Neurotransmission-related genetic polymorphisms, negative affectivity traits, and gender predict tobacco abstinence symptoms across 44 days with and without nicotine patch

The influence of temperament on stress-induced emotional eating in children

Background

Stress‐induced emotional eating is a risk factor for overweight and obesity. Previous research proposes both the human serotonin transporter gene (5‐HTTLPR) and child's reactive temperament are promising candidates to help explain individual differences in stress‐induced emotional eating and weight. Understanding the association between specific genotypes, reactive temperament factors, and stress‐induced emotional eating may inform the development of personalized and effective treatment for children who may be at risk for overweight and obesity.

Objective

The current study explored the conditional indirect effect of genetic and environmental susceptibility (i.e., the interaction between 5‐HTTLPR and reactive temperament) on weight (as measured by percent body fat) mediated by stress‐induced emotional eating.

Method

One hundred and forty‐seven children (4 to 6 years old; 50.3% female; 22.4% Hispanic), along with their primary caregiver, completed laboratory tasks and questionnaires that assessed the child's reactive temperament, stress‐induced emotional eating, and percent body fat.

Results

The interaction between 5‐HTTLPR and impulsivity as well as with negative affectivity significantly predicted percent body fat. The interaction between 5‐HTTLPR and impulsivity as well as with negative affectivity significantly predicted both total calorie consumption and rate of total calorie consumption. However, the mediation aspect of this statistical model was not supported.

Conclusions

Child reactive temperament is an important indicator of how children approach eating when stressed. Mental health providers may consider prescribing strategies to reduce emotional eating among children with the SL variant and moderate to high impulsivity as well as children with the LL variant and high negative affectivity.

Smoking abstinence symptoms across 67 days compared with randomized controls-Moderation by nicotine replacement therapy, bupropion, and negative-affect traits

Accurate knowledge of negative affect (NA)-related smoking abstinence symptoms (SAS) severity and duration and their moderation by pharmacotherapy and NA-related personality traits is critical for efficacious treatments given that elevated state and trait NA are predictors of relapse. However, SAS severity, duration, and moderation are not well characterized. To date, the longest randomized controlled trial (RCT) of NA-related SAS using randomized delayed-quit smoking controls only examined symptoms across 45 days, despite clinical evidence that SAS may last longer. The present RCT assessed SAS across 67 days in dependent smokers (N = 95) who were randomized either to quit or to delay quitting for the course of the trial. The quit group was further randomized to receive either nicotine replacement therapy (NRT), bupropion (BUP), or placebo. Abstinence-related increases in anger-irritability, depressive, anxiety, and general NA symptoms did not resolve relative to the delayed quit group (DQG) levels across the 67 days in any of the 3 quit groups, though craving fell to below DQG and prequit levels. While NRT attenuated Day 3 SAS relative to BUP and placebo, BUP and NRT generally did not reduce SAS. High scores on trait measures of NA/neuroticism predicted greater increases in and duration of NA-related SAS, potentially indicating that smoking abstinence unmasks affective symptoms. Positive affect was not impacted by abstinence or treatment. The results support the views that (a) prequit baseline values are not a valid index of NA SAS recovery, and (b) on average, NA-related SAS take longer than 67 days to resolve. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Risk of depressive disorders after tobacco smoking cessation: a retrospective cohort study in Fukuoka, Japan

OBJECTIVE

We sought to examine the effect of smoking cessation on subsequent development of depressive disorders.

DESIGN

This was a retrospective cohort study.

METHODS

We used administrative claim and health check data from fiscal years 2010 to 2014, obtained from the largest health insurance association in Fukuoka, Japan. Study participants were between 30 and 69 years old. The end-point outcome was incidence of depressive disorders. Survival analysis and Cox proportional hazards models were conducted. The evaluated potential confounders were sex, age, standard monthly income and psychiatric medical history.

RESULTS

The final number of participants was 87 255, with 7841 in the smoking cessation group and 79 414 in the smoking group. The result of survival analysis showed no significant difference in depressive disorders between the two groups. The results of Cox proportional hazards models showed no significant difference by multivariate analysis between participants, including users of smoking cessation medication (HR 1.04, 95% Cl 0.89 to 1.22) and excluding medication use (HR 0.97, 95% Cl 0.82 to 1.15).

CONCLUSIONS

The present study showed that there were no significant differences with respect to having depressive disorders between smoking cessation and smoking groups. We also showed that smoking cessation was not related to incidence of depressive disorders among participants, including and excluding users of smoking cessation medication, after adjusting for potential confounders. Although the results have some limitations because of the nature of the study design, our findings will provide helpful information to smokers, health professionals and policy makers for improving smoking cessation.

GLOBAL OPIOID EPIDEMIC: DOOMED TO FAIL WITHOUT GENETICALLY BASED PRECISION ADDICTION MEDICINE (PAM™): LESSONS LEARNED FROM AMERICA

It is a reality that globally opioid deaths have soared for men and women of all social, economic status and age from heroin and fentanyl overdoses. Specifically, in the United States, deaths from narcotic overdoses have reached alarming metrics since 2010. In fact, the Fentanyl rise is driven by drug dealers who sell it as heroin or who use it to lace cocaine or to make illegal counterfeit prescription opioids. The President's Commission on the crisis has linked the death toll as equivalent to "September 11th every three weeks." In fact, The U.S. Centre for Disease Control (CDC) released data showing that opioid-related overdoses were up 15% in the first three quarters of 2016 compared to 2015. Various governmental organizations including NIDA, are actively seeking solutions. However, we argue that unless the scientific community embraces genetic addiction risk coupled with potential precision or personalized medicine to induce "dopamine homeostasis" it will fail. We now have evidence that a ten-gene and eleven single nucleotide polymorphism (SNP) panel predicts Addiction Severity Index (ASI) for both alcohol and drugs of abuse (e.g., Opioids). In a large multi-addiction centre study involving seven diverse treatment programs, the genetic addiction risk score (GARS™) was shown to have a predictive relationship with ASI-MV derived alcohol (≥ seven alleles), and other drugs (≥ 4 alleles) severity risk scores. In a number of neuroimaging studies, we also display that in both animal (bench) and abstinent Chinese severe heroin-dependent patients (bedside), BOLD dopamine activation across the brain reward circuitry revealed increases in resting state functional connectivity as well volume connectivity. It is also known that published nutrigenomic (coupling gene polymorphisms with altered KB220z) studies reveal improved clinical outcomes related to obesity.

Pharmacotherapy for smoking cessation: effects by subgroup defined by genetically informed biomarkers

BACKGROUND

Smoking cessation therapies are not effective for all smokers, and researchers are interested in identifying those subgroups of individuals (e.g. based on genotype) who respond best to specific treatments.

OBJECTIVES

To assess whether quit rates vary by genetically informed biomarkers within pharmacotherapy treatment arms and as compared with placebo. To assess the effects of pharmacotherapies for smoking cessation in subgroups of smokers defined by genotype for identified genome-wide significant polymorphisms.

SEARCH METHODS

We searched the Cochrane Tobacco Addiction Group specialised register, clinical trial registries, and genetics databases for trials of pharmacotherapies for smoking cessation from inception until 16 August 2016.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) that recruited adult smokers and reported pharmacogenomic analyses from trials of smoking cessation pharmacotherapies versus controls. Eligible trials included those with data on a priori genome-wide significant (P < 5 × 10-8) single-nucleotide polymorphisms (SNPs), replicated non-SNPs, and/or the nicotine metabolite ratio (NMR), hereafter collectively described as biomarkers.

DATA COLLECTION AND ANALYSIS

We used standard methodological procedures expected by Cochrane. The primary outcome was smoking abstinence at six months after treatment. The secondary outcome was abstinence at end of treatment (EOT). We conducted two types of meta-analyses- one in which we assessed smoking cessation of active treatment versus placebo within genotype groups, and another in which we compared smoking cessation across genotype groups within treatment arms. We carried out analyses separately in non-Hispanic whites (NHWs) and non-Hispanic blacks (NHBs). We assessed heterogeneity between genotype groups using T², I², and Cochrane Q statistics.

MAIN RESULTS

Analyses included 18 trials including 9017 participants, of whom 6924 were NHW and 2093 NHB participants. Data were available for the following biomarkers: nine SNPs (rs1051730 (CHRNA3); rs16969968, rs588765, and rs2036527 (CHRNA5); rs3733829 and rs7937 (in EGLN2, near CYP2A6); rs1329650 and rs1028936 (LOC100188947); and rs215605 (PDE1C)), two variable number tandem repeats (VNTRs; DRD4 and SLC6A4), and the NMR. Included data produced a total of 40 active versus placebo comparisons, 16 active versus active comparisons, and 64 between-genotype comparisons within treatment arms.For those meta-analyses showing statistically significant heterogeneity between genotype groups, we found the quality of evidence (GRADE) to be generally moderate. We downgraded quality most often because of imprecision or risk of bias due to potential selection bias in genotyping trial participants. Comparisons of relative treatment effects by genotypeFor six-month abstinence, we found statistically significant heterogeneity between genotypes (rs16969968) for nicotine replacement therapy (NRT) versus placebo at six months for NHB participants (P = 0.03; n = 2 trials), but not for other biomarkers or treatment comparisons. Six-month abstinence was increased in the active NRT group as compared to placebo among participants with a GG genotype (risk ratio (RR) 1.47, 95% confidence interval (CI) 1.07 to 2.03), but not in the combined group of participants with a GA or AA genotype (RR 0.43, 95% CI 0.15 to 1.26; ratio of risk ratios (RRR) GG vs GA or AA of 3.51, 95% CI 1.19 to 10.3). Comparisons of treatment effects between genotype groups within pharmacotherapy randomisation armsFor those receiving active NRT, treatment was more effective in achieving six-month abstinence among individuals with a slow NMR than among those with a normal NMR among NHW and NHB combined participants (normal NMR vs slow NMR: RR 0.54, 95% CI 0.37 to 0.78; n = 2 trials). We found no such differences in treatment effects between genotypes at six months for any of the other biomarkers among individuals who received pharmacotherapy or placebo.

AUTHORS' CONCLUSIONS

We did not identify widespread differential treatment effects of pharmacotherapy based on genotype. Some genotype groups within certain ethnic groups may benefit more from NRT or may benefit less from the combination of bupropion with NRT. The reader should interpret these results with caution because none of the statistically significant meta-analyses included more than two trials per genotype comparison, many confidence intervals were wide, and the quality of this evidence (GRADE) was generally moderate. Although we found evidence of superior NRT efficacy for NMR slow versus normal metabolisers, because of the lack of heterogeneity between NMR groups, we cannot conclude that NRT is more effective for slow metabolisers. Access to additional data from multiple trials is needed, particularly for comparisons of different pharmacotherapies.

Negative affect subtypes and craving differentially predict long-term cessation success among smokers achieving initial abstinence

OBJECTIVE

This study aimed to examine the associations of individual trajectories of three types of negative affect (NA: anxiety, depression, and anger) and craving during a 44-day period of incentivized smoking abstinence period with cessation outcome at 3 months and at 1 year.

METHODS

Adult smokers (N = 140) completed questionnaire assessments of NA and craving during pre-quit baseline sessions and 15 postquit sessions over the 45 days of biochemically verified abstinence while on nicotine or placebo patch treatment. Growth curve and logistic regression analyses were used to examine the associations of trajectory parameters of the individual NA states and craving with the abstinence outcomes at 3 months and 1 year postquit.

RESULTS

Greater declines in anxiety, depression, and anger symptoms over the first 44 days of smoking cessation were predictive of higher odds of abstinence at both 3 months and 1 year. Moreover, the greater declines in anxiety and anger remained as significant predictors of abstinence at both time points, independent of the predictive ability of the trajectory profiles of craving.

CONCLUSIONS

The findings suggest that slower dissipation of NA, especially anxiety and anger, represents a greater risk for relapse to smoking beyond that predicted by craving during early abstinence. Thus, temporal profiles of the affective symptoms convey unique motivational significance in relapse. Reduction in NA during early abstinence may be a valid target for interventions to increase long-term cessation success rates particularly among individuals with refractory affective symptoms.

Molecular Genetic Testing in Pain and Addiction: Facts, Fiction and Clinical Utility

The Brain Reward Cascade (BRC) is an interaction of neurotransmitters and their respective genes to control the amount of dopamine released within the brain. Any variations within this pathway, whether genetic or environmental (epigenetic), may result in addictive behaviors as well as altered pain tolerance. While there are many studies claiming a genetic association with addiction and other behavioral infractions, defined as Reward Deficiency Syndrome (RDS), not all are scientifically accurate and in some case just wrong. Albeit our bias, we discuss herein the facts and fictions behind molecular genetic testing in RDS (including pain and addiction) and the significance behind the development of the Genetic Addiction Risk Score (GARSPREDX™), the first test to accurately predict one's genetic risk for RDS.

A review of pharmacogenetic studies of substance-related disorders

BACKGROUND

Substance-related disorders (SRDs) are a major cause of morbidity and mortality worldwide. Family, twin, and adoption studies have demonstrated the substantial heritability of SRDs. To determine the impact of genetic variation on risk for SRD and the response to treatment, researchers have conducted a number of secondary data analyses and quasi-experimental studies that target one or more candidate gene variants.

METHODS

This review examines studies in which candidate polymorphisms were examined as mediator variables to identify pharmacogenetic effects on subjective responses to drug administration or cues or outcomes of medication trials for SRDs. Efforts to use a meta-analytic approach to quantify these effects are premature because the number of available studies using similar methods and outcomes is limited, so the present review is qualitative.

RESULTS

Findings from these studies provide preliminary evidence of clinically relevant pharmacogenetic effects. However, independent replication of these findings has been sparse.

CONCLUSIONS

Although this growing body of literature has produced conflicting results, improved statistical controls may help to clarify the findings. Additionally, the use of empirically derived sub-phenotypes (i.e., which serve to differentiate distinct groups of affected individuals) may also help to identify genetic mediators of pharmacologic response in relation to SRDs. The identification of genetic mediators can inform clinical care both by identifying risk factors for SRDs and predicting adverse events and therapeutic outcomes associated with specific pharmacotherapies.

Molecular Genetic Testing in Reward Deficiency Syndrome (RDS): Facts and Fiction

Background

The Brain Reward Cascade (BRC) is an interaction of neurotransmitters and their respective genes to control the amount of dopamine released within the brain. Any variations within this pathway, whether genetic or environmental (epigenetic), may result in addictive behaviors or RDS, which was coined to define addictive behaviors and their genetic components.

Methods

To carry out this review we searched a number of important databases including: Filtered: Cochrane Systematic reviews; DARE; Pubmed Central Clinical Quaries; National Guideline Clearinghouse and unfiltered resources: PsychINFO; ACP PIER; PsychSage; Pubmed/Medline. The major search terms included: dopamine agonist therapy for Addiction; dopamine agonist therapy for Reward dependence; dopamine antagonistic therapy for addiction; dopamine antagonistic therapy for reward dependence and neurogenetics of RDS.

Results

While there are many studies claiming a genetic association with RDS behavior, not all are scientifically accurate.

Conclusion

Albeit our bias, this Clinical Pearl discusses the facts and fictions behind molecular genetic testing in RDS and the significance behind the development of the Genetic Addiction Risk Score (GARS_PREDX™), the first test to accurately predict one’s genetic risk for RDS.

The role of serotonin in drug use and addiction

The use of psychoactive drugs is a wide spread behaviour in human societies. The systematic use of a drug requires the establishment of different drug use-associated behaviours which need to be learned and controlled. However, controlled drug use may develop into compulsive drug use and addiction, a major psychiatric disorder with severe consequences for the individual and society. Here we review the role of the serotonergic (5-HT) system in the establishment of drug use-associated behaviours on the one hand and the transition and maintenance of addiction on the other hand for the drugs: cocaine, amphetamine, methamphetamine, MDMA (ecstasy), morphine/heroin, cannabis, alcohol, and nicotine. Results show a crucial, but distinct involvement of the 5-HT system in both processes with considerable overlap between psychostimulant and opioidergic drugs and alcohol. A new functional model suggests specific adaptations in the 5-HT system, which coincide with the establishment of controlled drug use-associated behaviours. These serotonergic adaptations render the nervous system susceptible to the transition to compulsive drug use behaviours and often overlap with genetic risk factors for addiction. Altogether we suggest a new trajectory by which serotonergic neuroadaptations induced by first drug exposure pave the way for the establishment of addiction.

Effects of nicotine on emotional distraction of attentional orienting: evidence of possible moderation by dopamine type 2 receptor genotype

INTRODUCTION

Growing evidence suggests that attentional bias to, and distraction by, emotional stimuli may moderate affective states and motivation for nicotine and other drug use.

METHODS

The present study assessed the effects of nicotine and dopamine receptor genotype on distraction by emotional pictures, during a modified spatial attention task, in 46 overnight-deprived smokers.

RESULTS

Relative to placebo, 14mg nicotine patch produced shorter overall reaction times (RTs) and individuals with two dopamine type 2 receptor (DRD2) A2 alleles exhibited the greatest RT benefit from nicotine following emotionally negative pictures after the longest cue-target delay (800ms), but benefitted least from nicotine following positive pictures after the shortest delay (400ms). In contrast, at the shortest delay, A1 carriers did not benefit from nicotine following emotionally negative pictures but did following positive ones.

CONCLUSIONS

These genetic differences in the effects of nicotine on attention immediately following emotionally positive versus negative stimuli may reflect differential excitatory and inhibitory transmitter processes related to approach (reward) and avoidance (punishment) sensitivities of dopamine-related neural networks that support positive and negative affect.

Comparative dynamics of four smoking withdrawal symptom scales

AIMS

  To examine the association of person-specific trajectories of withdrawal symptoms of urge-to-smoke, negative affect, physical symptoms and hunger during the first 7 days after smoking cessation with abstinence at end of treatment (EOT) and at 6 months.

DESIGN

  Hierarchical linear modeling (HLM) was used to model person-specific trajectory parameters (level, slope, curvature and volatility) for withdrawal symptoms.

SETTING

  University-based smoking cessation trials.

PARTICIPANTS

  Treatment-seeking smokers in clinical trials of transdermal nicotine versus nicotine spray (n = 514) and bupropion versus placebo (n = 421).

MEASUREMENTS

  Self-reported withdrawal symptoms for 7 days after the planned quit date, and 7-day point prevalence and continuous abstinence at EOT and 6 months.

FINDINGS

  In regressions that included trajectory parameters for one group of withdrawal symptoms, both urge-to-smoke and negative affect were predictive of abstinence while physical symptoms and hunger were generally not predictive. In stepwise regressions that included the complete set of trajectory parameters across withdrawal symptoms (for urge-to-smoke, negative affect, physical symptoms and hunger), with a single exception only the trajectory parameters for urge-to-smoke were predictive. Area under the receiver operator characteristic curve was 0.594 for covariates alone, and 0.670 for covariates plus urge-to-smoke trajectory parameters.

CONCLUSIONS

  Among a number of different withdrawal symptoms (urge-to-smoke, negative affect, physical symptoms and hunger) urge-to-smoke trajectory parameters (level, slope and volatility) over the first 7 days of smoking cessation show the strongest prediction of both short- and long-term relapse. Other withdrawal symptoms increase the predictive ability by negligible amounts.

Early cessation success or failure among women attempting to quit smoking: trajectories and volatility of urge and negative mood during the first postcessation week

Aversive symptoms of abstinence from nicotine have been posited to lead to smoking relapse and research on temporal patterns of abstinence symptoms confirms this assumption. However, little is known about the association of symptom trajectories early after quitting with postcessation smoking or about the differential effects of tonic (background) versus phasic (temptation-related) symptom trajectories on smoking status. The current study examined trajectories of urge and negative mood among 300 women using the nicotine patch during the first postcessation week. Ecological momentary assessments collected randomly and during temptation episodes were analyzed using hierarchical linear modeling yielding four individual trajectory parameters: intercept (initial symptom level), linear slope (direction and rate of change), quadratic coefficient (curvature), and volatility (scatter). Early lapsers, who lapsed during the first postcessation week, exhibited more severe tonic urge and phasic negative mood immediately after quitting, and more volatile tonic and phasic urge compared to abstainers. Late lapsers, who were abstinent during the first week but lapsed by 1 month, exhibited more severe tonic urge immediately after quitting compared to abstainers. These results demonstrate the importance of early postcessation urge and negative affect and highlight the value of examining both tonic and phasic effects of abstinence from nicotine.

The dynamics of the urge-to-smoke following smoking cessation via pharmacotherapy

AIMS

To examine person-specific urge-to-smoke trajectories during the first 7 days of abstinence and the relationship of trajectory parameters to continuous abstinence, demographics, medication and smoking history.

DESIGN

Hierarchical linear modeling was used to model person-specific trajectories for urge-to-smoke.

SETTING

Two university-based smoking cessation trials.

PARTICIPANTS

Treatment-seeking smokers in a clinical trial of transdermal nicotine (n = 275) versus nicotine spray (n = 239) and of bupropion (n = 223) versus placebo (n = 198).

MEASUREMENTS

Self-reported urge-to-smoke for 7 days after the planned quit date, and 7-day point prevalence and continuous abstinence at end of treatment (EOT) and 6 months.

FINDINGS

Urge-to-smoke trajectory parameters (average level, slope, curvature and volatility) varied substantially among individuals, had modest intercorrelations and predicted continuous and point prevalence abstinence at EOT and at 6 months. Higher trajectory level, slope and volatility were all significantly (P ≤ 0.001) associated with a reduced likelihood of abstinence at EOT (odds ratios 0.44-0.75) and at 6-month follow-up (odds ratios from 0.63 to 0.78), controlling for demographic, medication and smoking use variables.

CONCLUSION

Higher urge-to-smoke trajectory parameters of level, slope and volatility (measured over 7 days) predict continuous and 7-day point prevalence at EOT and 6 months. Although there were some associations of trajectory parameters with demographics and smoking history, the associations of trajectory parameters with relapse were relatively uninfluenced by demographics and smoking history.

Genetic variation in three candidate genes and nicotine dependence, withdrawal and smoking cessation in hospitalized patients

AIMS

This study evaluates the relationship of six polymorphisms found in the CHRNA3, DRD2 and COMT genes with nicotine dependence, the ability to quit smoking and the occurrence of withdrawal symptoms after short-term use of nicotine patch in hospitalized patients.

MATERIALS & METHODS

The study included 233 participants from a double-blind, placebo-controlled trial of nicotine patch substitution with a 6-month follow-up period. Nicotine dependence was assessed by the Fagerström Test for Nicotine Dependence (FTND) questionnaire, withdrawal symptoms by the Minnesota Nicotine Withdrawal Scale questionnaire and smoking cessation by self-reported abstinence at 1 week, 1 month and 6 months after treatment.

RESULTS

After correcting for multiple testing, three polymorphisms in the DRD2 gene (Taq1A, Taq1B and Pro319Pro) were significantly associated with nicotine dependence (p = 0.018, p = 0.048 and p = 0.006, respectively). Using a cutoff point for the FTND score, the CHRNA3 Tyr215Tyr (rs1051730) polymorphism was also associated with nicotine dependence (p = 0.037 and p = 0.074 after correction for multiple testing). No association of any of the studied polymorphisms was observed with either smoking cessation or the occurrence of withdrawal symptoms.

CONCLUSION

This study confirms the reported association of the CHRNA3 locus with nicotine dependence and shows the involvement of two independent DRD2 polymorphisms in nicotine dependence.

Refining the tobacco dependence phenotype using the Wisconsin Inventory of Smoking Dependence Motives: II. Evidence from a laboratory self-administration assay

Prior analyses of the Wisconsin Inventory of Smoking Dependence Motives (Piper et al., 2004) implicated 4 subscales as primary dependence motives (PDM) indexing the core features of tobacco dependence, with the remaining subscales reflecting secondary dependence motives (SDM; Piper et al., 2008). The current study extended this work by examining the correlates of PDM, SDM, their subscales, and other indicators of dependence in an operant self-administration paradigm. Smokers (N = 58) worked for cigarette puffs under differing fixed ratio schedules. Analyses focused on predicting self-administration under conditions of minimal constraint on tobacco access and on withdrawal and craving under conditions of severe constraint. Results support a 2-factor model of dependence, with the PDM factor showing relatively stronger relations with tobacco self-administration and the SDM factor showing relatively stronger relations with withdrawal symptomatology and distress-related craving. The PDM appears to index core features of tobacco dependence, but susceptibility to deprivation-contingent distress and craving may be better indexed by SDM.

Genetic sensitivity to the environment: the case of the serotonin transporter gene and its implications for studying complex diseases and traits

Evidence of marked variability in response among people exposed to the same environmental risk implies that individual differences in genetic susceptibility might be at work. The study of such Gene-by-Environment (GxE) interactions has gained momentum. In this article, the authors review research about one of the most extensive areas of inquiry: variation in the promoter region of the serotonin transporter gene (SLC6A4; also known as 5-HTT) and its contribution to stress sensitivity. Research in this area has both advanced basic science and generated broader lessons for studying complex diseases and traits. The authors evaluate four lines of evidence about the 5-HTT stress-sensitivity hypothesis: 1) observational studies about the serotonin transporter linked polymorphic region (5-HTTLPR), stress sensitivity, and depression in humans; 2) experimental neuroscience studies about the 5-HTTLPR and biological phenotypes relevant to the human stress response; 3) studies of 5-HTT variation and stress sensitivity in nonhuman primates; and 4) studies of stress sensitivity and genetically engineered 5-HTT mutations in rodents. The authors then dispel some misconceptions and offer recommendations for GxE research. The authors discuss how GxE interaction hypotheses can be tested with large and small samples, how GxE research can be carried out before as well as after replicated gene discovery, the uses of GxE research as a tool for gene discovery, the importance of construct validation in evaluating GxE research, and the contribution of GxE research to the public understanding of genetic science.

Neurogenetics of dopaminergic receptor supersensitivity in activation of brain reward circuitry and relapse: proposing "deprivation-amplification relapse therapy" (DART)

BACKGROUND AND HYPOTHESIS

It is well known that after prolonged abstinence, individuals who use their drug of choice experience a powerful euphoria that often precipitates relapse. While a biological explanation for this conundrum has remained elusive, we hypothesize that this clinically observed "supersensitivity" might be tied to genetic dopaminergic polymorphisms. Another therapeutic conundrum relates to the paradoxical finding that the dopaminergic agonist bromocriptine induces stronger activation of brain reward circuitry in individuals who carry the DRD2 A1 allele compared with DRD2 A2 allele carriers. Because carriers of the A1 allele relative to the A2 allele of the DRD2 gene have significantly lower D2 receptor density, a reduced sensitivity to dopamine agonist activity would be expected in the former. Thus, it is perplexing that with low D2 density there is an increase in reward sensitivity with the dopamine D2 agonist bromocriptine. Moreover, under chronic or long-term therapy with D2 agonists, such as bromocriptine, it has been shown in vitro that there is a proliferation of D2 receptors. One explanation for this relates to the demonstration that the A1 allele of the DRD2 gene is associated with increased striatal activity of L-amino acid decarboxylase, the final step in the biosynthesis of dopamine. This appears to be a protective mechanism against low receptor density and would favor the utilization of an amino acid neurotransmitter precursor like L-tyrosine for preferential synthesis of dopamine. This seems to lead to receptor proliferation to normal levels and results in significantly better treatment compliance only in A1 carriers.

PROPOSAL AND CONCLUSION

We propose that low D2 receptor density and polymorphisms of the D2 gene are associated with risk for relapse of substance abuse, including alcohol dependence, heroin craving, cocaine dependence, methamphetamine abuse, nicotine sensitization, and glucose craving. With this in mind, we suggest a putative physiological mechanism that may help to explain the enhanced sensitivity following intense acute dopaminergic D2 receptor activation: "denervation supersensitivity." Rats with unilateral depletions of neostriatal dopamine display increased sensitivity to dopamine agonists estimated to be 30 to 100 x in the 6-hydroxydopamine (6-OHDA) rotational model. Given that mild striatal dopamine D2 receptor proliferation occurs (20%-40%), it is difficult to explain the extent of behavioral supersensitivity by a simple increase in receptor density. Thus, the administration of dopamine D2 agonists would target D2 sensitization and attenuate relapse, especially in D2 receptor A1 allele carriers. This hypothesized mechanism is supported by clinical trials utilizing amino acid neurotransmitter precursors, enkephalinase, and catechol-O-methyltransferase (COMT) enzyme inhibition, which have resulted in attenuated relapse rates in reward deficiency syndrome (RDS) probands. If future translational research reveals that dopamine agonist therapy reduces relapse in RDS, it would support the proposed concept, which we term "deprivation-amplification relapse therapy" (DART). This term couples the mechanism for relapse, which is "deprivation-amplification," especially in DRD2 A1 allele carriers with natural D2 agonist therapy utilizing amino acid precursors and COMT and enkepalinase inhibition therapy.

DRD2-related TaqIA polymorphism modulates motivation to smoke

INTRODUCTION

TaqIA polymorphism, a genetic variant associated with the expression level of dopamine D2 receptors in the brain, has been linked to various aspects of smoking behavior, including smoking prevalence, affective withdrawal symptoms, and smoking cessation outcome. However, its involvement in motivation to smoke cigarettes has not been elucidated.

METHODS

The present study examined the possible differences in self-reported reasons to smoke and craving for smoking in 160 smokers participating in a clinical trial.

RESULTS

Individuals with at least one A1 allele of the TaqIA polymorphism were more likely to report smoking for stimulating effects and to reduce negative affect compared with those lacking an A1 allele. The association of the A1 genotype with a higher probability and stronger motive to smoker to enhance cognitive functioning was evident in female but not in male smokers. Female A1 carriers also expected a greater likelihood of smoking for pleasure than those without an A1 allele. A1 subjects reported stronger craving for cigarettes during early days and the last phase of a 6-week abstinence period.

DISCUSSION

These results support the idea that dopaminergic transmission plays an important role in the neurobiological basis of reasons for smoking and that the TaqIA variant is one of the genetic factors underlying individual differences in these aspects. These findings also have implications for improving treatment strategies to help individuals quit smoking by controlling their motivation to continue cigarette consumption.