious cosmic phenomenon known as "whistlers" -- very low frequency packets...

Im Focus: New interactive machine learning tool makes car designs more aerodynamic

Scientists develop first tool to use machine learning methods to compute flow around interactively designable 3D objects. Tool will be presented at this year’s prestigious SIGGRAPH conference.

When engineers or designers want to test the aerodynamic properties of the newly designed shape of a car, airplane, or other object, they would normally model...

Im Focus: Robots as 'pump attendants': TU Graz develops robot-controlled rapid charging system for e-vehicles

Researchers from TU Graz and their industry partners have unveiled a world first: the prototype of a robot-controlled, high-speed combined charging system (CCS) for electric vehicles that enables series charging of cars in various parking positions.

Global demand for electric vehicles is forecast to rise sharply: by 2025, the number of new vehicle registrations is expected to reach 25 million per year....

Im Focus: The “TRiC” to folding actin

Proteins must be folded correctly to fulfill their molecular functions in cells. Molecular assistants called chaperones help proteins exploit their inbuilt folding potential and reach the correct three-dimensional structure. Researchers at the Max Planck Institute of Biochemistry (MPIB) have demonstrated that actin, the most abundant protein in higher developed cells, does not have the inbuilt potential to fold and instead requires special assistance to fold into its active state. The chaperone TRiC uses a previously undescribed mechanism to perform actin folding. The study was recently published in the journal Cell.

Actin is the most abundant protein in highly developed cells and has diverse functions in processes like cell stabilization, cell division and muscle...

Im Focus: Lining up surprising behaviors of superconductor with one of the world's strongest magnets

Scientists have discovered that the electrical resistance of a copper-oxide compound depends on the magnetic field in a very unusual way -- a finding that could help direct the search for materials that can perfectly conduct electricity at room temperatur

What happens when really powerful magnets--capable of producing magnetic fields nearly two million times stronger than Earth's--are applied to materials that...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Within reach of the Universe

08.08.2018 | Event News

A journey through the history of microscopy – new exhibition opens at the MDC

27.07.2018 | Event News

2018 Work Research Conference

25.07.2018 | Event News

 
Latest News

Staying in Shape

16.08.2018 | Life Sciences

Diving robots find Antarctic seas exhale surprising amounts of carbon dioxide in winter

16.08.2018 | Earth Sciences

Protein droplets keep neurons at the ready and immune system in balance

16.08.2018 | Life Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>