Alcohol Acceptance, Preference, and Sensitivity in Mice.

Although the recombinant inbred strain method was designed for molecular genetic analysis of linkage, it also provides powerful quantitative genetic analyses of heritability and genetic correlations. Measures of alcohol acceptance, alcohol preference, and hypnotic dose sensitivity (HDS) were assessed in 21 strains of mice from the BXD Rl series. Sex differences were found to be significant at a phenotypic level. However, heritability estimates for acceptance, preference, and HDS are similar in males and females. Heritability estimates for the three measures are ∼0.20 for acceptance and preference, and 0.10 for HDS. Analyses of genetic correlations reveal that acceptance and preference share some degree of genetic influence, although they mostly operate under different genetically mediated mechanisms. HDS did not show a significant genetic relationship to either acceptance or preference. Strong correlations were obtained when acceptance, preference, and HDS strain means were correlated across male and female recombinant inbreds, suggesting substantial genetic similarity across sexes.     

Quantitative trait loci affecting ethanol sensitivity in BXD recombinant inbred mice

BACKGROUND: Genetic and environmental factors contribute to an individual's sensitivity to ethanol, although the exact genes underlying ethanol's effects are not known. Quantitative trait locus (QTL) mapping is one successful method for provisionally identifying genes participating in the mediation of a given behavior. QTL analyses seek to identify associations between a quantitative response and previously mapped marker genes across genetically diverse individuals. Many QTL analyses have been performed in BXD recombinant inbred (RI) strains of mice derived from a cross of C57BL/6J (B6) and DBA/2J (D2) progenitor strains. METHODS: We conducted a QTL analysis of ethanol-induced loss of righting reflex and ataxia using a panel of 25 BXD RI strains and the progenitors B6 and D2. We measured the duration of loss of righting reflex after injection and blood ethanol concentrations upon regaining of righting reflex. Ataxia was measured as the latency to fall from a vertical screen. RESULTS: Genome-wide QTL analyses correlating strain means with allelic status at >1500 markers identified several associations (p < or = 0.01). These provisional QTLs were on all chromosomes except 2, 5, 12, 13, and X, and several map near potential candidate genes. CONCLUSIONS: These results suggest that ethanol sensitivity is determined by the actions of multiple genes and further suggest their general chromosomal map locations. These provisional linkages will now be confirmed or rejected using additional genetically segregating populations.     

Voluntary Alcohol Consumption in BXD Recombinant Inbred Mice: Relationship to Alcohol Metabolism

Studies were initiated to characterize behaviorally and biochemically C57BL/6J and DBA/2J inbred mice, as well as BXD Recombinant Inbred (RI) strains derived from them. The C57BL/6J, DBA/2J, and 7 BXD RI strains were tested for voluntary alcohol consumption (VAC) by receiving 4 days of forced exposure to a 10% (w/v) solution of alcohol, followed by 3 weeks of free choice between water and 10% alcohol. Measures of VAC included the absolute intake of alcohol (g/kg), as well as alcohol preference. A wide range of VAC was displayed by the various BXD RI strains with a continuous (rather than bimodal) distribution, indicating that there is likely to be additive effects of several genes involved in regulating alcohol-related behaviors. Kinetic characteristics of aldehyde dehydrogenase and catalase in liver and brain of the C57BL/6J, DBA/2J, and BXD strains of mice were determined to test the hypothesis that the genetic regulation of the levels of alcohol-metabolizing enzymes mediate differences in VAC. Aldehyde dehydrogenase activity was determined spectrophotometrically by observing the change in absorption at 340 nm. Catalase activity was determined by measuring oxygen production with a Yellow Springs Biological Oxygen monitor and oxygen electrode. There was a strong negative relationship between VAC and brain catalase activity in the BXD RI and parental strains. These data suggest that RI strains are likely to be useful genetic models in the examination of quantitative trait loci controlling VAC and other responses to alcohol.     

The syntaxin binding protein 1 gene (Stxbp1) is a candidate for an ethanol preference drinking locus on mouse chromosome 2

BACKGROUND: We previously mapped a quantitative trait locus (QTL) for ethanol preference drinking to mouse chromosome 2 (mapped with high confidence, LOD = 15.5, p = 3 x 10(-16)). The specific gene(s) in the QTL interval responsible for phenotypic variation in ethanol preference drinking has not been identified. METHODS: In the current study, we investigated the association of the syntaxin binding protein 1 gene (Stxbp1) with ethanol preference drinking and other ethanol traits using a panel of B6 x D2 (BXD) recombinant inbred (RI) strains derived from the C57BL/6J (B6) and DBA/2J (D2) inbred mouse strains. Confirmation analyses for ethanol consumption and withdrawal were performed using a large B6D2 F2 cross, short-term selected lines derived from the B6 and D2 progenitor strains, and standard inbred strains. RESULTS: BXD RI strain analysis detected provisional associations between Stxbp1 molecular variants and ethanol consumption, as well as severity of acute ethanol withdrawal, ethanol-conditioned taste aversion, and ethanol-induced hypothermia. Confirmation analyses using three independent genetic models supported the involvement of Stxbp1 in ethanol preference drinking but not in ethanol withdrawal. CONCLUSIONS: Stxbp1 encodes a Sec1/Munc18-type protein essential for vesicular neurotransmitter release. The present study provides supporting evidence for the involvement of Stxbp1 in ethanol preference drinking.     

Effects of Acute and Repeated Ethanol Exposures on the Locomotor Activity of BXD Recombinant Inbred Mice

Investigations of ethanol's (EtOH's) complex response profile, including locomotor and other effects, are likely to lead to a more in-depth understanding of the constituents of alcohol addiction. Locomotor activity responses to acute and repeated EtOH (2 g/kg, ip) exposures were measured in BXD recombinant inbred (RI) mice and their C57BL/6J (B6) and DBA/2J (D2) progenitors. Both the acute response and the change in initial EtOH response with repeated treatments were strain-dependent. The coefficient of genetic determination was 0.38–0.49 for initial locomotor response to EtOH, and 0.29 for change in response. Changes in response were largely attributable to sensitization of locomotor stimulation. Quantitative trait loci (QTL) analyses identified significant marker associations with basal activity, acute locomotor response, and change in response. Markers were for QTL on several chromosomes, and there was only one case of overlap in marker associations among phenotypes. Acute locomotor response and locomotor sensitization were negatively correlated with 3% EtOH preference drinking data collected in BXD Rl strains. Overall, these results demonstrate locomotor sensitization induced by EtOH, suggest independence of genetic determination of locomotor responses to acute and repeated EtOH exposure, and partially support a relationship between reduced sensitivity to the locomotor stimulant/sensitizing effects of EtOH and EtOH consumption.     

Confirmation and genetic dissection of a major quantitative trait locus for alcohol preference drinking

OBJECTIVE: In previous work, we created congenic strains that carry the DBA/2IBG (D2) region for alcohol preference on chromosome 2, on an otherwise C57BL/6IBG (B6) background. Here, we report construction and testing of interval-specific congenic recombinant strains (ISCRSs) for the purpose of narrowing the quantitative trait loci (QTL) interval. METHODS: ISCRSs were derived by identifying mice that carry recombination events in the D2 interval, during the backcrossing for congenics. Recombinant mice were backcrossed to B6, and progeny that carry the reduced chromosome 2 region were tested for its effect on the alcohol preference phenotype. RESULTS: We developed multiple ISCR strains, which spanned the QTL interval. Three of these showed the D2 phenotype of reduced alcohol consumption. The overlap of two of these strains reduced the QTL interval from 66.8 to 3.5 Mb. A third positive ISCRS suggests the possibility of a second, linked QTL. CONCLUSIONS: Use of ISCRSs can narrow a QTL region to a few Mb. This reduced interval size will facilitate identification of candidate genes, through bioinformatics, gene expression, and DNA sequencing strategies. Potential difficulties, including reduced power as a result of variable phenotypes or small effect size, are discussed.     

Allelic variation in the GABA A receptor gamma2 subunit is associated with genetic susceptibility to ethanol-induced motor incoordination and hypothermia, conditioned taste aversion, and withdrawal in BXD/Ty recombinant inbred mice

BACKGROUND: Behavioral genomics has made dramatic progress toward mapping quantitative trait loci (QTLs) that contain genes responsible for phenotypic differences in a variety of behavioral responses to alcohol (ethanol). We previously identified a QTL on mouse Chromosome 11 that affects genetic predisposition to acute alcohol withdrawal. Among mice derived from the C57BL/6J (B6) and DBA/2J (D2) inbred strains, this QTL (Alcw3) accounts for 12% of the genetic variability in withdrawal liability. Candidate genes within this QTL encode the gamma-aminobutyric acid type A (GABA A) receptor gamma2, alpha1, alpha6, and beta2 subunits. We recently identified a coding sequence polymorphism between the B6 and D2 strains for the GABA A receptor gamma2 subunit gene (Gabrg2). In this study, we expand our analysis to a panel of BXD strains derived from the B6 and D2 progenitor strains. These BXD strains provide 26 fixed recombinant genotypes that can be used to examine genetic correlations, for example, between a phenotype of interest and allelic variation in a candidate gene. METHODS: Gabrg2 was cloned and sequenced from the 26 BXD recombinant inbred strains. We analyzed genetic correlations between allelic variation in Gabrg2 and alcohol phenotypes previously measured in the BXD strain means. RESULTS: Allelic variation in Gabrg2 is correlated genetically with predisposition to acute alcohol withdrawal and may underlie the Alcw3 locus. In addition, Gabrg2 is associated with ethanol-conditioned taste aversion, ethanol-induced motor incoordination, and ethanol-induced hypothermia. A trend is observed for chronic ethanol withdrawal, ethanol-induced loss of righting reflex, and tolerance to ethanol-induced hypothermia and ataxia. CONCLUSIONS: Functionally relevant variation in Gabrg2, or a closely linked gene, is correlated genetically with some, but not all, behavioral responses to alcohol. The alcohol-related phenotypes associated with Gabrg2 generally may be characterized as debilitating or motivationally negative.     

Identification of candidate genes for alcohol preference by expression profiling of congenic rat strains

Background: 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. Methods: 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. Results: 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. Conclusions: 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.     

Quantitative trait locus mapping for acute functional tolerance to ethanol in the L x S recombinant inbred panel

BACKGROUND: Acute functional tolerance (AFT) develops shortly after ethanol administration, and is determined as the change in brain or blood ethanol concentration (BEC) measured at 2 behavioral or physiological endpoints. Acute functional tolerance studies in some rodent strains support a long-held hypothesis that more sensitive strains develop more within-session tolerance. We used the new, 74-strain L x S recombinant inbred (RI) panel, developed from inbred long-sleep (ILS) and inbred short-sleep (ISS) strains, to revisit this hypothesis and to map quantitative trait loci (QTLs) for AFT. We report replication of QTL regions reported by earlier studies of AFT and preliminary application of a coarse single nucleotide polymorphism map analysis to limit QTL intervals for subsequent candidate gene hypotheses. METHODS: Acute functional tolerance was assayed using a test of ataxia: loss and regain of balance on a stationary wooden dowel. Following an initial dose of 1.75 g/kg, BEC was measured at initial loss (BEC(0)) and regain of balance (BEC(1)). A second injection (2.0 g/kg) was administered and blood taken at the second regain of balance (BEC(2)). Acute functional tolerance was calculated as a difference score in 2 ways: (1) between BEC at the 2 successive regains of balance (AFT(1)), or (2) as the difference in BEC at final regain and at initial loss of balance (AFT(2)). We mapped QTLs for BEC(0), a measure of initial sensitivity, and both AFT scores. RESULTS: All 4 parental strains (LS, SS, ILS, and ISS) developed tolerance, replicating previous published reports. There were significant sex effects for 3 of these strains. The L x S panel showed a 128-fold range in tolerance, with a few strains showing negative tolerance (sensitization). The ISS surpassed the next highest RI strain by 55% and was more than 4 times greater than SS. Heritability estimates for both AFT measures were close to 0.25 for both sexes. One significant QTL accounting for approximately 18% of phenotypic variance (V(P)), on chromosome 12 (AFT(1)), and 1 suggestive QTL (16% V(P)), on chromosome 16 (AFT(2)), were identified. These QTLs replicated regions reported in other studies. A multiple QTL model incorporating the effects of all significant interacting QTLs was developed, explaining almost 60% of V(P). The chromosome 12 region was further investigated by haplotype analysis, which identified many nonpolymorphic regions within the confidence interval, and possible candidate genes in the polymorphic regions. CONCLUSIONS: Both SS and ISS developed greater AFT, assessed by both methods, than LS and ILS; this difference was significant in virtually all sex by strain comparisons. In the L x S RI, there was no correlation between initial sensitivity, measured by BEC at initial loss of balance, and either measure of AFT, on a stationary dowel. These results indicate that in this model system, initial sensitivity does not predict tolerance. Several QTLs for tolerance were identified; candidates in the narrowed chromosome 12 region, which has been reported in 2 other mapping studies, merit additional study.     

Gene coding variant in Cas1 between the C57BL/6J and DBA/2J inbred mouse strains: linkage to a QTL for ethanol-induced locomotor activation

BACKGROUND: Among some (e.g., DBA/2J or D2) but not all (C57BL/6J or B6) inbred strains of mice, ethanol has a marked psychostimulant effect. Intercrosses formed from the D2 and B6 strains have been used to detect quantitative trait loci (QTLs) for this phenotype. The major QTL is found at the mid-region of chromosome 2 (Demarest et al., 1999). This QTL has also been detected in heterogeneous stock mice (Demarest et al., 2001). A potential candidate gene in this region is Cas1, which codes for catalase. The current studies were conducted to determine (a) if there was difference in the open reading frame (ORF) of Cas1 between the D2 and B6 strains; (b) if a difference was found, was it likely that the difference had functional effects; and (c) if it could be established that Cas1 meets the criteria for QTL to gene. METHODS: The open reading frame (ORF) of Cas1 was sequenced in both the D2 and B6 mouse strains. A single polymorphism was found between the strains (see below); the strain distribution pattern for this polymorphism was determined in the 36 strains of the B6XD2 (BXD) recombinant inbred (RI) series. These data were used to map the position of Cas1 as described by Cudmore et al. (1999). RESULTS: The only difference between the D2 and B6 strains in the coding region was found at #349, G->A. This will result in a difference in the amino acid sequence between the strains at amino acid #117-alanine is found in the D2 strain while threonine is found in the B6 strain. The RI strain distribution pattern for this polymorphism was used to determine the relative placement of Cas1. The estimate suggests that Cas1 is flanked by D2Mit12 and D2Mit43 and relative to D2Mit94 (which was set at 47 cM), Cas1 is located at approximately 57 cM, confirming previous estimates (see www.jax.org). CONCLUSIONS: Pharmacological data (Correa et al., 2001) strongly support the idea that Cas1 meets the criteria for QTL to gene. However, based on the mapping data, Cas1 is clearly not included in the QTL for heterogeneous stock mice. Finally, other genetic data suggest that the polymorphism is not sufficient to generate the QTL.     

Confirmation of Quantitative Trait Loci for Alcohol Preference in Mice

An F2 intercross derived from C57BL/6 and DBA/2 progenitor inbred strains was used to test for replication of quantitative trait loci (QTLs) for alcohol preference nominated by a previous study using BXD recombinant inbred (RI) strains (Rodriguez et al., Alcohol. Clin. Exp. Res. 19:367–379, 1995). Fourteen provisional QTLs were nominated in the original RI study with a p < 0.05 criterion. In the present study, a genome scan (101 microsatellite markers) was conducted on an F2 population (n - 218). Three significant QTLs were detected on chromosomes 1, 4, and 9, and three suggestive QTLs were detected on chromosomes 2, 3, and 10. Of these six QTLs, four were consistent with the previous RI nominations. The replication rate of 28.6% (4 of 14) is in agreement with the results of simulation studies performed by Belknap et al. (Behav. Genet. 26:149–160, 1996) and supports the methodological argument for a multistage research design for nominating and replicating QTLs.     

Fine mapping of polymorphic alcohol-related quantitative trait loci candidate genes using interval-specific congenic recombinant mice

BACKGROUND: The inbred long-sleep (ILS) and inbred short-sleep (ISS) strains of mice are widely studied as a model of initial sensitivity to alcohol. Recently, a large comparative DNA sequencing study of candidate genes located within the four Lore quantitative trait loci (QTLs) associated with the ethanol-induced loss of righting reflex in ILS and ISS mice has identified eight genes that contain coding region differences corresponding to amino acid changes. Here, recently developed interval-specific congenic recombinant mice (ISCRs) have been used to map these genes in relationship to newly narrowed QTL regions. METHODS: Regions of candidate genes containing DNA differences corresponding to previously identified amino acid changes between ISS and ILS mice were amplified from either genomic DNA or complementary DNA from ISCR mice using polymerase chain reaction. The products were purified and directly sequenced to determine the genotypes for each polymorphism. On the basis of these genotypic data, each candidate gene was determined to be located either within or outside of recently narrowed Lore QTL intervals. RESULTS: Of these eight candidates with protein-coding differences, five are now excluded from their respective Lore intervals. The other three (Znf142, Ptprn, and Znf133) have been localized to the narrowed QTL intervals. CONCLUSIONS: These three central nervous system genes (Znf142, Ptprn, and Znf133) represent promising candidates for involvement in the differential sensitivity to alcohol exhibited between ILS and ISS mice. This study also demonstrates how the combination of high-throughput comparative gene sequencing and concomitant genetic fine mapping of QTL regions with ISCRs can be an effective tool for accelerating the process of moving from QTL to gene.     

QTL mapping for low-dose ethanol activation in the LXS recombinant inbred strains

BACKGROUND: Most mouse quantitative trait loci (QTLs) for behavioral traits have been mapped using populations of mice derived from C57BL/6J (B6) and DBA/2J (D2). It is also important to identify QTLs for behavior in populations derived from other progenitors. We report results from QTL mapping for low-dose (ethanol) locomotor activation (LDA) using the recently developed LXS recombinant inbred (RI) strains, derived from Inbred Long Sleep (ILS) and Inbred Short Sleep (ISS) progenitors. The LXS RI panel has additional genetic variation, and greater power due to a larger number of strains, compared with other RI panels and strain crosses. METHODS: Mice were tested using a 3-day protocol in which activity levels were monitored for 15 minutes each day. On day 1, baseline activity was recorded; on day 2, mice were injected with saline before testing; and on day 3, mice were injected with 1.8 g/kg ethanol and tested. RESULTS: Several suggestive QTLs were found, on chromosomes 2, 3, 4, 7, 8, 12, and 13; 3 of these QTLs were sex-specific. CONCLUSIONS: Two apparently novel LDA QTLs were identified, on chromosomes 4 and 8. The other QTLs appear to replicate previously identified LDA QTLs. These replicated QTLs will be pursued in subsequent studies designed to identify candidate genes.     

Localization of Genes Affecting Alcohol Drinking in Mice

The genomic map locations of specific genes controlling behaviors can be identified by studying a panel of recombinant inbred (RI) mouse strains. The progenitor C57BL/6J (B6) and DBA/2J (D2) strains, and 19 of the BXD RI strains derived from an F2 cross of these progenitors, were tested for 3% and 10% ethanol (EtOH) intake. The test sequence began with two-bottle free choice between tap water and unsweetened ethanol, and ended with free choice between water and saccharin-sweetened ethanol. Saccharin preference was also measured. Correlational analyses indicated that 59% of the genetic variance in 10% ethanol and sweetened 10% ethanol consumption was held in common, 24% of the genetic variance in saccharin and sweetened 10% ethanol consumption was held in common, and only 7% of the genetic variance in saccharin and unsweetened 10% ethanol consumption was held in common. These percentages for 3% ethanol solutions were 21%, 36%, and 14%. In addition, the severity of handling-induced convulsions during ethanol withdrawal was found to be significantly associated with the amount of ethanol consumed from the sweetened ethanol drinking tubes, suggesting that genetic differences in avidity for ethanol could lead to the development of physical dependence. Quantitative trait loci (QTL) analyses revealed that several genetic markers were associated with ethanol consumption levels, including markers for the D2 dopamine receptor. QTL analyses of saccharin and sweetened ethanol consumption identified the sac locus, thought to determine the ability to detect saccharin. In general, our results suggest that saccharin and ethanol consumption are determined by the actions of multiple genes (QTL), some in common, and suggest specific map locations of several such QTL on the mouse genome.     

Strategies for Mapping and Identifying Quantitative Trait Loci Specifying Behavioral Responses to Alcohol

Most responses to alcohol in both humans and animals are heritable, and this genetic sensitivity to ethanol is determined by multiple genes. However, the number of genes, their identities, and just how they determine susceptibility to the actions of alcohol are unknown. Herein, we describe a multistage strategy for mapping quantitative trait loci (QTLs) using recombinant inbred strains and F2 mice. Precise mapping of the chromosome positions of these QTLs should increase our understanding of the genetic causes for individual differences in behavioral sensitivity to alcohol by (1) identifying genomic markers associated with sensitivity to alcohol, (2) allowing the genes specifying behavior to be cloned by position, and (3) elucidating "candidate" genes demonstrating linkage to markers associated with behavioral responses to alcohol. Syntenic conservation between the mouse and human genomes should facilitate the eventual mapping and cloning of human homologs of these QTLs. Ultimately, cloning of these genes may allow the development of gene therapies or other therapeutic interventions for management or prevention of alcoholism and alcohol abuse.     

Dopamine D2 receptor binding,Drd2 expression and the number of dopamine neurons in the BXD recombinant inbred series: genetic relationships to alcohol and other drug associated phenotypes

BACKGROUND: It has not been established to what extent the natural variation in dopamine systems contribute to the variation in ethanol response. The current study addresses this issue by measuring D2 dopamine (DA) receptor binding, the expression of Drd2, the number of midbrain DA neurons in the BXD recombinant inbred (RI) series and then compares these strain means with those previously reported for a variety of ethanol and other drug-related phenotypes. METHODS: Data were collected for 21 to 23 of the BXD RI strains and the parental strains. D2 DA receptor autoradiography was performed using 125I-epidepride as the ligand [ Kanes S, Dains K, Cipp L, Gatley J, Hitzemann B, Rasmussen E, Sanderson S, Silverman S, Hitzemann R (1996) Mapping the genes for haloperidol-induced catalepsy. J Pharmacol Exp Ther 277:1016-1025]. Drd2 expression was measured using the Affymetrix oligoarray system. Immunocytochemical techniques were used to determine the number of midbrain DA neurons [Hitzemann B, Dains K, Hitzemann R (1994) Further studies on the relationship between dopamine cell density and haloperidol response. J Pharmacol Exp Ther 271:969-976]. RESULTS AND CONCLUSIONS: The range of difference in receptor binding for the RI strains was approximately 2-fold in all regions examined, the core, the shell of the nucleus accumbens (NAc) and the dorsomedial caudate-putamen (CPu); heritability in all regions was moderate--(h2 approximately 0.35). Drd2 expression in forebrain samples from the RI and parental strains ranged 1.5- to h2-fold and was moderate-0.47. Variation in the number of tyrosine hydroxylase (TH) positive neurons was moderate, 41% and 26% and h2 was low--0.19 and 0.15 for the ventral tegmental area (VTA) and substantia nigra compacta (SNc), respectively. Significant correlations were found between D2 DA receptor binding and the low dose (1.33 g/kg) ethanol stimulant response. (p < 0.002) and between expression and conditioned place preference (CPP) (p < 0.0005). No significant correlations were detected between ethanol preference and either receptor binding or Drd2 expression; however, a significant correlation was found between preference and Ncam expression. Ncam is approximately 0.2 Mb from Drd2. Overall, the data suggest ethanol preference and CPP are associated with the expression of Drd2 or closely linked genetic loci.     

Common Quantitative Trait Loci for Alcohol-Related Behaviors and CNS Neurotensin Measures: Voluntary Ethanol Consumption

The C57BL/6, DBA/2, and recombinant inbred (RI) strains derived from them (B × D RIs) are the most frequently studied mouse strains with regard to genetic regulation of voluntary ethanol consumption (VEC). We have studied VEC in an alternate genetic model provided by the LS × SS RIs. These RI strains exhibit phenotypic extremes in VEC comparable to the C57BL/6 and DBA/2 mice and genotype-dependent sex differences in drinking behavior. A correlational analysis between various ethanol-related behaviors suggests genetic independence of VEC from high-dose neurosensitivity (sleep time), acute ethanol tolerance, hypothermia, and low-dose locomotor activity. A search for quantitative trait loci identified a number of putative quantitative trait loci (QTL), three of which are identical to those previously reported for 10% ethanol drinking in the B × D RIs. We also find a significant correlation between low-affinity neurotensin receptor densities (NTRJ in the frontal cortex and VEC, and more common QTL between these two phenotypes than expected by chance. This suggests a role for frontal cortex NTR_L in regulating voluntary ethanol intake     

Mapping of quantitative trait loci underlying ethanol metabolism in BXD recombinant inbred mouse strains

BACKGROUND: Genetic factors are well known to play an important role in determining individual differences in the metabolism of ethanol (EtOH), and several specific polymorphic loci have been identified that significantly contribute to the variability of EtOH metabolism in humans. However, these variant genes are either alcohol or aldehyde dehydrogenases, and the identification of new gene products that contribute to variation in alcohol metabolism would be useful. METHODS: To identify quantitative trait loci (QTLs), we correlated variation in polymorphic markers with blood EtOH concentration and the rate of EtOH metabolism (beta) in C57BL/6J and DBA/2J strains and in 25 of their recombinant inbred strains after 2 and 3 g/kg of EtOH intraperitoneally. RESULTS: A QTL associated with beta values for both doses was definitively mapped to the proximal region of chromosome 17, syntenic with human chromosome 6q25-27. Seven to 12 chromosomal regions were provisionally identified for each phenotype; several were associated with 2 or more phenotypes. Each QTL suggests the location of a gene or genes affecting EtOH pharmacokinetics. Candidate genes suggested by these analyses included several whose gene products are known to be induced by EtOH (e.g., superoxide dismutase, glutathione transferase, and cytochrome P450 2E1), as well as several whose gene products have signaling functions likely to contribute to this induction. CONCLUSIONS: These studies provide evidence for the existence of genes affecting EtOH metabolism in multiple chromosomal regions. Future studies will be required to identify the chromosome 17 gene product. Use of other genetic populations, such as B6D2F2 crosses, will be required to determine which of the provisional loci represent true and which represent false-positive associations.