Scientific Method —

Warning! Alarm pheromones detected

Scientists solved the mystery of how animals detect alarm pheromones that …

"Danger, Will Robinson! Danger!" 

Alarm pheromones warn animals of the same species that there is danger present, like predators, cause for injuries, or other distressing hazards. When animals pick up alarm pheromones, they react by freezing, running away, or attacking. For a while, scientists were puzzled by how animals detected these pheromones, but researchers from the University of Lausanne, Switzerland, found strong evidence that the Grueneberg ganglion is responsible for this recognition.

The Grueneberg ganglion is present in all mammals that have been examined for it, so we have them too. It is an olfactory subsystem that has a vital role in sensing particular chemicals. Neurons and glial cells (cells that provide support and nutrition for neurons) make up the Grueneberg ganglion, which sits at the tip of the nose, away from the main olfactory system. This places it in the optimal position for swift detection of alarm pheromones.

In order to test the functions of the Grueneberg ganglion, researchers obtained alarm pheromones by killing mice under severe stress with CO2. They then observed how murine Grueneberg ganglion cells reacted to the presence of alarm pheromones and several other stimuli, such as general pheromones, acidic conditions, and temperature fluctuations. Alarm pheromones induced a response in the Grueneberg ganglion cells, but none of the other stimuli caused a significant reaction.

As further proof, the scientists surgically damaged the Grueneberg ganglion in mice to see how this would affect their ability to detect the chemical messengers for danger. Normal mice froze in the presence of alarm pheromones, but the impaired mice had no trouble exploring their environment when they were exposed to the same conditions. The Grueneberg ganglion impairment did not appear to harm their general sense of smell, as both normal and damaged mice were equally capable of finding buried cookies.

Since it is favorable for survival to sense danger that affects one's own species, this warning system exists across the spectrum of living organisms. Even certain plants release alarm pheromones to produce bitter and astringent tannins, so they can become less appetizing to hungry animals. In modern life, our own response to alarm pheromones might be hard to notice, but it is entirely possible that we still inadvertently react to their presence.

Science, 2008. DOI: 10.1126/science.1160770

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