Under certain conditions, a female mouse’s nose turns a blind eye to the scent of a male. On infertile days, odor-sensing nose neurons fail to alert the brain to the presence of a potential mate, scientists report in the June 4 Cell.
The results offer a surprising instance of the nose controlling behavior, not the brain, says study coauthor Lisa Stowers of the Scripps Research Institute in La Jolla, Calif. “This was the craziest thing ever to me,” she says. “Sensory systems are supposed to just gather as much information as possible and pass it on to the brain,” but here, the nose is acting as an information gatekeeper. If our eyes behaved like this, it would be as if after a big meal, a person was literally blind to the sight of food, Stowers says.
Stowers and her colleagues studied female mice at different stages of their ovulation cycle. The scientists wanted to know why female mice become indifferent to males during the infertile period known as diestrus.
“We expected to be looking in the brain,” Stowers says. But their experiments led them to the nose instead. Odor-sensing nerve cells in a nose structure called the vomeronasal organ recognize the odor of male mice and alert the brain. But the message doesn’t seem to transmit during diestrus, when levels of the hormone progesterone are high. Progesterone kicks off a chain of molecular events that leaves these cells blind to the odor, the researchers found. Other nerve cells in the vomeronasal organ still recognize cat odor in the presence of progesterone, so the sensory shutdown seems specific to the male mouse scent.
“In this case, it really looks like the first cells in the olfactory pathway decide not to transmit the information that is there,” says neuroscientist Ivan Manzini of the University of Göttingen in Germany. “That is something special.”