Selective breeding, congenic strains, and other classical genetic approaches to the analysis of alcohol-related polygenic pleiotropisms

Alcohol exposure inhibits adult neural stem cell proliferation

Alcohol exposure can reduce adult proliferation and/or neurogenesis, but its impact on the ultimate neurogenic precursors, neural stem cells (NSCs), has been poorly addressed. Accordingly, the impact of voluntary consumption of alcohol on NSCs in the subventricular zone (SVZ) of the lateral ventricle was examined in this study. The NSC population in adult male C57BL/6J mice was measured after voluntary alcohol exposure in a two-bottle choice task using the neurosphere assay, while the number of NSCs that had proliferated 2 weeks prior to tissue collection was indexed using bromodeoxyuridine (BrdU) retention. There was a significant decrease in the number of BrdU-retaining cells in alcohol-consuming mice compared with controls, but no difference in the number of neurosphere-forming cells that could be derived from the SVZ of alcohol-consuming mice compared with controls. Additionally, PCNA-labeled cells in the SVZ tended to be lower, but there was no difference in BrdU labeling in the dentate gyrus following alcohol exposure. To determine alcohol's direct impact on NSCs and their progeny, neurospheres derived from naïve mice were treated with alcohol in vitro. Neurosphere formation was reduced by 100 mM alcohol without reducing cell viability. These findings are the first to assess the impact of moderate voluntary alcohol consumption on selective measures of adult NSCs and indicate that such exposure alters NSC proliferation dynamics in vivo and alcohol has direct but dissociable effects on the expansion and viability on NSCs and their progeny in vitro.

Dissecting impulsivity and its relationships to drug addictions

Addictions are often characterized as forms of impulsive behavior. That said, it is often noted that impulsivity is a multidimensional construct, spanning several psychological domains. This review describes the relationship between varieties of impulsivity and addiction-related behaviors, the nature of the causal relationship between the two, and the underlying neurobiological mechanisms that promote impulsive behaviors. We conclude that the available data strongly support the notion that impulsivity is both a risk factor for, and a consequence of, drug and alcohol consumption. While the evidence indicating that subtypes of impulsive behavior are uniquely informative--either biologically or with respect to their relationships to addictions--is convincing, multiple lines of study link distinct subtypes of impulsivity to low dopamine D2 receptor function and perturbed serotonergic transmission, revealing shared mechanisms between the subtypes. Therefore, a common biological framework involving monoaminergic transmitters in key frontostriatal circuits may link multiple forms of impulsivity to drug self-administration and addiction-related behaviors. Further dissection of these relationships is needed before the next phase of genetic and genomic discovery will be able to reveal the biological sources of the vulnerability for addiction indexed by impulsivity.

A verification of previously identified QTLs for cocaine-induced activation using a panel of B6.A chromosome substitution strains (CSS) and A/J x C57Bl/6J F2 mice

BACKGROUND

The objective of this study was to confirm provisional quantitative trait loci (QTL) for cocaine-induced locomotor activation, on chromosomes 1, 5, 6, 9, 12, 15, 16, 17, and 18, previously identified in the AXB/BXA recombinant inbred (RI) and AcB/BcA recombinant congenic (RC) strains of mice derived from A/J (A) and C57BL/6J (B6) progenitors. This was accomplished through a genetic analysis of cocaine-induced activity in an AxB6 F2 cross and a phenotypic survey across a panel of B6.A chromosome substitution strains (CSS) mice. Mice were tested for cocaine-induced activity, following administration of saline and cocaine (20 mg/kg), utilizing an open-field procedure.

RESULTS

Among AxB6 F2 mice, differences in cocaine-induced activity were associated with loci on chromosome 1 (D1Mit305), 5 (D5Mit409), 16 (D16Mit131), and 18 (D18Mit189). A survey of the CSS panel confirmed cocaine QTLs on chromosomes 5 and 15, previously identified in RI or RC strains. Overall, the regions on chromosomes 5 and 18 represent verification of QTL previously identified in both the RC and RI strains. Additionally, the B6 allele for these QTL was consistently associated with greater relative cocaine activation.

CONCLUSIONS

Collectively, chromosome 5 and 18 QTL have now been replicated in multiple independent crosses derived from the A/J and C57BL/6J progenitors. The use of an in silico analysis highlighted potential candidate genes on chromosomes 5 and 18. The present results complement the targeted gene approach currently prevalent in the study of cocaine and provide a broader empirically based focus for subsequent candidate gene studies.

Mice deficient in the alpha subunit of G(z) show changes in pre-pulse inhibition, anxiety and responses to 5-HT(1A) receptor stimulation, which are strongly dependent on the genetic background

RATIONALE

G(z), a member of the G(i) G protein family, is involved in the coupling of dopaminergic and serotonergic receptors. In the present study, we investigated behaviour of mice deficient in the alpha subunit of G(z) and focused on pre-pulse inhibition (PPI) and anxiety-like responses and the role of serotonin-1A (5-HT(1A)) receptors.

MATERIALS AND METHODS

We compared male and female wild-type and knock-out mice on either a C57Bl/6 or Balb/c background. We used automated startle boxes to assess startle and PPI and elevated plus maze to assess anxiety-like behaviours.

RESULTS

Balb/c mice showed higher baseline PPI than C57Bl/6 mice, and there was no difference between the genotypes. The 5-HT(1A) receptor agonist, 8-hydroxy-di-propylaminotetralin (8-OH-DPAT), had no effect on PPI in C57Bl/6 mice but markedly increased PPI in Balb/c mice, with the effect being attenuated in Galpha(z) knock-outs. On the elevated plus maze, there was little effect of the knock-out or 8-OH-DPAT in C57Bl/6 mice, whereas in Balb/c mice, Galpha(z) knock-outs showed a phenotype of high levels of anxiety-like behaviour. 8-OH-DPAT was anxiogenic in Balb/c mice, but this effect was attenuated in Galpha(z) knock-outs.

CONCLUSIONS

5-HT(1A) receptors couple to G(z). In a strictly background strain-dependent manner, Galpha(z) knock-out mice display high levels of anxiety-like behaviour and are less sensitive to the action of 8-OH-DPAT. Balb/c mice show much more clear effects of the Galpha(z) knock-out than C57Bl/6 mice, which are often considered the standard background strain for genetic modifications. Therefore, our results suggest caution when studying the behavioural effects of genetic modifications only in C57Bl/6 mice.

Different effects of stress on alcohol drinking behaviour in male and female mice selectively bred for high alcohol preference

AIMS

The purpose of the present study was to examine the effects of stress on alcohol drinking behaviour in male and female mice with a genetic predisposition toward high alcohol preference (HAP2 line).

METHODS

Alcohol-naïve male (n = 22) and female (n = 23) HAP2 mice were assigned to a restraint stress or no stress control group. Stress was initially applied for 2 h per day on 10 consecutive days. All mice were then given daily 2 h limited-access to a 10% v/v alcohol solution or water, with food freely available, for 21 days. Over the next 20 days, 2 h restraint stress was applied every other day immediately prior to 2 h access to alcohol and water. On intervening days, all mice received 2 h access to alcohol and water in the absence of stress. Following this phase of the study, the effects of restraint stress on acoustic startle reactivity was assessed in all mice. Finally, all mice were given continuous access to alcohol and water for 8 days.

RESULTS

Ten days of prior stress exposure did not significantly alter the acquisition of limited-access alcohol drinking. Subsequent exposures to intermittent restraint stress produced subtle but consistent effects on alcohol intake that differed in males vs females: stress increased alcohol intake in males and decreased alcohol intake in females. Restraint stress did not alter acoustic startle reactivity. Under continuous-access conditions after stress termination, the stress-induced increase in alcohol intake in males became more robust; however, in females, alcohol intake returned to the control group level.

CONCLUSIONS

These findings suggest that the effects of stress on alcohol drinking in mice with a genetic predisposition toward high alcohol preference depend on sex.

Conceptual, spatial, and cue learning in the Morris water maze in fast or slow kindling rats: attention deficit comorbidity

Rat lines selectively bred for differences in amygdala excitability, manifested by "fast" or "slow" kindling epileptogenesis, display several comorbid features related to anxiety and learning. To assess the nature of the learning deficits in fast kindling rats, performance was evaluated in several variants of a Morris water-maze test. Regardless of whether the location of the platform was fixed or varied over days (matching-to-place task), the fast rats displayed inferior performance, suggesting both working and reference memory impairments. Furthermore, when the position of the platform was altered after the response was acquired, fast rats were more persistent in emitting the previously acquired response. The poor performance of fast rats was also evident in both cued and uncued tasks, indicating that their disturbed learning was not simply a reflection of a spatial deficit. Moreover, fast rats could be easily distracted by irrelevant cues, suggesting that these animals suffered from an attentional disturbance. Interestingly, when rats received several training trials with the platform elevated, permitting them to develop the concept of facile escape, the performance of fast rats improved greatly. The performance disturbance in fast rats may reflect difficulties in forming a conceptual framework under conditions involving some degree of ambiguity, as well as greater distractibility by irrelevant cues. These various attributes of the fast rats may serve as a potentially useful animal model of disorders characterized by an attention deficit.

Sensitivity of AXB/BXA recombinant inbred lines of mice to the locomotor activating effects of cocaine: a quantitative trait loci analysis

The present study was conducted in order to characterize putative quantitative trait loci (QTL) for cocaine-induced activation in the AXB/BXA recombinant inbred (RI) lines of mice. Locomotor activity was measured in the AXB/BXA and progenitor A/J and C57BL/6J strains using a computerized open-field apparatus following saline or cocaine (0, 5, 10, 20 mg/kg) administration (i.p.). Analyses were conducted on phenotypes including both novelty (responses under initial saline conditions) and cocaine-induced locomotor activity. Significant differences were observed across RI lines on all measures. Gender differences in sensitivity to the activating effects of cocaine were not observed. The wide and continuous distributions of phenotypic responses in the AXB/BXA RI lines suggested polygenic regulation. Initial basal locomotor activity was significantly correlated with cocaine-induced activation (raw scores) (r = 0.60, P = 0.0021) but not with cocaine difference scores (r = 0.370, P = 0.082). Simple regression and interval mapping were used to initially identify significant gene markers associated with novelty and cocaine-induced activation. Subsequently, composite interval mapping was used to increase the accuracy in mapping individual loci. QTL analysis of cocaine-induced activation (difference scores--20 mg/kg dose) identified significant loci on chromosomes 12 (23 cM), and 15 (46.8 cM). The significant QTLs were identified on chromosomes 12 and 15 map to regions in proximity to genes for the somatostatin 1 (Smstr1 -23 cM) and 3 (Smstr3 -46.3 cM) receptors, respectively. Further research employing AcB/BcA recombinant congenic lines of mice will be employed to confirm the QTL on chromosomes 12 and 15 identified in the present study.

Acoustic startle and fear-potentiated startle in rats selectively bred for fast and slow kindling rates: relation to monoamine activity

The acoustic startle response, prepulse inhibition, fear-potentiated startle and monoamine activity induced by either, a novel stimulus or a cue previously paired with foot-shock (fear-conditioning), were assessed in rats selectively bred for differences in amygdala excitability (Fast vs. Slow kindling epileptogenesis). Comorbid differences of anxiety, which were dependent both on the rats' behavioural style and the kind of stressor, also characterized these strains. In the present investigation, Slow rats exhibited a greater startle reflex to noise relative to Fast rats, suggesting differences in generalized anxiety, but similar rates of startle habituation and prepulse inhibition. The fear-potentiated startle, however, was greater in Fast rats. When movement of the rat was restricted in a new environment, presentation of a novel stimulus (light) increased norepinephrine, dopamine and/or serotonin activity in brain regions typically associated with stressors (e.g. locus coeruleus, paraventricular hypothalamic nucleus). Generally, these effects were more pronounced in Fast rats, and norepinephrine utilization in the central amygdala was particularly highlighted in response to a conditioned fear stimulus. Thus, while generalized anxiety appeared greater in Slow rats, behavioural and central neurochemical reactivity in response to novel stimuli and to fear-eliciting stimuli, was greater in Fast rats. Similarly, basal dopamine activity in the prefrontal cortex was greater in Fast rats, but dopamine utilization elicited by a novel stimulus was more pronounced in Slow rats. This suggested that relative to Slow rats, dopamine neurons in prefrontal cortex of Fast rats do not react normally to environmental stimuli, and this phenomenon could lead to disturbances of attention or impulsivity.

Identification and confirmation of quantitative trait loci regulating alcohol consumption in congenic strains of mice

BACKGROUND

C57BL/6 inbred mice prefer alcohol whereas DBA/2 mice avoid it. We describe the construction of congenic strains of mice in which DBA/2 alleles for alcohol avoidance were placed on a C57BL/6 background using phenotypic selection.

METHODS

Mice were primed to drink 10% v/v ethanol in water for 2 days before a two-bottle choice paradigm. N2 males who demonstrated an alcohol-avoidance phenotype were backcrossed to B6 females to construct 15 independent lines.

RESULTS

Eight of these lines were lost due to failure to breed or absence of males with an alcohol-avoidance phenotype. The remaining sublines were split to form a total of 21 sublines. In the N7 and N9 generations, a genome scan located provisional quantitative trait loci (QTLs) on chromosomes 1, 2, 3, 6, and 9. Progeny testing confirmed QTLs on chromosomes 1 and 2.

CONCLUSIONS

The QTL on chromosome 2 overlaps the 95% confidence interval of Alcp1 whereas that on chromosome 1 is new and has been called Alcp5. Marker-assisted selection was used in the N9 and subsequent generations to maintain the congenic lines and produce congenic strains.

Acute sensitivity vs. context-specific sensitization to cocaine as a function of genotype

Individual variability in the acute and chronic effects of psychomotor stimulants is due, in part, to genetic factors. The purpose of this series of studies was to utilize a behavioral model of sensitization, namely increased locomotor activity, to assess individual variability in sensitization to the chronic effects of cocaine and its relationship to the acute stimulant effects of cocaine. Because the degree of sensitization is proportional to the training dose, genetic differences in acute sensitivity to cocaine were assessed and incorporated into the sensitization paradigm. Acute sensitivity and context-dependent sensitization were determined in six inbred mouse strains. Large quantitative and qualitative differences were found in the acute potency and efficacy of cocaine to stimulate locomotor activity. The ED50 was higher in the strains in which cocaine was most efficacious. Context-specific sensitization was determined via chronic administration of equiactive doses of cocaine (ED50) specifically paired with the test apparatus or with the home colony. Sensitization was time, environment, and genotype dependent. The differences in the number of trials required to show sensitization were unrelated to the acute locomotor stimulant effects of cocaine. These findings suggest that acute cocaine-induced locomotor activity and context-specific sensitization reflect different pharmacological properties of cocaine.

Congenic AB mice: a novel means for studying the (molecular) genetics of aggression

Congenic strains (CS) of mice were established to identify genomic regions which are associated with the male behavioral trait "isolation-induced aggression" (iia). For this purpose the trait was backcrossed for 10 generations onto the genetic background of a closely related, but nonaggressive, strain. Brother/sister matings were subsequently performed for 10 generations. Genomic screening for "iia-associated" markers was performed via multilocus DNA fingerprinting with a panel of oligonucleotide probes containing simple tandem repetitive motifs. Pools of DNAs from 10 mice each were composed from inbred generations to minimize residual genetic variability in the CS. The representation of iia-associated DNA fingerprint bands was additionally ascertained by investigating the individual mouse genomes constituting the pools. The CS system may allow rational approaches to the behavioral trait "aggression," even under various experimental conditions of different environments.

Identifying alcoholism vulnerability alleles

Identification of vulnerability alleles is one starting point for elucidating the web of interactions leading to alcoholism so that treatment and prevention can be improved. Heritability studies indicate that vulnerability alleles exist. Two molecular approaches for identifying them, direct analysis of candidate genes and genetic linkage, are highlighted in this review. Methodological problems that have been partially addressed and limitations for the applicability of the genetic findings are discussed.

Classical and neoclassical approaches to the genetic analysis of alcohol-related phenotypes

Theoretical descriptions are given for two breeding methods in animal genetics that might be of use in alcohol research. These methods are marker-based selection and marker-based development of congenic strains, both using DNA markers such as polymerase chain reaction-detectable polymorphisms as the criteria for breeding. Such designs would utilize these markers as indicators of adjacent Quantitative Trait Loci (QTL) that are influential on alcohol-related phenotypes. Issues in the logic and implementation of these methods, such as proximity of the markers and the QTL allele, are explored. A third method, development of congenic strains with phenotypic screening, is also described. This method is currently being used to create two sets of congenic lines on a C57BL/6 inbred mouse background. The criterion phenotype is locomotor activation to 1.5 g/kg (i.p.) ethanol. Data are reported on the success of transferring the activation phenotype from two strains, DBA/2Abg and MOLD/Rk-Abg, onto the nonactivated C57BL/6Abg background. The value of these methods in alcohol research is outlined with regard to both identification of relevant genes and for their use as tools in basic research on mechanism of alcohol action.

Biometrical genetic analysis of ethanol's psychomotor stimulant effect

Hereditary influences on psychomotor stimulant effects of ethanol (ETOH) were studied in a classical Mendelian cross of DBA/2Abg (D2) and C57BL/6Abg (B6) inbred mouse strains. A dose-response study with nine doses (0-3.5 g/kg ip) indicated that B6 mice lack the activational limb of the biphasic curve (< or = 1.5 g/kg), as assessed in a 15-min test. D2 mice ran greater distances and ran faster, at doses up to 2.5 g/kg. B6 mice showed no increments in speed or distance at these doses that activated D2 mice. Several other indices reinforced the conclusion of ETOH-induced behavioral activation in D2 mice and lack there of in B6 mice (traditional photobeam interruptions--horizontal counts; center distance; vertical movements; inactive time; as well as derived indices of running speed and average length of each movement). The F1, F2, and backcross generations produced dose-response curves that showed additive inheritance of the activational response to doses below 1.5 g/kg. A second study (n = 1446) examined response to 1.5 g/kg with a within-subjects design in the full Mendelian cross. This study verified the completely additive mode of inheritance for the total distance measure suggested in the dose-response study, and showed that sex linkage and sex differences were not present. Narrow sense heritability of the ETOH activation response (indexed by total distance) was calculated at 0.35 and approximately 3 loci were estimated to be responsible for the B6/D2 difference. The other phenotypes (described above) also showed strongly additive genetic control.(ABSTRACT TRUNCATED AT 250 WORDS)

Genetic influences on locomotor activating effects of ethanol and sodium pentobarbital

The paradoxical capability of sedative-hypnotics to produce behavioral disinhibition varies among genotypes. In DBA/2 mice ethanol (ETOH) produced strong locomotor stimulation with the peak of the biphasic curve at 1.5 g/kg IP. C57BL/6 mice showed no activation, and F1S were intermediate. These characterizations held for a variety of behavioral indices derived from 15 min tests, such as distance, speed, and rest time, at doses in the 0-2.0 g/kg range. Analogous studies with sodium pentobarbital (0-40 mg/kg) yielded a similar pattern of strain differences in locomotor stimulation. In contrast, loss of righting reflex durations (60 mg/kg PENTO, IP) were similar in the two strains, indicating dissociation of activating and sedative effects. In complementary studies, long- and short-sleep mice, which were bred for differences in soporific effects of ETOH, showed similar activation profiles at ETOH doses up to 1.5 g/kg and PENTO doses up to 30 mg/kg. These studies provide support for an hypothesis of common genetic control of the activation effect for ETOH and PENTO.

Genetic animal models of alcohol and drug abuse

Behavioral and pharmacological responses of selectively bred and inbred rodent lines have been analyzed to elucidate many features of drug sensitivity and the adverse effects of drugs, the underlying mechanisms of drug tolerance and dependence, and the motivational states underlying drug reward and aversion. Genetic mapping of quantitative trait loci (QTLs) has been used to identify provisional chromosomal locations of genes influencing such pharmacological responses. Recent advances in transgenic technology, representational difference analysis, and other molecular methods now make feasible the positional cloning of QTLs that influence sensitivity to drugs of abuse. This marks a new period of synthesis in pharmacogenetic research, in which networks of drug-related behaviors, their underlying pharmacological, physiological, and biochemical mechanisms, and particular genomic regions of interest are being identified.

Differential activating effects of ethanol in C57BL/6Abg and DBA/2Abg mice

A characteristic pattern of ETOH-induced locomotor activation in the DBA/2Abg strain (D2), small activation or sedation in the C57BL/6Abg (B6), and an intermediate position of the F1s was found using a between-group design and 1.5 g/kg ETOH. This pattern was consistent for a variety of behavioral indices not previously examined, including distance, rest time, movement speed and length, as well as the traditional horizontal counts. Using a within-subject, multiple day, repeated-testing procedure, the same three genotypes were also assessed after manipulating drug administration order, where ETOH exposure (1.5 g/kg) was on either the first or second test day. Another experiment examined the effect of lighting level on the response to 1.5 g/kg ETOH using a within-subjects approach. Neither the testing order nor lighting condition had any major influence on the magnitude of activation as measured by locomotor activity (distance). The pattern of additive genotypic influences exhibited by the B6, D2, and F1 mice is remarkably resistant to these contextual and procedural manipulations.