Mutant Mouse not afraid of cat.
http://www.telegraph.co.uk/earth/main.jhtml?xml=/earth/2007/11/07/scimouse107.xml
By Roger Highfield, Science Editor
Last Updated: 6:01pm GMT 07/11/2007
A mouse has befriended its mortal enemy, the cat, after scientists used genetic methods to tinker with its response to the smell of fear.
It gives me great pleasure to announce an end to hostilities between our peoples
The result is the stuff of nightmares for fans of Tom and Jerry: a rodent that, unlike its peers, shows no sign of anxiety or panic when presented with the smell of a cat, or even the real thing.
Using sophisticated genetic engineering, they tinkered with a brain circuit in research that both demonstrates the power of a new technique to show what brain circuit do and suggests mice, and humans, are born with a fear of certain smells.
The innate tendency of mice to shy away from the smell of danger can be switched off by simply turning off certain nerve cells that detect smells in the nose, even though the same mice can still be taught to avoid the odour of felines, says the study published today in Nature.
The resulting "delta-D" mutant mice were also able to discriminate other smells but "was not afraid of cat odours, and approached the cats without a sign of fear," said Dr Ko Kobayakawa, who did the work with his wife Reiko at the University of Tokyo.
To make sure that these intrepid mice did not end up being eaten, Dr Kobayakawa explained that they used specially-selected cats. "For this purpose, we selected meek and cowardly individuals from a number of cats, which are kept by students in the department of veterinary medicine."
Even the cowardly cats would eventually begin to stare, then raise a paw, a sign they were about to pounce, at which point the researchers whisked them away from their valiant GM mice.
"When the cat started to show these signs of hunting during the photo shoots, we changed to another cat as rapidly as possible," he said. "Fortunately, not a single delta-D mouse was sacrificed during the photo shoots."
To show that the genetic surgery had only affected the nerve cells in the nose - dorsal zone olfactory sensory neurons - that can trigger fear, and not the ability to quail and panic, they found that the altered mice still froze if they heard a cat meow.
"This observation may suggest that the delta-D mice only lacked the innate fear responses to cats' odours, but they did not lose the feeling of fear," said Dr Kobayakawa.
The technique has great potential in neuroscience, he added: "We think it as the power to clarify many unrevealed principles of the brain, those which generate emotions and behaviours in mammals."
The study is of basic interest because it shows this smell of fear response is not learned but hard wired into the mouse brain. Humans have this response too, though Dr Kobayakawa said that this is much diminished compared with mice.
"However, human beings still have a strong feeling of dislike to spoiled food smells," he said, and the study suggests that, like mice, we are born with a dislike of curdled and mouldy food.
"It is not clear if humans have such receptors, but we can assume that humans produce different body odour compounds under anxiety conditions and that other humans can recognise it - not as fear smell but they know that it smells different and then become alerted," commented Prof Karl Grammer of the Ludwig-Boltzmann-Institute for Urban Ethology, University of Vienna.
There is increasing evidence that humans do respond to the smell of signalling chemicals - pheromones, - added Dr Denise Chen, of Rice University, Houston. "Only a few years ago... many in the scientific community would not even entertain the idea of a human pheromone.
"The past couple of years have witnessed a paradigm shift in this belief, as a result of an explosion of findings about the involvement of the main olfactory system in pheromone sensing."
The idea of the presence of both learned and innate systems for processing smells within the main olfactory system may shed light on understanding and elucidating the differences in which humans process salient social chemosignals (for example, fearful sweat) and other types of smells (for example, non-emotional body odour or non-social smells)."
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