Mice reinvent the hamster wheel in zero gravity

Mice on the International Space Station found a way to duplicate one of their favourite Earth-bound activities — running on a wheel — by doing laps around the walls of their enclosure.  

April Ronca, a research scientist from NASA's Ames Research Center in Moffett Field, California told Quirks & Quarks host Bob McDonald that the odd behaviour didn't happen right away.

"We saw it emerge within two weeks of their introduction to microgravity. we observed it in single animals, and then within just a couple of days, more and more animals began to do this circling behavior."

Mice adapting to their habitat on the ISS.  The 'race-tracking' behaviour begins at about 1:30.

The mice were aboard the space station in the NASA Rodent Habitat in an experiment meant to help researchers learn how their behaviour might change during a long spaceflight. These experiments are part of the work researchers like Ronca are doing to understand the long-term impacts of space travel, which are vital for planning missions into deep space and Mars.

One long flight for a mouse

The experiment included 20 female mice divided into two age groups — some were 16 weeks old, others 32. They were observed on the ISS for 17 to 37 days in microgravity. This is considered a long duration flight given the lifespan of a mouse.

"If you look at the 37 day figure," said Ronca, "these mice were up there for about 1½ human years."

Despite the lack of gravity, the mice performed many of their conventional behaviours, including feeding, grooming, huddling together and interacting with other mice. Ronca says they adapted to weightlessness very quickly. They were able to anchor themselves to the bars of their habitat when they weren't exploring their new environment.

At the end of the flight, they weighed about the same as the control group on Earth, and they were in excellent health, which was a gratifying result for the researchers.

But their "race-tracking" behaviour was of the greatest interest.  

About seven days after the launch, the younger mice started a distinctive circling behaviour on the walls of the larger room in their enclosure. The mice ran around their habitat walls in what quickly came to be an organized group activity, with faster mice carefully moving around slower ones as they did their laps.

Effectively, they'd learned to turn their enclosure into the equivalent of a running wheel on Earth.

Although more research is needed in order to explain this peculiar behaviour, Ronca said they have several ideas for why the mice might be doing this.

"The first is related to the rewarding effects of physical exercise. Another hypothesis is whether the animals might be responding to stress. And then the third hypothesis is that because the vestibular system was not receiving input from gravity, the mice could potentially by running these circles to produce some vestibular input to their balance system. We don't have a definitive answer."

For now, Ronca and her colleagues are just happy to have even observed "race-tracking" as it will prove helpful in future mice studies in space.    

'Race tracking' by mice on the ISS is reminiscent for Bob McDonald of astronaut Alan Bean exercising on Skylab in 1973.

Of Mice and Men, and the Moon and Mars

As NASA prepares to send humans on long space flights back to the Moon and beyond to Mars, understanding what happens to the body in microgravity will help astronauts adapt and thrive during those long missions.

This experiment on board the International Space Station was one small step - or many tiny steps - in achieving that goal.

"One of the most important things is that we have a habitat that can support mice in space for long durations and that will enable us to ask questions of the mice that we cannot ask of the astronauts in terms of how their physiological systems are responding and how well they're adapting" Ronca said.."We can find out more from mice studies about what can affect the astronauts as we move forward on these extended missions that are planned."