Project description:The goal of this study was to identify candidate genes that may influence alcohol consumption by comparing gene expression in 5 brain regions of alcohol-naïve iP and P.NP rats. Background: Selectively bred P (alcohol preferring) and NP (alcohol non-preferring) rats differ greatly in alcohol preference, in part due to a highly significant QTL on chromosome 4. Reciprocal congenic strains in which the iP chromosome 4 QTL interval was transferred to the iNP background (NP.P) and the iNP chromosome 4 QTL was transferred to the iP background (P.NP) exhibited alcohol consumption scores that correlated with the introgressed interval. The goal of this study was to identify candidate genes that may influence alcohol consumption by comparing gene expression in 5 brain regions of alcohol-naïve iP and P.NP rats. Methods: RNA from the amygdala, nucleus accumbens, hippocampus, caudate putamen, and frontal cortex from each of 8 iP and 8 P.NP rats was labeled and analyzed on Affymetrix Rat Genome 230 2.0 microarrays. Expression levels were normalized using robust multi-chip average (RMA), and differential gene expression was measured in individual brain regions and in the average of the five brain regions. Differential gene expression was validated using quantitative real-time PCR. Meta-analysis was applied to compare microarray data from this experiment with data from the reciprocal congenic strains NP.P vs. iNP (Carr et al, 2007). Results: We detected between 72 (nucleus accumbens) and 89 (hippocampus) cis-regulated probe sets within the QTL that significantly differed between the strains in the five brain regions. There was significant overlap among the regions; 157 cis-regulated probe sets were detected in at least one brain region, of which 104 showed differential expression in more than one region. Fewer trans-regulated probe sets were detected, ranging from 7 in the amygdala to 54 in the caudate putamen, and most of these differed in only one region; only 10 of the 85 trans-regulated probe sets differed in more than one region. To increase the power to detect differentially expressed genes, data from the five discrete brain regions of each animal were averaged; in this analysis we detected 141 cis-regulated probe sets and 207 trans-regulated probe sets. Meta-analysis comparing the present results from iP vs. P.NP rats with an earlier experiment that used the reciprocal congenic NP.P vs. iP demonstrated that 74 cis-regulated probe sets were differentially expressed in the same direction and with a consistent magnitude of difference in both experiments. No consistent trans-regulated probe sets were identified. Conclusions: Cis-regulated candidate genes for alcohol consumption that lie within the chromosome 4 QTL were identified and confirmed by meta-analysis with the reciprocal congenic NP.P vs iNP study. These genes are strong candidates for producing the difference in alcohol preference and consumption between the iP and iNP rats. There was little evidence for consistent trans-acting effects. Keywords: comparison of gene expression profiles for strain1 (P rat) vs. strain2 (P.NP rat)

Project description:The goal of this study was to identify candidate genes that may influence alcohol consumption by comparing gene expression in 5 brain regions of alcohol-naïve iP and P.NP rats. Background: Selectively bred P (alcohol preferring) and NP (alcohol non-preferring) rats differ greatly in alcohol preference, in part due to a highly significant QTL on chromosome 4. Reciprocal congenic strains in which the iP chromosome 4 QTL interval was transferred to the iNP background (NP.P) and the iNP chromosome 4 QTL was transferred to the iP background (P.NP) exhibited alcohol consumption scores that correlated with the introgressed interval. The goal of this study was to identify candidate genes that may influence alcohol consumption by comparing gene expression in 5 brain regions of alcohol-naïve iP and P.NP rats. Methods: RNA from the amygdala, nucleus accumbens, hippocampus, caudate putamen, and frontal cortex from each of 8 iP and 8 P.NP rats was labeled and analyzed on Affymetrix Rat Genome 230 2.0 microarrays. Expression levels were normalized using robust multi-chip average (RMA), and differential gene expression was measured in individual brain regions and in the average of the five brain regions. Differential gene expression was validated using quantitative real-time PCR. Meta-analysis was applied to compare microarray data from this experiment with data from the reciprocal congenic strains NP.P vs. iNP (Carr et al, 2007). Results: We detected between 72 (nucleus accumbens) and 89 (hippocampus) cis-regulated probe sets within the QTL that significantly differed between the strains in the five brain regions. There was significant overlap among the regions; 157 cis-regulated probe sets were detected in at least one brain region, of which 104 showed differential expression in more than one region. Fewer trans-regulated probe sets were detected, ranging from 7 in the amygdala to 54 in the caudate putamen, and most of these differed in only one region; only 10 of the 85 trans-regulated probe sets differed in more than one region. To increase the power to detect differentially expressed genes, data from the five discrete brain regions of each animal were averaged; in this analysis we detected 141 cis-regulated probe sets and 207 trans-regulated probe sets. Meta-analysis comparing the present results from iP vs. P.NP rats with an earlier experiment that used the reciprocal congenic NP.P vs. iP demonstrated that 74 cis-regulated probe sets were differentially expressed in the same direction and with a consistent magnitude of difference in both experiments. No consistent trans-regulated probe sets were identified. Conclusions: Cis-regulated candidate genes for alcohol consumption that lie within the chromosome 4 QTL were identified and confirmed by meta-analysis with the reciprocal congenic NP.P vs iNP study. These genes are strong candidates for producing the difference in alcohol preference and consumption between the iP and iNP rats. There was little evidence for consistent trans-acting effects. Keywords: comparison of gene expression profiles for strain1 (P rat) vs. strain2 (P.NP rat) 40 samples each of P and P.NP (8 animals each of P and P.NP. 5 brain regions)

Project description:ObjectiveA primary focus of alcohol research is to provide novel targets for alcohol treatment by identifying genes that predispose individuals to drink alcohol. Animal models of alcoholism developed by selective breeding are invaluable tools to elucidate both the genetic nature and the underlying biological mechanisms that contribute to alcohol dependence. These selected lines (high alcohol preferring and low alcohol preferring) display phenotypic and genetic differences that can be studied to further our understanding of alcohol preference and related genetic traits. By combining molecular techniques, genetic and physiological factors that underlie the cause of alcoholism can be identified.MethodsTotal gene expression analysis was used to identify genes that are differentially expressed in specific brain regions between alcohol-naive, inbred alcohol-preferring (iP) and -nonpreferring (iNP) rats. Quantitative reverse transcriptase-polymerase chain reaction, in situ hybridization, Western blot, and sequence analysis were used to further characterize rat glutathione S-transferase 8-8 (rGST 8-8).ResultsLower expression of rGST 8-8 mRNA was observed in discrete brain regions of iP compared with iNP animals, and these expression differences were confirmed. To determine additional expression patterns of rGST 8-8, we used in situ hybridization. Rat GST 8-8 was highly expressed in hippocampus, the choroid plexus of the dorsal third ventricle and the lateral ventricle, and ependymal cells along the dorsal third ventricle and the third ventricle. Western blot analysis showed that rGST 8-8 protein levels were lower in the hippocampus and the amygdala of iP compared with iNP. A silent single-nucleotide polymorphism in the coding region and three single-nucleotide polymorphisms in the 3'-UTR were identified in the rGST 8-8 cDNA.ConclusionThere is regional variation of rGST 8-8 expression in the brain, at both the mRNA and protein level, and the iP strain has lower innate rGST 8-8 levels than the iNP strain in discrete brain regions.

Project description:A highly significant quantitative trait locus (QTL) on chromosome 4 that influenced alcohol preference was identified by analyzing crosses between the iP and iNP rats. 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 with 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 5 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 to look for both cis-regulated and trans-regulated genes. Expression levels were normalized using robust multi-chip average (RMA). Differential gene expression was validated using quantitative real-time polymerase chain reaction. Five individual brain regions (nucleus accumbens, frontal cortex, amygdala, hippocampus, and striatum) were analyzed to detect differential expression of genes within the introgressed QTL interval, as well as genes outside that region. To increase the power to detect differentially expressed genes, combined analyses (averaging data from the 5 discrete brain regions of each animal) were also carried out.Analyses within individual brain regions that focused on genes within the QTL interval detected differential expression in all 5 brain regions; a total of 35 genes were detected in at least 1 region, ranging from 6 genes in the nucleus accumbens to 22 in the frontal cortex. Analysis of the whole genome detected very few differentially expressed genes outside the QTL. Combined analysis across brain regions was more powerful. Analysis focused on the genes within the QTL interval confirmed 19 of the genes detected in individual regions and detected 15 additional genes. Whole genome analysis detected 1 differentially expressed gene outside the interval.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.

Project description:BACKGROUND:Corticotropin-releasing hormone (CRH) and urocortins (UCNs) bind to corticotropin-releasing hormone type 2 receptor (CRF2 receptor ), a Gs protein-coupled receptor that plays an important role in modulation of anxiety and stress responses. The Crhr2 gene maps to a quantitative trait locus (QTL) for alcohol preference on chromosome 4 previously identified in inbred alcohol-preferring (iP) and-nonpreferring (iNP) F2 rats. METHODS:Real-time polymerase chain reaction was utilized to screen for differences in Crhr2 mRNA expression in the central nervous system (CNS) of male iP and iNP rats. DNA sequence analysis was then performed to screen for polymorphism in Crhr2 in order to identify genetic variation, and luciferase reporter assays were then applied to test their functional significance. Next, binding assays were used to determine whether this polymorphism affected CRF2 receptor binding affinity as well as CRF2 receptor density in the CNS. Finally, social interaction and corticosterone levels were measured in the P and NP rats before and after 30-minute restraint stress. RESULTS:Crhr2 mRNA expression studies found lower levels of Crhr2 mRNA in iP rats compared to iNP rats. In addition, DNA sequencing identified polymorphisms in the promoter region, coding region, and 3'-untranslated region between the iP and iNP rats. A 7 bp insertion in the Crhr2 promoter of iP rats altered expression in vitro as measured by reporter assays, and we found that CRF2 receptor density was lower in the amygdala of iP as compared to iNP rats. Male P rats displayed decreased social interaction and significantly higher corticosterone levels directly following 30-minute restraint when compared to male NP rats. CONCLUSIONS:This study identified Crhr2 as a candidate gene of interest underlying the chromosome 4 QTL for alcohol consumption that was previously identified in the P and NP model. Crhr2 promoter polymorphism is associated with reduced mRNA expression in certain brain regions, particularly the amygdala, and lowered the density of CRF2 receptor in the amygdala of iP compared to iNP rats. Together, these differences between the animals may contribute to the drinking disparity as well as the anxiety differences of the P and NP rats.

Project description:Two-dimensional gel electrophoresis (2-DE) was used to separate protein samples solubilized from the nucleus accumbens and hippocampus of alcohol-naïve, adult, male inbred alcohol-preferring (iP) and alcohol-nonpreferring (iNP) rats. Several protein spots were excised from the gel, destained, digested with trypsin, and analyzed by mass spectrometry. In the hippocampus, 1629 protein spots were matched to the reference pattern, and in the nucleus accumbens, 1390 protein spots were matched. Approximately 70 proteins were identified in both regions. In the hippocampus, only 8 of the 1629 matched protein spots differed in abundance between the iP and iNP rats. In the nucleus accumbens, 32 of the 1390 matched protein spots differed in abundance between the iP and iNP rats. In the hippocampus, the abundances of all 8 proteins were higher in the iNP than iP rat. In the nucleus accumbens, the abundances of 31 of 32 proteins were higher in the iNP than iP rat. In the hippocampus, only 2 of the 8 proteins that differed could be identified, whereas in the nucleus accumbens 21 of the 32 proteins that differed were identified. Higher abundances of cellular retinoic acid-binding protein 1 and a calmodulin-dependent protein kinase (both of which are involved in cellular signaling pathways) were found in both regions of the iNP than iP rat. In the nucleus accumbens, additional differences in the abundances of proteins involved in (i) metabolism (e.g., calpain, parkin, glucokinase, apolipoprotein E, sorbitol dehydrogenase), (ii) cyto-skeletal and intracellular protein transport (e.g., beta-actin), (iii) molecular chaperoning (e.g., grp 78, hsc70, hsc 60, grp75, prohibitin), (iv) cellular signaling pathways (e.g., protein kinase C-binding protein), (v) synaptic function (e.g., complexin I, gamma-enolase, syndapin IIbb), (vi) reduction of oxidative stress (thioredoxin peroxidase), and (vii) growth and differentiation (hippocampal cholinergic neurostimulating peptide) were found. The results of this study indicate that selective breeding for disparate alcohol drinking behaviors produced innate alterations in the expression of several proteins that could influence neuronal function within the nucleus accumbens and hippocampus.

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Candidate genes for alcohol preference identified by expression profiling in alcohol-preferring and -nonpreferring reciprocal congenic rats.

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Candidate genes for alcohol preference identified by expression profiling in alcohol-preferring and -nonpreferring reciprocal congenic rats.

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