The adolescent
brain is far more sensitive to the effects of alcohol and nicotine than
the adult brain. The reason, researchers have found in separate experiments,
is a part of the brain crucial to learning is more easily damaged by these
substances in adolescents than in adults.
The research
was conducted with rats and presented at a conference sponsored by the
New York Academy of Sciences. In one study, the investigators found alcohol
exposure causes "a more powerful decrease in neural activity" in the hippocampus
of adolescent rats compared with adult rodents, said H. Scott Swartzwelder,
a neuropsychologist at Duke University and the VA Medical Centers in Durham,
N.C.
Swartzwelder
and colleagues also found adolescent rats given alcohol injections took
far longer than adults to swim to a platform in a small pool of water.
The task is a standard one used by researchers to measure learning in laboratory
animals.
The impact of
alcohol actually appears to extend beyond what we customarily think of
as adolescence. Looking at humans, Swartzwelder found when young adults
between ages 21 and 24 drank enough alcohol to accumulate a blood alcohol
content of just below 0.08 percent -- the legal standard for intoxication
in many states -- they performed far worse on a task requiring recall of
designs than did 25 to 29 year-olds who consumed the same amount.
Looking at a
brain chemical called GABA, Swartzwelder found adolescent rats show greater
resistance to the sedative effects of alcohol than adults. GABA is a neurotransmitter,
a chemical that carries messages between nerve cells. Its release is triggered
by alcohol and is a marker for sedation.
Normally alcohol
enhances GABA function in adults, but "adolescent rats injected with alcohol
showed a decreased responsiveness to GABA," Swartzwelder told United Press
International. Though he has not yet examined this effect in humans, he
said he expects the results to be similar, meaning adolescents could drink
more than adults before passing out.
"It would be
easier to drink to an impaired state without realizing it," he explained.
The results
seem to parallel MRI studies in teenagers with serious alcohol problems
conducted by Sandra Brown, a psychologist at the University of California,
San Diego, and the VA Healthcare System. Her scans found impaired brain
function on a variety of spatial and visual tasks compared to teenagers
with no alcohol problems.
"Adolescent
drinkers also retained less verbal and non-verbal information," Brown told
UPI.
The threats
to teen brains are not confined to alcohol, however. Nicotine also exerts
a powerful effect, said Frances Leslie, a neuropharmacologist at the University
of California, Irvine.
In a study of
adolescent rats, Leslie reported after only one injection of nicotine the
animals learned to prefer the side of a cage where they received the injection.
"There is an
increased reward value of nicotine in adolescence," she said.
George Koob,
a neuropharmacologist at the Scripps Research Institute in La Jolla, Calif.,
reported the "aversive effects of nicotine had less impact on adolescent
rats than on adults." In addition, adult rats showed fewer and less intensive
symptoms of nicotine withdrawal than adults, which suggests that anti-smoking
strategies might be effective when applied to teenagers.
--
Copyright 2003 by United
Press International.
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