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Mice are real gym bunnies

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Big wheel turning: mice love a good workout (Source: urbanraven/iStockphoto)

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Mice are real gym bunnies

Tuesday 10th February 2015 1:01 pm

You’ve probably heard of the hamster wheel or running wheel, it’s an exercise device used either for pets at home or in the laboratory, and mainly by hamsters and other small rodents. But it turns out that creatures in the wild love to have a go on it as well.

Now animal scientists have long used these running wheels to work out the effects of exercise on health, circadian rhythms and so on.

And indeed about 15 – 20 million lab rats and mice are given the opportunity to volunteer for laboratory testing each year.

But there has always been concern about whether the animals were running on the wheel because they were unhappy to be in a cage. Maybe the running was actually a neurotic, repetitive behaviour that actually showed the animals were deeply disturbed.

After all, in the aftermath of a major disaster or a personal calamity you’ll often see people repetitively rocking back and forth as their way of coping with the stress. It’s called stereotypic behaviour. It’s repetitive, unchanging and seems to have no obvious goal.

So Johanna H Meijer and Yuri Robbers from the Leiden University Medical Centre in the Netherlands took two running wheels out of the laboratory and into the wild. One set up that was in a “green urban area” — which is fancy scientific talk for Professor Mayer’s backyard. And the other one was set up in a sandy dune area that the public did not have general access to.

Now each of these running wheels was inside a cage with a small door so only small animals could get inside. The scientists put food inside the cage to attract local wildlife and in each case and infrared camera activated by a motion sensor was set up to record any running wheel activity.

Over the first two years about 1000 animals voluntarily went for a run in the backyard, and about 250 on the wheel in the dune area. The creatures were overwhelmingly wild mice, but a few rats, shrews, frogs, birds, snails and slugs also dropped in to do some running, hopping and slithering.

Sometimes the slugs would slither along for hours. Then the scientists got worried that maybe the animals had been attracted by the food. Perhaps the animals were under the delusion that if they kept on running more food would appear, so after two years the scientists stopped providing food.

But over the next 16 months the animals kept dropping in for a run. There weren’t as many, but they still went on the wheel. About half of the drop-ins were very young mice that were born since they’d stopped providing food. So they were definitely dropping in with the specific goal of running on the wheel. It was their neighbourhood mouse gym.

The mice knew what they were doing. They’d run for a bit, get off for a rest, and then hop back on the running wheel again. In fact the wild mice were taking their local gym quite seriously. Their average speed of running was a bit below that of the lab mice — 1.3 kilometres per hour as opposed to 2.3 kilometres per hour, but on the other hand, their top speed. Of 5.7 kilometres per hour was higher than lab mice ever reached, which was only 5.1 kilometres per hour.

We know that about two-thirds of early deaths in humans are related to lifestyle. Too much food, not enough exercise and the like. We also know that exercise helps you grow new brain cells, slows ageing and reduces the incidence of various cancers, diabetes, heart disease and stroke. In general, exercise is good for you.

At this stage, all we know for sure is that the wild mice are going for a run on the exercise wheel. But we don’t know why. Do they know that exercise is good for them? Were they getting the so-called ‘runner’s high’ from the endorphins or endocannabinoids? Or were they working on their thighs? Or were they simply playing and having fun?

I wonder if the scientists would get more mice on their running wheel if they installed mirrors in the cage and began blasting the doof-doof music …

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