MEN MAKE MICE MEEK

Scientists go to great lengths to eliminate bias from their work, but an unexpected influence has just been revealed: Men make rodents nervous. And because that stress can alter the animals’ behavior and decrease sensitivity, the effect has the potential to skew lab results. The new study involved giving mice inflammatory injections in the foot, then monitoring their behavior in the presence of researchers and when alone. The results indicated that male-attended mice felt 36 percent less pain than those watched by women or left solo. The mice also tended to defecate more often and hug the walls of their cages, both signs of fear, when men were present. Subsequent blood tests confirmed a surge in corticosterone, a pain-reducing stress hormone. Because pain signals weakness, the mice may suppress it as an instinctive response to the scent of a potentially dangerous male mammal. “Olfactory exposure to male stimuli is stressful for mice,” McGill University researcher Jeffrey Mogil tells Scientific American, “and just shockingly stressful compared with other known stressors.” Rodents account for more than 95 percent of all lab animals, and while researchers say the findings don’t undermine previous results, they do advise including scientists’ genders in future methodology reports.