A mouse feels panicky. It freezes; its little nose twitches. Something is in the air, and it doesn’t like the smell of it. Not one… little… bit.
In mice, the scent of predators causes a surge of stress hormones to course through the blood and induces behavioral changes. Quite a lot is known about olfaction in mice—Richard Axel and Linda Buck split the Nobel Prize in 2004 for elucidating the organization of the thousand or so unique odorant receptors expressed by the sensory neurons in those little noses.
But the neural circuits that transmit a threatening scent from the nose to the hypothalamus, where the stress hormones are released, were not known. Until now.