Study: BPA exposure might make male mice undesirable to females

For consumers, a major problem with judging the threat posed by the chemical bisphenol A -- a chemical used in the manufacture of many plastics that can mimic estrogens in the body -- is that researchers disagree about how dangerous it really is. (For more on this controversy, check out the related links to the left.)

Now researchers at the University of Missouri-Columbia studying deer mice are shedding light on another way to measure the chemical’s effects: Look at subtle changes in animals’ behavior and cognition -- specifically, sexually selected behavioral and cognitive traits that drive their ability to find and attract a mate.

The study was published Monday in the Proceedings of the National Academy of Sciences.

The team, led by associate professor Cheryl Rosenfeld, predicted that such hormonally regulated traits would be particularly sensitive to endocrine-disrupting compounds like BPA. To test out that hypothesis, they fed female deer mice three different diets: one enriched in BPA, one enriched in the synthetic estrogen enthinyl estradiol or a third control diet that wasn’t enriched in either chemical.

They then put the offspring of those mice through tests designed to measure behaviors that would influence ability to mate in the wild. The mice ran through a series of mazes designed to test the spatial abilities the males might need to expand their territorial range (and find potential mates.) The team also compared the amount of time female deer mice spent in “nose to nose contact” with control group versus BPA-exposed male mice (nose-to-nose contact is a behavioral indication of female mate choice).

Male mice whose mothers had eaten the BPA-enriched diets looked normal, and had normal testosterone levels, too. But they had trouble learning how to navigate the mazes -- suggesting, the researchers said, that they would also have trouble navigating new territory in the wild and meeting potential mates. What’s more, female mice spent less time examining in the BPA-exposed males, indicating that they found them less attractive.

The BPA had no effect on female offspring’s ability to navigate the mazes. This was expected, the research team wrote, because female mice have evolved to be different than males. Specifically, they don’t need to wander to attract mates. In fact, increased exploration could be a disadvantage for females, because it might increase their exposure to predators.

In and of itself, the discovery doesn’t shed direct light on the risk BPA poses to people. But Rosenfeld said the research could influence future studies on BPA’s impact on humans.

“Investigators looking for obvious BPA-induced differences, such as chromosome deletions or DNA mutations, could be missing subtle behavioral differences that eventually lead to long-term adverse outcomes,” she said, in a statement. “These findings presumably have broad implications to other species, including humans, where there are also innate differences between males and females in cognitive and behavioral patterns. In the wide scheme of things, these behavioral deficits could, in the long term, undermine the ability of a species such as the deer mouse to reproduce in the wild. Whether there are comparable health threats to humans remains unclear, but there clearly must be a concern.”