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.
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
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
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 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!