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NEW YORK, Sep 23, 2003 (United Press International via COMTEX) -- 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.