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发帖数: 40861 | 1 BPA exposure makes male deer mice less attractive to females
BIOLOGICAL SCIENCES
Latest research has implications for humans, other species
The latest research from the University of Missouri on bisphenol A shows
that the ubiquitous chemical causes male deer mice to become “
demasculinized,” leading scientists to conclude that exposure during human
development could be damaging to behavioral and cognitive traits that are
important in reproduction.
The MU research demonstrated a link between bisphenol A, or BPA, and severe
problems with spatial navigation abilities in captive male deer mice, said
Cheryl Rosenfeld, associate professor in biomedical sciences in the College
of Veterinary Medicine and investigator in the Bond Life Sciences Center.
Studies by other researchers have demonstrated that males of polygynous
species — one male breeding with several females — tend to possess
enhanced spatial navigation abilities compared to females. In the wild,
spatial navigation skills are crucial to males of polygynous species like
deer mice because it allows them to find mates that are dispersed throughout
the environment.
“The BPA-exposed deer mice in our study look normal; there is nothing
obviously wrong with them,” Rosenfeld said. “Yet, they are clearly
different. Females do not want to mate with BPA-exposed male deer mice, and
BPA-exposed males perform worse on spatial navigation tasks that assess
their ability to find female partners in the wild.”
The research will be published in the Proceedings of the National Academy of
Sciences. Rosenfeld collaborated with David Geary MU Curators’ Professor
of Psychological Sciences, and Todd Schachtman, professor from the
Department of Psychological Sciences. The primary author was a graduate
student in the MU Interdiscplinary Neurosciences Program, Eldin Jaš
arević, who conducted most of the experiments.
A known endocrine disruptor, BPA has been found to mimic the female hormone
estrogen, which can lead to a range of effects in both humans and animals.
“We know that the active form of BPA binds to our steroid receptors,
meaning it can affect estrogen, thyroid and testosterone function,”
Rosenfeld said. “It might also cause genetic mutations. Thus, this chemical
can hinder our ability to reproduce and possibly cause behavioral
abnormalities that we are just beginning to understand.”
The findings set the stage for researchers to examine how the chemical might
impact the behavioral and cognitive patterns of boys versus girls. “Our
study could suggest that boys may be more susceptible (to BPA exposure) than
girls would be,” Rosenfeld said.
It is not known yet if BPA exposure affects human spatial navigation skills.
As with mice, boys are typically more adept at this skill than girls.
According to a 1992 Indiana study, boys exposed while in the womb to a
different endocrine disruptor — diethylstilbestrol (DES), a potent estrogen
— exhibit spatial navigational defects, compared to boys whose mothers did
not take this compound. In the mid-twentieth century, before DES was banned
, physicians routinely prescribed it to prevent miscarriages.
As for BPA possibly inducing similar effects, Rosenfeld said other
researchers should be on the lookout. Some scientists are already tracking
children affected by BPA, so they might want to measure these children’s
spatial navigation abilities, their learning and memory abilities, and their
overall behavior patterns over time, she said.
In the recent study, female deer mice were fed BPA-supplemented diets two
weeks prior to breeding and throughout lactation. The mothers were given a
dosage equivalent to what the U.S. Food and Drug Administration considers
non-toxic and safe for mothers to ingest. At weaning (25 days of age), the
deer mice offspring were placed on a non-supplemented BPA diet. When the
mice became sexually mature, researchers tested each mouse’s ability to
navigate a maze. Each animal had two five-minute opportunities per day, for
seven days, to try to find its way into a home cage through one of several
holes placed around the edge of an open maze marked with visible
navigational cues. Many male mice that had been exposed to BPA early in
their development never found the correct exit.
By comparison, male mice that had not been exposed to BPA consistently found
the hole leading to their home cage within the time limit, some on the
first day. Moreover, the untreated mice quickly learned the most direct
approach to finding the correct hole, while the exposed males appeared to
employ a trial and error strategy, Rosenfeld said.
In addition, male deer mice exposed to BPA were less desirable to female
deer mice. Females primed to breed were tested in a so-called mate choice
experiment. The females’ level of interest was measured by observing
specific preferential behaviors, such as nose-to-nose sniffing and the
amount of time the female spent evaluating her potential partner. Rosenfeld
said that both non-exposed and BPA-exposed females favored control males
over BPA-exposed males on a two-to-one basis.
“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,” Rosenfeld said. “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.”
More than 8 billion pounds of BPA are produced every year, and more than 90
percent of people in the United States have measurable amounts of BPA in
their bodies. Exposure to BPA is primarily through diet because many plastic
and paper containers used to store food are formulated with the chemical.
However, in a recent study, Rosenfeld found that exposure to BPA through
diet has been underestimated by previous lab tests. In that study, funded by
the National Institute of Environmental Health and Sciences, researchers
compared BPA concentrations in mice that were given a steady diet
supplemented with BPA throughout the day, compared to the more common lab
method of single exposure, and found an increased absorption and
accumulation of BPA in the blood of mice.
“We believe that these mouse model studies where the BPA exposure is
through the diet is a more accurate representation of what happens to BPA as
the human body attempts to processes this toxic substance,” said Rosenfeld
. “When BPA is taken through the food, the active form may remain in the
body for a longer period of time than when it is provided through a single
treatment, which does not reflect the continuous exposure that occurs in
animal and human populations. We need to study this further to determine
where the ingested BPA becomes concentrated and subsequently released back
into the bloodstream to be distributed throughout the body.” |
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