A dose of nicotine, equivalent to that found in a single cigarette blocks estrogen production in women’s brains. This may explain several behavioural differences in women who smoke, including why they are more resistant than men to quitting smoking. This work is presented for the first time at the ECNP Congress in Vienna.
Lead researcher, Associate Professor
Erika Comasco (Uppsala University, Sweden) said:
“For the first time, we can see that nicotine works to
shuts down the estrogen production mechanism in the brain of women. We were
surprised to see that this effect could be seen even with a single dose of
nicotine, equivalent to just one cigarette, showing how powerful the effects of
smoking are on a woman’s brain. This is a newly-discovered effect, and it’s
still preliminary work. We’re still not sure what the behavioural or cognitive
outcomes are; only that nicotine acts on this area of the brain, however we
note that the affected brain system is a target for addictive drugs, such as
nicotine”.
The effect has been shown in the
thalamus, which is part of the limbic system in the brain. This system is
involved in behavioural and emotional responses.
The researchers, from Uppsala University
in Sweden, worked with a group of ten healthy female volunteers. The women were
given a commercially available nicotine dose intranasally, and at the same time
were injected with a radioactive tracer attached to a molecule which binds to
the enzyme aromatase: aromatase, also known as estrogen synthase, is the enzyme
responsible for the production of estrogen. MRI and PET brain scans enabled the
researchers to visualise both the quantity of aromatase, and where it was
located in the brain. The researchers found that a single dose moderately
reduced the amount of aromatase in the brain.
It has been known for some time that
women and men respond differently to nicotine, with women being more resistant
to nicotine replacement therapy, and showing a greater tendency than men to
relapse when trying to quit smoking. However, the biological basis for these
differences is not understood. This is the first time that this inhibitory
effect on aromatase production has been shown in humans. The effect on men was
not studied.
Professor Comasco continued “This
discovery leads us to believe that nicotine’s effect on estrogen production has
a significant impact on the brain, but perhaps also on other functions, such as
the reproductive system – we don’t know that yet. There are significant
differences in the way men and women react to smoking. Women seem to
be more resistant to nicotine replacement therapy, they experience more
relapses, show greater vulnerability for heritability of smoking, and are at
greater risk of developing primary smoking-related illnesses, such as lung
cancer and heart attacks. We need now to understand if this action of nicotine
on the hormonal system is involved in any of these reactions.
Of
course this is a comparatively small group of women, we need a larger sample to
confirm these findings. Nevertheless, the message is that nicotine has various
effects on the brain, including on the production of sex hormones such as
estrogen”.
Commenting, Professor Wim van den Brink,
Emeritus Professor of Psychiatry and Addiction at the Academic Medical Center,
University of Amsterdam said:
“This is indeed an important first finding. Smoking
has many adverse effects in men and in women, but this particular effect of
nicotine on the reduction of estrogen production in woman was not known before.
It should be noted, however, that tobacco addiction is a complex disorder with
many contributing factors. It’s unlikely that this specific effect of nicotine
on the thalamus (and the production of estrogen) explains all the observed
differences in the development, treatment and outcomes between male and female
smokers. It is still a long way from a nicotine induced reduction in estrogen
production to a reduced risk of nicotine addiction and negative effects of
treatment and relapse in female cigarette smokers, but this work merits further
investigation”.
Professor van den Brink was not involved in this work, it is an independent comment.
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