-- Mary Elizabeth Dallas
FRIDAY, March 30 (HealthDay News) -- Cold conditions may affect
the well-being of laboratory mice and influence the outcome of
research studies, a new study suggests.
Researchers from the Stanford University School of Medicine
found that nine of 10 drugs tested on mice that were housed in
chilly temperatures failed to work in people. They suggested this
may be because being cold triggers changes in mice's immune
function and slows their growth.
"If you want to design a drug that will help a patient in the hospital, you cannot reasonably do that in animals that are cold-stressed and are compensating with an elevated metabolic rate," study author Joseph Garner, an associate professor of comparative medicine, said in a Stanford news release. "This will change all aspects of their physiology -- such as how fast the liver breaks down a drug -- which can't help but increase the chance that a drug will behave differently in mice and in humans."
The study authors argued that one simple way to correct this
problem would be to allow laboratory mice to warm up, which would
make them more physiologically comparable to people.
"Why not let them do what they do in the wild, which is build nests? Mice can happily infest a meat freezer, with temperatures far below zero, but they survive and breed because they build these wonderful nests," Garner said.
To test their theory, the researchers created sets of two cages
linked by a small tube for 36 male and 36 female mice of three
common strains. In each of the sets, one cage was kept at a cool 68
degrees Fahrenheit and was equipped with various amounts of
shredded paper that the mice could use to make nests to keep warm
and provide themselves with shelter. The connected cage had no
nesting material and was kept at one of six temperatures, ranging
from 68 to 95 degrees Fahrenheit.
The mice were allowed to choose which side of the cage they
wanted to use. Although the strain and sex of the mice played a
role in their preferences, the study revealed none of the mice
chose to stay cold. Instead, whenever they had the option the mice
chose to move to a warmer cage.
The mice also moved nesting material from colder cages to warmer
cages, suggesting nests serve as more than a source of warmth for
mice. The researchers noted that nests could also be a source of
physical comfort or protection for mice that relieves their stress
The study authors added that nests also offer clues about how
the mice are doing physically. "The shape of the nest tells an
experienced person whether the animals are too hot or too cold,
whether they are sick or whether they are about to give birth,"
Garner said. "Once you learn how to 'speak mouse nest,' the nest is
a wonderful tool that anyone can use to assess the general state of
The study, published online March 30 in the journal
PLoS ONE, pointed out that simply raising the temperature in research laboratories wouldn't work because the mice would get too aggressive. The researchers concluded that laboratory mice should be routinely supplied with as much as 10 grams of nesting material.
The U.S. National Cancer Institute provides more information on
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