Solving the age-old chicken and the egg dilemma, Indiana University-Purdue University Indianapolis researchers report that genetic predisposition to impulsivity is a trait predictive of alcoholism. The study appears on the July print issue of the journal Alcoholism: Clinical and Experimental Research, available online on April 22.
The researchers, led by Nicholas Grahame, Ph.D., associate professor of psychology at the IUPUI School of Science, used selective breeding for 30 generations to produce mice who were high volume alcohol drinkers and others who avoided consuming alcohol. The genetically different mice were presented with a choice between a small, immediate reward and a large, delayed reward. By adjusting the quantity of the immediate reward up and down based on choice behavior, the task allowed the researchers to test the impulsivity of the rodents.
The mice with high alcohol preferring genes were more impulsive than their low drinking counterparts demonstrating that predisposition to impulsivity is predictive of alcoholism.
"Selective breeding allowed us to focus on whether changing genes changes behavior. Just like golden retrievers are bred to retrieve, we were able to breed mice genetically predisposed to drink alcohol voluntarily. Many drink enough to reach a blood alcohol level of .08," said Dr. Grahame, who is a behavioral geneticist.
In humans a blood alcohol level of .08 is produced by the consumption of two drinks an hour by a 120-pound individual or 3 drinks an hour by a 180-pound individual. At that level human concentration and judgment are impaired and all 50 states prohibit operation of a motor vehicle.
"It is well documented that humans with alcohol problems have impulsivity issues. High impulsivity, when defined as the tendency to choose small instantaneous rewards over larger delayed rewards – like getting drunk instead of going to work for that paycheck in 2 weeks— is more prevalent in alcoholics than in non-alcoholics. Because these mice had never had alcohol, we were able to show that it was the genes that increase drinking, rather than drinking itself, that yielded impulsive behavior," said Dr. Grahame.
"Our data can clearly be extrapolated to humans and strongly suggests that impulsivity contributes to high alcohol drinking. Consequently, the diagnosis of any disorder associated with impulsivity, such as attention deficit disorder or bipolar disorder, is cause for concern about future problems with alcoholism," he added.
Co-author of "High Alcohol Preferring Mice Are More Impulsive than Low Alcohol Preferring Mice as Measured in the Delay Discounting Task," is Brandon Gregg Oberlin, a doctoral candidate in the Program in Medical Neuroscience at the Indiana University School of Medicine. The study was funded by the IUPUI School of Science and the National Institute on Alcohol Abuse and Alcoholism.
- B. G. Oberlin and N. J. Grahame. High-Alcohol Preferring Mice Are More Impulsive Than Low-Alcohol Preferring Mice as Measured in the Delay Discounting Task. Alcoholism Clinical and Experimental Research, 2009; DOI: 10.1111/j.1530-0277.2009.00955.x
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