Scientists from McGill University in Montreal revealed that the gender of experimenters has a major impact on the stress levels of mice, which are commonly used in clinical studies. The research suggests how the animals are hardwired to react differently to men and women, demonstrating the importance of this study to lab studies involving mice because the experimenter's gender could affect study results.
Researchers reported how the rats and mice would produce a stress reaction to male experimenters by restraining them in a tube for 15 minutes or forcing the animals to swim for three minutes. The rats and mice became less sensitive to pain. Female experimenters did the same to the rats and mice but produced not much effect.
Previous studies showed that mice spent less time licking a sore part of their body when a person is in the lab even if the "person" was just a Paris Hilton cardboard cutout. The new study had scientists injecting an inflammatory substance into the rat or mouse's foot and sat nearby to read a book. There was a video camera that documented the animal's face assessed it pain level based on the team's grimace scale. There were various results. There were times when the rats and mice showed pain when a person was nearby, sometimes they appeared fine.
The scientists then controlled the gender of the experimenter near the rodents, revealing that the animals showed less signs of pain when the experimenter was male than when the researcher was a female or when no researcher was present at all. The rodents had an average score 36% lower on the grimace scale when the experimenter was a man.
Finally, the scientists placed their worn shirts where the injected mice and rats can smell it. When the experimenters were not present, results did not change. The rodents still scored 36% lower on the grimace scale when they smelled a man's shirt than that of a woman's. When a woman's shirt was next to a man's, it negated the result. The study also showed that female rodents were a bit more sensitive to the experiment.
It appears that the mice and rats which were exposed to the male experimenter were not concealing the hurt, they were feeling less pain. The male scent increased their stress and somehow killed the pain. The rodents were not only stressed because of the pain, the scent of men increased their corticosterone stress hormones and increased their body temperatures. It also shows that the rodents "are afraid of the smell of males of any species" because they also reacted to the scent of male guinea pigs, cats and dogs as well, says senior author and neuroscientist Jeffrey Mogil of McGill University in Montreal, Canada.
The researchers believe that the male scent made the rodents react this way because of competition. "It is a primordial response," Mogil said. "If you smell a solitary male nearby, chances are he's hunting or defending his territory."
Because of this new finding, Mogil said small changes to the procedures of experiments may just solve the problem.
