Key neural system at risk from
fetal alcohol exposure
September 14, 2005
by Terry Devitt
University Communications
 In
a study of adult monkeys who were exposed to moderate amounts of alcohol in
utero, scientists have found that prenatal exposure to alcohol - even in small
doses - has pronounced effects on the development and function later in life of
the brain's dopamine system, a critical component of the central nervous system
that regulates many regions of the brain.
Writing in the current issue (Sept. 15, 2005) of the journal Alcoholism:
Clinical and Experimental Research, a team of researchers led by
Mary
L. Schneider, a UW-Madison professor of occupational therapy and psychology,
reports that when a monkey exposes her fetus to alcohol by drinking, the
dopamine system of her offspring is altered. Effects on that key neural system,
according to the study's results, can manifest themselves up to five years after
birth, when the monkeys are fully grown.
The influence of alcohol on the dopamine system, depending on the timing of
exposure during gestation, varies, says Schneider, but illustrates yet another
biological consequence of drinking while pregnant.
"It appears that there is no safe time to drink," says the Wisconsin researcher.
"And because our study looked at the effects of lower doses of alcohol than most
previous studies, the results suggest there is no safe amount of alcohol that
can be consumed during pregnancy. Even moderate drinking can have effects that
persist to adulthood."
The new study, conducted at UW-Madison's Harlow Center for Biological
Psychology, looked at the effects of moderate drinking on the offspring of three
groups of pregnant rhesus macaques, each of which were provided access to
moderate amounts of alcohol during various stages of gestation. In addition,
there was a control group not exposed to alcohol.
Working with UW-Madison professor of medical physics Onofre DeJesus, Schneider's
group used PET scans to assess the function of the dopamine system of the adult
monkeys exposed to alcohol in utero.
Dopamine is a key chemical messenger in the brain, helping it perform an array
of functions ranging from simple movement to cognition to facilitating feelings
of enjoyment and motivation. Perhaps the best-known dopamine-related pathology
is Parkinson's disease, caused by the death of the brain cells that normally
secrete the chemical. But abnormalities in the functioning of the system can
also contribute to such things as addiction, issues of memory, attention and
problem solving, and more pronounced conditions such as schizophrenia.
In the new study, Schneider's group used positron emission tomography or PET on
the now-grown monkeys to evaluate the interplay of dopamine receptors and
enzymes at work in the system. Schneider and her colleagues were able to see the
chemical interplay in the brains of the monkeys exposed to alcohol in utero, and
detected a range of effects, especially in the striatum, a region of the brain
associated with cognition and other key functions.
"We're seeing receptors and enzymes that are important in producing dopamine,
and what was surprising to us was that dopamine was altered in opposite
directions" depending on when during gestation the monkey's developing brain was
exposed to alcohol.
For two groups of monkeys, those exposed during early gestation, when dopamine
neurons are first forming in the brain, and those exposed continuously
throughout pregnancy, the dopamine system appears to be blunted, Schneider says.
"If the dopamine system is blunted, you might not get the usual flushes of
dopamine in response toe environmental events, and you may seek alcohol or
drugs" as a substitute for the stimulation dopamine normally provides.
For the monkeys exposed to alcohol during middle-to-late gestation, the effect
was the opposite: "Animals exposed later had supersensitive (dopamine)
receptors. If you have supersensitive receptors, you're more susceptible to
sensory overload and environmental stimuli can become overwhelming."
The new results add to a long list of alcohol's negative effects on the
developing fetus. In the last 30 years, scientists have come to understand that
exposing the fetus to alcohol, the drug most widely abused by pregnant women,
leads to a host of health and development issues, including low birth weight,
facial deformities and mental retardation. The availability of powerful imaging
techniques such as PET, which can illustrate the brain at work, are helping
scientists make even finer distinctions, linking damage to the developing brain
to behavioral problems and learning disabilities later in life.
"This is a big problem," says Schneider. "People have been drinking since
Biblical times, but it's only been within the last few decades that we've begun
to understand the effects of drinking on fetal health. The term 'fetal alcohol
syndrome' wasn't even coined until 1973."
Studies of the effects of moderate drinking, says Schneider, are even more
recent. The monkeys in her study consumed the equivalent of just one or two
drinks a day.
"The blood alcohol content is about .04 or .05. If they were people, they could
still drive, but the unseen effects have significant consequences. The take home
message from this study is that there is no safe time to drink, even before
pregnancy is detected."
The new Wisconsin study was supported by a grant from the National Institute of
Alcoholism and Alcohol Abuse.
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