How Mice Smell Fear

All in all, one can see that the ganglion in a mouse's nose is a very special feature, enabling the mouse to smell fear. The following paragraphs provide a closer look at the physical structure of the ganglion and how the danger signals are sent from the ganglion to the brain.
The Grueneberg ganglion is an arrow-shaped structure at the end of the nasal cavity. It lines both sides of the nasal septum, which is also located at the end of the nose. The neurons in the Grueneberg ganglion are covered with skin, and have cilia — fingerlike projections often found on scent-detecting cells — and are wrapped with support cells called glia.
Approximately five hundred neurons are located in the ganglion which, when alerted, send danger signals that travel through the axons to the section of the brain that identifies smells. The brain then processes these signals and sends messages throughout the mouse's body causing it to freeze or run away.


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-A&P

Here is the article with the links to the magazine below.

How Mice Smell Fear

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.

You can usually tell when a person is afraid just by the look on his face. Mice can tell when other mice are afraid too. But instead of using their beady little eyes to detect fear in their fellow mice, they use their tiny pink noses.

Scientists are beginning to understand how mice sense fear. According to a new study, the animals use a structure called the Grueneberg ganglion, which sits inside the tip of their whiskered noses. The ganglion is made up of about 500 neurons — specialized cells that carry messages between the body and the brain.

Researchers discovered the Grueneberg ganglion in 1973. Since then, they have been trying to understand what the structure is used for.

“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 the Grueneberg ganglion 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 also pick up odors with accuracy. So, the 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, and acidity as well as 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. Below you can see what a mouse's ganglion looks like under a microscope. Based on what they saw, the Swiss scientists began to suspect that the ganglion 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 were dying of poisoning by carbon dioxide. 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 started 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 humans.

http://www.sciencenews.org/view/generic/id/36209/title/FOR_KIDS_Mice_sense_each_others_fear

http://www.sciencenews.org/view/generic/id/35672/title/How_mice_smell_fear