Rodents

Rodents are the workhorses of biomedical labs. So it's important to know if they're 1 out, which could affect results. Now we know that lab rodents may be regularly exposed to a big stressor: men.Researchers noticed that mice showed a lower pain 2 —a sign of stress—when a human was present. So they put mice and rats into clear cubicles, where their faces were visible, and 3 them with an irritant. The rodents expressed pain through grimacing when no humans were nearby. But when confronted with a male researcher, or even just his 4 T-shirt, the animals grimaced less.Female observers did not get the same rodent 5 .Turns out that smelling a human male made rodents produce higher levels of a stress hormone and increase their body 6 . That stress response also blunted their sensitivity to pain. The study is in the journal Nature Methods.Researchers may have to come up with ways to ward off the stress effects of male 7 . Because to a rodent, men smell like hell.