res. 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
Source:American Physiological Society
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