Dopamine D4 receptor gene (DRD4) is associated with Novelty Seeking (NS) and substance abuse: the saga continues

Coordination among frequent genetic variants imparts substance use susceptibility and pathogenesis

Determining the key genetic variants is a crucial step to comprehensively understand substance use disorders (SUDs). In this study, utilizing whole exome sequences of five multi-generational pedigrees with SUDs, we used an integrative omics-based approach to uncover candidate genetic variants that impart susceptibility to SUDs and influence addition traits. We identified several SNPs and rare, protein-function altering variants in genes, GRIA3, NCOR1, and SHANK1; compound heterozygous variants in LNPEP, LRP1, and TBX2, that play a significant role in the neurotransmitter-neuropeptide axis, specifically in the dopaminergic circuits. We also noted a greater frequency of heterozygous and recessive variants in genes involved in the structural and functional integrity of synapse receptors, CHRNA4, CNR2, GABBR1, DRD4, NPAS4, ADH1B, ADH1C, OPRM1, and GABBR2. Variant analysis in upstream promoter regions revealed regulatory variants in NEK9, PRRX1, PRPF4B, CELA2A, RABGEF1, and CRBN, crucial for dopamine regulation. Using family-and pedigree-based data, we identified heterozygous recessive alleles in LNPEP, LRP1 (4 frameshift deletions), and TBX2 (2 frameshift deletions) linked to SUDs. GWAS overlap identified several SNPs associated with SUD susceptibility, including rs324420 and rs1229984. Furthermore, miRNA variant analysis revealed notable variants in mir-548 U and mir-532. Pathway studies identified the presence of extensive coordination among these genetic variants to impart substance use susceptibility and pathogenesis. This study identified variants that were found to be overrepresented among genes of dopaminergic circuits participating in the neurotransmitter-neuropeptide axis, suggesting pleiotropic influences in the development and sustenance of chronic substance use. The presence of a diverse set of haploinsufficient variants in varying frequencies demonstrates the existence of extraordinary coordination among them in attributing risk and modulating severity to SUDs.

Reward Processing in Novelty Seekers: A Transdiagnostic Psychiatric Imaging Biomarker

BACKGROUND

Dysfunctional reward processing is implicated in multiple mental disorders. Novelty seeking (NS) assesses preference for seeking novel experiences, which is linked to sensitivity to reward environmental cues.

METHODS

A subset of 14-year-old adolescents (IMAGEN) with the top 20% ranked high-NS scores was used to identify high-NS-associated multimodal components by supervised fusion. These features were then used to longitudinally predict five different risk scales for the same and unseen subjects (an independent dataset of subjects at 19 years of age that was not used in predictive modeling training at 14 years of age) (within IMAGEN, n ≈1100) and even for the corresponding symptom scores of five types of patient cohorts (non-IMAGEN), including drinking (n = 313), smoking (n = 104), attention-deficit/hyperactivity disorder (n = 320), major depressive disorder (n = 81), and schizophrenia (n = 147), as well as to classify different patient groups with diagnostic labels.

RESULTS

Multimodal biomarkers, including the prefrontal cortex, striatum, amygdala, and hippocampus, associated with high NS in 14-year-old adolescents were identified. The prediction models built on these features are able to longitudinally predict five different risk scales, including alcohol drinking, smoking, hyperactivity, depression, and psychosis for the same and unseen 19-year-old adolescents and even predict the corresponding symptom scores of five types of patient cohorts. Furthermore, the identified reward-related multimodal features can classify among attention-deficit/hyperactivity disorder, major depressive disorder, and schizophrenia with an accuracy of 87.2%.

CONCLUSIONS

Adolescents with higher NS scores can be used to reveal brain alterations in the reward-related system, implicating potential higher risk for subsequent development of multiple disorders. The identified high-NS-associated multimodal reward-related signatures may serve as a transdiagnostic neuroimaging biomarker to predict disease risks or severity.

Distinct motivations to seek out information in healthy individuals and problem gamblers

As massive amounts of information are becoming available to people, understanding the mechanisms underlying information-seeking is more pertinent today than ever. In this study, we investigate the underlying motivations to seek out information in healthy and addicted individuals. We developed a novel decision-making task and a novel computational model which allows dissociating the relative contribution of two motivating factors to seek out information: a desire for novelty and a general desire for knowledge. To investigate whether/how the motivations to seek out information vary between healthy and addicted individuals, in addition to healthy controls we included a sample of individuals with gambling disorder-a form of addiction without the confound of substance consumption and characterized by compulsive gambling. Our results indicate that healthy subjects and problem gamblers adopt distinct information-seeking "modes". Healthy information-seeking behavior was mostly motivated by a desire for novelty. Problem gamblers, on the contrary, displayed reduced novelty-seeking and an increased desire for accumulating knowledge compared to healthy controls. Our findings not only shed new light on the motivations driving healthy and addicted individuals to seek out information, but they also have important implications for the treatment and diagnosis of behavioral addiction.

Increased novelty-induced locomotion, sensitivity to amphetamine, and extracellular dopamine in striatum of Zdhhc15-deficient mice

Novelty-seeking behaviors and impulsivity are personality traits associated with several psychiatric illnesses including attention deficits hyperactivity disorders. The underlying neural mechanisms remain poorly understood. We produced and characterized a line of knockout mice for zdhhc15, which encodes a neural palmitoyltransferase. Genetic defects of zdhhc15 were implicated in intellectual disability and behavioral anomalies in humans. Zdhhc15-KO mice showed normal spatial learning and working memory but exhibited a significant increase in novelty-induced locomotion in open field. Striatal dopamine content was reduced but extracellular dopamine levels were increased during the habituation phase to a novel environment. Administration of amphetamine and methylphenidate resulted in a significant increase in locomotion and extracellular dopamine levels in the ventral striatum of mutant mice compared to controls. Number and projections of dopaminergic neurons in the nigrostriatal and mesolimbic pathways were normal. No significant change in the basal palmitoylation of known ZDHHC15 substrates including DAT was detected in striatum of zdhhc15 KO mice using an acyl-biotin exchange assay. These results support that a transient, reversible, and novelty-induced elevation of extracellular dopamine in ventral striatum contributes to novelty-seeking behaviors in rodents and implicate ZDHHC15-mediated palmitoylation as a novel regulatory mechanism of dopamine in the striatum.

Why are Women More Religious than Men? Do Risk Preferences and Genetic Risk Predispositions Explain the Gender Gap?

Risk preference theory argues that the gender gap in religiosity is caused by greater female risk aversion. Although widely debated, risk preference theory has been inadequately tested. Our study tests the theory directly with phenotypic and genetic risk preferences in three dimensions-general, impulsive, and sensation-seeking risk. Moreover, we examine whether the effect of different dimension of risk preference on the gender gap varies across different dimensions of religiosity. We find that general and impulsive risk preferences do not explain gender differences in religiosity, whereas sensation-seeking risk preference makes the gender gap in self-assessed religiousness and church attendance insignificant, but not belief in God, prayer, or importance of religion. Genetic risk preferences do not remove any of the gender gaps in religiosity, suggesting that the causal order is not from risk preference to religiosity. Evidence suggests that risk preferences are not a strong predictor for gender differences in religiosity.

Temperament and character inventory (TCI) personality profile in metamphetamine abusers: a controlled study

We applied the temperament and character inventory (TCI) personality questionnaire in 41 inpatients dependent on metamphetamine, and 35 controls. Novelty seeking, harm avoidance and self-transcendence were significantly higher, and persistence, self-directedness and cooperativeness were significantly lower in the patients than in the healthy volunteers. The detected differences may be important for prevention and treatment.

Opioid Addiction, Genetic Susceptibility, and Medical Treatments: A Review

Opioid addiction is a chronic and complex disease characterized by relapse and remission. In the past decade, the opioid epidemic or opioid crisis in the United States has raised public awareness. Methadone, buprenorphine, and naloxone have proven their effectiveness in treating addicted individuals, and each of them has different effects on different opioid receptors. Classic and molecular genetic research has provided valuable information and revealed the possible mechanism of individual differences in vulnerability for opioid addiction. The polygenic risk score based on the results of a genome-wide association study (GWAS) may be a promising tool to evaluate the association between phenotypes and genetic markers across the entire genome. A novel gene editing approach, clustered, regularly-interspaced short palindromic repeats (CRISPR), has been widely used in basic research and potentially applied to human therapeutics such as mental illness; many applications against addiction based on CRISPR are currently under research, and some are successful in animal studies. In this article, we summarized the biological mechanisms of opioid addiction and medical treatments, and we reviewed articles about the genetics of opioid addiction, the promising approach to predict the risk of opioid addiction, and a novel gene editing approach. Further research on medical treatments based on individual vulnerability is needed.

Relation of personality factors and life events to waist/height ratio and percentage of visceral fat in women and men

PURPOSE

The investigation aimed to explore the association between personality traits, stressful life events, quality of life on anthropometric characteristics (waist/height ratio and percentage of visceral fat).

METHOD

A total of 227 participants took part in this cross-sectional study. Participants completed the Social Readjustment Rating Scale (SRRS), Temperament and Character Inventory-Revised, Type-D Scale (DS-14), EuroQol Group 5-Dimension Self-Report Questionnaire (EQ-5D), and demographic questionnaire. Two anthropometric parameters were measured: Waist/height ratio and Percentage of the visceral fat.

RESULTS

The average age of participants was 39.6±12.9 years, 60.4% women. The 41.8% of participants were overweight or obese. Regression analysis found a significant link between Harm-avoidance and EQ-5D visual analog scale (VAS) with Waist/height ratio in women and Reward dependence and Cooperativeness with Waist/height ratio in men. In regression analysis, the score of life events (SRRS) has statistically significant linked to Percentage of the visceral fat in women. The regression analysis also found a significant link between Novelty seeking, DS14, Negative affectivity, and EQ-5D VAS with Percentage of the visceral fat in women.

CONCLUSION

Significant associations between live events, personality traits, and body anthropometric measures were recognized. The differences were recognized between women and men. Outcomes propose some promising tools by which personality factors may influence overweight and obesity.

Associations Between the Dopamine D4 Receptor and DAT1 Dopamine Transporter Genes Polymorphisms and Personality Traits in Addicted Patients

Many factors are involved in addiction. The dopaminergic system is thought to be the key element in this process. The mesolimbic dopamine system is a crucial element in the reward system. Changes in this system are thought to be leading to substance use disorders and dependence. Therefore, for our study we chose an analysis of two polymorphisms in genes (Variable Number of Tandem Repeats in DRD4 and DAT1) responsible for dopaminergic transmission, which might be implicated in the scores of personality traits measured by the NEO-FFI test. The study group consisted of 600 male volunteers—299 addicted subjects and 301 controls. Both groups were recruited by psychiatrists; in the case group addiction was diagnosed; in the controls a mental illness was excluded. In both groups the same psychometric test and genotyping by the PCR VNTR method were performed. The results were investigated by a multivariate analysis of the main effects ANOVA. In the presented study no DRD4 main effects were found for any of the analyzed traits but the DRD4 main effects approximated to the statistical significance for the extraversion scale. However, no DAT1 main effects were found for any of the analyzed traits but the DAT1 main effects approximated to the statistical significance for the agreeability scale.These associations open new possibilities for addiction research.

Do Event-Related Evoked Potentials Reflect Apathy Tendency and Motivation?

Apathy is a mental state of diminished motivation. Although the reward system as the foundation of the motivation in the human brain has been studied extensively with neuroimaging techniques, the electrophysiological correlates of motivation and apathy have not been fully explored. Thus, in 14 healthy volunteers, we examined whether event-related evoked potentials (ERP) obtained during a simple number discrimination task with/without rewards reflected apathy tendency and a reward-dependent tendency, which were assessed separately using the apathy scale and the temperament and character inventory (TCI). Participants were asked to judge the size of a number, and received feedback based on their performance in each trial. The P3 amplitudes related to the feedback stimuli increased only in the reward condition. Furthermore, the P2 amplitudes related to the negative feedback stimuli in the reward condition had a positive correlation with the reward-dependent tendency in TCI, whereas the P3 amplitudes related to the positive feedback stimuli had a negative correlation with the apathy score. Our result suggests that the P2 and P3 ERPs to reward-related feedback stimuli are modulated in a distinctive manner by the motivational reward dependence and apathy tendency, and thus the current paradigm may be useful for investigating the brain activity associated with motivation.

Activity level in the lab: Overlap with shyness indicates it is more than pure motoric activity

The observation that children's activity level (AL) differs between novel and familiar situations is well established. What influences individual differences in how AL is different across these situations is less well understood. Drawing on animal literature, which links rats' AL when 1st placed in a novel setting with novelty seeking phenotypes, and child temperament literature, which links AL, novelty response, and shyness, we hypothesized that shyness would be an important component of children's AL in a novel situation. We examined this using mechanically assessed AL from 2 situations (the home and the lab) and 2 measures of shyness (1 parent-rated and 1 observer-rated) on up to 313 twin pairs (145 monozygotic and 168 dizygotic), at 2 and 3 years of age. Biometric genetic models removed from lab AL the variance shared with home AL, representing what was different in AL when the child entered the lab compared to the home. We report that almost half (43%) of the genetic component of AL in the lab was independent of AL in the home, and this unique genetic component shared genetic covariance with shyness. Shyness influences AL in a novel situation such as the lab, indicating that mechanically assessed AL represents more than global motoric activity and provides information on a child's temperamental response to novelty. (PsycINFO Database Record

Striatal Dopamine, Externalizing Proneness, and Substance Abuse: Effects on Wanting and Learning during Reward-Based Decision Making

We examined whether striatal dopamine moderates the impact of externalizing proneness (disinhibition) on reward-based decision-making. Participants completed disinhibition and substance abuse subscales of the brief form Externalizing Spectrum Inventory, and then performed a delay discounting task to assess preference for immediate rewards along with a dynamic decision-making task that assessed long-term reward learning (i.e., inclination to choose larger delayed versus smaller immediate rewards). Striatal tonic dopamine levels were operationalized using spontaneous eyeblink rate. Regression analyses revealed that high disinhibition predicted greater delay discounting among participants with lower levels of striatal dopamine only, while substance abuse was associated with poorer long-term learning among individuals with lower levels of striatal dopamine, but better long-term learning in those with higher levels of striatal dopamine. These results suggest that disinhibition is more strongly associated with the wanting component of reward-based decision-making, whereas substance abuse behavior is associated more with learning of long-term action-reward contingencies.

[The forecast of illicit drug use in adolescents with addictive behavior: personality traits and the level of genetic risk of substance dependence.]

AIM

To clarify the psychological mechanism underlying the genetic risk of substance addiction at the first stage of drug use by adolescents.

MATERIAL AND METHODS

Genetic risk was evaluated by genotyping of 5 polymorphisms of the dopaminergic system genes (dopamine receptor D2 and D4 genes and tyrosine hydroxylase gene). Psychological testing was performed using the Russian version of Temperament and Character Inventory (TCI-125). Seventy-five adolescents, aged 14-17 years, (girls 32%), who misused alcohol, including 22 adolescents using drugs, were examined.

RESULTS AND CONCLUSION

The level of genetic risk was directly correlated with the probability of drug use by boys, for girls the correlation was not confirmed. The increase of the level of genetic risk for boys was correlated with the increase on the scale «Self-directedness» of TCI-125 that may reflect a probable tendency to replacement of negative information, feeling of illusory wellbeing. The findings clarify the direction of measures for the prevention of drug use.

Witnessing substance use increases same-day antisocial behavior among at-risk adolescents: Gene-environment interaction in a 30-day ecological momentary assessment study

Many young adolescents are embedded in neighborhoods, schools, and homes where alcohol and drugs are frequently used. However, little is known about (a) how witnessing others' substance use affects adolescents in their daily lives and (b) which adolescents will be most affected. The current study used ecological momentary assessment with 151 young adolescents (ages 11-15) to examine the daily association between witnessing substance use and antisocial behavior across 38 consecutive days. Results from multilevel logistic regression models indicated that adolescents were more likely to engage in antisocial behavior on days when they witnessed others using substances, an association that held when substance use was witnessed inside the home as well as outside the home (e.g., at school or in their neighborhoods). A significant Gene × Environment interaction suggested that the same-day association between witnessing substance use and antisocial behavior was significantly stronger among adolescents with, versus without, the dopamine receptor D4 seven repeat (DRD4-7R) allele. The implications of the findings for theory and research related to adolescent antisocial behavior are discussed.

The effect of dopamine D4 receptor density on novelty seeking, activity, social interaction, and alcohol binge drinking in adult mice

The dopamine D4 receptor has been postulated to play a role in the pathophysiology of alcoholism. This study examined how varying levels of D4 expression and their associated behaviors in male and female mice correlate with future alcohol intake. We hypothesized that: (1) mice with low (Drd4(+/-) ) or deficient (Drd4(-/-) ) in D4 receptors would show enhanced ethanol consumption compared with control mice (Drd4(+/+) ), and (2) a specific phenotype in these mice is associated with future vulnerability for alcohol consumption. Individually housed mice were allowed free access to ethanol (20% vv) in the dark (DID). The behaviors measured in male and female mice were: novel object recognition, open-field locomotor activity, and social interaction. Correlation analyses showed that in male Drd4(-/-) mice (relative to Drd4(+/+) controls), anxiolytic behavior was significantly correlated with increased alcohol consumption. Also, in male Drd4(-/-) mice, there was a significant positive correlation between increased exploratory behavior and increased alcohol consumption. These findings were not observed in females. In conclusion, our data suggest that the dopamine D4 receptor gene has an important role in increased exploratory and anxiolytic behavior only in males and these behaviors were positively correlated with increased alcohol consumption. This interaction between sex hormones and dopamine D4 receptor genotype/function predicting future alcohol abuse and correlation with anxiolytic and exploratory behavior in male mice could have important implications for better understanding of vulnerabilities associated with addiction.

Discovery and Characterization of ML398, a Potent and Selective Antagonist of the D4 Receptor with in Vivo Activity

Herein, we report the structure-activity relationship of a chiral morpholine-based scaffold, which led to the identification of a potent and selective dopamine 4 (D4) receptor antagonist. The 4-chlorobenzyl moiety was identified, and the compound was designated an MLPCN probe molecule, ML398. ML398 is potent against the D4 receptor with IC50 = 130 nM and K i = 36 nM and shows no activity against the other dopamine receptors tested (>20 μM against D1, D2S, D2L, D3, and D5). Further in vivo studies showed that ML398 reversed cocaine-induced hyperlocomotion at 10 mg/kg.

Ondansetron and sertraline may interact with 5-HTTLPR and DRD4 polymorphisms to reduce drinking in non-treatment seeking alcohol-dependent women: exploratory findings

The purpose of this exploratory study was to examine the interaction of 5-HTTLPR and DRD4 exon III polymorphisms with gender in non-treatment seeking alcohol-dependent (AD) individuals while alternately taking ondansetron and sertraline. Evidence suggests that alcohol dependence may be influenced by a genetic interaction that may be gender-specific with temporal changes making pharmacological treatment with serotonergic drugs complex. The main trial was a within-subject double-blind placebo-controlled human laboratory study with 77 non-treatment-seeking AD individuals randomized (55 completed, 49 complete data) to receive 200 mg/day of sertraline or 0.5 mg/day of ondansetron for 3 weeks followed by an alcohol self-administration experiment (ASAE), then placebo for 3 weeks followed by a second ASAE, then receive the alternate drug, in a counterbalanced order, for 3 weeks followed by a third ASAE. Results for men were not significant. Women with the LL 5-HTTLPR genotype receiving ondansetron and SS/SL 5-HTTLPR genotype receiving sertraline (matched), drank significantly fewer drinks per drinking day (DDD) during the 7 days prior to the first and third ASAEs than women receiving the mismatched medication (i.e., sertraline to LL and ondansetron to SS/SL). In a 3-way interaction, 5-HTTLPR alleles by DRD4 alleles by medications, women with the LL genotype who received ondansetron and had DRD4≥7 exon III repeats drank significantly fewer DDD as did SS/SL women who received sertraline but conversely had DRD4<7 repeats in the 7-day period leading up to the first and third ASAEs. Consistent with these data was a significant reduction of milliliters consumed ad libitum during these same ASAEs. These exploratory findings add possible support to gender and genetic differences among AD individuals in response to serotonergic pharmacotherapies. Future trials should be powerful enough to take into account that endophenotypes and a targeting of serotonergic interactions may be essential to successfully treat alcohol dependence.

Genetic Addiction Risk Score (GARS): molecular neurogenetic evidence for predisposition to Reward Deficiency Syndrome (RDS)

We have published extensively on the neurogenetics of brain reward systems with reference to the genes related to dopaminergic function in particular. In 1996, we coined “Reward Deficiency Syndrome” (RDS), to portray behaviors found to have gene-based association with hypodopaminergic function. RDS as a useful concept has been embraced in many subsequent studies, to increase our understanding of Substance Use Disorder (SUD), addictions, and other obsessive, compulsive, and impulsive behaviors. Interestingly, albeit others, in one published study, we were able to describe lifetime RDS behaviors in a recovering addict (17 years sober) blindly by assessing resultant Genetic Addiction Risk Score (GARS™) data only. We hypothesize that genetic testing at an early age may be an effective preventive strategy to reduce or eliminate pathological substance and behavioral seeking activity. Here, we consider a select number of genes, their polymorphisms, and associated risks for RDS whereby, utilizing GWAS, there is evidence for convergence to reward candidate genes. The evidence presented serves as a plausible brain-print providing relevant genetic information that will reinforce targeted therapies, to improve recovery and prevent relapse on an individualized basis. The primary driver of RDS is a hypodopaminergic trait (genes) as well as epigenetic states (methylation and deacetylation on chromatin structure). We now have entered a new era in addiction medicine that embraces the neuroscience of addiction and RDS as a pathological condition in brain reward circuitry that calls for appropriate evidence-based therapy and early genetic diagnosis and that requires further intensive investigation.

Multivariate analysis of dopaminergic gene variants as risk factors of heroin dependence

BACKGROUND

Heroin dependence is a debilitating psychiatric disorder with complex inheritance. Since the dopaminergic system has a key role in rewarding mechanism of the brain, which is directly or indirectly targeted by most drugs of abuse, we focus on the effects and interactions among dopaminergic gene variants.

OBJECTIVE

To study the potential association between allelic variants of dopamine D2 receptor (DRD2), ANKK1 (ankyrin repeat and kinase domain containing 1), dopamine D4 receptor (DRD4), catechol-O-methyl transferase (COMT) and dopamine transporter (SLC6A3) genes and heroin dependence in Hungarian patients.

METHODS

303 heroin dependent subjects and 555 healthy controls were genotyped for 7 single nucleotide polymorphisms (SNPs) rs4680 of the COMT gene; rs1079597 and rs1800498 of the DRD2 gene; rs1800497 of the ANKK1 gene; rs1800955, rs936462 and rs747302 of the DRD4 gene. Four variable number of tandem repeats (VNTRs) were also genotyped: 120 bp duplication and 48 bp VNTR in exon 3 of DRD4 and 40 bp VNTR and intron 8 VNTR of SLC6A3. We also perform a multivariate analysis of associations using Bayesian networks in Bayesian multilevel analysis (BN-BMLA).

FINDINGS AND CONCLUSIONS

In single marker analysis the TaqIA (rs1800497) and TaqIB (rs1079597) variants were associated with heroin dependence. Moreover, -521 C/T SNP (rs1800955) of the DRD4 gene showed nominal association with a possible protective effect of the C allele. After applying the Bonferroni correction TaqIB was still significant suggesting that the minor (A) allele of the TaqIB SNP is a risk component in the genetic background of heroin dependence. The findings of the additional multiple marker analysis are consistent with the results of the single marker analysis, but this method was able to reveal an indirect effect of a promoter polymorphism (rs936462) of the DRD4 gene and this effect is mediated through the -521 C/T (rs1800955) polymorphism in the promoter.

Interaction between novelty seeking and the aldehyde dehydrogenase 2 gene in heroin-dependent patients

OBJECTIVES

Heroin dependence is a multifactor disorder. We investigated the association of genetic factors and heroin-dependent temperaments to determine whether a temperament-gene interaction is involved in the pathogenesis of heroin dependence.

METHODS

Three hundred seventy participants (259 heroin-dependent patients and 111 healthy controls) were recruited and finished the Tridimensional Personality Questionnaire to assess personality traits (temperament). The genotypes of the aldehyde dehydrogenase 2 (ALDH2) gene and the Val66Met polymorphism of the brain-derived neurotrophic factor (BDNF) gene using polymerase chain reactions plus restriction fragment length polymorphism analysis.

RESULTS

Multiple logistic regression analysis showed significant main effects for novelty seeking (P ≤ 0.001) and harm-avoidance (P = 0.001) scores, and a significant interaction effect between novelty seeking and ALDH2 genotypes (P = 0.016) in heroin-dependent patients compared with controls. When stratified by the ALDH2 genotypes, only heroin-dependent patients with the *1*2 and *2*2 genotypes at ALDH2 had higher novelty-seeking scores than did controls (heroin dependence = 15.94, controls = 12.46; P ≤ 0.001).

CONCLUSIONS

Our results provide initial evidence that the ALDH2 gene interacted with novelty seeking in heroin-dependent Han Chinese patients in Taiwan.

Modification of cocaine self-administration by buspirone (buspar®): potential involvement of D3 and D4 dopamine receptors

Converging lines of evidence indicate that elevations in synaptic dopamine levels play a pivotal role in the reinforcing effects of cocaine, which are associated with its abuse liability. This evidence has led to the exploration of dopamine receptor blockers as pharmacotherapy for cocaine addiction. While neither D1 nor D2 receptor antagonists have proven effective, medications acting at two other potential targets, D3 and D4 receptors, have yet to be explored for this indication in the clinic. Buspirone, a 5-HT1A partial agonist approved for the treatment of anxiety, has been reported to also bind with high affinity to D3 and D4 receptors. In view of this biochemical profile, the present research was conducted to examine both the functional effects of buspirone on these receptors and, in non-human primates, its ability to modify the reinforcing effects of i.v. cocaine in a behaviourally selective manner. Radioligand binding studies confirmed that buspirone binds with high affinity to recombinant human D3 and D4 receptors (∼98 and ∼29 nm respectively). Live cell functional assays also revealed that buspirone, and its metabolites, function as antagonists at both D3 and D4 receptors. In behavioural studies, doses of buspirone that had inconsistent effects on food-maintained responding (0.1 or 0.3 mg/kg i.m.) produced a marked downward shift in the dose-effect function for cocaine-maintained behaviour, reflecting substantial decreases in self-administration of one or more unit doses of i.v. cocaine in each subject. These results support the further evaluation of buspirone as a candidate medication for the management of cocaine addiction.

Temperamental exuberance and executive function predict propensity for risk taking in childhood

The present study utilized a multilevel approach to examine developmental trajectories in risk-taking propensity. We examined the moderating role of specific executive function components, attention shifting and inhibitory control, on the link between exuberant temperament in infancy and propensity for risk taking in childhood. Risk taking was assessed using a task previously associated with sensation seeking and antisocial behaviors. Two hundred ninety-one infants were brought into the lab and behaviors reflecting exuberance were observed at 4, 9, 24, and 36 months of age. Executive function was assessed at 48 months of age. Risk-taking propensity was measured when children were 60 months of age. The results indicated that exuberance and attention shifting, but not inhibitory control, significantly interacted to predict propensity for risk taking. Exuberance was positively associated with risk-taking propensity among children who were relatively low in attention shifting but unrelated for children high in attention shifting. These findings illustrated the multifinality of developmental outcomes for temperamentally exuberant young children and pointed to the distinct regulatory influences of different executive functions for children of differing temperaments. Attention shifting likely affords a child the ability to consider both positive and negative consequences and moderates the relation between early exuberance and risk-taking propensity.

The influence of five monoamine genes on trajectories of depressive symptoms across adolescence and young adulthood

The influence of five monoamine candidate genes on depressive symptom trajectories in adolescence and young adulthood were examined in the Add Health genetic sample. Results indicated that, for all respondents, carriers of the dopamine receptor D4 5-repeat allele were characterized by distinct depressive symptom trajectories across adolescence and early adulthood. Similarly, for males, individuals with the monoamine oxidase A 3.5-repeat allele exhibited unique depressive symptom trajectories. Specifically, the trajectories of those with the dopamine receptor D4 5-repeat allele were characterized by rising levels in the transition to adulthood, while their peers were experiencing a normative drop in depressive symptom frequency. Conversely, males with the monoamine oxidase A 3.5-repeat allele were shown to experience increased distress in late adolescence. An empirical method for examining a wide array of allelic combinations was employed, and false discovery rate methods were used to control the risk of false positives due to multiple testing. Special attention was given to thoroughly interrogate the robustness of the putative genetic effects. These results demonstrate the value of combining dynamic developmental perspectives with statistical genetic methods to optimize the search for genetic influences on psychopathology across the life course.

DRD2 and DRD4 in relation to regular alcohol and cannabis use among adolescents: does parenting modify the impact of genetic vulnerability? The TRAILS study

AIMS

The aims of the present study were to determine the direct effect of DRD2 and DRD4, as well as their interaction with parenting (i.e. rejection, overprotection and emotional warmth), on the development of regular alcohol and cannabis use in 1192 Dutch adolescents from the general population.

METHODS

Information was obtained by self-report questionnaires. Perceived rejection, overprotection and emotional warmth were assessed at age 10-12. Regular alcohol and cannabis use were determined at age 15-18 and defined as the consumption of alcohol on 10 or more occasions in the past four weeks, and the use of cannabis on 4 or more occasions in the past four weeks. Models were adjusted for age, sex, parental alcohol or cannabis use, and externalizing behavior.

RESULTS

Carrying the A1 allele of the DRD2 TaqIA polymorphism, or the 7 repeat DRD4, was not directly related to regular alcohol or cannabis use. In addition, adolescent carriers of these genetic risk markers were not more susceptible to the influence of less optimal parenting. Main effects for parenting indicated that overprotection increased the risk of regular alcohol use, whereas the risk of cannabis use was enhanced by parental rejection and buffered by emotional warmth.

CONCLUSIONS

Our findings do not support an association between DRD2/DRD4 and regular alcohol and cannabis use in adolescents. Given the substance-specific influences of rejection, overprotection and emotional warmth, these parenting factors might be promising candidates for prevention work.

Adolescent binge drinking alters adult brain neurotransmitter gene expression, behavior, brain regional volumes, and neurochemistry in mice

BACKGROUND

Binge drinking is common in human adolescents. The adolescent brain is undergoing structural maturation and has a unique sensitivity to alcohol neurotoxicity. Therefore, adolescent binge ethanol may have long-term effects on the adult brain that alter brain structure and behaviors that are relevant to alcohol-use disorders.

METHODS

To determine whether adolescent ethanol (AE) binge drinking alters the adult brain, male C57BL/6 mice were treated with either water or ethanol during adolescence (5 g/kg/d, i.g., postnatal days P28 to P37) and assessed during adulthood (P60 to P88). An array of neurotransmitter-specific genes, behavioral tests (i.e., reversal learning, prepulse inhibition, and open field), and postmortem brain structure using magnetic resonance imaging (MRI) and immunohistochemistry, were employed to assess persistent alterations in adult brain.

RESULTS

At P38, 24 hours after AE binge, many neurotransmitter genes, particularly cholinergic and dopaminergic, were reduced by ethanol treatment. Interestingly, dopamine receptor type 4 mRNA was reduced and confirmed using immunohistochemistry. Normal control maturation (P38 to P88) resulted in decreased neurotransmitter mRNA, e.g., an average decrease of 56%. Following AE treatment, adults showed greater gene expression reductions than controls, averaging 73%. Adult spatial learning assessed in the Morris water maze was not changed by AE treatment, but reversal learning experiments revealed deficits. Assessment of adult brain region volumes using MRI indicated that the olfactory bulb and basal forebrain were smaller in adults following AE. Immunohistochemical analyses found reduced basal forebrain area and fewer basal forebrain cholinergic neurons.

CONCLUSIONS

Adolescent binge ethanol treatment reduces adult neurotransmitter gene expression, particularly cholinergic genes, reduces basal forebrain and olfactory bulb volumes, and causes a reduction in the density of basal forebrain acetylcholine neurons. Loss of cholinergic neurons and forebrain structure could underlie adult reversal learning deficits following adolescent binge drinking.

MAOA-L carriers are better at making optimal financial decisions under risk

Genes can affect behaviour towards risks through at least two distinct neurocomputational mechanisms: they may affect the value assigned to different risky options, or they may affect the way in which the brain adjudicates between options based on their value. We combined methods from neuroeconomics and behavioural genetics to investigate the impact that the genes encoding for monoamine oxidase-A (MAOA), the serotonin transporter (5-HTT) and the dopamine D4 receptor (DRD4) have on these two computations. Consistent with previous literature, we found that carriers of the MAOA-L polymorphism were more likely to take financial risks. Our computational choice model, rooted in established decision theory, showed that MAOA-L carriers exhibited such behaviour because they are able to make better financial decisions under risk, and not because they are more impulsive. In contrast, we found no behavioural or computational differences among the 5-HTT and DRD4 polymorphisms.

Genetic and gene-environment interaction effects on preschoolers' social behaviors

This study examined effects from a specific dopamine receptor gene (DRD4), environmental influences from parents and peers, and the interaction between them, on aggressive and prosocial behaviors of preschoolers. Children were classified as DRD4-L (n = 27) if they had at least one DRD4 allele with six to eight repeats and as DRD4-S (n = 35) if not. Parent-child interactions were coded when children were 3-4 years old. Peer interaction data and parent questionnaires were collected at age 5. DRD4-L children shared less with each other and parents were less sensitive during parent-twin triadic interactions. Also, genotype interacted with peer aggression to affect children's aggression during a peer play interaction at age 5, and genotype interacted with prior parental sensitivity to affect later externalizing problems. Thus, children having a certain genetic disposition may be more sensitive to certain environmental stimuli and therefore more likely to exhibit aggressive behaviors under more stressful circumstances.

Constitutional mechanisms of vulnerability and resilience to nicotine dependence

The core nature of nicotine dependence is evident in wide variations in how individuals become and remain smokers. Individuals with pre-existing behavioral traits are more likely to develop nicotine dependence and experience difficulty when attempting to quit. Many molecular factors likely contribute to individual variations in the development of nicotine dependence and behavioral traits in complex manners. However, the identification of such molecules has been hampered by the phenotypic complexity of nicotine dependence and the complex ways molecules affect elements of nicotine dependence. We hypothesize that nicotine dependence is, in part, a result of interactions between nicotine and pre-existing behavioral traits. This perspective suggests that the identification of the molecular bases of such pre-existing behavioral traits will contribute to the development of effective methods for reducing smoking dependence and for helping smokers to quit.

Dopamine D4 receptor gene exon III polymorphism associated with binge drinking attitudinal phenotype

Although binge drinking is a serious public health problem, relatively few studies have investigated the relationship between specific dopaminergic genes such as the dopamine D4 receptor (DRD4) and binge drinking attitudinal phenotypes. This study used the DNA subsample (N=233, mean age 19.8, standard deviation,0.89) of the National Longitudinal Study of Adolescent Health to investigate the association between a 48 base-pair variable number of tandem repeats in the DRD4 gene and a measure of binge drinking. Multivariate regression models indicated that the 7-repeat (7R) allele of the exon III polymorphism is significantly positively associated (beta=0.16, P<.05) with binge drinking while controlling for low self-control and demographic variables. Findings were sturdy across race and gender. The present study provides unique evidence to the genetic underpinnings of binge drinking. Results suggest that the 7R allele may be an important contributor to the liability to binge drinking.

Infusing neuroscience into the study and prevention of drug misuse and co-occurring aggressive behavior

The etiology of behavioral precursors to substance misuse and aggression is viewed from the perspective of a developmental, multifactorial model of complex disorders. Beginning at conception, genetic and environmental interactions have potential to produce a sequence of behavioral phenotypes during development that bias the trajectory toward high-risk outcomes. One pathway is theorized to emanate from a deviation in neurological development that predisposes children to affective and cognitive delays or impairments that, in turn, generate dysregulatory behaviors. The plasticity of these neurobiological systems is highly relevant to the prevention sciences; their functions are reliant upon environmental inputs and can be altered, for better or for worse, contingent upon the nature of the inputs. Thus, social contextual factors confer significant influence on the development of this neural network and behavioral outcomes by increasing risk for, or protecting (1) against, dysregulatory outcomes. A well-designed intervention can exploit the brain's plasticity by targeting biological and social factors at sensitive time points to positively influence emergent neurobiological functions and related behaviors. Accordingly, prevention research is beginning to focus on perturbations in developmental neural plasticity during childhood that increase the likelihood of risky behaviors and may also moderate intervention effects on behavior. Given that the more complex features of neurobiological functions underlying drug misuse and aggression (e.g., executive cognitive function, coping skills, affect regulation) do not coalesce until early adulthood when prefrontal-limbic brain networks consolidate, it is critical that mechanisms underlying developmental risk factors are identified. An empirically driven prevention approach, thus, may benefit from consideration of (i) the type, effect, and developmental timing of the environmental impact on the brain, and (ii) the type and effect on brain function, and developmental timing of the intervention. This translational approach promises to eventually offer some direction for the design of effective interventions to prevent drug misuse and concomitant aggression.

Association Study of a Serotonin Receptor 2A Gene -1438A/G Polymorphism and Anxiety-Related Traits

OBJECTIVE

The aim of this study was to investigate the relationship between the -1438A/G polymorphism of serotonin receptor 2A (5HTR2A) and anxiety-related traits in Korean adolescent females.

METHODS

A total of 174 Korean adolescent females were tested for the -1438A/G polymorphism of 5HTR2A using polymerase chain reaction (PCR)-based methods. Anxiety-related traits were evaluated using the Anxiety Sensitivity Index (ASI) and the trait form of the Spielberg State-Trait Anxiety Inventory (T-STAI).

RESULTS

There was no difference between the genotypes with respect to scores pertaining to anxiety-related traits. Although the G allele carriers (GG or AG genotype) scored lower on the psychological subscale of the ASI (4.76+/-3.00 vs 5.98+/-4.00, p=0.038), this difference was not significant after Bonferroni correction.

CONCLUSION

These findings suggest that the -1438A/G polymorphism of 5HTR2A might not be associated with anxiety sensitivity or trait anxiety.

Bayesian surprise attracts human attention

We propose a formal Bayesian definition of surprise to capture subjective aspects of sensory information. Surprise measures how data affects an observer, in terms of differences between posterior and prior beliefs about the world. Only data observations which substantially affect the observer's beliefs yield surprise, irrespectively of how rare or informative in Shannon's sense these observations are. We test the framework by quantifying the extent to which humans may orient attention and gaze towards surprising events or items while watching television. To this end, we implement a simple computational model where a low-level, sensory form of surprise is computed by simple simulated early visual neurons. Bayesian surprise is a strong attractor of human attention, with 72% of all gaze shifts directed towards locations more surprising than the average, a figure rising to 84% when focusing the analysis onto regions simultaneously selected by all observers. The proposed theory of surprise is applicable across different spatio-temporal scales, modalities, and levels of abstraction.

Addiction science and its genetics

AIM

To assess the progress and impact of genetic studies in the addictions arena and to present this information in a form accessible to the general readership of Addiction.

METHODS

Review of the evidence that genes are involved in addiction, approaches to their identification, current findings and the potential implications.

RESULTS

Family, twin and adoption studies provide strong evidence that addiction runs in families and that this is determined in part by genetic factors. Two main molecular genetic approaches, namely linkage and association, have been adopted to identify the specific genes involved. Both methods are fraught with problems. Linkage is limited by issues of sensitivity, and association by false positives. Perhaps the strongest finding in psychiatric genetics to date is the impressive effect that a single genetic variant, in the aldehyde dehydrogenase 2 gene, has on drinking behaviour and reducing the risk of developing alcohol dependence. Other findings are currently less robust; however, the implications of elucidating the genetic underpinning of addiction will be profound.

CONCLUSIONS

Addiction genetics is a developing science that has yet to prove its worth in the clinical setting.

Dimensions of impulsivity are associated with poor spatial working memory performance in monkeys

Impulsive behavior and novelty seeking are dimensions of temperament that are behavioral determinants of risk for attention deficit/hyperactivity disorder and its neurocognitive endophenotypes, and variation in the dopamine D4 receptor gene (DRD4) explains at least a portion of the variance in the traits. To further characterize the dimensional phenotype associated with impulsiveness, adolescent male monkeys were evaluated using ecologically valid tests of impulsive approach and aggression in response to social or nonsocial stimuli; subsequently, a delayed response task was implemented to assess spatial working memory performance. Subjects were selected into this study based on their response to the social challenge task or by DRD4 genotype, resulting in three groups: low-impulsivity/common DRD4 allele, high-impulsivity/common DRD4 allele, or rare DRD4 allele. All animals acquired the delayed response task and could perform at near ceiling levels when a approximately 0 s delay version was imposed, but as delays were lengthened, high-impulsive animals, regardless of DRD4 genotype, made fewer correct responses than did low-impulsive subjects; an inverse relationship existed for working memory and impulsivity. Notably, impulsive behavior evoked by social and nonsocial stimuli explained overlapping and independent portions of the variance in working memory performance. CSF levels of monoamine metabolites did not significantly differentiate the high- and low-impulsive animals, although monkeys carrying the DRD4 rare allele tended to exhibit higher monoamine turnover. These data indicate that dimensions of impulsivity may impact on working memory performance in qualitatively similar ways but through different mechanisms.

Alcohol use, expectancies, and sexual sensation seeking as correlates of HIV risk behavior in heterosexual young adults

Most theoretical models of HIV risk behavior have not considered the role of personality factors, and few studies have examined mechanisms accounting for dispositional influences on sexual risk taking. This study elaborated on a conceptual model emphasizing sexual sensation seeking, alcohol expectancies, and drinking before sex as key predictors of HIV risk (S. C. Kalichman, L. Tannenbaum, & D. Nachimson, 1998). Multiple groups structural equation modeling was used to determine whether gender moderated relationships among these variables in a sample of 611 heterosexual, young adult drinkers (49% women, 76% Caucasian, mean age = 25 years). The model provided an excellent fit to the data, and gender differences were not substantiated. Sexual sensation seeking predicted HIV risk directly as well as indirectly via sex-related alcohol expectancies and drinking in sexual contexts. Findings suggest that expectancies and drinking before sex represent proximal mechanisms through which dispositional factors influence sexual risk outcomes. Moreover, these relationships appear to be similar in men and women. Interventions could benefit from targeting alcohol expectancies and drinking before sex in individuals with a dispositional tendency toward sexual risk taking.

The association of DRD4 and novelty seeking is found in a nonhuman primate model

OBJECTIVE

The association of novelty seeking with a repeat polymorphism in the coding region of the dopamine D4 receptor gene (DRD4) has been demonstrated in several human populations, but not in others. The objective of this study was to test the generality of the association in a captive nonhuman primate population of known history, using objective methods for assessing novelty seeking and a pedigree-based association design.

METHODS

Four hundred and fifty two socially-living vervet monkeys (Cercopithecus aethiops) from a large multigenerational pedigree at the UCLA-VA Vervet Research Colony were studied. Two variants in the 48 base pair repeat in exon III of the DRD4 gene have been found in this population, a six-repeat (92%) and a less common five-repeat (8%). Novelty seeking was measured by the latency to approach a large and potentially threatening novel object placed in the home enclosure. Heritability of novelty seeking and the association of novelty seeking with the DRD4 polymorphism were assessed using variance component modeling as implemented in Sequential Oligogenic Linkage Analysis Routines.

RESULTS

The variance component analysis indicated that the DRD4 variant explained a significant portion of the total variance in novelty seeking. The final model included a significant effect of the DRD4 polymorphism (P=0.03), which explained 13% of the phenotypic variance, and a significant remaining genetic effect (h=0. 467+/-0.095, P<0.0001).

CONCLUSIONS

The association of DRD4 with novelty seeking has now been replicated in a nonhuman primate species, the vervet monkey.

Association between equine temperament and polymorphisms in dopamine D4 receptor gene

The variable number of tandem repeats (VNTR) polymorphism of the dopamine D4 receptor (DRD4) gene has been reported to be associated with the personality trait of novelty-seeking in humans. In the genus Equus, this region includes an 18-bp repeat unit and there are inter- and intraspecies differences in the number of repetitions. Because horses are unique among livestock species in that their temperament is considered important, we investigated the possible role of this region on equine temperament in thoroughbred horses. We simultaneously determined the sequences of this polymorphic region and administered a questionnaire survey to horse caretakers with questions about 20 different traits of their horses' temperament. Although there was no difference in the number of repeats among the 136 thoroughbred horses studied, two single nucleotide polymorphisms (SNPs), one of which might cause an amino acid change (A-G substitution), existed. By analyzing the association between these SNPs and temperament scores, a significant association was revealed between two temperament traits (Curiosity and Vigilance) and the A-G substitution. Horses without the A allele had significantly higher Curiosity and lower Vigilance scores than those with the A allele at the A-G substitution. In addition, similar associations between both temperament scores and each genotype of the A-G substitution were observed in two subgroups divided according to the time of their introduction to the farm. These results suggested that the SNP in the VNTR region of the equine DRD4 gene might be related to individual differences in equine temperament.

Genetic influences on impulsivity, risk taking, stress responsivity and vulnerability to drug abuse and addiction

Genetic variation may partially underlie complex personality and physiological traits--such as impulsivity, risk taking and stress responsivity--as well as a substantial proportion of vulnerability to addictive diseases. Furthermore, personality and physiological traits themselves may differentially affect the various stages of addiction, defined chronologically as initiation of drug use, regular drug use, addiction/dependence and potentially relapse. Here we focus on recent approaches to the study of genetic variation in these personality and physiological traits, and their influence on and interaction with addictive diseases.

[35S]GTPgammaS binding at the human dopamine D4 receptor variants hD4.2, hD4.4 and hD4.7 following stimulation by dopamine, epinephrine and norepinephrine

Aim of the present study was to investigate possible differences between the human dopamine D4 receptor 48 bp polymorphism variants hD4.2, hD.4. and hD4.7 in agonist stimulated [35S]GTPgammaS binding, to investigate dopamine D4 receptor sodium sensitivity and to further characterize norepinephrine and epinephrine agonism at this receptor. G-protein activation at the receptor variants hD4.2, hD4.4 and hD4.7 expressed in CHO-K1 cells, following stimulation by dopamine, norepinephrine and epinephrine, was investigated using the [35S]GTPgammaS assay at experimental conditions of 10 and 100 mM sodium, respectively. Dopamine displayed a 2 fold higher potency of stimulating [35S]GTPgammaS binding at the hD4.2, compared to the hD4.4 and hD4.7 at 10 mM sodium. A significant difference in sodium sensitivity of basal [35S]GTPgammaS binding was found, with the hD4.7 being 1.7 fold more sensitive than the hD4.4 and 2.5 fold more sensitive than the hD4.2. Norepinephrine and epinephrine both produced concentration-dependent increases in [35S]GTPgammaS binding at all three receptor variants, and epinephrine showed only 2 fold less potency than dopamine. The present results are in certain line with previous reports of functional 2-3 fold differences between the dopamine D4 receptor variants. Agonism of norepinephrine and epinephrine at the dopamine D4 receptor may indicate an important way of cross-reactivity among the different monoamine neurotransmitter systems.

Increased brain dopamine D4-like binding after chronic ethanol is not associated with behavioral sensitization in mice

Dopaminergic D4 receptors have been hypothesized to be involved in neuropsychiatric disorders and substance abuse. In mice, repeated ethanol administration may induce behavioral sensitization, a phenomenon of increased sensitivity to the drug's stimulant properties. This study aimed to analyze brain D4 receptors binding in mice with different levels of behavioral sensitization to ethanol. Male Swiss mice received 2.2 g/kg ethanol (n = 64) or saline (n = 16) intraperitoneally daily for 21 days and were weekly tested for locomotor activity and for blood ethanol levels. According to the locomotor scores presented across test days, ethanol-treated mice were classified as "sensitized" or "nonsensitized." Twenty-four hours after the last administration, mice were sacrificed and brains were processed for autoradiography. Brain D4 binding was assessed by quantitative autoradiography using [3H]nemonapride + raclopride in three groups: saline-treated controls (n = 10), ethanol-sensitized (n = 11), and ethanol-nonsensitized (n = 9) mice. Both sensitized and nonsensitized mice showed higher D4 binding densities than saline-treated controls in the posterior caudate-putamen and the olfactory tubercle (p < .02), but only sensitized mice presented higher D4 binding than controls at the lateral septal nucleus (p < .02). However, there were no differences between sensitized and nonsensitized mice in any of the brain regions analyzed. Furthermore, sensitized and nonsensitized mice presented similar blood ethanol levels during the treatment. The higher D4 binding levels observed in both ethanol-treated subgroups (sensitized and nonsensitized) suggest that chronic ethanol treatment may induce upregulation of D4 receptors in specific brain regions. However, this mechanism does not seem to be associated with the differential ability to develop behavioral sensitization to ethanol in mice.

Cloninger's temperament dimensions and epidermal growth factor A61G polymorphism in Finnish adults

This study examines a link between human temperament and epidermal growth factor (EGF). There is evidence that dopaminergic neurotransmission in the central nervous system has a role in temperament, especially in novelty seeking. Functional polymorphism in EGF gene has an impact on EGF production, and EGF, in turn, appears to affect the development of midbrain dopaminergic neurons. Epidermal growth factor gene A61G polymorphisms were studied in a randomly selected sample of 292 Finnish adults. Their temperaments were assessed twice (with a 4-year test-retest interval) with Cloninger's Temperament and Character Inventory consisting of four dimensions, i.e. novelty seeking (NS), harm avoidance (HA), reward dependence (RD) and persistence (P). The findings on men showed a significant association between a presence of the G/G polymorphism and scoring in the highest tertile on NS in both test and retest. The same was true with men who scored high on RD, especially on sensitivity, in both tests. Among women, G/G polymorphism was associated with a stable high level of P. Importantly, temperament dimensions, as assessed with one test only, did not provide replicable associations with EGF polymorphism across the two measurements. Our results demonstrate the importance of reliable phenotype assessment and lend support to the hypothesis that dopaminergic activity is one factor underlying stable temperament.

Differential effects of DRD4 and DAT1 genotype on fronto-striatal gray matter volumes in a sample of subjects with attention deficit hyperactivity disorder, their unaffected siblings, and controls

Genetic influences on behavior are complex and, as such, the effect of any single gene is likely to be modest. Neuroimaging measures may serve as a biological intermediate phenotype to investigate the effect of genes on human behavior. In particular, it is possible to constrain investigations by prior knowledge of gene characteristics and by including samples of subjects where the distribution of phenotypic variance is both wide and under heritable influences. Here, we use this approach to show a dissociation between the effects of two dopamine genes that are differentially expressed in the brain. We show that the DAT1 gene, a gene expressed predominantly in the basal ganglia, preferentially influences caudate volume, whereas the DRD4 gene, a gene expressed predominantly in the prefrontal cortex, preferentially influences prefrontal gray matter volume in a sample of subjects including subjects with ADHD, their unaffected siblings, and healthy controls. This demonstrates that, by constraining our investigations by prior knowledge of gene expression, including samples in which the distribution of phenotypic variance is wide and under heritable influences, and by using intermediate phenotypes, such as neuroimaging, we may begin to map out the pathways by which genes influence behavior.