The past few weeks there have been several interesting studies to come out about lab mice and gender. First up, a study published in Nature Methods found that male researchers induce stress in lab rodents (mice and rats), that may dampen the pain response. The researchers found that the presence of a male researcher, or even the t-shirt he wore the day before, would cause the rodents to have elevated blood levels of the stress hormone corticosterone. They noted that this temporary increase in stress hormone levels caused the mice to have a 40% decrease in pain response, as measured by the mouse grimace scale. While the results of this study may seem trivial, they throw a curveball into many of the past rodent studies performed, and has some implications for future rodent studies. The authors suggest that a male researcher sit in the room with the rodents for 30 to 60 minutes before conducting experiments to lessen this confounding effect, as the stress response eases over time, but they note that this is an unlikely outcome. The authors also call for more transparency in the studies, listing not only the gender of rodents, but also the researchers handling the rodents.
Speaking of the gender of rodents, the National Institute of Health recently announced policy that aims to correct the gender imbalance in cell and animal studies (Scicurious has a great summary and discussion of the NIH mandate). The NIH notes that while over half of all NIH funded clinical research participants are women, animal and cell studies have not kept pace. It turns out that many researchers avoid using female animals out of fear that reproductive cycles and hormone fluctuations would confound the results of carefully controlled studies. Researchers (and many 80’s comedians) have long known about differences between women and men, including the way they react to various drugs and develop diseases. For example, women are more susceptible to multiple sclerosis than men, and some drugs, such as Ambien, need to be prescribed in lower doses for women. Despite these fundamental differences, preclinical research continues to include a majority (if not entirety) of male animals and tissues, which might explain the higher rate of adverse drug reactions seen in women today.
This gender bias in animal studies actually extends further than just the medical field. Ed Yong recently asked “Where’s All The Animal Vagina Research?” In the article, he discusses a paper that examined 364 studies in the last 25 years that dealt with genital evolution. That paper found that 49% only looked at male genitals, 8% only looked at female genitals, and 44% looked at both. Interestingly the gender of the researcher was not a factor, as male and female scientists each seemed to skew equally towards male genital research. The authors of the paper believe the bias towards male genital research stems from longstanding gender stereotypes that have seeped into evolutionary biology, mainly that males play a dominant role in sex, and females are passive, a stereotype that has been proven many times to be false.
And one last bit of rodent research that is on a bit of a lighter note, it turns out that wild mice like to run on wheels. This finding is important for several reasons, but mainly it gives me an excuse to post this video.