New genetically engineered mice show no fear of cats, according to the Japanese scientists who created the rodents. The modified mice may also shed new light on mammal behavior.

Scientists at the University of Tokyo say they have used genetic engineering to successfully switch off a mouse's instinct to cower at the smell or presence of cats - evidence that fear may be genetically hardwired and not learned through experience, as commonly believed.

Kobayakawa developed the fearless mice by shutting down receptors in their olfactory bulb - the area of the brain that processes information about smells - which would normally induce panic as soon as they get so much as a whiff of a cat.

"Mice are naturally terrified of cats and usually panic or flee at the smell of one. But mice with certain nasal cells removed through genetic engineering didn't display any fear," - research leader Ko Kobayakawa said.

Rather than flee or freeze when confronted with their feline enemy, the mice sniffed and even played with them, blissfully unaware of the potential dangers.

"The mice approached the cat, even snuggled up to it and played with it. The discovery that fear is genetically determined and not learned after birth is very interesting and goes against what was previously thought," - Ko Kobayakawa said.

According to him, the findings suggest that the human aversion to dangerous smells like that of rotten food, for example, could also be genetically predetermined.

Kobayakawa said his findings, published in the science journal Nature last month, should help researchers shed further light on how the brain processes information about the outside world.

"Once removing innate elements by which mice fear cats from them, we are able to make mice who can get along with cats. So by applying this theory to other mammals, we will probably be able to make other animals that are not afraid of their natural enemies," - he said.

Also, according to the researchers, even the modified mice froze in fear whenever the cats miaowed.