DURHAM, N.C. -- A new animal study at Duke University, combined with earlier ones, has found that small amounts of alcohol pose a dual danger to young brains but no danger to adult brains.
Not only are young rats more sensitive to alcohol-induced learning and memory deficits as reported last year, but alcohol doesn't make them as sleepy -- potentially allowing them to drink more and thus cause more harm, according to researchers at Duke University Medical Center and the Durham VA Medical Center.
If confirmed in humans, the findings would reinforce the earlier Duke research to support legal bans on under-age drinking, said Scott Swartzwelder, lead investigator of the study.
"We've shown that the developing brain has exactly the wrong combination of sensitivities to alcohol," said Swartzwelder, associate professor of psychiatry at Duke and a research scientist at the Durham VA Medical Center. "It's capable of staying awake through a prolonged bout of drinking, but at the same time, it is sustaining far more damage to memory and learning systems than an adult brain receiving an equivalent amount of alcohol."
The studies suggest as little as two drinks could inhibit learning and memory in a young person but would have little effect on an adult, Swartzwelder said.
Such damage is occurring at a time in the life span when the brain is most receptive to learning, he said. At no other time can the brain absorb and retain so much information, and alcohol potently depresses that ability.
Results of Swartzwelder's latest study, funded by the National Institute of Drug Abuse and the Alcoholic Beverage Medical Research Foundation, are published in the November issue of Alcoholism: Clinical and Experimental Research. Co-authors of the study were Patrick Little, Cynthia M. Kuhn and Wilkie A. Wilson of Duke University and the Durham VA Medical Center.
In their study, the researchers showed that when young rats were injected with alcohol, they took longer to fall asleep and slept less than half the length of time of adult rats given equivalent amounts of alcohol. The young rats also woke up with higher levels of alcohol in their blood.
"Historically, there has been no compelling evidence to deter the youth of America from drinking, other than a moral or authoritarian message," Swartzwelder said. "At least now, we can back our message with scientific evidence showing that even occasional and moderate drinking might impair a youth's memory systems more than it would an adult's."
Swartzwelder demonstrated the memory-impairing effect in rats last year with a series of experiments on the hippocampus, a region of the brain critical for learning and memory. He stimulated slices of hippocampal tissue with electrical currents, then applied low doses of alcohol -- equivalent to about two drinks in a human -- to the tissue.
The alcohol had no effect on the adult brain, but it potently inhibited the action of a specific nerve receptor, called the NMDA receptor, in young brains. When NMDA receptors are inhibited, they cannot receive electrical signals from other nerve cells, thereby preventing the acquisition and storage of new information. Those findings were published in May and December last year in Alcoholism: Clinical and Experimental Research.
"Young brains are built to learn," Swartzwelder said. "They have more NMDA receptors than adult brains, and their receptors are formulated with a different balance of proteins. This could account for why young brains experience such dramatic decreases in NMDA-mediated activity when they are exposed to low doses of alcohol."
In the next phases of research, Swartzwelder is studying how alcohol affects rats' ability to learn and remember their way through a maze, and how alcohol affects learning and memory in adult humans of various ages.