Genes influence impulsive behavior, preceding the development of alcoholism

* Highly impulsive behavior is prevalent in drug addicts and alcoholics compared to those without addictions.
* New mice findings show that genes influence impulsivity.
* Impulsivity in humans may also be affected by their genes, influencing their risk for alcoholism.

Numerous studies have shown that highly impulsive behavior – defined as the tendency to choose small, immediate rewards over larger, delayed rewards – is more prevalent in drug addicts and alcoholics compared to individuals without addictions. A new study using mice has found that genes influence impulsivity, which may then contribute to the risk for developing alcoholism.

Results will be published in the July issue of Alcoholism: Clinical & Experimental Research and are currently available at Early View.

"There is increasing evidence that the character trait of impulsivity predisposes towards addiction in all its forms, such as drugs, alcohol, gambling," said Nicholas J. Grahame, associate professor of psychology at Indiana University-Purdue University at Indianapolis. "Data from the National Epidemiologic Survey on Alcoholism and Related Conditions suggest that a variety of disorders that increase impulsivity – from bipolar disorder, to conduct disorder, and antisocial personality disorder (ASPD) – are associated with an increase in risk for alcoholism."

"The relationship between high impulsivity and drug use raises many questions," added Suzanne H. Mitchell, associate professor in behavioral neuroscience at Oregon Health & Science University. "For example, is an impulsive individual more likely to experiment with drugs, and then develop a problem? If such a relationship was found, identifying children or adolescents with high levels of impulsivity might, in theory, allow us to identify individuals at risk for developing a substance-use disorder like alcoholism."

Grahame and his colleagues tested several selected lines of alcohol-naïve mice: offspring of High Alcohol Preferring (HAP) mice, HAP1 and HAP2; offspring of Low Alcohol Preferring (LAP) mice, LAP2; as well as offspring of low-drinking progenitor (HS/Ibg) mice. All of the mice were tested on a delay-discounting task, which employs two levers to provide subjects with a choice between a small, immediate or a large, delayed saccharin reward.

"We first used selective breeding to obtain mice genetically predisposed to drink alcohol," said Grahame. "The experiment was to create lines of animals that differ in genes related to alcohol drinking, and the central question was: 'Are any of the genes affected by this manipulation related to impulsivity?' To study this, we used a task that is widely used in both human and animal studies, which was to give a choice between an immediate but small reward and a delayed but large reward. The mice that had the genes to drink, the HAP1 and HAP2 mice, were more impulsive than their low-drinking counterparts, the LAP2 and HS/IBG mice."