Alcoholism: the dissection for endophenotypes

A translational rodent model of individual differences in sensitivity to the aversive properties of ethanol

BACKGROUND

A strong relationship exists between individual sensitivity to the aversive properties of ethanol and risk for alcohol use disorder (AUD). Despite this, our understanding of the neurobiological mechanisms underlying the subjective response to ethanol is limited. A major contributor to this lack of knowledge is the absence of preclinical models that enable exploration of this individual variability such as is possible in studies of humans.

METHODS

Adult male and female Long-Evans rats were trained to associate a novel tastant (saccharin) with acute exposure to either saline or ethanol (1.5 g/kg or 2.0 g/kg i.p.) over three conditioning days using a standard conditioned taste aversion (CTA) procedure. Variability in sensitivity to ethanol-induced CTA was phenotypically characterized using a median split across the populations studied.

RESULTS

When examining group averages, both male and female rats exposed to saccharin paired with either dose of ethanol exhibited lower saccharin intake relative to saline controls indicative of ethanol-induced CTA. Examination of individual data revealed a bimodal distribution of responses uncovering two distinct phenotypes present in both sexes. CTA-sensitive rats exhibited a rapid and progressive reduction in saccharin intake with each successive ethanol pairing. In contrast, saccharin intake was unchanged or maintained after an initial decrease from baseline levels in CTA-resistant rats. While CTA magnitude was similar between male and female CTA-sensitive rats, among CTA-resistant animals females were more resistant to the development of ethanol-induced CTA than males. Phenotypic differences were not driven by differences in baseline saccharin intake.

CONCLUSIONS

These data parallel work in humans by revealing individual differences in sensitivity to the aversive properties of ethanol that emerge immediately after initial exposure to ethanol in both sexes. This model can be used in future studies to investigate the neurobiological mechanisms that confer risk for AUD.

A translational rodent model of individual differences in sensitivity to the aversive properties of ethanol

Background

A strong relationship exists between individual sensitivity to the aversive properties of ethanol and risk for alcohol use disorder (AUD). Despite this, our understanding of the neurobiological mechanisms underlying subjective response to ethanol is relatively poor. A major contributor to this is the absence of preclinical models that enable exploration of this individual variability similar to studies performed in humans.

Methods

Adult male and female Long-Evans rats were trained to associate a novel tastant (saccharin) with acute exposure to either saline or ethanol (1.5 g/kg or 2.0 g/kg i.p.) over three conditioning days using a standard conditioned taste aversion (CTA) procedure. Variability in sensitivity to ethanol-induced CTA was phenotypically characterized using a median split across the populations studied.

Results

When examining group averages, both male and female rats that had saccharin paired with either dose of ethanol exhibited reduced saccharin intake relative to saline controls of ethanol-induced CTA. Examination of individual data revealed a bimodal distribution of responses uncovering two distinct phenotypes present in both sexes. CTA-sensitive rats exhibited a rapid and progressive reduction in saccharin intake with each successive ethanol pairing. In contrast, saccharin intake was unchanged or maintained after an initial decrease from baseline levels in CTA-resistant rats. While CTA magnitude was similar between male and female CTA-sensitive rats, CTA-resistant females were more resistant to the development of ethanol-induced CTA than their male counterparts. Phenotypic differences were not driven by differences in baseline saccharin intake. CTA sensitivity correlated with behavioral signs of intoxication in only a subset of rats.

Conclusions

These data parallel work in humans by revealing individual differences in sensitivity to the aversive properties of ethanol that emerge immediately after initial exposure to ethanol in both sexes. This model can be leveraged in future studies to investigate the neurobiological mechanisms that confer risk for AUD.

Alcohol craving in the natural environment: Moderating roles of cue exposure, drinking, and alcohol sensitivity

Effects of cue exposure and alcohol consumption (e.g., priming doses) on craving for alcohol have been examined in largely separate literature, limiting what is known about their potential interaction. Individuals with low alcohol sensitivity, a known risk factor for alcohol use disorder (AUD), exhibit stronger cue-elicited craving than their higher-sensitivity (HS) peers in both laboratory and real-world contexts. Here, underage drinkers (N = 155) completed a 21-day ecological momentary assessment (EMA) protocol in which they recorded exposure to alcohol cues and levels of craving during both nondrinking and postdrinking moments. Multilevel modeling detected a significant interaction of cue exposure and postdrinking status on craving. Cue-induced craving was increased in postdrinking moments compared to nondrinking moments. Contrary to prediction, cue-elicited increase in craving during nondrinking moments was stronger in participants reporting higher sensitivity to alcohol. In the presence of cues, lower sensitivity was robustly related to craving intensity in the postdrinking state but unrelated to craving during nondrinking moments. Craving during drinking episodes in the natural environment is magnified by the presence of alcohol cues, potentially contributing to the maintenance or acceleration of drinking episodes. Moreover, lower-sensitivity drinkers may be particularly susceptible to the combined effects of cue exposure and postdrinking status on alcohol craving. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Genetic and environmental etiology of drinking motives in college students

BACKGROUND

Drinking motives are robust proximal predictors of alcohol use behaviors and may mediate distinct etiological pathways in the development of alcohol misuse. However, little is known about the genetic and environmental etiology of drinking motives themselves and their potential utility as endophenotypes.

METHODS

Here, we leverage a longitudinal study of college students from diverse racial/ethnic backgrounds (phenotypic N = 9889, genotypic N = 4855) to investigate the temporal stability and demographic and environmental predictors of four types of drinking motives (enhancement, social, coping, and conformity). Using genome-wide association study (GWAS) and in silico tools, we characterize their associated genes and genetic variants (single nucleotide polymorphisms or SNPs).

RESULTS

Drinking motives were stable across four years of college (ICC >0.74). Some robust environmental predictors of alcohol misuse (parental autonomy granting and peer deviance) were broadly associated with multiple types of drinking motives, while others (e.g., trauma exposure) were type specific. Genome-wide analyses indicated modest SNP-based heritability (14-22%, n.s.) and several suggestive genomic loci that corroborate findings from previous molecular genetic studies (e.g., PECR and SIRT4 genes), indicating possible differences in the genetic etiology of positive versus negative reinforcement drinking motives that align with an internalizing/externalizing typology of alcohol misuse. Coping motives were significantly genetically correlated with alcohol use disorder diagnoses (r_g  = 0.71, p = 0.001). However, results from the genetic analyses were largely underpowered to detect significant associations.

CONCLUSIONS

Drinking motives show promise as endophenotypes but require further investigation in larger samples to further our understanding of the etiology of alcohol misuse.

Associations of NLRP3 and CARD8 gene polymorphisms with alcohol dependence and commonly related psychiatric disorders: a preliminary study

We investigated two functional polymorphisms in NLRP3 inflammasome genes (NLRP3 rs35829419 and CARD8 rs2043211) and their association with alcohol dependence and related anxiety, depression, obsession-compulsion, or aggression in 88 hospitalised alcohol-dependent patients, 99 abstinent alcohol-dependent participants, and 94 controls, all male Caucasian. Alcohol dependence-related psychiatric disorders were assessed with the Zung Depression and Anxiety scale, Buss-Durkee Hostility Inventory, Alcohol Use Disorders Identification Test, Brief Social Phobia Scale, Obsessive Compulsive Drinking Scale, and Yale-Brown Obsessive-Compulsive Scale. For genotyping we used the allele-specific quantitative polymerase chain reaction-based methods. The three groups differed significantly in CARD8 rs2043211 distribution (P=0.049; chi-squared=9.557; df=4). The NLPR3 rs35829419 polymorphism was not significantly associated with alcohol dependence. In hospitalised alcohol-dependent patients the investigated polymorphisms were not associated with scores indicating alcohol consumption or comorbid symptoms. In abstinent alcohol-dependent subjects homozygotes for the polymorphic CARD8 allele presented with the highest scores on the Zung Anxiety Scale (p=0.048; df=2; F=3.140). Among controls, CARD8 genotype was associated with high scores on the Obsessive Compulsive Drinking Scale (P=0.027; df=2; F=3.744). In conclusion, our results reveal that CARD8 rs2043211 may play some role in susceptibility to alcohol dependence, expression of anxiety symptoms in abstinent alcohol-dependent subjects, and in obsessive compulsive drinking in healthy controls. However, further studies with larger cohorts are required to confirm these preliminary findings.

Systems genetics analysis of the LXS recombinant inbred mouse strains:Genetic and molecular insights into acute ethanol tolerance

We have been using the Inbred Long- and Short-Sleep mouse strains (ILS, ISS) and a recombinant inbred panel derived from them, the LXS, to investigate the genetic underpinnings of acute ethanol tolerance which is considered to be a risk factor for alcohol use disorders (AUDs). Here, we have used RNA-seq to examine the transcriptome of whole brain in 40 of the LXS strains 8 hours after a saline or ethanol "pretreatment" as in previous behavioral studies. Approximately 1/3 of the 14,184 expressed genes were significantly heritable and many were unique to the pretreatment. Several thousand cis- and trans-eQTLs were mapped; a portion of these also were unique to pretreatment. Ethanol pretreatment caused differential expression (DE) of 1,230 genes. Gene Ontology (GO) enrichment analysis suggested involvement in numerous biological processes including astrocyte differentiation, histone acetylation, mRNA splicing, and neuron projection development. Genetic correlation analysis identified hundreds of genes that were correlated to the behaviors. GO analysis indicated that these genes are involved in gene expression, chromosome organization, and protein transport, among others. The expression profiles of the DE genes and genes correlated to AFT in the ethanol pretreatment group (AFT-Et) were found to be similar to profiles of HDAC inhibitors. Hdac1, a cis-regulated gene that is located at the peak of a previously mapped QTL for AFT-Et, was correlated to 437 genes, most of which were also correlated to AFT-Et. GO analysis of these genes identified several enriched biological process terms including neuron-neuron synaptic transmission and potassium transport. In summary, the results suggest widespread genetic effects on gene expression, including effects that are pretreatment-specific. A number of candidate genes and biological functions were identified that could be mediating the behavioral responses. The most prominent of these was Hdac1 which may be regulating genes associated with glutamatergic signaling and potassium conductance.

On the path towards personalized medicine: Implications of pharmacogenetic studies of alcohol use disorder medications

Introduction

The heritability of alcohol use disorder (AUD) is estimated to be ~50%; however, the genetic basis of the disease is still poorly understood. The genetic variants identified thus far only explain a small percentage of AUD phenotypic variability. While genome-wide association studies (GWAS) are impacted by technical and methodological limitations, genetic variants that have been identified independently of GWAS findings can moderate the efficacy of AUD medications.

Areas Covered

This review discusses findings from clinical pharmacogenetic studies of AUD medications. While the pharmacogenetic studies reviewed involve several genetic variants in the major neurotransmitter systems, genetic loci in the opioid system have garnered the most attention.

Expert Opinion

The clinical utility of pharmacogenetics in AUD populations is uncertain at this time. There are several ongoing prospective clinical trials that will enhance knowledge regarding the applicability of pharmacogenetics in clinical populations. We recommend that future work in this area consider reverse translating from genotype to phenotype, mapping genes to stages of the addiction cycle, mapping genes to neural circuits, and harnessing large population-based cohorts.

Naltrexone effects on subjective responses to alcohol in the human laboratory: A systematic review and meta-analysis

Naltrexone (NTX) has been widely studied for the treatment of alcohol use disorder with overall support for its efficacy. The mechanisms of action of naltrexone are thought to involve attenuation of the hedonic effects of alcohol and potentiation of its aversive effects. In order to provide a quantitative estimate of the effects of naltrexone on subjective response to alcohol, the aims of this meta-analytic review are to examine the effects of naltrexone across four domains of subjective response. Meta-analyses of naltrexone effects on alcohol craving (k = 16, N = 686), stimulation (k = 15, N = 675), sedation (k = 18, N = 777), and negative mood (k = 9, N = 281) suggested that under laboratory conditions and compared with placebo, naltrexone reduces craving (Hedges g = -0.252; SE = 0.054; 95% CI, -0.375 to -0.130; P < 0.01), reduces stimulation (g = -0.223; SE = 0.067; 95% CI, -0.372 to -0.074; P < 0.01), increases sedation (g = 0.251; SE = 0.064; 95% CI, 0.112-0.389; P < 0.01), and increases negative mood (g = 0.227; SE = 0.047; 95% CI, 0.100-0.354; P < 0.01). Results were robust when drinks per month and alcohol dose were added to the models as covariates. The effects of naltrexone varied by severity of alcohol use with medication effects on craving and stimulation being observed in sample of both heavy drinkers and AUD individuals. These results are consistent with the hypothesized mechanisms of action of NTX, although the effects are of small magnitude. This meta-analysis aggregates across multiple human laboratory studies of NTX's effects on subjective response to alcohol, providing a comprehensive summary of a key mechanism of NTX efficacy, namely, alteration of the subjective experience of alcohol.

The Relationship Between Regional Cerebral Blood Flow Estimates and Alcohol Problems at 5-Year Follow-Up: The Role of Level of Response

BACKGROUND

Acute alcohol consumption is associated with temporarily increased regional cerebral blood flow (CBF). The extent of this increase appears to be moderated by individual differences in the level of response (LR) to alcohol's subjective effects. The low LR phenotype is a known risk factor for the development of alcohol problems. This study investigates how the low LR phenotype relates to the relationship between alcohol-related changes in CBF and alcohol problems 5 years later.

METHODS

Young adults (ages 18 to 25) were selected based on their LR to alcohol and underwent a neuroimaging protocol including arterial spin labeling and functional scans. These participants were recontacted ~5 years later and assessed on alcohol outcomes. A final sample of 107 subjects (54 low and 53 high LR subjects) was included in the analyses. Whole-brain analysis revealed 5 clusters of significant alcohol-induced, versus placebo-induced, CBF changes that were consistent with a previous report. Peak alcohol-placebo CBF response was extracted from these regions and, along with the LR group, submitted to a hierarchical linear regression predicting alcohol problems. Analyses controlled for age, sex, and baseline alcohol problems.

RESULTS

In the regression analysis, greater alcohol-placebo CBF difference in the right middle/superior/inferior frontal gyri and bilateral anterior cingulate gyri clusters predicted greater future alcohol problems for the low LR group, whereas this relationship was not found to be significant in the high LR group.

CONCLUSIONS

This study demonstrates a clinically important relationship between CBF and future alcohol problems, particularly in individuals with a low LR phenotype. These initial results help to elucidate the neurobiological pathways involved in the development of alcohol use disorders for individuals with low LR.

Polygenic Risk Score Prediction of Alcohol Dependence Symptoms Across Population-Based and Clinically Ascertained Samples

BACKGROUND

Despite consistent evidence of the heritability of alcohol use disorders (AUDs), few specific genes with an etiological role have been identified. It is likely that AUDs are highly polygenic; however, the etiological pathways and genetic variants involved may differ between populations. The aim of this study was thus to evaluate whether aggregate genetic risk for AUDs differed between clinically ascertained and population-based epidemiological samples.

METHODS

Four independent samples were obtained: 2 from unselected birth cohorts (Avon Longitudinal Study of Parents and Children [ALSPAC], N = 4,304; FinnTwin12 [FT12], N = 1,135) and 2 from families densely affected with AUDs, identified from treatment-seeking patients (Collaborative Study on the Genetics of Alcoholism, N = 2,097; Irish Affected Sib Pair Study of Alcohol Dependence, N = 706). AUD symptoms were assessed with clinical interviews, and participants of European ancestry were genotyped. Genomewide association was conducted separately in each sample, and the resulting association weights were used to create polygenic risk scores in each of the other samples (12 total discovery-validation pairs), and from meta-analyses within sample type. We then tested how well these aggregate genetic scores predicted AUD outcomes within and across sample types.

RESULTS

Polygenic scores derived from 1 population-based sample (ALSPAC) significantly predicted AUD symptoms in another population-based sample (FT12), but not in either clinically ascertained sample. Trend-level associations (uncorrected p < 0.05) were found for polygenic score predictions within sample types but no or negative predictions across sample types. Polygenic scores accounted for 0 to 1% of the variance in AUD symptoms.

CONCLUSIONS

Though preliminary, these results provide suggestive evidence of differences in the genetic etiology of AUDs based on sample characteristics such as treatment-seeking status, which may index other important clinical or demographic factors that moderate genetic influences. Although the variance accounted for by genomewide polygenic scores remains low, future studies could improve gene identification efforts by amassing very large samples, or reducing genetic heterogeneity by informing analyses with other phenotypic information such as sample characteristics. Multiple complementary approaches may be needed to make progress in gene identification for this complex disorder.

Post-GWAS in Psychiatric Genetics: A Developmental Perspective on the "Other" Next Steps

As psychiatric genetics enters an era where gene identification is finally yielding robust, replicable genetic associations and polygenic risk scores, it is important to consider next steps and delineate how that knowledge will be applied to ultimately ameliorate suffering associated with substance use and psychiatric disorders. Much of the post-genome-wide association study discussion has focused on the potential of genetic information to elucidate the underlying biology and use this information for the development of more effective pharmaceutical treatments. In this review we focus on additional areas of research that should follow gene identification. By taking genetic findings into longitudinal, developmental studies, we can map the pathways by which genetic risk manifests across development, elucidating the early behavioral manifestations of risk, and studying how various environments and interventions moderate that risk across developmental stages. The delineation of risk across development will advance our understanding of mechanism, sex differences and risk and resilience processes in different racial/ethnic groups. Here, we review how the extant twin study literature can be used to guide these efforts. Together, these new lines of research will enable us to develop more informed, tailored prevention and intervention efforts.

Personality as an intermediate phenotype for genetic dissection of alcohol use disorder

Genetic and environmental interactive influences on predisposition to develop alcohol use disorder (AUD) account for the high heterogeneity among AUD patients and make research on the risk and resiliency factors complicated. Several attempts have been made to identify the genetic basis of AUD; however, only few genetic polymorphisms have consistently been associated with AUD. Intermediate phenotypes are expected to be in-between proxies of basic neuronal biological processes and nosological symptoms of AUD. Personality is likely to be a top candidate intermediate phenotype for the dissection of the genetic underpinnings of different subtypes of AUD. To date, 38 studies have investigated personality traits, commonly assessed by the Cloninger's Tridimensional Personality Questionnaire (TPQ) or Temperament and Character Inventory (TCI), in relation to polymorphisms of candidate genes of neurotransmitter systems in alcohol-dependent patients. Particular attention has been given to the functional polymorphism of the serotonin transporter gene (5-HTTLPR), however, leading to contradictory results, whereas results with polymorphisms in other candidate monoaminergic genes (e.g., tryptophan hydroxylase, serotonin receptors, monoamine oxidases, dopamine receptors and transporter) are sparse. Only one genome-wide association study has been performed so far and identified the ABLIM1 gene of relevance for novelty seeking, harm avoidance and reward dependence in alcohol-dependent patients. Studies investigating genetic factors together with personality could help to define more homogenous subgroups of AUD patients and facilitate treatment strategies. This review also urges the scientific community to combine genetic data with psychobiological and environmental data to further dissect the link between personality and AUD.

Short-term selection for high and low ethanol intake yields differential sensitivity to ethanol's motivational effects and anxiety-like responses in adolescent Wistar rats

Alcohol use disorders are modulated by genetic factors, but the identification of specific genes and their concomitant biological changes that are associated with a higher risk for these disorders has proven difficult. Alterations in the sensitivity to the motivational effects of ethanol may be one way by which genes modulate the initiation and escalation of ethanol intake. Rats and mice have been selectively bred for high and low ethanol consumption during adulthood. However, selective breeding programs for ethanol intake have not focused on adolescence. This phase of development is associated with the initiation and escalation of ethanol intake and characterized by an increase in the sensitivity to ethanol's appetitive effects and a decrease in the sensitivity to ethanol's aversive effects compared with adulthood. The present study performed short-term behavioral selection to select rat lines that diverge in the expression of ethanol drinking during adolescence. A progenitor nucleus of Wistar rats (F₀) and filial generation 1 (F₁), F₂, and F₃ adolescent rats were derived from parents that were selected for high (STDRHI) and low (STDRLO) ethanol consumption during adolescence and were tested for ethanol intake and responsivity to ethanol's motivational effects. STDRHI rats exhibited significantly greater ethanol intake and preference than STDRLO rats. Compared with STDRLO rats, STDRHI F₂ and F₃ rats exhibited a blunted response to ethanol in the conditioned taste aversion test. F₂ and F₃ STDRHI rats but not STDRLO rats exhibited ethanol-induced motor stimulation. STDRHI rats exhibited avoidance of the white compartment of the light-dark box, a reduction of locomotion, and a reduction of saccharin consumption, suggesting an anxiety-prone phenotype. The results suggest that the genetic risk for enhanced ethanol intake during adolescence is associated with lower sensitivity to the aversive effects of ethanol, heightened reactivity to ethanol's stimulating effects, and enhanced innate anxiety.

A prospective study of genetic factors, human laboratory phenotypes, and heavy drinking in late adolescence

Subjective responses to alcohol are considered candidate endophenotypes for alcohol use disorder and appear to anticipate future consumption. However, prospective studies have been rare, and laboratory research has typically examined subjective responses absent measures of self-administration. This study examined the association of subjective responses with subsequent laboratory self-administration, also evaluating laboratory phenotypes in relation to putative genetic risk factors [family history (FH) of alcohol dependence and OPRM1 genotype] and subsequent heavy drinking. Participants (N = 61, M = 19.89 years, SD = 0.86) completed laboratory sessions involving intravenous alcohol challenge (Session 1) and free-access intravenous self-administration (Session 2), followed by prospective assessments. Multilevel modeling showed that higher reported stimulation and lower sedation during Session 1 independently predicted greater alcohol self-administration during Session 2. Although self-administration did not differ by FH group, participants with the OPRM1 118G allele evidenced steeper breath alcohol concentration (BrAC) trajectories and greater peak BrAC relative to 118A homozygous participants. Prospective analyses supported significant indirect associations between Session 1 subjective responses and 6-month heavy drinking via peak BrAC in Session 2. Additionally, significant indirect associations of FH (via Session 1 stimulation and Session 2 peak BrAC) and OPRM1 (via peak BrAC) with follow-up heavy drinking were observed. These results further support the utility of human laboratory phenotypes in prospective studies of alcohol use disorder risk and highlight the potential role of self-administration phenotypes in longitudinal research.

Heterogeneity of emotional and interpersonal difficulties in alcohol-dependence: A cluster analytic approach

BACKGROUND

Emotional and interpersonal impairments have been largely reported in alcohol-dependence, and their role in its development and maintenance is widely established. However, earlier studies have exclusively focused on group comparisons between healthy controls and alcohol-dependent individuals, considering them as a homogeneous population. The variability of socio-emotional profiles in this disorder thus remains totally unexplored. The present study used a cluster analytic approach to explore the heterogeneity of affective and social disorders in alcohol-dependent individuals.

METHODS

296 recently-detoxified alcohol-dependent patients were first compared with 246 matched healthy controls regarding self-reported emotional (i.e. alexithymia) and social (i.e. interpersonal problems) difficulties. Then, a cluster analysis was performed, focusing on the alcohol-dependent sample, to explore the presence of differential patterns of socio-emotional deficits and their links with demographic, psychopathological and alcohol-related variables.

RESULTS

The group comparison between alcohol-dependent individuals and controls clearly confirmed that emotional and interpersonal difficulties constitute a key factor in alcohol-dependence. However, the cluster analysis identified five subgroups of alcohol-dependent individuals, presenting distinct combinations of alexithymia and interpersonal problems ranging from a total absence of reported impairment to generalized socio-emotional difficulties.

CONCLUSIONS

Alcohol-dependent individuals should no more be considered as constituting a unitary group regarding their affective and interpersonal difficulties, but rather as a population encompassing a wide variety of socio-emotional profiles. Future experimental studies on emotional and social variables should thus go beyond mere group comparisons to explore this heterogeneity, and prevention programs proposing an individualized evaluation and rehabilitation of these deficits should be promoted.

Rasch analysis of alcohol abuse and dependence diagnostic criteria in persons with spinal cord injury

STUDY DESIGN

Cross-sectional.

OBJECTIVE

The objective of the study is to examine whether alcohol use disorders should be conceptualized categorically as abuse and dependence as in the 'Diagnostic and Statistical Manual of Mental Disorders' 4th edition or on a single continuum with mild to severe category ratings as in the 'Diagnostic and Statistical Manual of Mental Disorders' 5th edition in people with spinal cord injury (SCI).

SETTING

United States of America.

METHODS

Data from 379 individuals who sustained SCI either traumatically or non-traumatically after the age of 18 and were at least 1 year post injury. Rasch analyses used the alcohol abuse and dependence modules of the Structured Clinical Interview for DSM-IV-TR Axis I Disorders Non-patient Edition (SCID-I/NP).

RESULTS

Fifty-seven percent (n=166) of the entire sample endorsed criteria for alcohol abuse, and 25% (n=65) endorsed criteria for alcohol dependence. Fit values were generally acceptable except for one item (for example, alcohol abuse criterion 2), suggesting that the items fit the expectation of unidimensionality. Examination of the principal components analysis did not provide support for unidimensionality. The item-person map illustrates poor targeting of items.

CONCLUSIONS

Alcohol abuse and dependence criterion appear to reflect a unidimensional construct, a finding that supports a single latent construct or factor consistent with the DSM-5 diagnostic model.

Effects of Evaluative Context in Implicit Cognitions Associated with Alcohol and Violent Behaviors

Introduction

A large body of literature has substantiated the relationship between alcohol use and violent behaviors, but little consideration has been given to implicit interactions between the two. This study examines the implicit attitudes associated with alcoholic drinks and violent behaviors, and their relationship to explicit reports of problematic behaviors associated with alcohol use.

Methods

The Go/No-Go Association Task (GNAT; Nosek & Banaji, 2001) was used to test the effect of distracters (noise) on implicit cognitions associated with alcoholic drinks and violent behaviors. Data was collected from 148 students enrolled in a Midwestern university.

Results

Irrespective of contextual distractions, participants consistently exhibited negative implicit cognitions associated with violent behaviors. However, context impacted the valence of cognitions associated with alcoholic beverages. Implicit cognitions associated with alcoholic beverages were negative when nonalcoholic beverages were used as distracters, but were positive when licit and illicit drugs were used as distracters. Implicit cognitions associated with alcoholic drinks were correlated with implicit cognitions associated with violent behaviors and explicit measures of problem drinking, problem drug-related behaviors, and measures of craving, to name a few.

Conclusion

Evaluative context can have an effect on the expressed appraisal of implicit attitudes. Implications, limitations, and future directions for using the GNAT in addictions research are discussed.

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Implicit cognitions associated with violent behaviors were always negative.

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Implicit cognitions of alcohol were negative when drinks were used as distracters.

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Implicit cognitions of alcohol were positive when drugs were used as distracters.

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Evaluative context had an effect on the expressed appraisal of implicit attitudes.

Associations of OPRM1 A118G and alcohol sensitivity with intravenous alcohol self-administration in young adults

Human laboratory and animal models implicate variation in the μ-opioid receptor gene (OPRM1) as relevant for alcohol-related reward. OPRM1 is associated with alcohol self-administration in non-human primate studies, but the relevance of this finding to human models is unclear. This study used computer-assisted self-infusion of ethanol (CASE) to examine associations among OPRM1 A118G genotype, subjective responses to alcohol and intravenous alcohol self-administration in young heavy drinkers (n = 40, mean age = 19.95 years, SD = 0.82). Participants completed a 2-hour CASE session comprising a priming phase followed by ad libitum self-administration in a free-access paradigm. Participants achieved a mean peak breath alcohol concentration (BrAC) of 81.18 mg% (SD = 24.96). Those with the OPRM1 118G variant (GA or GG genotypes) achieved significantly higher peak BrAC (M = 94.90 mg%, SD = 16.56) than those with the AA genotype (M = 74.46 mg%, SD = 25.36), reflecting a significantly greater number of alcohol requests among GA/GG participants. Eighty percent of GA/GG participants surpassed a threshold defining a laboratory analog of heavy alcohol exposure (80 mg%) compared with 46 percent of AA participants. Results indicated significant associations between subjective measures of alcohol sensitivity and CASE outcomes, although the pattern of findings differed across self-report measures. Subjective responses did not differ by OPRM1 status. These results offer further support for the feasibility of the CASE paradigm and provide initial evidence for an association of OPRM1 with alcohol self-administration in a human laboratory context.

Supplier-dependent differences in intermittent voluntary alcohol intake and response to naltrexone in Wistar rats

Alcohol use disorder (AUD) is a worldwide public health problem and a polygenetic disorder displaying substantial individual variation. This work aimed to study individual differences in behavior and its association to voluntary alcohol intake and subsequent response to naltrexone in a seamless heterogenic group of animals. Thus, by this approach the aim was to more accurately recapitulate the existing heterogeneity within the human population. Male Wistar rats from three different suppliers (Harlan Laboratories B.V., RccHan™:WI; Taconic Farms A/S, HanTac:WH; and Charles River GmbH, Crl:WI) were used to create a heterogenic group for studies of individual differences in behavior, associations to intermittent voluntary alcohol intake and subsequent response to naltrexone. The rats were tested in the open field prior to the Y-maze and then given voluntary intermittent access to alcohol or water in the home cage for 6 weeks, where after, naltrexone in three different doses or saline was administered in a Latin square design over 4 weeks and alcohol intake and preference was measured. However, supplier-dependent differences and concomitant skew subgroup formations, primarily in open field behavior and intermittent alcohol intake, resulted in a shifted focus to instead study voluntary alcohol intake and preference, and the ensuing response to naltrexone in Wistar rats from three different suppliers. The results showed that outbred Wistar rats are diverse with regard to voluntary alcohol intake and preference in a supplier-dependent manner; higher in RccHan™:WI relative to HanTac:WH and Crl:WI. The results also revealed supplier-dependent differences in the effect of naltrexone that were dose- and time-dependent; evident differences in high-drinking RccHan™:WI rats relative to HanTac:WH and Crl:WI rats. Overall these findings render RccHan™:WI rats more suitable for studies of individual differences in voluntary alcohol intake and response to naltrexone and further highlight the inherent heterogeneity of the Wistar strain. The overall results put focus on the importance of thoroughly considering the animals used to aid in study design and for comparison of reported results.

Variation in the Serotonin Transporter Gene and Alcoholism: Risk and Response to Pharmacotherapy

SLC6A4, the gene encoding the serotonin transporter protein (5-HTT), has been extensively examined as a risk factor for alcohol dependence (AD). More recently, variability in the transporter gene was identified to be a potential moderator of treatment response to serotonergic medications such as ondansetron and sertraline. There is an insertion-deletion polymorphism in the promoter region (5-HTTLPR) of the SLC6A4, with the most common alleles being a 14-repeat short (S) allele and a 16-repeat long (L) allele. The S allele has often been associated with AD. By contrast, the L allele has been associated with pharmacological responsiveness in some individuals with AD. Differences in clinical phenotype may determine the utility of the 5-HTTLPR polymorphism as a moderator of pharmacological interventions for AD. We review the AD typology and disease onset in the context of pharmacogenetic and genomic studies that examine the utility of 5-HTTLPR in improving treatment outcomes.

Subjective response as a consideration in the pharmacogenetics of alcoholism treatment

Currently available pharmacological treatments for alcoholism have modest efficacy and high individual variability in treatment outcomes, both of which have been partially attributed to genetic factors. One path to reducing the variability and improving the efficacy associated with these pharmacotherapies may be to identify overlapping genetic contributions to individual differences in both subjective responses to alcohol and alcoholism pharmacotherapy outcomes. As acute subjective response to alcohol is highly predictive of future alcohol related problems, identifying such shared genetic mechanisms may inform the development of personalized treatments that can effectively target converging pathophysiological mechanisms that convey risk for alcoholism. The focus of this review is to revisit the association between subjective response to alcohol and the etiology of alcoholism while also describing genetic contributions to this relationship, discuss potential pharmacogenetic approaches to target subjective response to alcohol in order to improve the treatment of alcoholism and examine conceptual and methodological issues associated with these topics, and outline future approaches to overcome these challenges.

Endophenotypes for Alcohol Use Disorder: An Update on the Field

The endophenotype concept was first proposed as a strategy to use (purportedly) genetically simpler phenotypes in gene identification studies for psychiatric disorders, and is distinct from the closely related concept of intermediate phenotypes. In the area of alcohol use disorder (AUD) research, two candidate endophenotypes have produced replicable genetic associations: level of response to alcohol and neurophysiology markers (e.g., event-related oscillations and event-related potentials). Additional candidate endophenotypes from the cognitive, sensory, and neuroimaging literatures show promise, although more evidence is needed to fully evaluate their potential utility. Translational approaches to AUD endophenotypes have helped characterize the underlying neurobiology and genetics of AUD endophenotypes and identified relevant pharmacological interventions. Future research that capitalizes on the polygenic nature of endophenotypes and emphasizes endophenotypes that may change across development will enhance the usefulness of this concept to understand the genetically-influenced pathways toward AUD.

Interactive effects of OPRM1 and DAT1 genetic variation on subjective responses to alcohol

AIMS

Subjective response to alcohol represents a marker of alcoholism risk. The A118G single-nucleotide polymorphism (SNP) of the mu opioid receptor (OPRM1) gene has been associated with subjective response to alcohol. Recently, the dopamine transporter (DAT1) variable number of tandem repeat (VNTR; SLC6A3) has been found to interact with the OPRM1 A118G SNP in predicting neural and behavioral responses to naltrexone and to alcohol. This exploratory study examines the OPRM1 × DAT1 interaction on subjective responses to alcohol.

METHODS

Non-treatment-seeking problem drinkers (n = 295) were assessed in the laboratory for alcohol dependence. Following prospective genotyping for the OPRM1 gene, 43 alcohol-dependent individuals were randomized to two intravenous infusion sessions, one of alcohol (target BrAC = 0.06 g/dl) and one of saline. Measures of subjective responses to alcohol were administered in both infusion sessions.

RESULTS

Analyses revealed significant Alcohol × OPRM1 × DAT1 interactions for alcohol-induced stimulation, vigor and positive mood as well as significant Alcohol × OPRM1 × DAT1 × Time interactions for stimulation and positive mood. These effects were such that, compared with other genotype groups, OPRM1 G-allele carriers + DAT1 A10 homozygotes reported steeper increases in stimulation and positive mood across rising BrAC, when compared with placebo. All Alcohol × OPRM1 × DAT1 interactions remained significant when analyses were restricted to a subsample of Caucasian participants (n = 34); however, 4-way interactions did not reach statistical significance in this subsample.

CONCLUSIONS

This study suggests that the contribution of OPRM1 genotype to alcohol-induced stimulation, vigor and positive mood is moderated by DAT1 genotype. These findings are consistent with the purported interaction between opioidergic and dopaminergic systems in determining the reinforcing properties of alcohol.

Consensus paper of the WFSBP task force on biological markers: biological markers for alcoholism

OBJECTIVES

This article presents an overview of the current literature on biological markers for alcoholism, including markers associated with the pharmacological effects of alcohol and markers related to the clinical course and treatment of alcohol-related problems. Many of these studies are well known, while other studies cited are new and still being evaluated.

METHODS

In this paper we first describe known biomarkers of alcohol-related disorders, review their features and the problems involved in their use. We then consider future developments on biomarkers and their possible impact on the field.

RESULTS

More recent findings cited include the work on type 7 adenylcyclase (AC) polymorphism and its lower expression levels in female alcoholics. Neuroimaging studies involving biomarkers have also reported brain volume reductions of gray and white matter, including amygdala and subcortical regions in alcoholic patients, while a high association between the copy number variations (CNVs) in 6q14.1/5q13.2 and alcohol dependence has more recently been identified in genetic studies.

CONCLUSIONS

In addition to their possible importance for diagnosis, biomarkers may have utility for predicting prognosis, progression of the disorder, the development of new treatments, and monitoring treatment effects. Although such findings should be verified in independent studies, the search for new biomarkers is continuing. Several potential candidate biomarkers have been found recently in blood, imaging, and genetic studies with encouraging results.

The CRHR1 gene, trauma exposure, and alcoholism risk: a test of G × E effects

The corticotropin-releasing hormone type I receptor (CRHR1) gene has been implicated in the liability for neuropsychiatric disorders, particularly under conditions of stress. On the basis of the hypothesized effects of CRHR1 variation on stress reactivity, measures of adulthood traumatic stress exposure were analyzed for their interaction with CRHR1 haplotypes and single-nucleotide polymorphisms (SNPs) in predicting the risk for alcoholism. Phenotypic data on 2533 non-related Caucasian individuals (1167 alcoholics and 1366 controls) were culled from the publically available Study of Addiction: Genetics and Environment genome-wide association study. Genotypes were available for 19 tag SNPs. Logistic regression models examined the interaction between CRHR1 haplotypes/SNPs and adulthood traumatic stress exposure in predicting alcoholism risk. Two haplotype blocks spanned CRHR1. Haplotype analyses identified one haplotype in the proximal block 1 (P = 0.029) and two haplotypes in the distal block 2 (P = 0.026, 0.042) that showed nominally significant (corrected P < 0.025) genotype × traumatic stress interactive effects on the likelihood of developing alcoholism. The block 1 haplotype effect was driven by SNPs rs110402 (P = 0.019) and rs242924 (P = 0.019). In block 2, rs17689966 (P = 0.018) showed significant and rs173365 (P = 0.026) showed nominally significant, gene × environment (G × E) effects on alcoholism status. This study extends the literature on the interplay between CRHR1 variation and alcoholism, in the context of exposure to traumatic stress. These findings are consistent with the hypothesized role of the extra hypothalamic corticotropin-releasing factor system dysregulation in the initiation and maintenance of alcoholism. Molecular and experimental studies are needed to more fully understand the mechanisms of risk and protection conferred by genetic variation at the identified loci.

Subjective response to alcohol among alcohol-dependent individuals: effects of the μ-opioid receptor (OPRM1) gene and alcoholism severity

BACKGROUND

Subjective response to alcohol has been examined as a marker of alcoholism risk. The A118G single-nucleotide polymorphism (SNP) of the mu-opioid receptor (OPRM1) gene has been previously associated with subjective response to alcohol in heavy drinkers. This study seeks to extend the literature by examining the effect of OPRM1 genotype on responses to alcohol in a sample of alcohol-dependent individuals. A secondary aim of this study is to examine alcoholism severity as a predictor of subjective responses to alcohol.

METHODS

Nontreatment seeking problem drinkers (n = 295) were assessed in the laboratory for clinical dimensions of alcohol dependence. Following prospective genotyping, 43 alcohol-dependent individuals across the 2 genotype conditions (AA, n = 23 and AG/GG, n = 20) were randomized to 2 intravenous infusion sessions: 1 of alcohol (target breath alcohol concentration = 0.06 g/dl) and 1 of saline. Measures of subjective responses to alcohol were administered in both infusion sessions.

RESULTS

Alcohol-dependent G-allele carriers reported greater alcohol-induced stimulation, vigor, and positive mood, as compared to A-allele homozygotes. There was no genotype effect on alcohol-induced sedation or craving. There was a statistical trend-level severity × alcohol interaction such that individuals at higher levels of severity reported greater alcohol-induced tension reduction.

CONCLUSIONS

These results support the hypothesis that OPRM1 genotype moderates the hedonic effects of alcohol, but not the sedative and unpleasant effects of alcohol, in a sample of alcohol-dependent patients. Results are discussed in light of a clinical neuroscience framework to alcoholism.

The genetics of alcohol dependence: advancing towards systems-based approaches

BACKGROUND

Personalized treatment for psychopathologies, in particular alcoholism, is highly dependent upon our ability to identify patterns of genetic and environmental effects that influence a person's risk. Unfortunately, array-based whole genome investigations into heritable factors that explain why one person becomes dependent upon alcohol and another does not, have indicated that alcohol's genetic architecture is highly complex. That said, uncovering and interpreting the missing heritability in alcohol genetics research has become all the more important, especially since the problem may extend to our inability to model the cumulative and combinatorial relationships between common and rare genetic variants. As numerous studies begin to illustrate the dependency of alcohol pharmacotherapies on an individual's genotype, the field is further challenged to identify new ways to transcend agnostic genomewide association approaches. We discuss insights from genetic studies of alcohol related diseases, as well as issues surrounding alcohol's genetic complexity and etiological heterogeneity. Finally, we describe the need for innovative systems-based approaches (systems genetics) that can provide additional statistical power that can enhance future gene-finding strategies and help to identify heretofore-unrealized mechanisms that may provide new targets for prevention/treatments efforts. Emerging evidence from early studies suggest that systems genetics has the potential to organize our neurological, pharmacological, and genetic understanding of alcohol dependence into a biologically plausible framework that represents how perturbations across evolutionarily robust biological systems determine susceptibility to alcohol dependence.

Subjective Effects of Thiopental in Young Adults with and without a Family History of Alcoholism

BACKGROUND

The development of alcohol use disorders is genetically influenced, and may be mediated through differences in the subjective response to alcohol. There is some evidence to suggest that response differences to alcohol could be conveyed by heritable differences in GABA_A receptors. The purpose of this study was to investigate whether individuals with a family history positive (FHP) for alcohol dependence would experience alterations in response to the GABA_A receptor agonist thiopental, in comparison to family history negative (FHN) subjects.

METHODS

73 subjects (24 FHP and 49 FHN) between the ages of 21 and 30 years were administered sub-anesthetic doses of the GABA_A receptor agonist thiopental and placebo on two separate test days. Various alcohol-related measures were administered, including those examining subjective effects, coordination, and cognition.

RESULTS

Sub-anesthetic doses of thiopental produced alcohol-like subjective effects, as well as alcohol-like impaired coordination and cognition in healthy subjects. While there were no significant main effects in subjective, coordination, or cognitive effects between FHP and FHN individuals, analysis of peak effects suggested FHP had blunted sedative, but not stimulant effects compared to FHN.

CONCLUSION

Thiopental produced alcohol-like effects and perceived similarities to alcohol in healthy individuals. Subtle differences in sedative effects are consistent with reports of blunted FHP response to the negative but not stimulant effects of alcohol. Future studies are needed to better understand how this insight informs our understanding of the heritable risk for alcoholism and the treatment of alcohol use disorders.

The role of the Asn40Asp polymorphism of the mu opioid receptor gene (OPRM1) on alcoholism etiology and treatment: a critical review

The endogenous opioid system has been implicated in the pathophysiology of alcoholism as it modulates the neurobehavioral effects of alcohol. A variant in the mu opioid receptor gene (OPRM1), the Asn40Asp polymorphism, has received attention as a functional variant that may influence a host of behavioral phenotypes for alcoholism as well as clinical response to opioid antagonists. This paper will review converging lines of evidence on the effect of the Asn40Asp SNP on alcoholism phenotypes, including: (i) genetic association studies; (ii) behavioral studies of alcoholism; (iii) neuroimaging studies; (iv) pharmacogenetic studies and clinical trials; and (v) preclinical animal studies. Together, these lines of research seek to elucidate the effects of this functional polymorphism on alcoholism etiology and treatment response.

Decision-making capacities and affective reward anticipation in DWI recidivists compared to non-offenders: a preliminary study

OBJECTIVES

Impaired decision making is seen in several problem behaviours including alcoholism and problem gambling. Decision-making style may contribute to driving while impaired with alcohol (DWI) in some offenders as well. The Somatic Marker Framework theorizes that decision making is the product of two interacting affective neural systems, an impulsive, rapid, amygdala-dependent process for emotionally signalling the immediate negative or positive consequences of an option, and a reflective, longer-lasting, ventral medial prefrontal cortex dependent system for emotionally signalling the future negative or positive prospects of an option. This study tested the hypothesis that offenders who showed disadvantageous decision-making would be at higher risk for recidivism than those who showed more advantageous decision-making. In addition, in line with the Somatic Marker Hypothesis, offenders who showed disadvantageous decision-making would exhibit a distinct pattern of somatic activation compared to offenders who showed more advantageous decision-making.

METHODS

A sample of 21 DWI offenders with from 2 to 7 past DWI convictions and a reference group consisting of 19 non-offender (N-O) drivers were recruited and administered the Iowa Gambling Task (IGT), as well as evaluated on sociodemographic, driving and alcohol use dimensions. In addition, anticipatory skin conductance response (aSCR) was measured in the 5s prior to each of a 100 card draws on the IGT.

RESULTS

Median split of the DWI offender sample based upon overall performance on the IGT yielded two subgroups (IGT-R Hi and IGT-R Lo). Hypothesis 1 was supported, as the IGT-R Lo group possessed significantly greater frequency of past DWI convictions and severity of past drinking. Descriptive analyses revealed that on the IGT, IGT-R Hi group performed similarly to the N-O reference group while the IGT-R Lo group performed significantly worse. Hypothesis 2 was not supported.

CONCLUSIONS

Decision making is a plausible explanatory neurocognitive pathway to severer forms of DWI. The role of emotional processing in DWI risk is uncertain. Subtyping DWI offenders using neurocognitive criteria seems a promising avenue for improving clinically meaningful methods of DWI risk assessment and intervention.

Responding in a test of decision-making under risk is under moderate genetic control in the rat

BACKGROUND

Risk-taking, measured with laboratory tasks such as the Balloon Analog Risk Task (BART), is associated with real-life manifestations of risky behaviors, which may be an important component of inherited liability to alcohol use disorders. To identify genomic factors that influence these traits, the current study (i) characterized performance of a rodent version of the BART in multiple inbred rat strains, (ii) tested the degree to which performance was under genetic control, (iii) explored sex differences in performance, and (iv) evaluated the risk-taking behavior of F1 progeny of high-risk- and low-risk-taking strains to examine modes of inheritance.

METHODS

Male and female rats (N = 100) from 5 inbred strains (Wistar-Furth, Fischer-344, Lewis, Spontaneously Hypertensive, Brown Norway) and Wistar-Furth × Fischer-344 hybrids were tested in the rat-BART, as well as in tests of locomotor activity, sucrose preference, and general motivation.

RESULTS

About 55% of the variance in risk-taking behavior was attributable to heritable factors. The Fischer-344 strain was the most risk-taking and the most variable in responding. The mating of low-risk-taking Wistar-Furth and Fischer-344 rats produced progeny that behaved most like the Fischer-344 strain. Consistent with prior research in this laboratory (Jentsch et al., 2010), all rats were sensitive to changes in both risk and reinforcement parameters in the rat-BART; rats decreased voluntary risk-taking in the face of increasing risk and increased lever pressing when reinforcement probabilities were reduced.

CONCLUSIONS

Our results endorse a moderately heritable pattern of risk-taking behavior in rats. The behavior of the hybrid progeny suggests a polygenic model with most gene effects transmitted by mode of dominant inheritance. The identification of high-risk and low-risk strains allows for isolation of quantitative trait loci associated with task performance and for probing the relationships between risk-taking and dimensions of alcohol use disorders.

The neurobiology of binge-like ethanol drinking: evidence from rodent models

Binge alcohol (ethanol) drinking is a destructive pattern of ethanol consumption that may precipitate ethanol dependence-a chronic, debilitating, and prevalent health problem. While an abundance of research has focused on the neurochemical underpinnings of ethanol dependence, relatively little is known about the mechanisms underlying the heavy consumption characteristic of binge ethanol drinking. Recently, a simple preclinical model termed "drinking in the dark" (DID) was developed to examine binge-like ethanol consumption in a rodent population. This assay capitalizes on the predisposition of C57BL/6J mice to voluntarily consume substantial quantities of a high concentration (20% v/v) ethanol solution, resulting in pharmacologically relevant blood ethanol concentrations (BECs). This review provides a comprehensive overview of recent literature utilizing this model to investigate the neuromodulatory systems that may influence binge ethanol drinking. Studies examining the glutamatergic and opioidergic systems not only provide evidence for these systems in the modulation of binge-like ethanol consumption, but also suggest this preclinical model has predictive validity and may be an appropriate tool for screening novel pharmacological compounds aimed at treating binge ethanol drinking in the human population. Additionally, this review presents evidence for the involvement of the GABAergic, dopaminergic, nicotinic, and endocannabinoid systems in modulating binge-like ethanol consumption. Finally, recent evidence shows that corticotropin-releasing factor (CRF), agouti-related protein (AgRP), neuropeptide Y (NPY), and ghrelin are also implicated as impacting this pattern of ethanol consumption.

Subjective response to alcohol challenge: a quantitative review

BACKGROUND

Individual differences in subjective response to alcohol, as measured by laboratory-based alcohol challenge, have been identified as a candidate phenotypic risk factor for the development of alcohol-use disorders (AUDs). Two models have been developed to explain the role of subjective response to alcohol, but predictions from the 2 models are contradictory, and theoretical consensus is lacking.

METHODS

This investigation used a meta-analytic approach to review the accumulated evidence from alcohol-challenge studies of subjective response as a risk factor. Data from 32 independent samples (total N = 1,314) were aggregated to produce quantitative estimates of the effects of risk-group status (i.e., positive family history of AUDs or heavier alcohol consumption) on subjective response.

RESULTS

As predicted by the Low Level of Response Model (LLRM), family history-positive groups experienced reduced overall subjective response relative to family history-negative groups. This effect was most evident among men, with family history-positive men responding more than half a standard deviation less than family history-negative men. In contrast, consistent with the Differentiator Model (DM), heavier drinkers of both genders responded 0.4 standard deviations less on measures of sedation than did the lighter drinkers but nearly half a standard deviation more on measures of stimulation, with the stimulation difference appearing most prominent on the ascending limb of the blood alcohol concentration curve.

CONCLUSIONS

The accumulated results from 3 decades of family history comparisons provide considerable support for the LLRM. In contrast, results from typical consumption comparisons were largely consistent with predictions of the DM. The LLRM and DM may describe 2 distinct sets of phenotypic risk, with importantly different etiologies and predictions for the development of AUDs.

Subjective responses to alcohol consumption as endophenotypes: advancing behavioral genetics in etiological and treatment models of alcoholism

Individual differences in subjective responses to alcohol consumption represent genetically mediated biobehavioral mechanisms of alcoholism risk (i.e., endophenotype). The objective of this review is three-fold: (1) to provide a critical review the literature on subjective response to alcohol and to discuss the rationale for its conceptualization as an endophenotype for alcoholism; (2) to examine the literature on the neurobiological substrates and associated genetic factors subserving individual differences in subjective response to alcohol; and (3) to discuss the treatment implications of this approach and to propose a framework for conceptualizing, and systematically integrating, endophenotypes into alcoholism treatment.

Repeated ethanol administration modifies the temporal structure of sucrose intake patterns in mice: effects associated with behavioral sensitization

Neuroadaptations supporting behavioral sensitization to abused drugs are suggested to underlie pathological, excessive motivation toward drugs and drug-associated stimuli. Drug-induced sensitization has also been linked to increased appetitive responses for non-drug, natural reinforcers. The present research investigated whether ethanol (EtOH)-induced neural changes, inferred from psychomotor sensitization, can modify consumption and intake dynamics for the natural reinforcer, sucrose. The effects of EtOH-induced sensitization in mice on the temporal structure of sucrose intake patterns were measured using a lickometer system. After sensitization, sucrose intake dynamics were measured for 1 hour daily for 7 days and indicated more rapid initial approach and consumption of sucrose in EtOH-sensitized groups; animals showed a shorter latency to the first intake bout and an increased number of sucrose bottle licks during the initial 15 minutes of the 1-hour sessions. This effect was associated with increased frequency and size of bouts. For the total 1-hour session, sucrose intake and bout dynamics were not different between groups, indicating a change in patterns of sucrose intake but not total consumption. When sensitization was prevented by the gamma-aminobutyric acid B receptor agonist, baclofen, the increased rate of approach and consumption of sucrose were also prevented. Thus, EtOH-induced sensitization, and not the mere exposure to EtOH, was associated with changes in sucrose intake patterns. These data are consistent with current literature suggesting an enhancing effect of drug-induced sensitization on motivational processes involved in reinforcement.

Quantitative trait loci contributing to physiological and behavioural ethanol responses after acute and chronic treatment

The aim of the present study was the identification of gene loci that contribute to the development and manifestation of behaviours related to acute and chronic alcohol exposure, as well as to alcohol withdrawal. For this purpose, we performed a serial behavioural phenotyping of 534 animals from the second filial (F2) generation of a C57BL/6J and C3H/HeJ mice intercross in paradigms with relevance to alcohol dependence. First, ethanol-induced hypothermia was determined in ethanol-naive animals. The mice then received an ethanol solution for several weeks as their only fluid source. Ethanol tolerance, locomotor activity and anxiety-related behaviours were evaluated. The ethanol was next withdrawn and the withdrawal severity was assessed. The ethanol-experienced animals were finally analysed in a two-bottle choice paradigm to determine ethanol preference and stress-induced changes in ethanol preference. The genotypes of these mice were subsequently assessed by microsatellite marker mapping. We genotyped 264 markers with an average marker distance of 5.56 cM, which represents a high-density whole genome coverage. Quantitative trait loci (QTL) were subsequently identified using univariate analysis performed with the R/qtl tool, which is an extensible, interactive environment for mapping QTL in experimental crosses. We found QTL that have already been published, thus validating the serial phenotyping protocol, and identified several novel loci. Our analysis demonstrates that the various responses to ethanol are regulated by independent groups of genes.

Subjective response to alcohol: a critical review of the literature

BACKGROUND

Subjective response to alcohol (SR), which reflects individual differences in sensitivity to the pharmacological effects of alcohol, may be an important endophenotype in understanding genetic influences on drinking behavior and alcohol use disorders (AUDs). SR predicts alcohol use and problems and has been found to differ by a range of established risk factors for the development of AUDs (e.g., family history of alcoholism). The exact pattern of SR associated with increased risk for alcohol problems, however, remains unclear. The Low Level of Response Model (LLR) suggests that high-risk individuals experience decreased sensitivity to the full range of alcohol effects, while the Differentiator Model (DM) asserts that high risks status is associated with increased sensitivity to alcohol's positive effects but decreased sensitivity to negative effects.

AIMS

The current paper (1) reviews two prominent models of subjective response, (2) reviews extant laboratory-based research on subjective response, (3) highlights remaining gaps in our understanding and assessment of subjective response, and (4) encourages collaborative efforts to address these methodological and conceptual concerns.

METHODS

This paper reviews studies which employed placebo-controlled and non-placebo-controlled alcohol challenge paradigms to assess a range of alcohol effects including impairment, stimulation, and sedation.

RESULTS

The research literature provides at least partial support for both the LLR and DM models. High-risk individuals have been shown to have a reduced response to alcohol with respect to sedative or impairing effects, particularly on the descending limb of the blood alcohol curve (BAC). There is also evidence that ascending limb stimulant effects are more pronounced or operate differently for high-risk individuals.

DISCUSSION

Despite commendable advances in SR research, important questions remain unanswered. Inconsistent results across studies may be attributable to a combination of an inadequate understanding of the underlying construct and methodological differences across studies (e.g., number and timing of assessments across the BAC, inclusion of a placebo condition). With respect to the underlying construct, existing measures fail to adequately distinguish between cognitive/behavioral impairment and sedation, aspects of which may be perceived positively (e.g., anxiolysis) due to their ability to act as negative reinforcers.

CONCLUSIONS

Addressing the concerns raised by the current review will be integral to making meaningful scientific progress in the field of subjective response.

Priming deficiency in male subjects at risk for alcoholism: the N4 during a lexical decision task

BACKGROUND

While there is extensive literature on the relationship between the P3 component of event-related potentials (ERPs) and risk for alcoholism, there are few published studies regarding other potentially important ERP components. One important candidate is the N4(00) component in the context of semantic processing, as abnormalities in this component have been reported for adult alcoholics.

METHOD

A semantic priming task was administered to nonalcohol dependent male offspring (18 to 25 years) of alcoholic fathers [high risk (HR) n = 23] and nonalcoholic fathers [low risk (LR) n = 28] to study whether the 2 groups differ in terms of the N4 component. Subjects were presented with 150 words and 150 nonwords. Among the words, 50 words (primed) were preceded by their antonyms (prime, n = 50), whereas the remaining 50 words were unprimed. For the analysis, N4 amplitude and latency as well as behavioral measures for the primed and unprimed words were considered.

RESULTS

A significant interaction effect was observed between semantic condition and group, where HR subjects did not show N4 attenuation for primed stimuli.

CONCLUSION

The lack of N4 attenuation to primed stimuli and/or inability to differentiate between primed and unprimed stimuli, without latency and reaction time being affected, suggest deficits in semantic priming, especially in semantic expectancy and/or postlexical semantic processing in HR male offspring. Further, it indicates that it might be an electrophysiological endophenotype that reflects genetic vulnerability to develop alcoholism.

Diagnosing alcohol abuse in alcohol dependent individuals: diagnostic and clinical implications

In DMS-IV, the diagnosis of alcohol abuse is precluded by the diagnosis of alcohol dependence. The goal of this study was to examine the diagnostic and clinical implications of diagnosing alcohol abuse among alcohol dependent individuals. Treatment-seeking psychiatric outpatients with a lifetime history of alcohol dependence (n=544), some of whom (n=45) did not meet lifetime criteria for alcohol abuse completed in-depth, face-to-face, semi-structured clinical assessments of DSM-IV axis I and axis II psychopathology. Alcohol dependent patients who did not meet criteria for alcohol abuse were significantly more likely to be female, have a later age of onset for alcohol dependence, have fewer dependence symptoms, and have a lower rate of positive family history for alcoholism, and were less likely to report a lifetime history of DSM-IV drug use disorders and PTSD. These findings suggest that diagnosing alcohol abuse among alcohol dependent patients may be clinically useful as an index of severity and higher likelihood of comorbid drug abuse and dependence. Future studies are needed to establish whether these differences are clinically significant in terms of the course of the disorder and response to treatment.

Proton magnetic resonance spectroscopy in alcohol use disorders: a potential new endophenotype?

BACKGROUND

Current effort is directed at defining new classification schemes for alcohol use disorders (AUD) based on genetic/biological, physiological, and behavioral endophenotypes.

METHODS

We describe briefly findings of in vivo brain proton magnetic resonance spectroscopy ((1)H MRS) studies in AUD and propose that they be further explored and expanded regarding their value as a potential endophenotype for AUD.

RESULTS

In vivo (1)H MRS, as part of the emerging field of "imaging genomics," may provide readily accessible, objective, functionally significant and region-specific neurobiological measures that successfully link genotypes to neurocognition and to psychiatric symptomatology in relatively small patient cohorts. We discuss several functional gene variants that may affect specific (1)H MRS-detectable metabolites and provide recent data from our own work that supports the view of genetic effects on metabolite measures.

CONCLUSIONS

MRS-genetics research will not only offer clues to the functional significance and downstream effects of genetic differences in AUD, but, via monitoring and/or predicting the efficacy of pharmacological and behavioral interventions as a function of genotype, has the potential to influence future clinical management of AUD.

Acute effects of acamprosate and MPEP on ethanol Drinking-in-the-Dark in male C57BL/6J mice

BACKGROUND

Recently, a simple procedure in mice, Drinking-in-the-Dark (DID), was hypothesized to have value for medication development for human alcoholism. In DID, mice are offered intermittent, limited access to ethanol over a series of days during the dark phase that results in rapid drinking to intoxication in predisposed genotypes.

METHODS

We measured the effects of acamprosate or MPEP, metabotropic glutamate 5 receptor (mGluR5) antagonist, on intake of 20% ethanol, plain tap water or 10% sugar water using the DID procedure in male C57BL/6J mice.

RESULTS

Acamprosate (100, 200, 300, or 400 mg/kg) dose dependently decreased ethanol drinking with 300 mg/kg reducing ethanol intake by approximately 20% without affecting intake of plain water or 10% sugar water. MPEP (1, 3, 5, 10, 20, or 40 mg/kg) was more potent than acamprosate with 20 mg/kg reducing ethanol intake by approximately 20% and for longer duration without affecting intake of plain water or 10% sugar water.

CONCLUSIONS

These results support the hypothesis that mGluR5 signaling plays a role in excessive ethanol intake in DID and suggest DID may have value for screening novel compounds that reduce overactive glutamate signaling for potential pharmaceutical treatment of excessive ethanol drinking behavior.

Human gamma-aminobutyric acid A receptor alpha2 gene moderates the acute effects of alcohol and brain mRNA expression

Gamma-aminobutyric acid A (GABA(A)) receptors moderate several of the behavioral effects of alcohol. In fact, recent studies have shown an association between the gene for the alpha2-subunit of the GABA(A) receptor (GABRA2) and alcoholism. In the present study, we examined the functional relevance of the GABRA2 gene in alcohol dependence by assessing brain GABRA2 mRNA and GABA(A)alpha2-subunit protein levels in post-mortem prefrontal cortical tissue collected from control and alcohol-dependent individuals. In addition, using an endophenotype approach, we tested whether the GABRA2 gene moderates sensitivity to the acute effects of alcohol in two independent samples from distinct human alcohol challenge studies. Results indicated that GABRA2 mRNA levels significantly differed by GABRA2 genotype. GABRA2 single nucleotide polymorphisms (rs573400, rs279871 and rs279858) were significantly associated with sensitivity to the acute effects of alcohol. Specifically, there was a significant main effect of GABRA2 x breath alcohol concentration on several measures of subjective responses to alcohol, including the hedonic value of alcohol. Importantly, reanalysis of a previous intravenous alcohol administration study confirmed the results of the oral alcohol challenge study. In summary, these results extend previous findings and provide new insights into the putative biobehavioral mechanisms that may moderate the association between the GABRA2 gene, sensitivity to the acute effects of alcohol and ultimately alcohol dependence.

Gene transcription alterations associated with decrease of ethanol intake induced by naltrexone in the brain of Wistar rats

Preclinical and clinical studies suggest that the administration of the opioid antagonist naltrexone decreases the intake of ethanol. However, the neuroplastic adaptations in the brain associated to reduction of ethanol consumption remains to be elucidated. The aim of the study was to identify gene transcription alterations underlying the attenuation of voluntary ethanol intake by administration of naltrexone in rats. Increasing doses of naltrexone (0.7 mg/kg, 4 days and 1.4 mg/kg/day, 4 days) to rats with acquired high preferring ethanol consumption (>3.5 g of ethanol/kg/day) decreased voluntary ethanol intake (50%). Voluntary ethanol consumption altered mu-opioid receptor function in the cingulate cortex, caudate-putamen (CPu), nucleus accumbens core (Acb C) and shell (Acb S), the expression of tyrosine hydroxylase (TH) in the ventral tegmental area and substantia nigra, proenkephalin (PENK) in the piriform cortex, olfactory tubercle, CPu, Acb C and Acb S, ventromedial nucleus (VMN) and paraventricular nucleus (PVN) of the hypothalamus, corticotropin releasing factor (CRF) in PVN, cannabinoid CB(1) receptor (CB1-R) in the CPu, hippocampus and VMN, and serotonin transporter (5-HTT) in the dorsal and median raphe nuclei. The reduction of ethanol intake induced by naltrexone was associated with a blockade or significant reduction of the changes produced by ethanol in the expression of these genes in key regions related to drug dependence. These results point to a role for the mu-opioid receptor, TH, PENK, CRF, CB1-R, and 5-HTT genes in specific brain regions in the modulation of neuroadaptative mechanisms associated to the decrease of ethanol intake induced by naltrexone.

Heterogeneous Effects of Alcohol on Dopamine Release in the Striatum: A PET Study

BACKGROUND

A dopaminergic response to alcohol in humans has not been demonstrated consistently with positron emission tomography (PET). We hypothesized that the effect of alcohol on striatal dopamine (DA) release may be anatomically heterogeneous between subjects. Our approach was to identify voxels that exhibited alcohol-induced DA responses within the striatum, and to determine the relationships between DA responses and alcohol-related behavior.

METHODS

A novel method was developed to examine the anatomic extent and magnitude of striatal DA responses to alcohol across subjects. Thirteen healthy control subjects underwent 2 PET scans with [11C]raclopride (1 at baseline, 1 with an i.v. alcohol infusion to a target breath alcohol concentration of either 60 or 80 mg%). Parametric images of striatal binding potential (BP) were used to create maps of change in BP (deltaBP, an index of changes in DA levels). The anatomic extent and magnitude of DA responses were determined with voxel extraction methods. Subjective responses ("High," "Intoxication") to the alcohol infusion and behavioral data from the 90-day time-line follow back were assessed for relationships with DA responses to alcohol.

RESULTS

A voxel-wise t-test between baseline and alcohol BP images did not show any differences in D2/D3 receptor availability between the conditions. Data from the striatal deltaBP maps nevertheless showed that the anatomic extent and magnitude of alcohol-induced DA release in the striatum are correlated with subjective responses to alcohol.

CONCLUSIONS

The heterogeneity of dopaminergic responses to alcohol across subjects may be a reason for the lack of reports demonstrating DA involvement in alcohol-related behaviors. By allowing for different spatial patterns of DA release within each subject's striata, we showed correlations between alcohol-induced DA release in the striata and behavioral outcomes related to alcohol.

Studying alcohol elimination using the alcohol clamp method

Researchers studying alcohol absorption and metabolism in humans have been aided by the alcohol clamp method, in which alcohol is administered intravenously, allowing study participants to achieve and maintain a target breath alcohol concentration (BrAC) for an extended period of time. This tool minimizes the variability in BrACs that occurs after alcohol consumption by administering alcohol at a dose and rate that is computed for each person individually. The alcohol clamp can be used to evaluate several influences on alcohol elimination, including gender, ethnicity, genetic variations in alcohol-metabolizing enzymes, and food consumption.