Many people, including researchers themselves, are concerned about the lack of reliability and replicability of nonhuman animal (animal) models in biomedical research (for detailed summaries see also and). Often, when results cannot be replicated, the reasons remain unclear. Now, some light has been shed on why this is so. It turns out that the scent of the experimenter wreaks havoc on the data that are collected.

Male experimenter odors cause stress and analgesia in rats

A team of researchers has recently reported that human male, but not human female odors, cause stress and analgesia in laboratory mice and rats. Both male and female rodents become less sensitive to pain. A summary of the research article titled "Olfactory exposure to males, including men, causes stress and related analgesia in rodents" can be found in an essay called "The scent of a man: Gender of experimenter has big impact on rats' stress levels, explains lack of replication of some findings." Pain inhibition "was shown by placing cotton T shirts, worn the previous night by male or female experimenters, alongside the mice; the effects were identical to those caused by the presence of the experimenters, themselves."

What other subtle and unknown factors influence the results of research?

This study is a very significant heads-up about the use of animals in pain and other biomedical research because animal models are frequently used to make inferences about human disease. And, mice and rats, rodents who are known to display empathy, are used by the millions and they are not protected by the Animal Welfare Act in the United States. Indeed, they aren't even considered to be "animals". A quote from the federal register reads as follows: "We are amending the Animal Welfare Act (AWA) regulations to reflect an amendment to the Act's definition of the term animal. The Farm Security and Rural Investment Act of 2002 amended the definition of animal to specifically exclude birds, rats of the genus Rattus, and mice of the genus Mus, bred for use in research" (Vol. 69, no. 108, 4 June 2004). (my emphasis)

It's about time to amend and to update the federal Animal Welfare Act

It's about time that the Animal Welfare Act is amended and updated to recognize mice and rats as the animals they really are and to reflect what we now know about the emotional lives of the tens of millions of rodents and other animals who are freely used and abused in research. Indeed, it's long overdue. Research clearly shows that they really do care about what happens to them and to other animals. However, researchers and others refuse to incorporate what we know into legislation to protect them, most likely because it serves them well not to do so. 

Who knows what other undiscovered factors play a role in biomedical research on animals that render the research of very limited use for humans? We should all be very concerned about this recent discovery and the continued use of animals to learn about human disease given the skepticism of many researchers themselves. 

Marc Bekoff's latest books are Jasper's story: Saving moon bears (with Jill Robinson; see also), Ignoring nature no more: The case for compassionate conservation (see also)and Why dogs hump and bees get depressed (see also). Rewilding our hearts: Building pathways of compassion and coexistence will be published fall 2014. (; @MarcBekoff)

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