The researchers then compared how mice with and without their Grueneberg ganglia responded to alarm pheromones.
The contrast was very striking, Broillet said.
"The normal mouse immediately gets scared and goes to the corner of the box and freezes," she said. But mice without the ganglia carried on as before, seemingly unaware of the danger signals.
Both groups were able to sniff out cookies hidden in their cages, however, suggesting the altered group's sense of smell was otherwise unaffected.
(Related: "Elephants Distinguish Human Friends From Foes by Smell" [October 18, 2007].)
The chemical sensor's nose-tip location is ideal for early detection of pheromones, Broillet added.
Stuart Firestein, professor of biology at Columbia University, New York, said that the new finding represents two important scientific advances.
"First of all, it extends a growing appreciation that the olfactory system is not a singular system but is really made up of several subsystems," he said.
Second, the study advances the understanding of how body cells and molecules function together within the nervous system.
The newfound mouse alarm detection system introduces "a new and likely powerful model" for such investigations, Firestein said.
The chemical makeup of alarm pheromones and where they are produced in the body remains unknown.
But the discovery of the pheromone sensor should finally enable researchers to identify the molecules involved, study co-author Broillet said.
Alarm pheromones, if they can be artificially produced, could have various uses, such as repelling pests or dispersing crowds, she added.
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