Curious mice need room to run

Lab mice like a little extra space and a cage with a few frills.

A plusher cage could lead to happier mice, and more reliable results. Credit: © Alamy.com

Laboratory mice may need to satisfy their curiosity just as much as they need food and water, according to a study of mouse behaviour1. They'll even take antidepressants if they aren't given the chance to run around and explore2.

Christopher Sherwin, an animal welfare scientist from Bristol University, wanted to see whether confinement to a standard-sized cage stresses laboratory mice. He trained mice in normal laboratory cages to press a lever to open a door into an adjoining cage. He then varied the number of times the lever had to be pressed before the door would open, and monitored how willing the mouse was to keep working in order to get access to more space.

Surprisingly, the amount of work the mouse was willing to put in was similar to the amount of work that mice generally do to gain access to extra food and water.

It doesn't seem to matter how big the adjoining cage is, says Sherwin. Mice were just as willing to work to get a little bit of extra space as they were to get into a larger area, indicating that they were simply curious to explore.

"This kind of study is important," says Donald Broom, an animal behaviour scientist at the department of veterinary medicine at the University of Cambridge, as it tries to measure the things that are important to a lab animal's welfare. But, he notes, it is hard to compare how much work one mouse will do for more space under one set of conditions to how much work other mice will do for food in a different environment. The comparison, he says, might not be valid.

Still, Sherwin says, the study points out that mice do put a lot of value on having room to run around. "I am surprised that the mice's demand for space is so high," says Kathleen Mathers, who is head of biological services at the National Institute for Medical Research.

On drugs

Sherwin then carried out a second experiment to show that mice are less stressed in larger, plusher cages. He gave mice a way to self-administer antidepressant drugs-the less anxious or fearful the mouse, the less it would be expected to dose itself up.

Sherwin found that mice were more likely to drink water spiked with antidepressants than plain water when living in standard housing, but switched to more of the plain stuff when given accommodation with a few more frills - such as a bit more space and material to chew or nest in.

“We will consider anything we can do to make mice happier Kathleen Mathers , National Institute for Medical Research”

Some studies suggest that relaxed, unstressed animals are likely to act more 'normally' and produce more reliable results in studies of their behaviour, says Sherwin. His results show that just a little extra effort could provide unstressed conditions, he says, and that should make for better experiments. "The data would be better if the welfare is better," he says.

Mathers says all studies that assess the value of giving lab animals more luxuries are welcome, and adds that it's a burgeoning area of study. "We will consider anything we can do to make mice happier," she says. Her own group is also developing low-cost cage accessories for mice.

References

  1. 1

    Sherwin, C. M. The motivation of group-housed laboratory mice, Mus musculus, for additional space. Animal Behaviour, doi:10.1016/j.anbehav.2003.08.018, (2004).

  2. 2

    Sherwin, C. M. & Olsson, I. A. S. Housing conditions affect self-administration of anxiolytic by laboratory mice. Animal Welfare, 13, 33 - 39, (2004).

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National Institute for Medical Research

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Nelson, L. Curious mice need room to run. Nature (2004). https://doi.org/10.1038/news040209-6

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