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Mice sense each other's fear

Scientists have figured out how mice use their noses to sniff out fear in other mice.

People can usually tell when others are afraid just by the look on their

faces. Mice can tell when other mice are afraid too. But instead of

using their beady little eyes to detect fear in their fellows, they use

their pink little noses.

FEAR-OMONE: Mice smell fear in other mice using a structure called the Grueneberg ganglion. The ganglion has about 500 nerve cells that carry messages between a mouse's nose and brain.

FEAR-OMONE: Mice smell fear in other mice using a structure called the Grueneberg ganglion. The ganglion has about 500 nerve cells that carry messages between a mouse's nose and brain.

Science/AAAS

Scientists are beginning to understand how mice sense fear. According to

a new study, the animals use a structure which sits inside the tip of

their whiskered noses. This Grueneberg ganglion is made up of about 500

specialized cells - neurons - that carry messages between the body and

the brain.

Researchers discovered this ganglion in 1973. Since then, they have been

trying to figure out what it does.

"It's ... something the field has been waiting for, to know what these

cells are doing," says Minghong Ma, a neuroscientist at the University

of Pennsylvania School of Medicine in Philadelphia.

Researchers already knew that this structure sends messages to the part

of the brain that figures out how things smell. But there are other

structures in a mouse's nose that pick up odors. So, this ganglion's

true function remained a mystery.

To investigate further, researchers from Switzerland began testing the

ganglion's response to a variety of odors and other things, including

urine, temperature, pressure, acidity, breastmilk and message-carrying

chemicals called pheromones. The ganglion ignored everything the team

threw at it. That only deepened the mystery of what the ganglion was

actually doing.

Next, the scientists used highly detailed microscopes (called electron

microscopes) to analyze the ganglion in fine detail. Based on what they

saw, the Swiss scientists began to suspect that the structure detects a

certain kind of pheromone - one that mice release when they're afraid or

in danger. These substances are called alarm pheromones.

To test their theory, the researchers collected alarm chemicals from

mice that had encountered a poison - carbon dioxide - and were now dying

Then, the scientists exposed living mice to these chemical warning

signals. The results were revealing.

Cells in the Grueneberg ganglions of the living mice became active, for

one thing. At the same time, these mice began acting fearful: They ran

away from a tray of water that contained alarm pheromones and froze in

the corner.

The researchers conducted the same experiment with mice whose Grueneberg

ganglions had been surgically removed. When exposed to alarm pheromones,

these mice continued exploring as usual. Without the ganglion, they

couldn't smell fear. Their sense of smell wasn't completely ruined,

however. Tests showed that they were able to smell a hidden Oreo cookie.

Not all experts are convinced that the Grueneberg ganglion detects alarm

pheromones, or that there is even such a thing as an alarm pheromone.

What's clear, however, is that mice do have a much more fine-tuned

ability to sense chemicals in the air than do humans.

When people are afraid, they usually yell or wave for help. If humans

were more like mice, imagine how scary it might be just to inhale the

air in an amusement park!

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