In what is being considered a serious problem for biomedical research, scientists from McGill University have discovered that rodents become stressed and more timid when they can smell a male researcher, while the presence of a woman has no effect on them.
This is yet another example of why mice models are among the most unreliable test subjects. As this new Nature Methods study shows — and as has been long suspected — the presence of researchers affects the behavior of rodents. But now it appears that the level of experimental contamination is exacerbated and complexified by markedly different responses to the presence of male and female researchers. Clearly, the finding could have major implications for laboratory experiments using mice and rats.
"Scientists whisper to each other at conferences that their rodent research subjects appear to be aware of their presence, and that this might affect the results of experiments, but this has never been directly demonstrated until now," noted lead researcher Jeffrey Mogil of McGill University in a statement.
Indeed, the research suggests that animal-based experiments need to be refined and qualified.
"At the very least, published papers should state the gender of the experimenter who performed the behavioral testing," added Mogil.
The mechanism for the behavior change is likely due to scent chemicals, called pheromones, produced by male mammals. It's an adaptive trait that lets a rodent know when a solitary male may be nearby who's hunting or defending his territory. And indeed, these chemical signals are often used in the animal world to mark out territory.
Mogil's team learned that the presence of an unknown man causes rodents to experience the same level of stress as being held in a closed tube for 15 minutes, or being forced to swim for three minutes (as measured via pain inhibition). Importantly, the same effect occurred after the mice were in the presence of a t-shirt previously worn by a man. The same effect was not replicated around female researchers or their clothing. This would make sense given that females produce less of these pheromones than males.
Read the entire study at Nature Methods: "Olfactory exposure to males, including men, causes stress and related analgesia in rodents." Supplemental information via Science AAAS & Telegraph.