A Human-Like Menstrual Cycle Has Been Discovered in the Spiny Mouse

When it comes to studying menstruation, mice have been all but useless—they don’t have periods.

Rather, mice have what’s called an estrous cycle. They reabsorb the uterine lining if conception fails to occur, instead of shedding it through menstruation.

However, researchers at Monash University in Clayton, Australia have evidence to suggest that the spiny mouse does indeed have a menstruation cycle.

The spiny mouse is the first rodent known to have a menstrual cycle.

The belief that rodents don’t menstruate has led scientists to consider them poor models when studying women’s reproductive issues. But this new finding could change how we study reproductive health.

The African spiny mouse is native to the deserts of Africa, though it has since spread to southwest Asia and southern Europe. They have been used previously in tissue regeneration research due to their ability to regrow lost skin.

The study, involving 14 female spiny mice, showed that the mice possessed a menstrual cycle similar to that of women. While the menstrual cycle in the mice lasted only 9 days, the ratio of time spent bleeding was 20-40%, compared to 15-35% time bleeding for women.

Scientists stumbled upon the menstruation discovery unexpectedly. Here’s Anna Nowogrodzki reporting for Nature:

Study co-author Hayley Dickinson, a reproductive physiologist at Monash University, says that the mouse discovery was hiding in plain sight. Monash established a breeding colony of spiny mice in 2003, and later transferred the animals to the nearby Hudson Institute for Medical Research. When Dickinson’s lab announced the menstruation discovery, several past students asked her how they could have missed it.

“The answer, as with many discoveries in science, is that no one really looked,” Dickinson says. “Everyone knew that rodents didn’t menstruate.”

Up to this point, reproductive health research has had to focus on primates, which is time-consuming and expensive.

With this discovery, the Monash team is beginning further research examining the processes surrounding the breaking down and regrowing of the mice’s uterine lining.

When it comes to human menstruation, there are many parts that remain a mystery. Scientists still don’t know the source of the cells used to repopulate the uterine lining after each menstrual cycle, according Francesco DeMayo, a reproductive biologist at the U.S. National Institute of Environmental Health Sciences quoted in Nature.

Although this finding is the first of its kind, it will take much more research to prove that the spiny mouse is a good model for human menstruation. But doctors and scientists like DeMayo are hopeful that these findings will kickstart a new wave of research into the female reproductive system.