Exposure to bisphenol A (BPA) demasculinizes male deer mice, makes them less attractive to females of the species and hampers their navigational abilities, according to new US research.
Scientists from the University of Missouri said the results suggest that human exposure to the chemical during development could damage the behavioural and cognitive traits that are unique to each sex and important in reproduction.
Results were not conclusive but did raise enough concerns to necessitate further investigation, they said
“The BPA-exposed deer mice in our study look normal; there is nothing obviously wrong with them. Yet, they are clearly different,” said lead researcher Cheryl Rosenfeld, associate professor in biomedical sciences in the College of Veterinary Medicine and investigator in the Bond Life Sciences Center.
She added that female mice did not want to mate with BPA-exposed male deer counterparts and that the animals performed worse on spatial navigation tasks that could harm their chances of finding female partners in the wild.
“This study sets the stage for BPA researchers to examine how BPA might differentially impact the behavioural and cognitive patterns of boys versus girls”, said Rosenfeld.
The assistant professor added: “Investigators looking for obvious BPA-induced differences, such as chromosome deletions or DNA mutations, could be missing subtle behavioural differences that eventually lead to long-term adverse outcomes, including demasculinization of male behaviours with ensuing decreased reproductive fitness.”
Stuck in the maze
In the research female mice were given BPA-supplemented diets – at levels deemed safe by the US Food and Drug Administration - two week before breeding and throughout lactation.
After 25 days the mice offspring were transferred to a non-BPA supplemented diet and their behaviour examined upon reaching adulthood.
A maze test designed to assess spatial navigational ability showed that male mice exposed to the substance early in life never found their way through the labyrinth to their cage.
However, untreated mice were consistently successful and appeared to learn how to find the most direct route. Conversely, BPA-exposed animals seemed to employ a random, trial and error approach.
Navigational ability is one factor that helps male mice find mates and is therefore significant, said the study.
Rosenfeld said the treated male mice were also less attractive to females which had been “primed to breed”. Preferential behaviour, such as nose-to-nose sniffing was observed, and it was found that females favoured non-treated males over their BPA-exposed rivals by a ratio of 2:1.
“These findings presumably have broad implications to other species, including humans, where there are also innate differences between males and females in cognitive and behavioural patterns,” said Rosenfeld. “In the wide scheme of things, these behavioural 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.”
David Geary, MU Curators’ Professor of Psychological Sciences, said this evolutionary approach to BPA study can be used to determine the best way to assess differences in risks to boys and girls from early exposure to the substance.