Identification of Candidate Genes for Alcohol Preference by Expression Profiling of Congenic Strains

A highly significant quantitative trait locus (QTL) that influenced alcohol preference was identified in the iP/iNP rats on chromosome 4. Congenic strains in which the iP chromosome 4 QTL interval was transferred to the iNP (NP.P) exhibited the expected increase in alcohol consumption compared to the iNP background strain. This study was undertaken to identify genes in the chromosome 4 QTL interval that might contribute to the differences in alcohol consumption between the alcohol-naïve congenic and background strains. RNA from five brain regions from each of 6 NP.P and 6 iNP rats was labeled and analyzed separately on an Affymetrix Rat Genome 230 2.0 microarray. Expression levels were normalized using robust multi-chip average (RMA). Differential gene expression was validated using quantitative real-time PCR. An analysis combining five brain regions, including nucleus accumbens, frontal cortex, amygdala, hippocampus, and striatum, identified twenty three transcripts and nine ESTs that were differentially expressed between the NP.P and iNP. Of the twenty three observed transcripts, thirteen were known genes, 9 were predicted genes and all but one were located in the chromosome 4 QTL interval. Very interesting cis-regulated candidate genes for alcohol consumption were identified using microarray profiling of gene expression differences in congenic animals carrying a QTL for alcohol preference. Keywords: alcohol, congenic, rat, gene expression, brain, nucleus accumbens, amygdala, frontal cortex, hippocampus, striatum Brain regions (accumbens, amygdala, frontal cortex, hippocampus, and striatum) from 6 biologic replicates of the selected non-preferring line NP and from a NP.P congenic line were dissected and subjected to microarray analysis for comparison.