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The neurobiology of addiction

Thanks to a four-year, $2.4 million grant from the National Institutes of Health, University of Minnesota researchers have launched a multidisciplinary effort to examine the role impulsivity plays in addiction. Research at the new Center for the Study of Impulsivity in Addiction will focus on drug abuse and binge-eating disorder—addictions that share behavioral and neurobiological traits, says center director Kelvin O. Lim, M.D., professor and vice chair for research in the Department of Psychiatry.

The impulsivity that University of Minnesota scientists and others have linked to various addictions can actually be seen in the brain’s chemistry, says Lim, who holds the Drs. T. J. and Ella M. Arneson Land-Grant Chair in Human Behavior. Specifically, addicts have reduced levels of GABA (gamma-aminobutyric acid), an amino acid that is the major inhibitory neurotransmitter in the brain. Center researchers will use imaging technology to noninvasively measure GABA levels in the brains of humans and rats, both addicts and nonaddicts, Lim says, to try to establish whether GABA deficiency is a cause or a result of addiction.

The center will encompass three projects: Lim’s study of cocaine addiction in humans; a study of patients with binge-eating disorder by psychiatry professor Nancy Raymond, M.D., and Sheila Specker, M.D., associate professor of psychiatry; and related studies of laboratory rats by Marilyn Carroll, Ph.D., also a psychiatry professor.

For several years, Carroll has bred rats that are “sweet-preferrers”—biologically predisposed to prefer sweet tastes. Those rats appear to be significantly more vulnerable to cocaine addiction. “The sweet-preferrers are more impulsive [than other rats], they take a lot more cocaine, they relapse faster to cocaine, and they escalate their intake,” Carroll explains. “Escalation is thought to be a major marker of addiction.”

Do those tendencies hold true in humans? Says Carroll, “That’s one of the questions we want to ask: Are Kelvin Lim’s patients who are addicted to cocaine also sweet-preferrers? Are Sheila Specker’s and Nancy Raymond’s patients who are binge-eaters also sweet-preferrers?” The answers could have implications for the treatment and prevention of a variety of addictions.

Besides brain imaging, studies at the Center for the Study of Impulsivity in Addiction will include extensive behavioral testing. “The center should help improve our understanding of the neurobiology of inhibitory control, which will lead to new approaches to prevention and treatment,” Lim says.

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