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.     

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.     

Genetic analyses of ethanol-induced hyperglycemia

BACKGROUND: Genetic sensitivity to ethanol-induced hyperglycemia was hypothesized to be related to sensitivity to ethanol-induced hypothermia and conditioned taste aversion. These hypotheses were explored by characterizing blood glucose changes after ethanol exposure in BXD recombinant inbred mice. METHODS: Adult male and female BXD recombinant inbred mice were acutely exposed to 4 g/kg of ethanol or saline with the order of exposure counterbalanced, and separated by a 1-week interval. Tail blood samples and rectal temperatures were determined immediately before ethanol/saline exposure and 2 hr after exposure. RESULTS: Substantial strain differences in ethanol-induced hyperglycemia and hypothermia were noted. In addition, sex also determined sensitivity to ethanol-induced hyperglycemia and interacted with strain. Correlational analyses using strain means indicated that ethanol-induced hyperglycemia was genetically independent from ethanol-induced hypothermia or conditioned taste aversion. Quantitative trait locus (QTL) analyses indicated provisional QTL for ethanol-induced hyperglycemia on chromosomes 1, 3, 4, 6, 7, 9, 12, 14, and 18, which, in part, were sex specific. CONCLUSIONS: These findings indicate important sex differences in the glycemic response to ethanol. In addition, multiple genes likely control this response, independent from genes that are important for the thermic or aversive effects of ethanol.     

Ethanol-Induced Conditioned Taste Aversion in BXD Recombinant Inbred Mice

Genetic differences in sensitivity to ethanol's aversive effects may play an important role in the development of alcohol-seeking behavior and alcoholism. The present study examined the development of ethanol-induced conditioned taste aversion in 20 BXD/Ty recombinant inbred strains of mice and their progenitor inbred strains, C57BL/6J (B6) and DBA/2J (D2). Adult male mice were given 1-hr access to a saccharin-flavored solution every 48 hr for 12 days. After all but the first and last saccharin access periods, they received ethanol injections (0, 2, or 4 g/kg, ip). Separate groups of unpaired control mice received 4 g/kg of ethanol 1 hr after water access. Saline control mice were also used for examining preference across a wide range of saccharin concentrations (0.019 to 4.864% w/v). As expected, saccharin consumption during taste conditioning declined over conditioning trials in a dose-dependent manner, indicating development of ethanol-induced conditioned taste aversion. Correlational analyses using strain means from recently published papers indicated no significant genetic correlation between taste conditioning and two phenotypes thought to reflect ethanol reinforcement or reward (ethanol drinking, conditioned place preference). However, there were significant genetic correlations between taste conditioning at the high dose and sensitivity to ethanol-induced hypothermia, rotarod ataxia, and acute withdrawal. Quantitative trait locus (QTL) analyses of strain means indicated that taste aversion was associated (p 0.01) with genetic markers on nine chromosomes (1, 2, 3, 4, 6, 7, 9,11, and 17). These QTLs were located near several candidate genes, including genes encoding several different acetylcholine receptor subunits, the 6 opioid receptor, and two serotonin receptors (lB and 1D). QTLs for saccharin preference were located on several of the same chromosomes (2,3,4,6, and 11). Two of these saccharin QTLs overlap candidate genes influencing sensitivity to sweet or bitter taste stimuli. In general, these findings support the conclusion that multiple genes influence ethanol-induced conditioned taste aversion. Some of these genes appear to influence taste sensitivity, whereas others appear to mediate sensitivity to aversive pharmacological effects of ethanol.     

Alcohol Acceptance, Preference, and Sensitivity in Mice. II. Quantitative Trait Loci Mapping Analysis Using BXD Recombinant Inbred Strains

Quantitative trait loci (QTL) mapping of complex phenotypes has emerged as an important feature of the recombinant inbred (Rl) strain methodology. In this second study of our series on alcohol-related behaviors in mice, we examine alcohol acceptance, preference, and hypnotic dose sensitivity (HDS) to a standard dose of alcohol measured in BXD RI strains to identify candidate QTL regions responsible for their heritability. We detected highly significant marker associations for acceptance on chromosome 12 (Eif4e) , for preference on chromosome 1 (D1Rti2) and chromosome 7 (D7Mit7) , and for HDS on chromosome 7 (Mpmv1). These are the strongest QTL associations that we detected, but several other candidate QTL regions are reported. Given the limited number of BXD RI strains available, the large number of markers used herein, and the consequent chance of identifying false marker associations, these RI QTL mapping results must be seen as tentative, but an important first step toward identifying QTL for alcohol-related behaviors.     

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.     

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.     

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     

Quantitative trait loci regulating relative lymphocyte proportions in mouse peripheral blood.

Relative proportions of peripheral blood (PB) B lymphocytes (B220%) as well as CD4 (CD4%) and CD8 (CD8%) T lymphocytes differ significantly among inbred mouse strains: B220% is high in C57BL/6J (B6) and C57BR/cdJ, intermediate in BALB/cByJ (BALB) and DBA/2J (D2), and low in NOD/LtJ (NOD) and SJL/J (SJL) mice, whereas CD4% and CD8% are high in NOD and SJL mice and low in the other 4 strains. By following segregating genetic markers linked to these traits in (B6 x D2) recombinant inbred (BXD RI) mice, the study defined 2 quantitative trait loci (QTLs) for the B220% phenotype: Pbbcp1 (peripheral blood B cell percentage 1, logarithm of odds [LOD] 4.1, P <.000 01) and Pbbcp2 (LOD 3.7, P <.000 04) on chromosome 1 (Chr 1) at about 63 cM and 48 cM; one suggestive locus for the CD4% phenotype (LOD 2.6, P <.000 57) on Chr 8 at about 73 cM; and one QTL for the CD8% phenotype: Pbctlp1 (peripheral blood cytotoxic T lymphocyte percentage 1, LOD 3.8, P <.000 02) on Chr 19 at about 12 cM. The study further segregated PB lymphocyte proportions in B6SJLF2 mice by using DNA markers adjacent to these mapped QTLs and found that the Pbbcp1 locus (LOD 5.6, P <.000 01) was also important in this mouse population. In both BXD RI and B6SJLF2 mice, QTLs regulating B-cell proportions showed no significant effect on T-cell proportions and vice versa. Thus, PB B- and T-lymphocyte proportions are regulated separately by different genetic elements.     

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.     

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.     

Differential effects of ethanol on gamma-aminobutyric acid-A receptor-mediated synaptic currents in congenic strains of inbred long and short-sleep mice

BACKGROUND: Ethanol enhances gamma-aminobutyric acid (GABA)A receptor-mediated responses in the brain, and this enhancement is greater in a mouse line behaviorally more sensitive to ethanol (long sleep) than in a line (short sleep) behaviorally less ethanol sensitive (assayed by loss of righting; sleep time). Quantitative trait locus (QTL) analysis of inbred long sleep (ILS) and inbred short sleep (ISS) phenotypes revealed four chromosomal regions (Lore1, Lore2, Lore4, and Lore5) that together account for approximately 50% of ethanol-induced sleep-time variance. Congenic strains were generated, each of which is homozygous for one of four ISS Lore QTLs on the ILS background. These congenic mouse strains are ideally suited for asking which QTL regions might correlate with other phenotypes that differ between ILS and ISS mice. Here we used the congenics to investigate altered GABAA responses to ethanol. METHODS: Evoked GABAA receptor-mediated inhibitory postsynaptic currents (IPSCs) were measured by whole-cell voltage-clamp recording procedures in CA1 pyramidal neurons in hippocampal brain slices. RESULTS: GABAA IPSC responses in hippocampal brain slices from ILS mice were significantly enhanced by 80 mM ethanol, whereas those from ISS mice were not affected. ILS.Lore2 and ILS.Lore5 congenic strains were significantly enhanced by 80 mM ethanol, similar to the background (control) ILS mice. However, ethanol had no significant effect on GABAA responses in ILS.Lore1 and ILS.Lore4 congenic mice, similar to the ISS mice, thus reflecting the influence of ISS alleles on the ILS phenotype. CONCLUSIONS: Our results suggest that alleles located in the Lore1 and Lore4 QTL regions confer ethanol sensitivity of GABAA receptor-mediated IPSCs. Thus, for these QTLs, GABAA IPSCs may represent an endophenotype of sedative/hypnotic sensitivity to ethanol. Although the Lore2 and Lore5 QTL regions have a significant effect on sleep time, they do not play a significant role in the differential ethanol enhancement of GABAA IPSCs between ILS and ISS mice.     

Quantitative trait loci analysis of tail tendon break time in mice of C57BL/6J and DBA/2J lineage

Tail tendon break time (TTBT), a measure of collagen cross-linking, shown to increase with age differs significantly among inbred strains of mice, indicating underlying genetic influences. This study was aimed to identify quantitative trait loci (QTLs) associated with tail tendon break time at three ages (200, 500, and 800 days of age) for 23 BxD recombinant inbred strains of mice and B6D2F(2) mice derived from C57BL/6J and DBA/2J strains. Heritability estimates were calculated, and QTL analyses were conducted using interval-mapping methods. Mean tail tendon break time values were higher in males and increased nonlinearly with age. Eight total QTLs were nominated in the B6D2F(2) mice at the three measured ages, with the QTL at 800 days confirmed in the recombinant inbred strains. Allelic effect modeling for the identified QTLs suggests differences in gene action between sexes. Candidate genes in the QTL regions include collagen genes and an advanced glycation end-product receptor. The QTLs identified demonstrate influence at some but not all ages.     

Genetically determined variation in the number of phenotypically defined hematopoietic progenitor and stem cells and in their response to early-acting cytokines

Quantitative trait analysis may shed light on mechanisms regulating hematopoiesis in vivo. Strain-dependent variation existed among C57BL/6 (B6), DBA/2, and BXD recombinant inbred mice in the responsiveness of primitive progenitor cells to the early-acting cytokines kit ligand, flt3 ligand, and thrombopoietin. A significant quantitative trait locus was found on chromosome 2 that could not be confirmed in congenic mice, however, probably because of epistasis. Because it has been shown that alleles of unknown X-linked genes confer a selective advantage to hematopoietic stem cells in vivo in humans and in cats, we also analyzed reciprocal male D2B6F1 and B6D2F1 mice, revealing an X-linked locus regulating the responsiveness of progenitor and stem cells to early-acting factors. Among DBA/2, B6, and BXD recombinant inbred mice, correlating genetic variation was found in the absolute number and frequency of Lin(-)Sca1(++)kit(+) cells, which are highly enriched in hematopoietic progenitor and stem cells, and in the number of Lin(-)Sca1(++)kit(-) cells, a population whose biologic significance is unknown, suggesting that both populations are functionally related. Suggestive quantitative trait loci (QTLs) for the number of Lin(-)Sca1(++) cells on chromosomes 2, 4, and 7 were confirmed in successive rounds of mapping. The locus on chromosome 2 was confirmed in congenic mice. We thus demonstrated genetic variation in the response to cytokines critical for hematopoiesis in vivo and in the pool size of cells belonging to a phenotype used to isolate essentially pure primitive progenitor and stem cells, and we identified loci that may be relevant to the regulation of hematopoiesis in steady state.     

Decreased ethanol sensitivity and tolerance development in gamma-protein kinase C null mutant mice is dependent on genetic background

Initial sensitivity and tolerance development to the sedative-hypnotic and hypothermic effects of ethanol were investigated in gamma-protein kinase C (PKC) null mutant mice. Null mutants from a C57BL/6J x 129/SvJ mixed genetic background demonstrated decreased ethanol sensitivity and failed to develop chronic tolerance after 10 days of ethanol liquid diet. However, when the null mutation was introgressed onto a C57BL/6J background for six generations, the "no tolerance" phenotype for sedative-hypnotic and hypothermic effects of ethanol was no longer apparent Outcrossing the gamma-PKC null mutation to a C57BL/6J x 129/SvEvTac mixed background restored the "no tolerance" phenotype to ethanol-induced sedation after chronic ethanol diet; however, as measured by hypothermia, tolerance was still evident in the null mutant mice. These observations and the results of tests of chronic tolerance in the C57BL/6J, 129/SvJ, and 129/SvEvTac background inbred strains indicate that gamma-PKC plays an important role in initial sensitivity and tolerance to ethanol. However, the impact of gamma-PKC is modulated by the background genotype. These results stress the importance of including the effect of genetic background when evaluating the effects of single gene mutations on quantitative behavioral traits.     

Possible pleiotropic effects of genes specifying sedative/hypnotic sensitivity to ethanol on other alcohol-related traits

BACKGROUND: Initial sensitivity to ethanol is a predictor of alcohol abuse that has been studied extensively in both human and animal populations. Selection for initial sensitivity to the sedative/hypnotic effects of ethanol resulted in the long-sleep and short-sleep lines of mice. Some of the genes selected in these lines could also specify differential responses in other ethanol-related phenotypes and, perhaps, for other drugs of abuse. We assessed congenic mice carrying a single quantitative trait locus (QTL) from the inbred long-sleep (ILS) or inbred short-sleep (ISS) strain on the reciprocal background for a number of ethanol- and pentobarbital-related phenotypes. METHODS: Each congenic strain was tested for ethanol elimination rates at 4.1 g/kg, ethanol-induced ataxia at 2.0 g/kg, ethanol-induced hypothermia at 4.1 g/kg, and pentobarbital-induced loss of righting reflex (LORR) at 60 mg/kg. Additionally, the ILS.ISS congenics were tested for low-dose ethanol-induced activation (LDA) at five doses ranging from 0.6 to 1.2 g/kg ethanol, and the ISS.ILS congenics were tested for LDA at 1.8 g/kg of ethanol. RESULTS: There was little difference in the ethanol elimination rate between congenics and background strains, although a modest sex effect was found, with the females eliminating ethanol more rapidly than the males. We were unable to replicate previous differences found in LDA for the congenic on the ISS background, because none of the congenics differed from controls for LDA. congenics showed a differential effect of pentobarbital-induced LORR in the expected directions. The congenics on the ISS background showed more ethanol-induced ataxia than the ISS controls. Additionally, the hypothermic response seems affected by and and maybe others. CONCLUSIONS: At least two regions carrying a QTL specifying sensitivity to high doses of ethanol cospecify altered sensitivity in other measures of alcohol action. Specifically, these QTLs clearly affect ethanol-induced hypothermia and pentobarbital-induced LORR and possibly ethanol-induced ataxia.     

Genetic determination of cardiac mass in normotensive rats: results from an F344xWKY cross

Genetic determinants affect adult cardiac mass and the predisposition to develop cardiac hypertrophy. The aim of this study was to identify quantitative trait loci (QTL) that control heart and left ventricular (LV) weight by use of normotensive inbred rat strains that differ in their adult cardiac mass phenotype. We studied 126 male F2 rats derived from a cross of normotensive Wistar-Kyoto and Fischer 344 rats. At 12 weeks of age, total heart weight and LV weight were measured. Genomic DNA from these animals was screened by use of polymorphic microsatellite markers across the whole genome (excluding the sex chromosomes). In this cross, the genetic contribution to total heart weight variation was 56%, and the genetic contribution for LV weight was 55%. Using the Mapmaker/QTL computer package, we identified a significant QTL on chromosome 3 with a log10 likelihood (LOD) score of 4.8, which accounted for 16.5% of the total variance of LV weight. This QTL was centered close to the marker D3Rat29. The QTL was also found to be significantly linked with total heart weight (LOD=4.4). These data provide the first demonstration of a QTL on chromosome 3 that plays a role in determining the difference in LV mass between normotensive Fischer 344 and Wistar- Kyoto inbred rat strains. The prostaglandin synthase 1 gene is located within the QTL.     

Strain differences in alcohol-induced neurochemical plasticity: a role for accumbens glutamate in alcohol intake

Background: Repeated alcohol administration alters nucleus accumbens (NAC) basal glutamate content and sensitizes the capacity of alcohol to increase NAC extracellular glutamate levels. However, the relevance of alcohol‐induced changes in NAC glutamate for alcohol drinking behavior is under‐investigated. Methods: To examine the relationship between genetic variance in alcohol consumption and alcohol‐induced neuroadaptations within the NAC, in vivo microdialysis was conducted in the alcohol‐preferring C57BL/6J (B6) and alcohol‐avoiding DBA2/J (D2) mouse strains on injections 1 and 8 of repeated alcohol treatment (8 × 2 g/kg, IP). To confirm an active role for NAC glutamate in regulating alcohol drinking behavior, the glutamate reuptake inhibitor dl ‐threo‐β‐benzyloxyaspartic acid (TBOA) (300 μM) and the Group 2 metabotropic glutamate autoreceptor agonist (2R,4R)‐4‐aminopyrrolidine‐2,4‐dicarboxylate (APDC) (50 μM) were infused into the NAC of B6 and D2 mice prior to alcohol consumption in a 4 bottle‐choice test. Results: While strain differences were not apparent for NAC basal levels of dopamine, serotonin or γ‐amino butyric acid (GABA), repeated alcohol treatment elevated NAC basal glutamate content only in B6 mice. Strain differences in both the acute and the sensitized neurochemical responses to 2 g/kg alcohol were observed for all neurotransmitters examined. While the alcohol‐induced rise in NAC dopamine and glutamate levels sensitized in B6 mice, a sensitization was not observed in D2 animals. Moreover, B6 mice exhibited a sensitized serotonin and GABA response to alcohol followed repeated treatment, whereas neither tolerance nor sensitization was observed in D2 animals. An intra‐NAC APDC infusion reduced alcohol intake in both B6 and D2 mice by approximately 50%. In contrast, TBOA infusion elevated alcohol intake selectively in B6 mice. Conclusions: These data indicate an active role for NAC glutamate in regulating alcohol consumption in mice and support the hypothesis that predisposition to high alcohol intake involves genetic factors that facilitate alcohol‐induced adaptations in glutamate release within the NAC.     

Association analysis of sequence variants of GABA(A) alpha6, beta2, and gamma2 gene cluster and alcohol dependence

Quantitative trait analyses in mice suggest a vulnerability locus for physiological alcohol withdrawal severity on a chromosomal segment that harbors the genes encoding the alpha1, alpha6, beta2, and gamma2 subunits of the gamma-aminobutyric acid type-A receptor (GABR). We tested whether genetic variation at the human GABA(A) alpha6, beta2, and gamma2 gene cluster on chromosome 5q33 confers vulnerability to alcohol dependence. The genotypes of three nucleotide substitution polymorphisms of the GABRA6, GABRB2, and GABRG2 genes were assessed in 349 German alcohol-dependent subjects and in 182 ethnically matched controls. To eliminate some of the genetic variance, three more homogeneous subgroups of alcoholics were formed by: (1) a history of alcohol withdrawal seizure or delirium (n = 106); (2) a history of parental alcoholism (n = 120); and (3) a comorbidity of dissocial personality disorder (n = 57). We found no evidence that any of the investigated allelic variants confers vulnerability to either alcohol dependence or severe physiological alcohol withdrawal symptoms or familial alcoholism (p > 0.05). The frequency of the T allele of the GABRA6 polymorphism was significantly increased in dissocial alcoholics [f(T) = 0.799] compared with the controls [f(T) = 0.658; p = 0.002; OR(T+) = 7.26]. Taking into account the high a priori risk of false-positive association findings due to multiple testing, further replication studies are necessary to examine the tentative phenotype-genotype relationship of GABRA6 gene variants and dissocial alcoholism.