Knocking off olfactory cells makes mice fearless in the face of danger

November 14th, 2007 - 10:17 am ICT by admin  
Hitoshi Sakano, a neuroscientist at the university, says the new finding suggests that smells pass through distinct circuits reaching from the nose to the brain.

The olfactory neurons are located in a special structure in the nasal cavity called the olfactory epithelium, which has two major regions called dorsal and ventral.

In order to determine the difference between the dorsal and ventral neurons, Sakano and his colleagues engineered a strain of mice that had no olfactory neurons in their dorsal epithelium. They then tested the mice for their response to a handful smells, good and bad.

The researcher say that normal mice were drawn to smells of peanut butter and mouse urine, but they were tried to escape the scents of rotting food, fox glands, and the urine of snow leopards.

However, mice engineered to lose olfactory neurons showed less interest in the sweet smells and little aversion to the scents that were dreaded by normal mice.

The researchers said that the mice were still able to detect those smells, and could learn to hate the odours if they were made sick while delivering the ‘nasty’ smells.

Based on their findings, the researchers came to the conclusion that the dorsal olfactory neurons transmit innate fear responses to the brain, whereas the ventral neurons convey learned aversion.

The researchers also noted a difference in the brains of the mice. While a scent secreted by fox anal glands called trimethyl-thiazoline stimulated the normal mice’s brains to make adrenocorticotropic hormone, a sign of stress, the fearless mutants did not show any such stimulation.

Catherine Dulac, a neuroscientist at Harvard University in Cambridge, Massachusetts, described this work as a big step forward in explaining how odours are translated into actions.

Sakano believes that humans may also be having a similar system for discerning smells. He, however, says that learned behaviours can sometimes over-rule innate ones.

He supported his proposition with the example that Natto, fermented soya beans with rancid smell, is a popular snack in Tokyo probably because people have learnt to like it.

“I think an innate smell will tell us it’s dangerous and don’t eat it. But based on the associative learning, some people in the Tokyo area learn to like it,” Nature magazine quoted Sakano as saying. (ANI)

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