Danger mouse gets cosy with cats
8 November 2007
Japanese scientists have bred a fearless mouse, shedding light on how the rodents sniff out danger. It turns out that being scared of cats is an instinct in a mouse's genes. Antenna investigates...
This research was published in the journal Nature on 8 November 2007.
Image: Ko and Reiko Kobayakawa
Mice have very sensitive noses, and over a thousand different genes dedicated just to smell. These help them sniff out and run away from unpleasant odours such as the scent of predators or rotten food.
Until now, scientists thought mice usually learnt to avoid these nasty smells. But now a team from the University of Tokyo, Japan, have bred mutant mice that have no smell-based fear, showing that this instinct is coded in the genes.
Normal mice run away from the scent of cats, but this mutant mouse is happy playing in a cat's collar.
Image: Ko and Reiko Kobayakawa
What did the scientists do?
The researchers genetically modified mice so that specific sets of smell-receptive nerve cells in the nose - olfactory sensory nerves - didn't grow. With no nerve cells to connect to, the areas of the brain that process smell didn't develop properly.
The researchers genetically modified mice so that specific sets of smell-receptive nerve cells in the nose - olfactory sensory nerves - didn't grow. With no nerve cells to connect to, the areas of the brain that process smell didn't develop properly.
The mutant mouse on the left isn't afraid of the fox-scented paper, but the normal mouse on the right is frozen in terror.
Video: Ko and Reiko Kobayakawa
The team tested out the behaviour of their mutant mice on a range of different smells and compared them to mice with fully functioning noses. |
Image: Ko and Reiko Kobayakawa
Although normal mice avoided rotting food smells and the scent of predatory cats and foxes, the mutant mice didn't shy away from danger. Instead, they were happy to sniff the whiff of foxes and get up close to cats, usually their deadliest enemies. |
Playing cat and mouse...
But their sense of fear wasn't switched off completely. The mutant mice could still be taught to avoid perilous pongs. And if a cat meowed the mice froze - only their automatic smell fear response was out of action.
Researcher Ko Kobayakawa from the University of Tokyo explains: 'Our mutant mice approached cats defencelessly and they sometimes ran in under kittens. But our results also showed that the mice could still detect these smells with their remaining intact sensory nerve cells.
'In mice at least, it seems there are different areas of the brain that process information about smell - one area for instinctive smell recognition and another area for smells that have to be learned.'
Reiko (left) and Ko (right) Kobayakawa from the University of Tokyo, Japan, with their mutant mice.
Image: Ko and Reiko Kobayakawa
So do humans have instinctive fears and could they too be down to our genes?
'Although humans no longer respond strongly to predator odours, we do still have a strong feeling of dislike towards rotten food smells,' explains Ko. 'The receptors that detect these smells in mice are also present in humans, so it's possible these adverse reactions are also instinctive in us and that our genes are partly responsible.'
Image: Stock.XCHNG/ JR Goleno