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Genotype Found to Affect Brain's Response to Addiction Cues

A new study has found that a certain genotype can affect the brain’s responses to addiction cues, such as the smell of alcohol. This finding could help scientists develop more effective ways to prevent relapse in recovering addicts.

Previous research has suggested a link between single nucleotide polymorphisms (SNPs), which occur when one nucleotide in the genome sequence is altered, and alcohol addiction. In these cases, the SNPs are located in a gene that encodes some of the brain’s GABA-A receptors.

David A. Kareken, corresponding author for the study and director of the department of neurology's neuropsychology section at Indiana University School of Medicine, said that people learn to associate the appearance, smell, and taste of alcohol with its intoxicating effects, and that this association strengthens with increased drinking. Similar to the way in which Pavlov’s experiments with dogs responding to a ringing bell and associating the bell with food, this experiment found that experienced drinkers link the taste and smell of alcohol to being intoxicated. For some people, this link can lead to cravings, which can lead to relapse in recovering alcoholics.

Instead of studying salivation as Pavlov did, these researchers examined the activity in the brain’s reward system. The researchers also wanted to find out whether a variation in the GABRA2 gene, which seems to be more common among alcoholics, affected the brain’s response to alcohol cues.

For the study, the researchers exposed 36 patients to the smells of their favorite alcoholic drinks in addition to food and environmental odors, and the researchers examined the brain’s response to these odors using functional magnetic resonance imaging (fMRI).

They found that participants with extra GABRA2 carriers had responses in the brain’s reward evaluation system, whereas those with only one copy of the gene had responses in a different section of the brain’s reward system. The same differences occurred even when the participants were intoxicated, which means that the difference in responses wasn’t dependent on alcohol. This suggests a genetic link to a physiological response to alcohol among those with multiple carriers of the GABRA2 gene.

Kareken noted that alcohol dependence involves both genetic and environmental causes, but that this study should help researchers understand how genes can affect the brain’s reward system and the ways in which it responds to environmental cues.

Source: Science Daily, Sensitivity to Alcohol Odors May Indicate a Genetic Predisposition to Alcohol Dependence, September 1, 2010