Why do mice sniff?
Daphnee Reichel
2025-07-23 10:43:24
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Mice have about 1200 kinds of odor receptors, and 14 kinds of TAARs. In comparison, humans —who rely more on vision than smell— have about 350 odor receptors and five TAARs. One of the things that’s really new here is that this is a generalized predator kairomone that’s volatile. For rodents, it’s the smell of danger. Ferrero identified the compound that activates TAAR4 as 2-phenylethylamine, a product of protein metabolism. He then obtained specimens from 38 species of mammals and found elevated levels of 2-phenylethylamineby 18 of 19 species of carnivores, but not by non-carnivores. In a series of behavior tests, rats and mice showed a clear, innate avoidance to the smell of 2-phenylethylamine. The behavioral studies were repeated using a carnivore samples that had been depleted of 2-phenylethylamine. Rats failed to show full avoidance of the depleted carnivore urine, indicating that 2-phenylethylamine is a key trigger for predator avoidance.
Unique Lowe
2025-07-23 09:54:34
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Mice have two different ways to pick up scents: their nose and a specialized organ inside their nose called the vomeronasal organ (VNO), which helps them detect other mouse pheromones. Suspecting that VNO might help the rodents sniff out predators as well, neurobiologist Lisa Stowers of The Scripps Research Institute in San Diego, California, dropped cotton balls laced with either cat saliva, rat urine, or snake skin essence into the cages of both normal and mutant mice with inactive VNOs. The normal mice cowered in the corner, as if a predator were present. Meanwhile, the mutants weren't afraid at all, even when an anesthetized rat was placed in their cage. In addition, using dyes that light up when neurons are activated, the team saw neurons associated with VNOs turn on in response to the scents. These mice were inbred in labs for hundreds of generations, none of them having ever seen a predator, Stowers notes. This isn't the mouse learning to recognize these cues, he's born with the ability to detect them. The team separated the components of the whole predator scent and introduced them to mice on cotton balls. Only one—a class of proteins found in urine and other secretions known as Mups, for major urinary proteins—elicited the same fear response as the whole predator scent in the mice.
Lilian Willms
2025-07-23 08:41:16
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For a rodent, sniffing, otherwise known as voluntary inhalation, happens at up to four times the baseline respiration rate. The animal decides when and where to sample space, thereby updating an internal representation of its environment that ultimately guides its behaviour. Just as rapid eye movement precedes fixation on a certain spot, sniffing the area enables selection of an air-borne plume or surface-borne trail. Sensory perception is an active process. Active sensing means the environment is sampled and then attention drawn to the important target.
Alysha Hoppe
2025-07-23 07:02:08
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Mice can sense extremely fast and subtle changes in the structure of odours and use this to guide their behaviour. Odour plumes, like the steam off a hot cup of coffee, are complex and often turbulent structures, and can convey meaningful information about an animal’s surroundings, like the movements of a predator or the location of food sources. But it has previously been assumed that mammalian brains can’t fully process these temporal changes in smell because they happen so rapidly, much faster than an animal can sniff. Using behavioural experiments where mice were exposed to incredibly short bursts of odour, neural imaging, electrophysiology and computer models, the scientists found that mice can, in fact, detect very rapid fluctuations within odour plumes, at rates previously not thought possible. They also showed that mice can use this information to distinguish whether odours are coming from the same or different sources, even if they are very close to each other. Andreas Schaefer says: It isn’t just processing chemicals from odours but can also calculate information about physical distance and source. This suggests that the mammalian olfactory system, responsible for the sense of smell, is also key in processing the awareness of physical space and surroundings, guiding decisions important to survival.
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