You all have the image of someone you know or you’ve seen on
TV in the past when you hear the term “a man’s man”. Big, tough, pillars of masculinity wound
tightly around a body of bulging muscles and brawn. How, or better yet, when does this masculinization
actually occur? Is it something that is
learned? Or is there a chemical game of
football that goes on in the body that seals the deal? It’s probably a little of both, but without
certain chemical processes happening at particular stages of development, the
line in the sand between male and female behavior gets a little blurred.
In rats, testicular androgen is believed to be in charge of masculinization
and feminization, which occurs sometime between days 18 and 27 after conception
and involves the conversion of androgen to estrogen by the enzyme brain
aromatase. Timing of this conversion
process, as well as other chemical dances involved, is critical to establish
sexual differentiated behavior. In other
words, the timing of certain sex-related hormone conversion is very important
in establishing “typical male behaviors” and “typical female behaviors”,
respectively.
Blurred Lines
As you can imagine, something that needs to occur in such a
specific time frame can be very sensitive to bumps in the road. What happens if this process of
androgen-estrogen conversion does not occur at the proper time or does not
occur in the proper amounts? When this
happens, you get a sort of fuzzy distinction between male and female behaviors,
with the de-masculinization of males or de-feminization of females. Since this process is completed by hormonal balances,
anything that can disrupt this balance can potentially interfere with the
distinction in behaviors between the male and females sexes.
Endocrine disruptors, for example Bisphenol A (BPA), a
commonly used chemical in plastic coating of food cans, baby bottles, lining of
trash cans, and dental sealants, act in similar manners and interact with the
same receptors of which androgens, estrogens, and other hormones also interact
and function. That being said, could
these endocrine disrupting chemicals cause problems with sexual differentiation
and sex-related behaviors in those living things that are exposed to them?
Endocrine Disruptors and Behavior
Nearly all studies to date related to endocrine disruptors
effects on sexual behavior has been done in rodents, or at least species other
than humans. However, since studies in
rodents can often be comparable to those in humans, it is certainly a good
starting point for asking more specific questions humans. In rats, BPA exposure has been linked to
increased anxiety levels, changes in “typical” behaviors for the individual
sexes, as well as changes in spatial learning.
In a few studies, when pregnant rats were given BPA during their
pregnancy and also during the lactation period after pregnancy, changes in some
sex-specific behaviors were observed at doses as low as 1ppm.
One of the few studies with humans focused on
diethylstilbestrol (DES), a synthetic estrogen-like compound that at one time
(between the 1940s and 1970s) had been given to women with the thought that it
would protect them against problems in pregnancy. In fact, DES had quite the opposite effect,
causing major complications and birth defects in those children born from women
who were given the drug. In regards to
behavior, one study found that children of those women given DES during
pregnancy had increased rates of various psychiatric complications or diseases,
including depression and anxiety.
BPA and Sexual Differentiation in Rats
Building upon this knowledge, a team of researchers from the
Department of Brain Science and Engineering at Kyushu Institute of Technology
and the Department of Otorhinolaryngology at Chidoribashi Hospital in
Kitakyushu and Fukuoka, Japan, respectively, sought to answer the question of
whether or not BPA, an endocrine disruptor with similar mechanistic properties
as DES, has any effects on the sexual differentiation in rats, in particular focusing
on sexually differentiated behaviors.
What they found was very interestingà after giving pregnant rats
BPA at levels LOWER than the supposed “safe” levels in both the United States
and Japan, sexual differentiation of rearing behavior as well as
depression-like behaviors were observed.
Specifically, the male offspring of rats that were exposed to BPA were observed
to rear for a longer period of time than their non-BPA exposed counterparts, indicating
a sort of change in behavior there by not being able to leave their mothers at
a “normal” age. Also, it was observed
that during swimming tests, male rats that were born from mothers exposed to
BPA moved their limbs significantly less than rats born from non-BPA exposed
mothers, leading the team of researchers to conclude that BPA exposure in utero
increased depression-like behaviors in the male offspring of rats given BPA
during a certain period of time during pregnancy.
Let’s hear it for the boys!
It was noted in this study with rats that these altered
behaviors based on BPA exposure during the critical time of sexual
differentiation only seemed to affect the males, while female offspring
appeared unaffected.
How could this be?
Since sexual differentiation involved conversion of
androgen, and since BPA has been shown to have anti-androgenic activity, then
it can be surmised that BPA may cause a feminizing effect as a result of this
antagonistic behavior of the BPA chemicals.
BPA may disrupt the process and “get in the way” of the masculinization
of the rats, and possibly humans, which has profound effects on the sexual differentiation
between males and females, as well as the “typical” behaviors of each therein.
It’s highly possible that BPA and other endocrine disruptors
could play similar roles in the development of male and female humans and that
exposure during these critical stages of embryonic development are kept endocrine-disruptor
free so that there isn’t this apparent de-masculinization of males.
Source: Fujimoto, T., Kubo, K.,
and Aou, S. 2006. Prenatal exposure to bisphenol A impairs sexualdifferentiation of exploratory behavior and increases depression-like behaviorin rats. Brain Research 1068: 49-55.
No comments:
Post a Comment