Rampant sexism in mice may have tainted years of research

A recent paper, published in Nature Methods casts doubt over the validity of decades of published and peer-reviewed research by suggesting that mice fear men, but not women.

The paper has also raised the suggestion that there are further effects caused by the presence of male researchers that do not occur with females. The lead author, Jeffrey Mogil, is a pain researcher at McGill University, Quebec.

The researchers claim to have found that, when studying rats and mice, “male-related stimuli induced a robust physiological stress response that results in stress-induced analgesia”. Using a scale to measure pain responses in rodents, consisting of observable factors such as paw and tail withdrawal, it was found that mice confronted with a male smell, human or otherwise, experienced less pain.

In the presence of a female smell, no such effect was noted. If the pain threshold of an animal is lowered then, during times of stress, it will continue as normal until the pain is overwhelming ñ an evolutionary trait intended to aid escape by ignoring minor pain. However, the unnoticed effect of this is often to increase the severity of an injury.

Furthermore, rodents were shown to have increased body temperatures and levels of stress hormones as a response to male scents. It is suggested that this may be due to the territorial, competitive nature of mice, rather than any kind of predatory nature. “If you put a male-worn T-shirt and a female-worn T-shirt in the same room, the female T-shirt counteracts the effect of a male T-shirt,” Mogil notes, suggesting that only a lone male is problematic. Furthermore, the stress of a male, even alone, becomes less severe over time, suggesting that there may be ways to counter this problem in future.

“Fire all the men – or have them chaperoned by a woman,” Mogil jokingly suggested. He does note, however, that requiring a scientist to sit in a room for almost an hour before collecting data, giving the stress effect chance to completely dissipate from the mice involved, would be “too boring”.

The paper makes important recommendations, strongly suggesting: ‘standard laboratory practice should account for experimenter sex when investigating any phenomenon possibly affected by stress’.

Mogil suggests that “we will have to wait and see” whether researchers intend to return to prior studies to check whether results were tainted. With studies growing larger, it is important to note that researchers who begin the work may not be there at the end, and that researcher roles will often be rotated or switched throughout, obviously without consideration of gender.

“I expect to hear stories, to hear people telling me that this sort of explains mysteries about experimenters not replicating each other,” Mogil added.

Robert Barraclough