Effects of dopamine D2 receptor (DRD2) and transporter (SLC6A3) polymorphisms on smoking cue-induced cigarette craving among African-American smokers

The association of genetic polymorphisms within the dopaminergic system with nicotine dependence: A narrative review

Nicotine, the main compound in cigarettes, leads to smoking addiction. Nicotine acts on the limbic dopamine reward loop in the midbrain by binding to nicotinic acetylcholine receptors, promoting the release of dopamine, and resulting in a rewarding effect or satisfaction. This satisfaction is essential for continued and compulsive tobacco use, and therefore dopamine plays a crucial role in nicotine dependence. Numerous studies have identified genetic polymorphisms of dopaminergic pathways which may influence susceptibility to nicotine addiction. Dopamine levels are greatly influenced by synthesis, storage, release, degradation, and reuptake-related genes, including genes encoding tyrosine hydroxylase, dopamine decarboxylase, dopamine transporter, dopamine receptor, dopamine 3-hydroxylase, catechol-O-methyltransferase, and monoamine oxidase. In this paper, we review research progress on the effects of polymorphisms in the above genes on downstream smoking behavior and nicotine dependence, to offer a theoretical basis for the elucidation of the genetic mechanism underlying nicotine dependence and future personalized treatment for smoking cessation.

Attitudes about Cigarette Smoking, Perceived Consequences of Smoking, and Seeking Assistance with Cessation among Black and White Cigarette Smokers: A Qualitative Study

Introduction

Research has identified significant racial differences in cigarette smoking behavior, associated disease risk, likelihood of cessation, and mortality from smoking-related diseases. The current study assessed, via qualitative narrative analysis, racial differences in participants' motivations for smoking, perceived consequences of smoking, and how participants deal with cravings/withdrawal, as well as thoughts and feelings about quitting, seeking assistance with quitting, and the importance of social support in quitting.

Methods

Semistructured interviews were conducted with 11 Black and 11 White cigarette smokers. Data were analyzed using the Thematic Networks Analysis process, which entailed coding the data and constructing thematic networks by identifying basic and organizing themes.

Results

While there were no descriptive racial differences identified in participants' motivation for smoking or perceived consequences of smoking, differences existed between Blacks and Whites in terms of approaches in dealing with smoking cravings and withdrawal, perceived self-efficacy in controlling cravings, preferred methods of learning about and receiving smoking cessation assistance, and overall preference for receiving cessation-related support.

Conclusions

Further investigation is needed into racial differences in methods to deal with cigarette cravings and withdrawal, preferences for receiving cessation information, and social support for cessation. This research will further develop our understanding of and ability to address factors underlying racial disparities in smoking behavior and cessation, as well as inform the development of future smoking cessation interventions.

Translational Research in Nicotine Addiction

While commendable strides have been made in reducing smoking initiation and improving smoking cessation rates, current available smoking cessation treatment options are still only mildly efficacious and show substantial interindividual variability in their therapeutic responses. Therefore, the primary goal of preclinical research has been to further the understanding of the neural substrates and genetic influences involved in nicotine's effects and reassess potential drug targets. Pronounced advances have been made by investing in new translational approaches and placing more emphasis on bridging the gap between human and rodent models of dependence. Functional neuroimaging studies have identified key brain structures involved with nicotine-dependence phenotypes such as craving, impulsivity, withdrawal symptoms, and smoking cessation outcomes. Following up with these findings, rodent-modeling techniques have made it possible to dissect the neural circuits involved in these motivated behaviors and ascertain mechanisms underlying nicotine's interactive effects on brain structure and function. Likewise, translational studies investigating single-nucleotide polymorphisms (SNPs) within the cholinergic, dopaminergic, and opioid systems have found high levels of involvement of these neurotransmitter systems in regulating the reinforcing aspects of nicotine in both humans and mouse models. These findings and coordinated efforts between human and rodent studies pave the way for future work determining gene by drug interactions and tailoring treatment options to each individual smoker.

Exploring the role of the Ser9Gly (rs6280) Dopamine D3 receptor polymorphism in nicotine reinforcement and cue-elicited craving

Preclinical studies show that the dopamine D3 receptor (D3R) is involved in the reinstatement of drug seeking and motivation for drugs of abuse. A D3R gene variant, Ser9Gly (rs6280) has been linked to nicotine dependence, yet the mechanisms underlying its involvement in nicotine dependence is unclear. This study investigated the relationship between the Ser9Gly variant and measures of both nicotine reinforcement and cue-elicited craving. Phenotypes of smoking behaviors were assessed in genetically grouped (Glycine vs. No Glycine carriers) current smokers (n = 104, ≥ 10 cigarettes per day). Laboratory measures included a forced choice session (to measure reinforcement of nicotine containing vs. denicotinized cigarettes), and a cue-reactivity session (to measure smoking cues vs. neutral cues elicited craving). The forced choice procedure revealed that subjective ratings were significantly higher in response to nicotinized compared to denicotinized cigarettes; however the Ser9Gly variant did not influence this effect. By comparison, smoking cues elicited greater craving over time compared to neutral cues, and Glycine carriers of the Ser9Gly D3R variant seem to experience a significant blunted cue-elicited craving effect. Results support D3R involvement in nicotine cue reactivity. However, more research is needed to reveal how this gene variant modulates various aspects of nicotine dependence.

Direct and Indirect Effects of Psychological Distress on Stress-Induced Smoking

OBJECTIVE

Numerous studies have modeled the effects of stress in the laboratory, demonstrating that smokers who are exposed to experimental stressors exhibit significant increases in acute psychological distress. Whether these stress reactions are predictive of stress-induced smoking during an actual quit attempt, however, has not been examined. Furthermore, the possibility that such effects are particularly strong among smokers with higher ambient levels of distress has not been addressed.

METHOD

Nicotine-dependent smokers (N = 60; 40 women, 20 men) completed the Brief Symptoms Index (BSI) and then participated in a laboratory stress task 1 week before a quit attempt. Acute psychological distress was measured immediately before and after exposure to stressful and neutral stimuli. After they quit, participants completed a smoking diary for 14 days in which they recorded the degree to which their smoking was precipitated by emotional stress.

RESULTS

Consistent with our hypotheses, BSI scores predicted both exaggerated laboratory stress responses (p < .005) and smoking that was attributable to stress during the 14-day postquit period (p < .01). Laboratory stress reactions were predictive of stress-induced smoking (p < .01), and acute psychological stress reactions mediated the effects of BSI on stress-induced smoking.

CONCLUSIONS

Acute psychological stress reactivity is a potential mechanism underlying the effect of stress-induced smoking during a quit attempt.

Gender and Impulsivity: Effects on Cue-Induced Alcohol Craving

BACKGROUND

Numerous studies have demonstrated that trait impulsivity is linked to increased risk of developing alcohol-use disorders and other substance abuse. Impulsivity has also been shown in some studies to potentiate cue-induced drug cravings. Despite considerable evidence of gender differences in impulsivity and drug craving among individuals suffering from alcohol dependence and other drug use, little research has focused on these processes in healthy young men and women who may be at risk for developing alcohol-use disorders. The objective of this study was to investigate the relationship between impulsivity and cue-induced craving, as well as possible gender differences in these effects among healthy young adults.

METHODS

To that end, female (n = 22) and male (n = 14) social drinkers aged 18 to 25, recruited from an urban university campus, completed the Barratt Impulsiveness Scale and reported their alcohol cravings immediately before and after laboratory exposure to alcohol cues.

RESULTS

Findings indicated that exposure to cues elicited increased alcohol cravings, but these effects did not differ by gender. Interestingly, a significant interaction of impulsivity and gender revealed that impulsivity predicted significantly higher cue-induced cravings in women, but not men.

CONCLUSIONS

Findings underscore the importance of better understanding the interaction of situational factors (e.g., exposure to alcohol cues) and dispositional factors (e.g., impulsivity) as potential contributors to drinking motivation. Future prospective research is needed to identify gender-specific risk factors for the development of problem drinking.

Individual variation in incentive salience attribution and accumbens dopamine transporter expression and function

Cues (conditioned stimuli; CSs) associated with rewards can come to motivate behavior, but there is considerable individual variation in their ability to do so. For example, a lever-CS that predicts food reward becomes attractive and wanted, and elicits reward-seeking behavior, to a greater extent in some rats ('sign-trackers'; STs) than others ('goal-trackers'; GTs). Variation in dopamine (DA) neurotransmission in the nucleus accumbens (NAc) core is thought to contribute to such individual variation. Given that the DA transporter (DAT) exerts powerful regulation over DA signaling, we characterized the expression and function of the DAT in the accumbens of STs and GTs. STs showed greater DAT surface expression in ventral striatal synaptosomes than GTs, and ex vivo fast-scan cyclic voltammetry recordings of electrically evoked DA release confirmed enhanced DAT function in STs, as indicated by faster DA uptake, specifically in the NAc core. Consistent with this, systemic amphetamine (AMPH) produced greater inhibition of DA uptake in STs than in GTs. Furthermore, injection of AMPH directly into the NAc core enhanced lever-directed approach in STs, presumably by amplifying the incentive value of the CS, but had no effect on goal-tracking behavior. On the other hand, there were no differences between STs and GTs in electrically-evoked DA release in slices, or in total ventral striatal DA content. We conclude that greater DAT surface expression may facilitate the attribution of incentive salience to discrete reward cues. Investigating this variability in animal sub-populations may help explain why some people abuse drugs while others do not.

Sibling genes as environment: Sibling dopamine genotypes and adolescent health support frequency dependent selection

While research consistently suggests siblings matter for individual outcomes, it remains unclear why. At the same time, studies of genetic effects on health typically correlate variants of a gene with the average level of behavioral or health measures, ignoring more complicated genetic dynamics. Using National Longitudinal Study of Adolescent Health data, we investigate whether sibling genes moderate individual genetic expression. We compare twin variation in health-related absences and self-rated health by genetic differences at three locations related to dopamine regulation and transport to test sibship-level cross-person gene-gene interactions. Results suggest effects of variation at these genetic locations are moderated by sibling genes. Although the mechanism remains unclear, this evidence is consistent with frequency dependent selection and suggests much genetic research may violate the stable unit treatment value assumption.

Parental smoke exposure and the development of nicotine craving in adolescent novice smokers: the roles of DRD2, DRD4, and OPRM1 genotypes

BACKGROUND

Among adolescent novice smokers, craving is often the first, and is the most reported, symptom of nicotine dependence. Until now, little has been known about the development of craving symptoms in novice smokers. The aim of this study was to identify specific genetic (i.e., DRD2 Taq1A, DRD4 48 bp VNTR, and OPRM1 A118G polymorphisms) and environmental mechanisms that underlie the emergence of both cue-induced and cognitive craving among adolescent novice smokers.

METHOD

A five-wave longitudinal, genetically-informed survey study was conducted with intervals of four months. The sample included 376 early adolescent smokers (12-13 years of age at baseline). Self-report questionnaires were completed regarding smoking behavior, observed parental smoking behavior, and both cue-induced and cognitive craving.

RESULTS

Data were analyzed with a latent growth curve approach. For both cue-induced and cognitive craving, significant interaction effects were found for DRD2 Taq1A with parental smoke exposure. A1-allele carriers did not seem to be influenced by the environment with regard to craving development. Adolescents who are homozygous for the A2-allele and who are more exposed to parental smoking experience the highest levels of both types of craving over time. No significant interaction effects were found between parental smoke exposure and DRD4 48 bp VNTR or OPRM1 A118G.

CONCLUSIONS

Previous studies identified DRD2 Taq1A A1-allele carriers as vulnerable to developing nicotine dependence. However, this study showed that parental smoking increased the chances of developing dependence more rapidly for early adolescents who are considered to be less sensitive to the rewarding effects of nicotine according to their DRD2 Taq1A genotype. It is thus especially important that these young people not be exposed to smoking in their social environment.

Genetic influence of dopamine receptor, dopamine transporter, and nicotine metabolism on smoking cessation and nicotine dependence in a Japanese population

Background

This study investigated whether polymorphisms of the ankyrin repeat and kinase domain containing 1 gene (ANKK1), which is adjacent to the dopamine D2 receptor gene (DRD2), and the dopamine transporter (SLC6A3) and cytochrome P450 2A6 (CYP2A6) genes influence smoking cessation and nicotine dependence in a Japanese population. In 96 current and former smokers, genotyping frequencies for the ANKK1/DRD2 TaqIA, SLC6A3 VNTR, and CYP2A6 polymorphisms were subjected to chi-square analysis, and regression analyses were used to determine the association of the genotypes of current smokers with a Heavy Smoking Index, in addition to evaluating the effect of the subjects’ smoking history on the association.

Results

Genotyping results suggested that nicotine dependence among current smokers homozygous for the SLC6A3 10r allele was lower than that of smokers carrying the minor alleles, and that the CYP2A6 polymorphism might mediate this association. Furthermore, the age at which current smokers began smoking might moderate the association between their genetic polymorphisms and nicotine dependence.

Conclusions

This study provides preliminary findings on the influence of genetic variants on the smoking phenotypes in a Japanese population.

Reward dependence moderates smoking-cue- and stress-induced cigarette cravings

BACKGROUND

Cigarette cravings following exposure to smoking cues in a smoker's environment are thought to play an important role in cessation failure. The possibility that dispositional factors may impact cue-induced cravings, though intriguing, has received little attention. According to Cloninger's Tridimensional Personality Theory, factors such as reward dependence (RD), harm avoidance (HA), and novelty seeking (NS) may figure prominently in risk for addiction, as well as relapse, in individuals attempting to abstain from drug and alcohol use. Particularly interesting in this regard is the possibility that smokers with higher levels of RD, who are especially sensitive to reward signals, will have heightened craving reactions to smoking cues.

METHODS

To that end, non-treatment-seeking nicotine dependent smokers (n=96, mean age=41.1, 47% African American, 17% Caucasian, 22% Hispanic, 19.3cigs/day, FTND=7.5) underwent a classic experimental cue-induction, during which they were exposed to imagery of: (1) smoking, (2) neutral, and (3) stress cues, and reported their cigarette cravings (0-100) before and after each exposure. Participants also completed the Tridimensional Personality Questionnaire.

RESULTS

Not surprisingly, smoking and stress cues (but not neutral cues) elicited significant elevations in craving (p's<0.0001). Consistent with study hypothesis, smokers who scored higher on RD had stronger craving reactions to both smoking cues (p<.02) and stress cues (p<.03).

CONCLUSIONS

Findings raise the possibility that dispositional characteristics, in particular, reward dependence, influence smoking by potentiating reactions to environmental smoking cues. Furthermore, the similar effects of RD on stress-induced craving suggest that both cue-and stress-induced cravings may be influenced by a common underlying disposition.

The impact of nicotine lozenges and stimulus expectancies on cigarette craving

Reduced craving associated with nicotine replacement therapy use is frequently attributed to the effects of nicotine pharmacology, however non-pharmacological factors may also play a role. This study examined the impact of nicotine pharmacology and non-pharmacological components of an acute nicotine lozenge (4 mg) on cigarette craving, mood and heart rate in 70 daily smokers (36 male). Smoking-related stimuli were used to assess cue-induced craving. Participants were randomly assigned to one of four conditions in a balanced placebo design where half the participants were provided deceptive information regarding the nicotine content of a lozenge. Subjective ratings of craving and mood were collected and heart rate was assessed before and after neutral and smoking cues. Nicotine expectancy reduced withdrawal-related craving (p = 0.006) regardless of actual nicotine administration while combined nicotine expectancy and administration reduced intentions to smoke (p = 0.046) relative to each of the other conditions. Exposure to smoking-related stimuli increased cigarette craving (p ≤ 0.001) and negative affect (p ≤ 0.001) regardless of expectancy or pharmacology. Following the smoking cue, women reported a greater increase in withdrawal-related craving than men (p = 0.027). Findings suggest that both pharmacological and non-pharmacological components of nicotine lozenge administration contribute to its acute effects on craving, yet neither appears effective in preventing craving triggered by exposure to environmental smoking stimuli.

Gene x abstinence effects on drug cue reactivity in addiction: multimodal evidence

Functional polymorphisms in the dopamine transporter gene (DAT1 or SLC6A3) modulate responsiveness to salient stimuli, such that carriers of one 9R-allele of DAT1 (compared with homozygote carriers of the 10R-allele) show heightened reactivity to drug-related reinforcement in addiction. Here, using multimodal neuroimaging and behavioral dependent variables in 73 human cocaine-addicted individuals and 47 healthy controls, we hypothesized and found that cocaine-addicted carriers of a 9R-allele exhibited higher responses to drug cues, but only among individuals who had used cocaine within 72 h of the study as verified by positive cocaine urine screens (a state characterized by intense craving). Importantly, this responsiveness to drug cues was reliably preserved across multimodal imaging and behavioral probes: psychophysiological event-related potentials, self-report, simulated cocaine choice, and fMRI. Because drug cues contribute to relapse, our results identify the DAT1R 9R-allele as a vulnerability allele for relapse especially during early abstinence (e.g., detoxification).

Effects of non-invasive neurostimulation on craving: a meta-analysis

This meta-analysis was conducted to evaluate the available evidence regarding the effects of non-invasive neurostimulation of the dorsolateral prefrontal cortex (DLPFC), on craving in substance dependence and craving for high palatable food. Non-invasive neurostimulation techniques were restricted to repetitive Transcranial Magnetic Stimulation (rTMS) and transcranial Direct Current Stimulation (tDCS). A total of 17 eligible studies were identified. Random effects analysis revealed a pooled standardized effect size (Hedge's g) of 0.476 (CI: 0.316-0.636), indicating a medium effect size favouring active non-invasive neurostimulation over sham stimulation in the reduction of craving (z=5.832, p<0.001). No significant differences were found between rTMS and tDCS, between the various substances of abuse and between substances of abuse and food, or between left and right DLPFC stimulation. In conclusion, this meta-analysis provides the first clear evidence that non-invasive neurostimulation of the DLPFC decreases craving levels in substance dependence.

Cue-induced cigarette and food craving: a common effect?

Cue-induced cravings may hinder behavior change efforts such as smoking cessation. Correlation of cue-induced cravings across multiple stimuli would provide evidence for a cue-reactive phenotype that may have implications for behavior change therapies. The purpose of this study was to examine relationships between cue-induced cravings for cigarettes and cue-induced cravings for a highly preferred food (chocolate) in a sample of smokers not subjected to lengthy deprivation for either of these two appetitive outcomes. Adult smokers (N=164) were assessed for chocolate cravings before and after exposure to chocolate cues and cigarette cravings before and after exposure to smoking cues. Consistent with previous reports, cigarette cravings increased significantly post-cue exposure and chocolate cravings increased significantly post-cue exposure (p's<.0001). Consistent with study hypotheses, the magnitude of the increase in chocolate cravings after cue-exposure was significantly related to the increase in post-cue cigarette cravings (r=0.38; p<.0001), and was significantly related to scores on a retrospective, self-report, measure of cue-induced food cravings in daily life. These findings are consistent with the idea of a general "cue-reactive" phenotype that varies across individuals, a conceptualization of risk that may point the way toward improved interventions for a variety of hedonically mediated behaviors with negative health outcomes.

The CHRNA3 rs578776 Variant is Associated with an Intrinsic Reward Sensitivity Deficit in Smokers

A compromised brain reward system has been postulated as a key feature of drug dependence. We examined whether several polymorphisms of genes found to regulate nicotinic acetylcholine receptor (nAChR) and dopamine expression were related to an intrinsic reward sensitivity (IRS) deficit we previously identified among a subgroup of smokers using event-related potentials (ERPs). We examined genetic polymorphisms within the CHRNA5-A3-B4 gene cluster (CHRNA3 rs578776, CHRNA5 rs16969968, LOC123688 rs8034191, and CHRNA3 rs1051730), the ANKK1 gene (rs1800497), and the D2 dopamine receptor gene (DRD2 rs1079597, DRD2 rs1799732) from 104 smokers of European ancestry in a smoking cessation trial. Prior to treatment, we recorded ERPs evoked by emotional (both pleasant and unpleasant), neutral, and cigarette-related pictures. Smokers were assigned to two groups (IRS+/IRS-) based on the amplitude of the late positive potential (LPP) component to the pictures, a neural marker of motivational salience. Smokers (n = 42) with blunted brain responses to intrinsically rewarding (pleasant) pictures and enhanced responses to cigarette pictures were assigned to the IRS- group, while smokers (n = 62) with the opposite pattern of LPP responding were assigned to the IRS+ group. Carriers of the protective minor T allele (T/T, C/T) of the CHRNA3 rs578776 were less likely to be members of the IRS- group than those homozygous for the at-risk C allele (C/C). The CHRNA3 rs578776 polymorphism did not differ on questionnaires of nicotine dependence, depressed mood, or trait affective disposition and did not predict abstinence at 6 months after the quit date. These results suggest that polymorphisms of genes influencing nAChR expression are related to an endophenotype of reward sensitivity in smokers.

Mouse models for studying genetic influences on factors determining smoking cessation success in humans

Humans differ in their ability to quit using addictive substances, including nicotine, the major psychoactive ingredient in tobacco. For tobacco smoking, a substantial body of evidence, largely derived from twin studies, indicates that approximately half of these individual differences in ability to quit are heritable genetic influences that likely overlap with those for other addictive substances. Both twin and molecular genetic studies support overlapping influences on nicotine addiction vulnerability and smoking cessation success, although there is little formal analysis of the twin data that support this important point. None of the current datasets provides clarity concerning which heritable factors might provide robust dimensions around which individuals differ in ability to quit smoking. One approach to this problem is to test mice with genetic variations in genes that contain human variants that alter quit success. This review considers which features of quit success should be included in a comprehensive approach to elucidate the genetics of quit success, and how those features may be modeled in mice.

Genetic predictors of cue- and stress-induced cigarette craving: an exploratory study

Cigarette cravings in response to environmental cues and stressors are widely recognized as important predictors of smoking cessation outcomes. Accumulating evidence suggests that genetics plays a role in these craving responses, as well as in smoking cessation more generally. Previous studies of genetic polymorphisms have been limited by examination of single candidate genes and the use of broadly defined phenotypes (e.g., smoking history). In addition, research examining the similarities and differences between cue- and stress-induced cravings has been limited, although some evidence has suggested that they may have common genetic underpinnings. In the current study, we examined associations between a panel of 1,350 candidate genetic polymorphisms and craving responses to laboratory smoking cues and stressors. We hypothesized that common genetic polymorphisms would be predictive of both cue- and stress-induced craving. Nicotine-dependent smokers (n = 210) donated a blood sample, were exposed to neutral, smoking-related, and stress-related stimuli, and completed craving questionnaires immediately prior to and following each stimulus. Findings indicated that craving responses to smoking cues and stressors were moderately correlated (r = .44). However, genetic analysis revealed that cue and stress-induced cigarette craving were predicted by different polymorphisms, such that variants in the glycine and dopamine pathways were predictive of cue-induced craving, whereas variants in the stress-corticotropin pathway predicted stress-induced craving.

CONCLUSIONS

Study results provide no support for the hypothesis that cue- and stress-induced craving have the same genetic predictors.

Cue-induced cigarette cravings and smoking cessation: the role of expectancies

INTRODUCTION

Cue-induced cigarette cravings have been oft studied as potentially important predictors of smoking cessation outcomes. The literature on the relationship between cue-induced cravings and cessation, however, remains mixed. One possible explanation for the discrepant results in the literature may be the as-yet untested variability in expectancies of craving. Indeed, as with many interoceptive responses, cravings and their downstream consequences may be influenced by expectancies. To date, no study has examined the influence of expected cravings following smoking cue exposures on actual craving experiences and cessation outcomes. The objective of this study, therefore, was to test the possibility that smokers' expected craving levels in response to smoking cues would be related to actual cravings following cue exposure and that expected cravings would be related to cessation outcomes.

METHODS

Nicotine-dependent adult smokers (n = 153) were exposed to sets of neutral and smoking cues and completed questionnaires assessing (a) prior to the exposures, the cigarette craving levels they expected to experience following the cue exposures and (b) following the exposures, their actual craving levels. Participants also reported the duration of their most recent quit attempt and their perceived future quit difficulty.

RESULTS

Findings indicated that expected cravings assessed prior to the cue exposures were significantly related to actual cravings following the exposures. In addition, both expected cravings and actual cravings were related to shorter previous quit duration and higher perceived quit difficulty.

CONCLUSIONS

Study results highlight the importance of considering both expected and actual cravings in cue-induced craving paradigms.

Exposure to smoking cues: cardiovascular and autonomic effects

Laboratory exposures to smoking cues have been shown to reliably induce self-reported cigarette cravings among smokers, a model of environmentally triggered urges to smoke that can contribute to poorer cessation success. Several studies have also demonstrated that cue exposures give rise to changes in heart rate and blood pressure. Few studies, however, have investigated possible cue effects on heart rate and blood pressure variability (HRV and BPV). Particularly intriguing in this regard are cardiac oscillations in the low (i.e., 0.04-0.15 Hz), and high (i.e., 0.15-0.50 Hz) frequency range, which are thought to reflect components of autonomic control and response to environmental challenges. A closer examination of cardiovascular reactivity may thus help characterize the autonomic response to smoking cue exposure. To that end, an experimental study was conducted in which nicotine dependent daily smokers (n=98) were exposed to guided imagery of neutral and smoking situations, while continuous, noninvasive, beat-to-beat cardiovascular data were collected. Consistent with previous research, the findings revealed significant increases in both systolic and diastolic blood pressure during smoking imagery, relative to neutral imagery. In addition, power spectral density analyses of heart rate and blood pressure variability revealed elevated HRV and BPV in both the low- and high-frequency ranges during the smoking imagery. The results suggest the presence of an autonomic component to smoking cue reactivity, and also raise the possibility of long-term negative cardiac consequences for smokers who ubiquitously encounter cues in their daily environments.

Dopamine-based reward circuitry responsivity, genetics, and overeating

Data suggest that low levels of dopamine D2 receptors and attenuated responsivity of dopamine-target regions to food intake is associated with increased eating and elevated weight. There is also growing (although mixed) evidence that genotypes that appear to lead to reduced dopamine signaling (e.g., DRD2, DRD4, and DAT) and certain appetite-related hormones and peptides (e.g., ghrelin, orexin A, leptin) moderate the relation between dopamine signaling, overeating, and obesity. This chapter reviews findings from studies that have investigated the relation between dopamine functioning and food intake and how certain genotypes and appetite-related hormones and peptides affect this relation.

Effects of dopamine antagonists on drug cue-induced reinstatement of nicotine-seeking behavior in rats

Dopaminergic neurotransmission has been implicated in associative learning processes related to drugs of abuse. However, it is not clear whether blockade of activation of dopamine receptors alters conditioned incentive properties of nicotine-associated cues. Using a response-reinstatement procedure, this study examined the effects of antagonists selective for the D1 and the D2 subtypes of dopamine receptors on cue-induced reinstatement of nicotine-seeking behavior. Male Sprague-Dawley rats were trained in 30 daily 1 h sessions to intravenously self-administer nicotine (0.03 mg/kg/infusion) on a fixed ratio 5 schedule and associate a conditioned stimulus (cue) with each nicotine delivery. After extinction of responding by withholding nicotine (saline substitution) and its cue, the reinstatement tests were conducted following subcutaneous administration of a D1 antagonist SCH23390 (0, 5, 10, 30 microg/kg) or a D2 antagonist eticlopride (0, 5, 10, 30 microg/kg) in different groups of animals. Both SCH23390 and eticlopride significantly attenuated the magnitude of cue-elicited reinstatement of nicotine-seeking responding. These results indicate that activation of dopaminergic D1 and D2 receptors may play a role in mediating the conditioned motivational effects of nicotine-associated cues as measured in the response-reinstatement procedure. These findings suggest that manipulation of dopaminergic neurotransmission at D1 and/or D2 receptors may prove to be a potential target for the development of pharmacotherapy for prevention of environmental nicotine cue-triggered smoking relapse.

Parent-child concordance of Taq1 A1 allele predicts similarity of parent-child weight loss in behavioral family-based treatment programs

Family-based treatments show positive relationships between parent and child weight losses. One mechanism for similar parent-child changes may be a common genetic predisposition to respond similarly to a structured weight loss program. We examined whether concordance of the Taq1 A1 allele of the dopamine D2 receptor (DRD2) predicts similarities in zBMI change in 26 families with obese parents and overweight/obese 8-12-year-old children. Results showed a relationship between parent and child zBMI change over 6 and 12 months (rs=.69, .77, ps<0.001), and concordance for the number of Taq1 A1 alleles predicted the similarity in parent and child weight loss at 6 (p=0.003) and 12 (p=0.025) months. These results show concordance of the Taq1 A1 allele of the DRD2 between parents and children may be one mechanism for the similar response to family-based treatments within families.

Epidemiology, determinants, and consequences of cigarette smoking in African American women: an integrative review

Tobacco smoking is a national public health problem that has been associated with numerous adverse health effects, including increased disease and cancer rates. Previous review articles on smoking in specific demographic populations have focused on smoking in women and on smoking in African Americans, but have not considered the dual roles of ethnicity and gender in smoking behavior. African American women (AAW) are an important subgroup to study because they are distinct from non-AAW and their male African American counterparts on biopsychosocial factors that are relevant to smoking behavior. The purpose of the present review paper is to integrate and summarize the current literature on the epidemiology, determinants, and consequences of cigarette smoking among AAW, by contrasting them to relevant comparison groups (non-AAW and African American men). Evidence suggests that AAW are generally more likely to be light smokers and initiate smoking later. The prevalence rates of AAW smokers have decreased over the past 25years, yet AAW are disproportionately affected by several smoking-related illnesses when compared to their ethnic and gender comparison groups. AAW smokers are distinct from relevant comparison groups in metabolic sensitivity to nicotine, aspects of smoking topography, and several psychosocial factors that influence smoking. Although a small literature on smoking in AAW is emerging, further empirical research of AAW smokers could inform the development of tailored interventions for AAW.

Pharmacogenetics of drug dependence: role of gene variations in susceptibility and treatment

Drug dependency is a highly prevalent mental health disorder that imposes a significant burden on those directly affected, health care systems, and society in general. There is substantial heritability in the susceptibility to drug addiction, which indicates that there are genetic risk factors. Variation in the human genome is abundant and can directly affect drug dependency phenotypes, for example, by altering the function of a gene product or by altering gene expression. Pharmacogenetic studies can assess the effects of genetic variation on the risk for a particular phenotype (e.g., being an alcoholic). In addition, pharmacogenetic variability in treatment efficacy and adverse reactions can be investigated to identify particular genetic variants associated with altered responses. This review highlights examples of genetic variations that are important in the development and maintenance of specific drug dependencies as well as those that affect the response to treatment.

Real-time craving differences between black and white smokers

Black and White smokers may experience aspects of nicotine dependence, including craving, differently. This study used a naturalistic technique, ecological momentary assessment (EMA), to explore differences in craving, mood, expectancy, and smoking enjoyment between Black and White smokers. Participants carried personal digital assistants (PDAs) programmed to obtain multiple daily assessments. Black smokers reported higher craving after smoking and at random assessment times and higher cigarette enjoyment. No differences were found in mood or expectancy. Racial differences in psychological factors related to smoking are explored in the contexts of genetic, sociological, and psychophysiological distinctions. Implications for practice and research are discussed. (Am J Addict 2010;00:1-5).

Chromosome 5p Region SNPs Are Associated with Risk of NSCLC among Women

In a population-based case-control study, we explored the associations between 42 polymorphisms in seven genes in this region and non-small cell lung cancer (NSCLC) risk among Caucasian (364 cases; 380 controls) and African American (95 cases; 103 controls) women. Two TERT region SNPs, rs2075786 and rs2853677, conferred an increased risk of developing NSCLC, especially among African American women, and TERT-rs2735940 was associated with a decreased risk of lung cancer among African Americans. Five of the 20 GHR polymorphisms and SEPP1-rs6413428 were associated with a marginally increased risk of NSCLC among Caucasians. Random forest analysis reinforced the importance of GHR among Caucasians and identified AMACR, TERT, and GHR among African Americans, which were also significant using gene-based risk scores. Smoking-SNP interactions were explored, and haplotypes in TERT and GHR associated with NSCLC risk were identified. The roles of TERT, GHR, AMACR and SEPP1 genes in lung carcinogenesis warrant further exploration.

Common and unique biological pathways associated with smoking initiation/progression, nicotine dependence, and smoking cessation

Twin and family studies reveal a significant genetic contribution to the risk of smoking initiation and progression (SI/P), nicotine dependence (ND), and smoking cessation (SC). Further, numerous genes have been implicated in these smoking-related behaviors, especially for ND. However, no study has presented a comprehensive and systematic view of the genetic factors associated with these important smoking-related phenotypes. By reviewing the literature on these behaviors, we identified 16, 99, and 75 genes that have been associated with SI/P, ND, and SC, respectively. We then determined whether these genes were enriched in pathways important in the neuronal and brain functions underlying addiction. We identified 9, 21, and 13 pathways enriched in the genes associated with SI/P, ND, and SC, respectively. Among these pathways, four were common to all of the three phenotypes, that is, calcium signaling, cAMP-mediated signaling, dopamine receptor signaling, and G-protein-coupled receptor signaling. Further, we found that serotonin receptor signaling and tryptophan metabolism pathways were shared by SI/P and ND, tight junction signaling pathway was shared by SI/P and SC, and gap junction, neurotrophin/TRK signaling, synaptic long-term potentiation, and tyrosine metabolism were shared between ND and SC. Together, these findings show significant genetic overlap among these three related phenotypes. Although identification of susceptibility genes for smoking-related behaviors is still in an early stage, the approach used in this study has the potential to overcome the hurdles caused by factors such as genetic heterogeneity and small sample size, and thus should yield greater insights into the genetic mechanisms underlying these complex phenotypes.

Modeling complex genetic and environmental influences on comorbid bipolar disorder with tobacco use disorder

Background

Comorbidity of psychiatric and substance use disorders represents a significant complication in the clinical course of both disorders. Bipolar Disorder (BD) is a psychiatric disorder characterized by severe mood swings, ranging from mania to depression, and up to a 70% rate of comorbid Tobacco Use Disorder (TUD). We found epidemiological evidence consistent with a common underlying etiology for BD and TUD, as well as evidence of both genetic and environmental influences on BD and TUD. Therefore, we hypothesized a common underlying genetic etiology, interacting with nicotine exposure, influencing susceptibility to both BD and TUD.

Methods

Using meta-analysis, we compared TUD rates for BD patients and the general population. We identified candidate genes showing statistically significant, replicated, evidence of association with both BD and TUD. We assessed commonality among these candidate genes and hypothesized broader, multi-gene network influences on the comorbidity. Using Fisher Exact tests we tested our hypothesized genetic networks for association with the comorbidity, then compared the inferences drawn with those derived from the commonality assessment. Finally, we prioritized candidate SNPs for validation.

Results

We estimate risk for TUD among BD patients at 2.4 times that of the general population. We found three candidate genes associated with both BD and TUD (COMT, SLC6A3, and SLC6A4) and commonality analysis suggests that these genes interact in predisposing psychiatric and substance use disorders. We identified a 69 gene network that influences neurotransmitter signaling and shows significant over-representation of genes associated with BD and TUD, as well as genes differentially expressed with exposure to tobacco smoke. Twenty four of these genes are known drug targets.

Conclusions

This work highlights novel bioinformatics resources and demonstrates the effectiveness of using an integrated bioinformatics approach to improve our understanding of complex disease etiology. We illustrate the development and testing of hypotheses for a comorbidity predisposed by both genetic and environmental influences. Consistent with our hypothesis, the selected network models multiple interacting genetic influences on comorbid BD with TUD, as well as the environmental influence of nicotine. This network nominates candidate genes for validation and drug testing, and we offer a panel of SNPs prioritized for follow-up.

A review of smoking behavior and smokers evidence (chemical modification, inducing nicotine metabolism, and individual variations by genotype: dopaminergic function and personality traits)

The nicotine metabolism of CYP2A6 (CYP2A6*1A,*1B, and *1C), and the cholecystokinin (CCK; which modulates the release of dopamine) and CCK-A receptor gene and personality traits for NEO-FFI, was investigated for the mechanism for elucidation of the smoking behavior in Japanese populations. The frequency of the CYP2A6*4C allele, which is a whole deleted allele of the human CYP2A6 gene, was higher, whereas that of CYP2A6*1A/*1B heterozygotes with higher nicotine metabolism activity was lower in nonsmokers than in smokers. There was also a significant difference between the current smoking and nonsmoking groups in the allele frequency of the CCK -45C/T polymorphism. It was also shown that the Openness (O) factor for smokers was significantly higher than that of nonsmokers; however, there were no significant differences in the Neuroticism (N), Extraversion (E), Agreeable (A), and Conscientiousness (C) scores among smokers than nonsmokers. It was suggested that the CYP2A6*4C allele may prevent the carrier from smoking, and being a CYP2A6*1A/*1B heterozygote and the CCK T allele may be risk factors for developing smoking behavior. Also, it is possible that persons with a low score in Openness may be refraining from smoking because they have a general negative impression toward smoking.

Dopamine genes and nicotine dependence in treatment-seeking and community smokers

We utilized a cohort of 828 treatment-seeking self-identified white cigarette smokers (50% female) to rank candidate gene single nucleotide polymorphisms (SNPs) associated with the Fagerström Test for Nicotine Dependence (FTND), a measure of nicotine dependence which assesses quantity of cigarettes smoked and time- and place-dependent characteristics of the respondent's smoking behavior. A total of 1123 SNPs at 55 autosomal candidate genes, nicotinic acetylcholine receptors and genes involved in dopaminergic function, were tested for association to baseline FTND scores adjusted for age, depression, education, sex, and study site. SNP P-values were adjusted for the number of transmission models, the number of SNPs tested per candidate gene, and their intragenic correlation. DRD2, SLC6A3, and NR4A2 SNPs with adjusted P-values <0.10 were considered sufficiently noteworthy to justify further genetic, bioinformatic, and literature analyses. Each independent signal among the top-ranked SNPs accounted for approximately 1% of the FTND variance in this sample. The DRD2 SNP appears to represent a novel association with nicotine dependence. The SLC6A3 SNPs have previously been shown to be associated with SLC6A3 transcription or dopamine transporter density in vitro, in vivo, and ex vivo. Analysis of SLC6A3 and NR4A2 SNPs identified a statistically significant gene-gene interaction (P=0.001), consistent with in vitro evidence that the NR4A2 protein product (NURR1) regulates SLC6A3 transcription. A community cohort of N=175 multiplex ever-smoking pedigrees (N=423 ever smokers) provided nominal evidence for association with the FTND at these top ranked SNPs, uncorrected for multiple comparisons.

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.

Script-guided imagery of social drinking induces both alcohol and cigarette craving in a sample of nicotine-dependent smokers

Laboratory exposure to alcoholic beverage cues has been demonstrated to elicit urges to drink. Less well examined is the possibility that imaginal cues also elicit such urges, providing a model of conditioned effects not dependent on the presence of physical stimuli associated with alcohol. Studies of possible cross-reactivity between smoking and drinking cues are also scarce. To that end, nicotine-dependent nonalcoholic smokers (n=54) were exposed to social drinking-relevant, and for comparison, neutral and smoking-relevant standardized script-guided imagery. Cravings were measured before and after each imaginal exposure. As hypothesized, the drinking script induced alcohol and cigarette cravings, providing support for both direct and cross-cue reactivity effects. Further validating the social-drinking script, craving reactions were significantly stronger among participants who reported frequent drinking in social situations. Finally, smoking imagery induced both cigarette and alcohol cravings, providing further support for the cross-cue-induced craving phenomenon. Results suggest that the present alcohol script may be a useful tool for eliciting craving responses under laboratory conditions, and provide an additional means for better understanding addiction.

DAT genotype modulates brain and behavioral responses elicited by cigarette cues

We previously demonstrated differential activation of the mesocorticolimbic reward circuitry in response to cigarette cues independent of withdrawal. Despite robust effects, we noted considerable individual variability in brain and subjective responses. As dopamine (DA) is critical for reward and its predictive signals, genetically driven variation in DA transmission may account for the observed differences. Evidence suggests that a variable number of tandem repeats (VNTRs) polymorphism in the DA transporter (DAT) SLC6A3 gene may influence DA transport. Brain and behavioral responses may be enhanced in probands carrying the 9-repeat allele. To test this hypothesis, perfusion fMR images were acquired during cue exposure in 19 smokers genotyped for the 40 bp VNTR polymorphism in the SLC6A3 gene. Contrasts between groups revealed that 9-repeat (9-repeats) had a greater response to smoking (vs nonsmoking) cues than smokers homozygous for the 10-repeat allele (10/10-repeats) bilaterally in the interconnected ventral striatal/pallidal/orbitofrontal cortex regions (VS/VP/OFC). Activity was increased in 9-repeats and decreased in 10/10-repeats in the VS/VP/OFC (p<0.001 for all analyses). Brain activity and craving was strongly correlated in 10/10-repeats in these regions and others (anterior cingulate, parahippocampal gyrus, and insula; r(2)=0.79-0.86, p<0.001 in all regions). Alternatively, there were no significant correlations between brain and behavior in 9-repeats. There were no differences in cigarette dependence, demographics, or resting baseline neural activity between groups. These results provide evidence that genetic variation in the DAT gene contributes to the neural and behavioral responses elicited by smoking cues.

SLC6A3 and body mass index in the Prostate, Lung, Colorectal and Ovarian Cancer Screening Trial

Background

To investigate the contribution of the dopamine transporter to dopaminergic reward-related behaviors and anthropometry, we evaluated associations between polymorphisms at the dopamine transporter gene(SLC6A3) and body mass index (BMI), among participants in the Prostate, Lung, Colorectal and Ovarian (PLCO) Cancer Screening Trial.

Methods

Four polymorphisms (rs6350, rs6413429, rs6347 and the 3' variable number of tandem repeat (3' VNTR) polymorphism) at the SLC6A3 gene were genotyped in 2,364 participants selected from the screening arm of PLCO randomly within strata of sex, age and smoking history. Height and weight at ages 20 and 50 years and baseline were assessed by questionnaire. BMI was calculated and categorized as underweight, normal, overweight and obese (<18.5, 18.5–24.9, 25.0–29.9, or ≥ 30 kg/m², respectively). Odds ratios (ORs) and 95% confidence intervals (CIs) of SLC6A3 genotypes and haplotypes were computed using conditional logistic regression.

Results

Compared with individuals having a normal BMI, obese individuals at the time of the baseline study questionnaire were less likely to possess the 3' VNTR variant allele with 9 copies of the repeated sequence in a dose-dependent model (** is referent; OR_*9 = 0.80, OR₉₉ = 0.47, p_trend = 0.005). Compared with individuals having a normal BMI at age 50, overweight individuals (A-C-G-* is referent; OR_A-C-G-9 = 0.80, 95% CI 0.65–0.99, p = 0.04) and obese individuals (A-C-G-* is referent; OR_A-C-G-9 = 0.70, 95% CI 0.49–0.99, p = 0.04) were less likely to possess the haplotype with the 3'variant allele (A-C-G-9).

Conclusion

Our results support a role of genetic variation at the dopamine transporter gene, SLC6A3, as a modifier of BMI.

Association of the DRD2 gene Taq1A polymorphism and smoking behavior: a meta-analysis and new data

INTRODUCTION

Many studies have investigated the association of the dopamine type-2 receptor (DRD2) Taq1A polymorphism with tobacco use and cigarette smoking behaviors, but findings remain equivocal. There is a biological basis for considering that this association differs by sex, and differences in subpopulations might explain some of the contradictory evidence.

METHODS

Our a priori hypothesis was that the association of the DRD2 Taq1A polymorphism with smoking behavior would be more prominent in females than males. We therefore investigated the strength of evidence for an association between the DRD2 Taq1A polymorphism and smoking behavior in a large sample of females and used meta-analytic techniques to synthesize existing published data and explore the role of sex in explaining any heterogeneity between studies.

RESULTS

We did not observe any strong evidence of association between the DRD2 Taq1A polymorphism and smoking behavior, including smoking initiation, smoking persistence, and smoking rate, either in our female sample or in our meta-analysis of 29 studies, comprising 28 published studies and the data from the present study. Metaregression suggested an association between the proportion of male participants in a study and the individual study effect size, indicating a larger effect size with a greater proportion of male participants for smoking initiation and smoking persistence. This effect did not appear to be due to the inclusion of the data from the present study.

DISCUSSION

Available evidence does not support an association between the DRD2 Taq1A polymorphism and smoking behavior. Contrary to our a priori hypothesis, we found evidence of a stronger association in males than in females.

Gene-environment interactions across development: Exploring DRD2 genotype and prenatal smoking effects on self-regulation

Genetic factors dynamically interact with both pre- and postnatal environmental influences to shape development. Considerable attention has been devoted to gene-environment interactions (G x E) on important outcomes (A. Caspi & T. E. Moffitt, 2006). It is also important to consider the possibility that these G x E effects may vary across development, particularly for constructs like self-regulation that emerge slowly, depend on brain regions that change qualitatively in different developmental periods, and thus may be manifested differently. To illustrate one approach to exploring such developmental patterns, the relation between variation in the TaqIA polymorphism, related to D2 dopamine receptor expression and availability, and prenatal exposure to tobacco was examined in two exploratory studies. First, in 4-week-old neonates, genotype-exposure interactions were observed for attention and irritable reactivity, but not for stress dysregulation. Second, in preschool children, genotype was related to Preschool Trail Making Test (K. A. Espy and M. F. Cwik, 2004) task performance on conditions requiring executive control; children with both the A1+ genotype and a history of prenatal tobacco exposure displayed disproportionately poor performance. Despite study limitations, these results illustrate the importance of examining the interplay between genetic and prenatal environmental factors across development.

Race and nicotine replacement treatment outcomes among low-income smokers

BACKGROUND

Prior research suggests that racial/ethnic minority smokers experience more difficulty with cessation than white smokers and access formal treatment less often. Minority smokers may respond differently to treatment interventions than white smokers. This prospective, observational cohort study compared long-term cessation outcomes among four racial/ethnic groups after an aided quit attempt using nicotine replacement therapy (NRT).

METHODS

A random cohort of smokers (N=1782) who recently filled a prescription for NRT was selected, stratified by race, using Minnesota Health Care Programs (e.g., Medicaid) pharmacy claims databases between July 2005 and September 2006. The primary outcome was 7-day point prevalence abstinence, which was assessed about 8 months after the NRT index prescription fill date using a mixed-mode survey protocol.

RESULTS

The overall survey response was 58.2%. Overall, abstinence outcomes did not significantly vary by race. Unadjusted comparisons show that among survey respondents, at 8 months, 7-day point prevalence abstinence was 13.8% among whites, 13.6% among blacks, 14.1% among American Indians/Alaska Natives, and 20.7% among Asians (p=0.42). Similarly, the 30-day duration abstinence was 10.0% among whites, 11.5% among blacks, 8.9% among American Indians/Alaska Natives, and 18.3% among Asians (p=0.14). In multivariate analysis using propensity adjustment for potential confounding and response bias, there was no evidence that the effectiveness of NRT was lower for racial/ethnic minority smokers compared to white smokers.

CONCLUSIONS

These findings indicate that racial/ethnic minorities are as likely to quit smoking at a level similar to whites when using cessation treatment that includes NRT. Given documented disparities in the use of evidence-based cessation treatments such as NRT, interventions are sorely needed to improve access and utilization of these treatments in racial/ethnic minority groups.

Examining the heritability of a laboratory-based smoking endophenotype: initial results from an experimental twin study

The objective of this study was to examine the heritability of an endophenotype relevant to nicotine dependence, namely tension reduction after smoking. This study also examined whether common genetic, shared environmental, and nonshared environmental factors influence this endophenotype measured repeatedly during an experimental paradigm. Twin and sibling pairs, all of whom were regular smokers, completed a laboratory paradigm in which they reported on levels of tension at baseline and after smoking each of 3 cigarettes. Univariate twin analyses suggested a sizeable role of additive genetic effects on tension reduction, with heritability estimates ranging between 47 and 68%. Result of multivariate Cholesky analyses indicated that there were additive genetic influences common to tension reduction assessed after cigarettes 1, 2, and 3. Multivariate models including genetic and nonshared environmental effects provided the best fit to the data. To the best of our knowledge, this is the first study to examine the genetic basis of a laboratory smoking endophenotype, in this case tension reduction after smoking. Implications for genetic association studies are discussed.

Interaction between BDNF Val66Met and dopamine transporter gene variation influences anxiety-related traits

The involvement in neural plasticity and the mediation of effects of repeated stress exposure and long-term antidepressant treatment on hippocampal neurogenesis supports a critical role of brain-derived neurotrophic factor (BDNF) in the pathophysiology of affective and other stress-related disorders. A previously reported valine to methionine substitution at amino-acid position 66 (BDNF Val66Met) seems to account for memory disturbance and hippocampal dysfunction. In the present study, we evaluated the impact of the BDNF Val66Met polymorphism on individual differences in personality traits in a sample of healthy volunteers in relation to other common gene variants thought to be involved in the pathophysiology of affective disorders, such as the serotonin transporter promoter polymorphism (5-HTTLPR) and a variable number of tandem repeat polymorphism of the dopamine transporter gene (DAT VNTR). Personality traits were assessed using the NEO personality inventory (NEO-PI-R) and Tridimensional Personality Questionnaire (TPQ). There was a significant DAT VNTR-dependent association between NEO-PI-R Neuroticism and the BDNF Val66Met polymorphism. Among individuals with at least one copy of the DAT 9-repeat allele, carriers of the BDNF Met allele exhibited significantly lower Neuroticism scores than noncarriers. This interaction was also observed for TPQ Harm Avoidance, a personality dimension related to Neuroticism. Our results support the notion that allelic variation at the BDNF locus--in interaction with other gene variants--influences anxiety- and depression-related personality traits.

Smoking-related videos for use in cue-induced craving paradigms

Environmental cues (e.g., the sight of a cigarette) have long been recognized as important triggers for craving in smokers. Available imaging technologies (e.g., fMRI) allow investigation of the neural mechanisms for cue-induced craving, but there stands a need for a cue-delivery system compatible with an MRI environment. We developed a standardized set of 24 high-resolution videos, 12 containing cigarette smoking scenes (e.g., lighting up), and 12 containing neutral scenes (e.g., reading a book), each 30 s long, with comparable lighting, visual complexity, and background filmed by a professional cinematographer. Study participants were 20 smokers (mean age=37.7 years, 50% female). Each was exposed to the 24 videos in a random order under laboratory conditions. Dependent measures included heart rate, blood pressure, skin conductance, skin temperature, and self-reported craving (0-100) following each video. Overall findings indicated that smokers had greater reactivity to the smoking videos than to neutral videos (p<.01). Follow-up univariate analyses revealed significant cue effects on self-reported craving, galvanic skin response, and skin temperature. Interestingly, exploratory examination of gender revealed that men had higher blood pressure and skin temperature responses than women, and that women had higher responses when viewing videos of women smoking than when viewing men smoking. Results support this set of videos as an effective tool for investigation of cue-elicited craving, and raise the possibility of unique gender effects in cue reactivity.

Stress- and cue-induced cigarette craving: effects of a family history of smoking

Individuals with multiple smokers among first-degree relatives (FH+) are significantly more likely to be persistent smokers themselves. The mechanisms underlying this relationship are unknown. An independent line of research has suggested that persistent smoking is more common among smokers with heightened levels of cigarette craving after being exposed to smoking cues and stressors. The present study experimentally tested the hypothesis that FH+ smokers would exhibit stronger stress- and cue-induced craving reactions compared to FH- smokers. We also explored gender and ethnicity-related differences in these effects. To that end, 160 smokers were recruited by advertisement and exposed to neutral (changing a light bulb), stressful (dental work), and smoking (lighting up after a meal) situations, using script-guided imagery under controlled laboratory conditions. Participants completed craving questionnaires before and after each condition. Supporting the hypotheses, even after controlling smoking history and strength of habit, FH+ smokers (n=86) displayed stronger craving reactions to both dental and smoking imagery (p's<0.05) than FH- smokers (n=74). Interestingly, women had higher stress-, but not smoking cue-induced cravings, than men, with FH+ women exhibiting the highest levels of stress-induced craving. Findings suggest a mechanism through which a family history of smoking leads to poorer cessation success, especially among women.

Ancillary risk information and pharmacogenetic tests: social and policy implications

Some pharmacogenetic tests may provide ancillary disease risk information. To evaluate evidence and assess the social and policy implications of ancillary disease risk information associated with candidate pharmacogenetic variants, We conducted a literature search and abstract review of disease susceptibility studies for each of 42 gene variants potentially associated with drug response. Twenty-two variants (53%) had suggested association with disease risk in at least two studies, and sixteen (38%) were for diseases other than the pharmacogenetic indication. Seven variants (16%) were associated with risk for at least two different diseases. Pharmacogenetic tests have the potential to provide ancillary disease risk information, and this potential should be considered as pharmacogenetic tests are brought into clinical use. Implications will vary with each test but tests should be evaluated individually within a framework that outlines the potential implications of ancillary information.

Effects of craving and DRD4 VNTR genotype on the relative value of alcohol: an initial human laboratory study

BACKGROUND

Craving for alcohol is a highly controversial subjective construct and may be clarified by Loewenstein's visceral theory, which emphasizes craving's behavioral effects on the relative value of alcohol. Based on the visceral theory, this study examined the effects of a craving induction on the relative value of alcohol as measured by a behavioral choice task. In addition, based on previous evidence of its role in the expression of craving, the influence of DRD4 VNTR genotype (DRD4-L vs. DRD4-S) was also examined.

METHODS

Thirty-five heavy drinkers (54% male; 31% DRD4-L) were randomly assigned to receive either a craving induction (exposure to personally relevant alcohol cues) or a control induction (exposure to neutral cues), which was followed by an alcohol-money choice task. Participants were assessed for craving and positive/negative affect throughout the procedure, and relative value of alcohol was derived from participant choices for alcohol versus money. DRD4 VNTR status was assessed retrospectively via buccal samples using previously established protocols.

RESULTS

Factorial analysis of the craving induction revealed that it was associated with significant increase in craving (p < .001), but not greater relative value of alcohol. Factorial analyses including DRD4 VNTR genotype of did not suggest an influence on reactivity to the craving induction, although this analysis was substantially compromised by small cell sample sizes. Continuous analyses revealed that craving was significantly associated with the relative value of alcohol (p < .05) and possession of the DRD4-L allele further amplified this relationship (p < .001).

CONCLUSION

These results are interpreted as generally supporting Loewenstein's visceral theory of craving and evidence of a functional role of DRD4 VNTR genotype in the expression of craving for alcohol. Methodological limitations, mechanisms underlying these findings, and future directions are discussed.

Overview of the pharmacogenomics of cigarette smoking

Cigarette smoking increases the risk of numerous health problems, including cancer, cardiovascular and pulmonary disorders, making smoking the leading cause of preventable death in the world. Nicotine is primarily responsible for the highly addictive properties of cigarettes. Although the majority of smokers express a desire to quit, few are successful in doing so. Twin and family studies have indicated substantial genetic contributions to smoking behaviors. One major research focus has been to elucidate the specific genes involved; this has been accomplished primarily through genome-wide linkage analyses and candidate gene association studies. Much attention has focused on genes involved in the neurotransmitter pathways for the brain reward system and genes altering nicotine metabolism. This paper reviews the current state of knowledge for genetic factors implicated in smoking behaviors, and examines how genetic variations may affect therapeutic outcomes for drugs used to assist smoking cessation.

Examining impulsivity as an endophenotype using a behavioral approach: a DRD2 TaqI A and DRD4 48-bp VNTR association study

Background

Research on the genetic basis for impulsivity has revealed an array of ambiguous findings. This may be a result of limitations to self-report assessments of impulsivity. Behavioral measures that assess more narrowly defined aspects of impulsivity may clarify genetic influences. This study examined the relationship between possession of the DRD2 TaqI A and DRD4 48 bp VNTR genetic polymorphisms and performance on a behavioral measure of impulsivity, the delay discounting task (DDT), and three traditional self-report measures.

Methods

195 individuals (42% male) were recruited from a university campus and were assessed in small group sessions using personal computers. Genotyping was conducted using previously established protocols. For the DRD2 TaqI A locus, individuals were designated as possessing at least one copy of the A1 allele (A1+) or not (A1-), and for the DRD4 48-bp VNTR locus, individuals were designated as having at least one long allele (7 repeats or longer, L+) or not (L-). Principal analyses used multiple univariate factorial 2 (A1+/A1-) × 2 (L+/L-) analyses of variance.

Results

A significant main effect of A1+ status on DDT performance was evident (p = .006) as well as a significant interaction effect (p = .006) between both genes. No other significant effects were evident on the self-report measures, with the exception of a trend toward an interaction effect on the Sensation Seeking Scale. Exploratory analyses suggested that the significant effects were not a function of population stratification or gender.

Discussion

These data suggest that the DRD2 TaqI A and DRD4 VNTR polymorphisms influence impulsivity as measured with a delay discounting task. Specifically, these findings suggest that an interaction between the functional effects of the two unlinked genotypes results in significant difference in the balance of mesolimbic dopaminergic activation relative to frontal-parietal activation. However, these findings are also the first in this area and must be replicated.

Conclusion

These findings suggest a meaningful interaction between the DRD2 TaqI A and DRD4 VNTR polymorphisms in the expression of impulsivity and provide initial support for the utility of using behavioral measures for clarifying genetic influences on impulsivity.

Drugs and genotypes: how pharmacogenetic information could improve smoking cessation treatment

Current smoking cessation treatments are not optimal as the long-term abstinence rates are low. Nicotine replacement therapy and bupropion are the only pharmacotherapies widely available to smokers and there is a need to improve current cessation treatments and to develop new drug therapies. Our goal is to use pharmacogenetic information to improve smoking cessation treatments. Candidate genes include those involved in central mechanisms (such as genes encoding the nicotinic acetylcholine receptors, dopamine receptors, dopamine transporters and opioid receptors) and peripheral mechanisms (such as genes encoding the drug-metabolizing enzymes CYP2A6 and CYP2B6). Pharmacogenetics could be used to improve current smoking cessation treatments through two general approaches. The first would be to identify novel drug targets based on genetic variants that are associated with a natural protection against nicotine dependence, decreased smoking behaviour and/or increased smoking cessation. This knowledge could be used to develop drugs that can mimic these advantages, reducing the risk for acquisition, block the rewarding effects of smoking, decreasing the amount smoked and increasing cessation. The second would be to identify smokers with particular genetic variants who are likely to respond better to one treatment (or dose) versus another and to individualize their treatment to maximize long-term abstinence. This review will highlight examples of how pharmacogenetic information from central and peripheral candidate genes could contribute to improving smoking cessation outcomes by these two approaches.

Dopamine D4 receptor polymorphism modulates cue-elicited heroin craving in Chinese

RATIONALE

Subjective craving, which contributes to the continuation of drug use in active abuser and the occurrence of relapse in detoxified abusers, is considered to be a central phenomenon in addiction. Dopamine pathway has been implicated in the mechanism underlying the cue-elicited craving for a variety of addictive substances.

OBJECTIVES

The objective of this study was to test the hypothesis that heroin addicts carrying D4 dopamine receptor gene (DRD4) variable number tandem repeat (VNTR) long type allele would have higher craving after exposure to a heroin-related cue.

MATERIALS AND METHODS

Craving was induced by a series of exposure to neutral and heroin-related cue and were assessed in a cohort of Chinese heroin abusers (n=420) recruited from the Voluntary Drug Dependence Treatment Center at Shanghai.

RESULTS

Significantly stronger cue-elicited heroin craving was found in individuals carrying DRD4 VNTR long type allele than the non-carriers (F=31.040, p<0.001). As for baseline craving and mean change in craving responding to neutral stimuli, no significance was found (1.06+/-0.34 vs 1.07+/-0.36, F=0.067, p=0.797 and 0.42+/-0.34 vs 0.45+/-0.37, F=0.277, p=0.599, respectively).

CONCLUSIONS

The results of our study suggest that DRD4 VNTR polymorphism contributes to cue-elicited craving in heroin dependence, indicating DRD4 VNTR represents one of potential genetic risk factors for cue-induced craving.