Dopamine transporter density and novelty seeking among alcoholics

Molecular Imaging Studies of Alcohol Use Disorder

Alcohol use disorder (AUD) is a serious public health problem in many countries, bringing a gamut of health risks and impairments to individuals and a great burden to society. Despite the prevalence of a disease model of AUD, the current pharmacopeia does not present reliable treatments for AUD; approved treatments are confined to a narrow spectrum of medications engaging inhibitory γ-aminobutyric acid (GABA) neurotransmission and possibly excitatory N-methyl-D-aspartate (NMDA) receptors, and opioid receptor antagonists. Molecular imaging with positron emission tomography (PET) and single-photon emission computed tomography (SPECT) can open a window into the living brain and has provided diverse insights into the pathology of AUD. In this narrative review, we summarize the state of molecular imaging findings on the pharmacological action of ethanol and the neuropathological changes associated with AUD. Laboratory and preclinical imaging results highlight the interactions between ethanol and GABA A-type receptors (GABAAR), but the interpretation of such results is complicated by subtype specificity. An abundance of studies with the glucose metabolism tracer fluorodeoxyglucose (FDG) concur in showing cerebral hypometabolism after ethanol challenge, but there is relatively little data on long-term changes in AUD. Alcohol toxicity evokes neuroinflammation, which can be tracked using PET with ligands for the microglial marker translocator protein (TSPO). Several PET studies show reversible increases in TSPO binding in AUD individuals, and preclinical results suggest that opioid-antagonists can rescue from these inflammatory responses. There are numerous PET/SPECT studies showing changes in dopaminergic markers, generally consistent with an impairment in dopamine synthesis and release among AUD patients, as seen in a number of other addictions; this may reflect the composite of an underlying deficiency in reward mechanisms that predisposes to AUD, in conjunction with acquired alterations in dopamine signaling. There is little evidence for altered serotonin markers in AUD, but studies with opioid receptor ligands suggest a specific up-regulation of the μ-opioid receptor subtype. Considerable heterogeneity in drinking patterns, gender differences, and the variable contributions of genetics and pre-existing vulnerability traits present great challenges for charting the landscape of molecular imaging in AUD.

Medication overuse and drug addiction: a narrative review from addiction perspective

Chronic headache is particularly prevalent in migraineurs and it can progress to a condition known as medication overuse headache (MOH). MOH is a secondary headache caused by overuse of analgesics or other medications such as triptans to abort acute migraine attacks. The worsening of headache symptoms associated with medication overuse (MO) generally ameliorates following interruption of regular medication use, although the primary headache symptoms remain unaffected. MO patients may also develop certain behaviors such as ritualized drug administration, psychological drug attachment, and withdrawal symptoms that have been suggested to correlate with drug addiction. Although several reviews have been performed on this topic, to the authors best knowledge none of them have examined this topic from the addiction point of view. Therefore, we aimed to identify features in MO and drug addiction that may correlate. We initiate the review by introducing the classes of analgesics and medications that can cause MOH and those with high risk to produce MO. We further compare differences between sensitization resulting from MO and from drug addiction, the neuronal pathways that may be involved, and the genetic susceptibility that may overlap between the two conditions. Finally, ICHD recommendations to treat MOH will be provided herein.

Effects of sedative drug use on the dopamine system: a systematic review and meta-analysis of in vivo neuroimaging studies

Use of alcohol, cannabis and opioids is highly prevalent and is associated with global disease burden and high economic costs. The exact pathophysiology of abuse or addiction associated with these sedative substances is not completely understood, but previous research implicates the important role of the striatal dopamine system in the addiction process. Multiple studies investigated changes in the striatal dopamine systems of users of sedative substances, but currently these results are very heterogeneous. Therefore, we conducted a meta-analysis of in vivo neuroimaging studies investigating dopaminergic alterations in the striatum of users of alcohol, opioids or cannabis. Analyses for each substance were conducted separately for the availability of D2/D3 dopamine receptors, dopamine transporters and dopamine synthesis capacity. In total, 723 substance users and 752 healthy controls were included. The results indicated a significant lower striatal D2/D3 receptor availability in alcohol users compared to controls (g = 0.46) but no difference in dopamine transporter availability or dopamine synthesis capacity. Our analysis indicated that changes of dopamine receptors and transporters are moderated by the duration of abstinence. Comparing opioid users with controls revealed a significant lower D2/D3 receptor availability (g = 1.17) and a significantly lower transporter availability (g = 1.55) in opioid users. For cannabis users, there was no significant difference in receptor availability compared to controls and too few studies provided information on dopamine transporter availability or synthesis capacity. Our analysis provides strong evidence for a central role of the striatal dopamine system in use of alcohol or opioids. Further studies are needed to clarify the impact of the dopamine system in cannabis users.

Ventral striatal dopamine transporter availability is associated with lower trait motor impulsivity in healthy adults

Impulsivity is a transdiagnostic feature of a range of externalizing psychiatric disorders. Preclinical work links reduced ventral striatal dopamine transporter (DAT) availability with heightened impulsivity and novelty seeking. However, there is a lack of human data investigating the relationship between DAT availability, particularly in subregions of the striatum, and the personality traits of impulsivity and novelty seeking. Here we collected PET measures of DAT availability (BP_ND) using the tracer ¹⁸F-FE-PE2I in 47 healthy adult subjects and examined relations between BP_ND in striatum, including its subregions: caudate, putamen, and ventral striatum (VS), and trait impulsivity (Barratt Impulsiveness Scale: BIS-11) and novelty seeking (Tridimensional Personality Questionnaire: TPQ-NS), controlling for age and sex. DAT BP_ND in each striatal subregion showed nominal negative associations with total BIS-11 but not TPQ-NS. At the subscale level, VS DAT BP_ND was significantly associated with BIS-11 motor impulsivity (e.g., taking actions without thinking) after correction for multiple comparisons. VS DAT BP_ND explained 13.2% of the variance in motor impulsivity. Our data demonstrate that DAT availability in VS is negatively related to impulsivity and suggest a particular influence of DAT regulation of dopamine signaling in VS on acting without deliberation (BIS motor impulsivity). While needing replication, these data converge with models of ventral striatal functions that emphasize its role as a key interface linking motivation to action.

Trait Impulsivity and the Externalizing Spectrum

This article reviews evidence that trait impulsivity-expressed early in life as the hyperactive-impulsive and combined presentations of attention-deficit/hyperactivity disorder (ADHD)-is a bottom-up, subcortically mediated vulnerability to all externalizing disorders. This vulnerability arises from deficient mesolimbic dopamine responding, which imbues psychological states (irritability, discontentment) that motivate excessive approach behavior (hyperactivity, impulsivity). Through complex interactions with (a) aversive motivational states that arise from largely independent subcortical systems, (b) emotion regulatory mechanisms that arise from top-down, cortical modulation of subcortical neural function, and (c) environmental risk factors that shape and maintain emotion dysregulation, trait impulsivity confers vulnerability to increasingly severe externalizing behaviors across development. This perspective highlights the importance of identifying transdiagnostic neural vulnerabilities to psychopathology; dovetails with the hierarchical, latent structure of psychopathology; and suggests that progression along the externalizing spectrum is an ontogenic process whereby a common, multifactorially inherited trait interacts with endogenous and exogenous influences to yield increasingly intractable externalizing behaviors across development.

Regional Cerebral Glucose Metabolism in Novelty Seeking and Antisocial Personality: A Positron Emission Tomography Study

Novelty seeking (NS) and antisocial personality (ASP) are commonly exhibited by those who suffer from addictions, such as substance abuse. NS has been suggested to be a fundamental aspect of ASP. To investigate the neurobiological substrate of NS and ASP, we tested the relationship between regional cerebral glucose metabolism and the level of NS, determining the differences between individuals with and without ASP. Seventy-two healthy adults (43 males, mean age±SD=38.8±16.6 years, range=20~70 years; 29 females, 44.2±20.1 years, range=19~72 years) underwent resting-state brain positron emission tomography (PET) 40 minutes after (18)F-fluorodeoxyglucose (FDG) injection. Within 10 days of the FDG PET study, participants completed Cloninger's 240-item Temperament and Character Inventory (TCI) to determine NS scores. Participants with and without ASP were grouped according to their TCI profiles. Statistical parametric mapping analysis was performed using the FDG PET and TCI profile data. NS scores positively correlated with metabolism in the left anterior cingulate gyrus and the insula on both sides of the brain and negatively correlated with metabolism in the right pallidum and putamen. Participants with ASP showed differences in cerebral glucose metabolism across various cortical and subcortical regions, mainly in the frontal and prefrontal areas. These data demonstrate altered regional cerebral glucose metabolism in individuals with NS and ASP and inform our understanding of the neurobiological substrates of problematic behaviors and personality disorders.

Positive Association Between Limbic Metabotropic Glutamate Receptor 5 Availability and Novelty-Seeking Temperament in Humans: An 18F-FPEB PET Study

Heritable temperament traits have been linked to several neuropsychiatric illnesses, including disorders associated with metabotropic glutamate receptor 5 (mGluR5) and dopaminergic dysfunctions. Considering its modulating effect on neurotransmission, we hypothesized that cerebral mGluR5 availability is associated with temperament traits in healthy humans.

METHODS

Forty-four nonsmoking healthy volunteers (mean age ± SD, 40 ± 14 y; age range, 22-66 y; 22 women) were included in this cross-sectional investigation. Brain mGluR5 availability was quantified on both a voxel-by-voxel and a volume-of-interest basis using the total distribution volume of the radioligand ¹⁸F-3-fluoro-5-[(pyridin-3-yl)ethynyl]benzonitrile (¹⁸F-FPEB) with 90-min dynamic PET and arterial input function. Moreover, glutamate-glutamine concentrations in the anterior cingulate cortex were measured using MR spectroscopy. These measures were related to the temperament traits of the 240-item Cloninger temperament and character inventory using a regression analysis with age and sex as nuisance variables.

RESULTS

High novelty-seeking temperament was robustly associated with increased mGluR5 availability in various regions including the thalamus (r = 0.71; the strongest association), amygdala, parahippocampus, insula, anterior and posterior cingulate cortex, and several primary sensory areas (all r > 0.58; P < 0.05, corrected for familywise error). These associations were specific because no correlations were found with other temperament scales or with spectroscopic measures of glutamatergic transmission.

CONCLUSION

Overall, these data posit mGluR5 in key paralimbic areas as a strong determinant of the temperament trait novelty seeking. These data add to our understanding of how brain neurochemistry accounts for the variation in human behavior and strongly support further research on mGluR5 as a potential therapeutic target in neuropsychiatric disorders associated with abnormal novelty-seeking behaviors.

Internalizing and externalizing psychopathology as predictors of cannabis use disorder onset during adolescence and early adulthood

Risk-related liabilities associated with the development of cannabis use disorders (CUDs) during adolescence and early adulthood are thought to be established well before the emergence of the index episode. In this study, internalizing and externalizing psychopathology from earlier developmental periods were evaluated as risk factors for CUDs during adolescence and early adulthood. Participants (N = 816) completed 4 diagnostic assessments between the ages 16 and 30, during which current and past CUDs were assessed as well as a full range of psychiatric disorders associated with internalizing and externalizing psychopathology domains. In unadjusted and adjusted time-to-event analyses, externalizing but not internalizing psychopathology from proximal developmental periods predicted subsequent CUD onset. A large proportion of adolescent and early adult cases, however, did not manifest any externalizing or internalizing psychopathology during developmental periods before CUD onset. Findings are consistent with the emerging view that externalizing disorders from proximal developmental periods are robust risk factors for CUDs. Although the identification of externalizing liabilities may aid in the identification of individuals at risk for embarking on developmental pathways that culminate in CUDs, such liabilities are an incomplete indication of overall risk.

Heart rate variability as a transdiagnostic biomarker of psychopathology

The Research Domain Criteria (RDoC), developed by the National Institute of Mental Health as a neuroscience-informed alternative to traditional psychiatric nosology, is an explicitly dimensional system in which classification of psychopathology is derived inductively (i.e., from basic science), across multiple levels of analysis (e.g., genetic, neural, psychophysiological, and behavioral). Although RDoC is often presented as paradigmatically revolutionary, a review of the history of psychophysiology suggests that roots of RDoC thinking extend at least as far back as the mid-20th Century. In this paper, we briefly and selectively review the historical emergence of neurobiologically-informed dimensional trait models of psychopathology, and we summarize our thinking regarding high frequency heart rate variability (HF-HRV) as a transdiagnostic biomarker of self-regulation and cognitive control. When functional interactions between HF-HRV and systems of behavioral approach and avoidance are considered, diverse patterns of behavioral maladjustment can be subsumed into a single model. This model accommodates the general bifactor structure of psychopathology, and suggests that HF-HRV can be viewed as an autonomic, transdiagnostic biomarker of mental illness.

Reduced Dopamine Transporter Availability and Neurocognitive Deficits in Male Patients with Alcohol Dependence

Dopamine plays an important role in the development of alcohol dependence, cognitive dysfunction, and is regulated via dopamine transporter activity. Although dopamine transporter activity is critically involved in alcohol dependence, studies observing this relationship are limited. Thus the current study examined whether dopamine transporter availability is associated with developing of alcohol dependence and cognitive dysfunction. Brain imaging with ^99mTc-TRODAT-1 as a ligand was used to measure dopamine transporter availability among 26 male patients with pure alcohol dependence and 22 age- and sex- matched healthy volunteers. The Wisconsin Card Sorting Test (WCST) and Tridimensional Personality Questionnaire (TPQ) were administered to assess neurocognitive functioning and personality traits, respectively. Compared to healthy controls, patients with alcohol dependence showed a significant reduction in dopamine transporter availability (p < 0.001), as well as diminished performance on the WCST (p < 0.001). Dopamine transporter availability was negatively correlated with both total and perseverative WCST errors among healthy controls, but only patients with alcohol dependence showed a positive correlation between dopamine transporter availability and a harm avoidance personality profile. Thus, reductions in dopamine transporter availability may play a pathophysiological role in the development of pure alcohol dependence, given its association with neurocognitive deficits. Moreover, personality may influence the development of pure alcohol dependence; however, additional clinical subgroups should be examined to confirm this possibility.

Neural responses to monetary incentives among self-injuring adolescent girls

Rates of self-inflicted injury among adolescents have risen in recent years, yet much remains to be learned about the pathophysiology of such conduct. Self-injuring adolescents report high levels of both impulsivity and depression behaviorally. Aberrant neural responding to incentives, particularly in striatal and prefrontal regions, is observed among both impulsive and depressed adolescents, and may mark common vulnerability to symptoms of anhedonia, irritability, and low positive affectivity. To date, however, no studies have examined associations between central nervous system reward responding and self-injury. In the current study, self-injuring (n = 19) and control (n = 19) adolescent females, ages 13-19 years, participated in a monetary incentive delay task in which rewards were obtained on some trials and losses were incurred on others. Consistent with previous findings from impulsive and depressed samples, self-injuring adolescents exhibited less activation in both striatal and orbitofrontal cortex regions during anticipation of reward than did controls. Self-injuring adolescents also exhibited reduced bilateral amygdala activation during reward anticipation. Although few studies to date have examined amygdala activity during reward tasks, such findings are common among adults with mood disorders and borderline personality disorder. Implications for neural models of impulsivity, depression, heterotypic comorbidity, and development of both self-injury and borderline personality traits are discussed.

Regulation of ethanol intake under chronic mild stress: roles of dopamine receptors and transporters

Studies have shown that exposure to chronic mild stress decreases ethanol intake and preference in dopamine D2 receptor wild-type mice (Drd2 (+/+)), while it increases intake in heterozygous (Drd2 (+/-)) and knockout (Drd2 (-/-)) mice. Dopaminergic neurotransmission in the basal forebrain plays a major role in the reinforcing actions of ethanol as well as in brain responses to stress. In order to identify neurochemical changes associated with the regulation of ethanol intake, we used in vitro receptor autoradiography to measure the levels and distribution of dopamine D1 and D2 receptors and dopamine transporters (DAT). Receptor levels were measured in the basal forebrain of Drd2 (+/+), Drd2 (+/-), and Drd2 (-/-) mice belonging to one of four groups: control (C), ethanol intake (E), chronic mild stress exposure (S), and ethanol intake under chronic mild stress (ES). D2 receptor levels were higher in the lateral and medial striatum of Drd2 (+/+) ES mice, compared with Drd2 (+/+) E mice. Ethanol intake in Drd2 (+/+) mice was negatively correlated with striatal D2 receptor levels. D2 receptor levels in Drd2(+/-) mice were the same among the four treatment groups. DAT levels were lower in Drd2(+/-) C and Drd2 (-/-) C mice, compared with Drd2 (+/+) C mice. Among Drd2(+/-) mice, S and ES groups had higher DAT levels compared with C and E groups in most regions examined. In Drd2(-/-) mice, ethanol intake was positively correlated with DAT levels in all regions studied. D1 receptor levels were lower in Drd2(+/-) and Drd2(-/-) mice, compared with Drd2(+/+), in all regions examined and remained unaffected by all treatments. The results suggest that in normal mice, ethanol intake is associated with D2 receptor-mediated neurotransmission, which exerts a protective effect against ethanol overconsumption under stress. In mice with low Drd2 expression, where DRD2 levels are not further modulated, ethanol intake is associated with DAT function which is upregulated under stress leading to ethanol overconsumption.

Polymorphisms in genes encoding dopamine signalling pathway and risk of alcohol dependence: a systematic review

BACKGROUND

Alcohol dependence (AD) is one of the major elements that significantly influence drinking pattern that provoke the alcohol-induced organ damage. The structural and neurophysiologic abnormalities in the frontal lobes of chronic alcoholics were revealed by magnetic resonance imaging scans. It is well known that candidate genes involved in dopaminergic pathway are of immense interest to the researchers engaged in a wide range of addictive disorders. Dopaminergic pathway gene polymorphisms are being extensively studied with respect to addictive and behavioral disorders.

METHODS

From the broad literature available, the current review summarizes the specific polymorphisms of dopaminergic genes that play a role in alcohol dependence.

RESULTS

No evidence indicating any strong association between AD and polymorphisms of dopamine pathway genes has emerged from the literature.

DISCUSSION

Further studies are warranted, considering a range of alcohol-related traits to determine the genes that influence alcohol dependence.

Pharmacological, experimental therapeutic, and transcranial magnetic stimulation treatments for compulsivity and impulsivity

Obsessive-compulsive disorder (OCD) has been recently drawn apart from anxiety disorder by the Diagnostic and Statistical Manual of Mental Disorders, 5th edition (DSM-5) and clustered together with related disorders (eg, hoarding, hair pulling disorder, skin picking), which with it seems to share clinical and neurophysiological similarities. Recent literature has mainly explored brain circuitries (eg, orbitofrontal cortex, striatum), molecular pathways, and genes (eg, Hoxb8, Slitrk5, Sapap3) that represent the new target of the treatments; they also lead the development of new probes and compounds. In the therapeutic field, monotherapy with cognitive behavioral therapy (CBT) or selective serotonin reuptake inhibitors (SSRIs) is recommendable, but combination or augmentation with a dopaminergic or glutamatergic agent is often adopted. A promising therapy for OCD is represented by repetitive transcranial magnetic stimulation (rTMS), which is suitable to treat compulsivity and impulsivity depending on the protocol of stimulation and the brain circuitries targeted.

Comorbidities and continuities as ontogenic processes: toward a developmental spectrum model of externalizing psychopathology

Research on child and adolescent mental health problems has burgeoned since the inaugural issue of Development and Psychopathology was published in 1989. In the quarter century since, static models of psychopathology have been abandoned in favor of transactional models, following the agenda set by editor Dante Cicchetti and other proponents of the discipline. The transactional approach, which has been applied to autism, depression, self-injury, and delinquency, (a) specifies vulnerabilities and risk factors across multiple levels of analysis spanning genes to cultures, (b) identifies multifinal and equifinal pathways to psychopathology, and (c) transcends traditional disciplinary boundaries. However, as noted by Rutter and Sroufe (2000), specific mechanisms of continuity, discontinuity, and comorbidity of psychopathology must be identified if we wish to understand etiology fully. In this article, we present a model of early-onset externalizing behavior in which comorbidities and continuities are viewed as ontogenic processes: products of complex longitudinal transactions between interdependent individual-level vulnerabilities (e.g., genetic, epigenetic, allostatic) and equally interdependent contextual risk factors (e.g., coercive parenting, deviant peer group affiliations, neighborhood criminality). Through interactions across levels of analysis, some individuals traverse along the externalizing spectrum, beginning with heritable trait impulsivity in preschool and ending in antisociality in adulthood. In describing our model, we note that (a) the approach outlined in the DSM to subtyping externalizing disorders continues to obscure developmental pathways to antisociality, (b) molecular genetics studies will likely not identify meaningful subtypes of externalizing disorder, and (c) ontogenic trait approaches to psychopathology are much more likely to advance the discipline in upcoming years.

Personality and the acute subjective effects of d-amphetamine in humans

There is evidence that subjective responses to psychoactive drugs are related to personality traits. Here, we extend previous findings by examining personality measures in relation to acute responses to d-amphetamine (AMPH) in a large sample of healthy volunteers. Healthy adults (n=286) completed the Multidimensional Personality Questionnaire Brief Form (MPQ-BF) and participated in four sessions during which they received oral AMPH (0, 5, 10, 20 mg), under double-blind conditions. Subjective responses to the drug were measured using the Profile of Mood States, Addiction Research Center Inventory, and Drug Effects Questionnaire. Drug responses were reduced via principal components analysis to three higher-order factors ('Euphoria', 'Arousal', 'Dysphoria'). Participants were rank ordered on selected MPQ-BF scales; the top and bottom third on each trait were compared on the drug response factors. High trait physical fearlessness was significantly associated with greater amphetamine-related Arousal, and high trait reward sensitivity was significantly associated with greater Euphoria. In addition, high trait impulsivity was significantly associated with greater Arousal and Euphoria. These results provide further evidence that individual differences in the subjective effects of AMPH are partially explained by differences in personality, and are consistent with the idea that both personality and responses to stimulants depend upon shared neurochemical systems.

Hair pulling disorder (trichotillomania): genes, neurobiology, and a model for understanding impulsivity and compulsivity

Hair pulling disorder (trichotillomania) affects at least 3.7 million people in the United States and results in marked functional impairment. This article reviews empirical research investigating the genetics and neurobiology of hair pulling disorder (HPD). We also discuss recent advances in the characterization of this phenotype which have led to evidence supporting the existence of at least two disparate pulling styles-automatic and focused pulling. These pulling styles exhibit facets of behavioral processes, impulsivity and compulsivity, characteristic of several classes of disorders (e.g., obsessive-compulsive spectrum disorders, impulse control disorders). Available genetic, neurobiological, and clinical data support the importance of impulsivity for conceptualizing HPD. Impulsivity alone is insufficient to fully understand this complex phenotype. Characterizations of both automatic and focused pulling as well as preliminary findings from affective neuroscience across species highlight the importance of compulsivity for understanding HPD. Opposing and complementary aspects to impulsivity-compulsivity provide a more comprehensive conceptualization of HPD and supports HPD's potential importance for advancing scientific inquiry in relation to the pathogenesis and treatment of related phenotypes. This review concludes with a description of areas-phenotype, neurobiology, and genes-in need of further study.

Genetics of dopamine receptors and drug addiction

Dopamine plays a key role in reward behavior, yet the association of drug dependence as a chronic, relapsing disorder with the genes encoding the various dopaminergic receptor subtypes remains difficult to delineate. In the context of subsequent genome-wide association (GWAS) research and post-GWAS investigations, we summarize the novel data that link genes encoding molecules involved in the dopaminergic system (dopamine receptors, transporter and enzymes in charge of its metabolism) to drug addiction. Recent reports indicate that the heritability of drug addiction should be high enough to allow a significant role for a specific set of genes, and the available genetic studies, which might not be already conclusive because of the heterogeneity of designs, methods and recruited samples, should support the idea of a significant role of at least one gene related to dopaminergic system. Evolutionary changes in primates and non-primate animals of genes coding for molecules involved in dopaminergic system highlight why addictive disorders are mainly limited to humans. Restricting the analyses to more specific intermediate phenotypes (or endophenotypes) such as attention allocation, stress reactivity, novelty seeking, behavioral disinhibition and impulsivity, instead of the broad addictive disorder concept can be instrumental to identify novel genes associated with these traits in the context of genome-wide studies.

Reward-related genes and personality traits in alcohol-dependent individuals: a pilot case control study

Components of the brain reward system, i.e. the mesolimbic dopamine, laterodorsal cholinergic and ghrelin signaling systems, have been implicated in alcohol reward in preclinical studies. Genetic variants of these systems have previously been linked to alcohol dependence. Here, we genotyped 31 single nucleotide polymorphisms (SNPs): 1 SNP in the dopamine D₂ receptor (DRD2) gene, 20 SNPs in 5 different nicotinic acetylcholine receptor subunit (CHRN*) genes, and 10 SNPs in the genes encoding pro-ghrelin (GHRL) and its receptor (GHSR), in a pilot study of type 1 alcoholics (n = 84) and healthy controls (n = 32). These individuals were characterized using the Temperament and Character Inventory. None of the SNPs were associated with risk of alcohol dependence in this population. The GG genotype of SNP rs13261190 in the CHRNB3 was associated with increased novelty seeking, while SNPs of the ghrelin signaling system were associated with decreased self-directedness (AA of rs495225, GHSR) and alterations in self-transcendence (AA of both rs42451 and rs35680, GHRL). In conclusion, this pilot study suggests that reward-related genes are associated with altered personality scores in type 1 alcohol dependence, which warrants future studies of these associations in larger study samples.

Alcohol and the human brain: a systematic review of different neuroimaging methods

BACKGROUND

Imaging techniques have been in widespread use in the scientific community for more than 3 decades. They facilitate noninvasive, in vivo studies of the human brain in both healthy and diseased persons. These brain-imaging techniques have contributed significantly to our understanding of the effects of alcohol abuse and dependence on structural and functional changes in the human brain. A systematic review summarizing these contributions has not previously been conducted, and this is the goal of the current paper.

METHODS

The databases PubMed, PsycINFO, and PSYNDEX were searched using central key words. Fulfilling the inclusion criteria were 140 functional and structural imaging studies, together comprising data from more than 7,000 patients and controls. The structural imaging techniques we considered were cranial computerized tomography and various magnetic resonance imaging-based techniques, including voxel-based morphometry, deformation-based morphometry, diffusion tensor magnetic resonance imaging, and diffusion-weighted magnetic resonance imaging. The functional methods considered were magnetic resonance spectroscopy, positron emission tomography, single photon emission computed tomography, and functional magnetic resonance imaging.

RESULTS

Results from studies using structural imaging techniques have revealed that chronic alcohol use is accompanied by volume reductions of gray and white matter, as well as microstructural disruption of various white matter tracts. These changes are partially reversible following abstinence. Results from functional imaging methods have revealed metabolic changes in the brain, lower glucose metabolism, and disruptions of the balance of neurotransmitter systems. Additionally, functional imaging methods have revealed increased brain activity in the mesocorticolimbic system in response to alcohol-themed pictures relative to nondrug-associated stimuli, which might be of predictive value with regard to relapse.

CONCLUSIONS

There has been tremendous progress in the development of imaging technologies. Use of these technologies has clearly demonstrated the structural and functional brain abnormalities that can occur with chronic alcohol use. The study of the alcoholic brain provides an heuristic model which furthers our understanding of neurodegenerative changes in general, as well as their partial reversibility with sustained abstinence. Additionally, functional imaging is poised to become an important tool for generating predictions about individual brain functioning, which can then be used as a basis for personalized medicine.

Population-based case-control study of DRD2 gene polymorphisms and alcoholism

Several independent lines of evidence for genetic contributions to vulnerability to alcoholism exist. Dopamine is thought to play a major role in the mechanism of reward and reinforcement in response to alcohol. D2 dopamine receptor (DRD2) gene has been among the stronger candidate genes implicated in alcoholism. In this study, alcohol use was assessed in 196 randomly selected Kota individuals of Nilgiri Hills, South India. Six DRD2 SNPs were assessed in 81 individuals with alcoholism and 151 controls to evaluate the association between single nucleotide polymorphisms (SNPs) and alcoholism. Of the three models (dominant, recessive, and additive) tested for association between alcoholism and DRD2 SNPs, only the additive model shows association for three loci (rs1116313, TaqID, and rs2734835). Of six studied polymorphisms, five are in strong linkage disequilibrium forming onesingle haplotype block. Though the global haplotype analysis with these five SNPs was not significant, haplotype analysis using all six SNPs yielded a global P value of .033, even after adjusting for age. These findings support the importance of dopamine receptor gene polymorphisms in alcoholism. Further studies to replicate these findings in different populations are needed to confirm these results.

Neither single-marker nor haplotype analyses support an association between the dopamine transporter gene and heroin dependence in Han Chinese

Much evidence suggests that dysfunction of dopamine transporter-mediated dopamine transmission may be involved in the pathophysiology of substance abuse and dependence. The aim of this study was to examine whether the dopamine transporter gene (DAT1; SLC6A3) is associated with the development of heroin dependence (HD) and whether DAT1 influences personality traits in patients with HD. Polymorphisms of DAT1 were analyzed in a case-control study of 1046 Han Chinese (615 patients and 431 controls). All participants were screened using a Chinese version of the modified Schedule of Affective Disorder and Schizophrenia-Lifetime and all patients met the criteria for HD. Furthermore, a Chinese version of the Tridimensional Personality Questionnaire (TPQ) was used to assess personality traits in the patient group and examine the association between their personality traits and DAT1 polymorphisms. Of the patient group, 271 completed the TPQ. No statistically significant differences in allele or genotype frequencies of all investigated variants between HD patients and controls were observed. In haplotype analyses, four haplotype blocks of DAT1 were not associated with the development of HD. These DAT1 polymorphisms did not influence novelty seeking and harm avoidance scores in HD patients. This study suggests that the DAT1 gene may not contribute to the risk of HD and specific personality traits in HD among the Han Chinese population.

Imaging receptor changes in human drug abusers

This chapter will review the literature on differences in the brain chemistry of alcohol- and drug-dependent individuals compared to healthy controls as measured with positron emission tomography and single photon emission computed tomography. Specifically, alterations in dopamine, serotonin, opioid, and GABA systems in cocaine, alcohol, nicotine, and heroin dependence have been examined. These neurochemical systems are integrated and play significant roles in a final common pathway mediating addiction in the brain. One recurrent finding is that dopaminergic dysfunction is prevalent in both alcohol and drug dependent populations, and specifically there is a lower availability of dopamine type 2/3 receptors in cocaine-, alcohol-, nicotine-, and heroin-dependent individuals compared to healthy controls. The development of novel radiotracers that target additional receptor systems will further our understanding of the neurochemical basis of addiction.

Financial and psychological risk attitudes associated with two single nucleotide polymorphisms in the nicotine receptor (CHRNA4) gene

With recent advances in understanding of the neuroscience of risk taking, attention is now turning to genetic factors that may contribute to individual heterogeneity in risk attitudes. In this paper we test for genetic associations with risk attitude measures derived from both the psychology and economics literature. To develop a long-term prospective study, we first evaluate both types of risk attitudes and find that the economic and psychological measures are poorly correlated, suggesting that different genetic factors may underlie human response to risk faced in different behavioral domains. We then examine polymorphisms in a spectrum of candidate genes that affect neurotransmitter systems influencing dopamine regulation or are thought to be associated with risk attitudes or impulsive disorders. Analysis of the genotyping data identified two single nucleotide polymorphisms (SNPs) in the gene encoding the alpha 4 nicotine receptor (CHRNA4, rs4603829 and rs4522666) that are significantly associated with harm avoidance, a risk attitude measurement drawn from the psychology literature. Novelty seeking, another risk attitude measure from the psychology literature, is associated with several COMT (catechol-O-methyl transferase) SNPs while economic risk attitude measures are associated with several VMAT2 (vesicular monoamine transporter) SNPs, but the significance of these associations did not withstand statistical adjustment for multiple testing and requires larger cohorts. These exploratory results provide a starting point for understanding the genetic basis of risk attitudes by considering the range of methods available for measuring risk attitudes and by searching beyond the traditional direct focus on dopamine and serotonin receptor and transporter genes.

Neurological correlates of reward responding in adolescents with and without externalizing behavior disorders

Opposing theories of striatal hyper- and hypodopaminergic functioning have been suggested in the pathophysiology of externalizing behavior disorders. To test these competing theories, the authors used functional MRI to evaluate neural activity during a simple reward task in 12- to 16-year-old boys with attention-deficit/hyperactivity disorder and/or conduct disorder (n = 19) and in controls with no psychiatric condition (n = 11). The task proceeded in blocks during which participants received either (a) monetary incentives for correct responses or (b) no rewards for correct responses. Controls exhibited striatal activation only during reward, shifting to anterior cingulate activation during nonreward. In contrast, externalizing adolescents exhibited striatal activation during both reward and nonreward. Externalizing psychopathology appears to be characterized by deficits in processing the omission of predicted reward, which may render behaviors that are acquired through environmental contingencies difficult to extinguish when those contingencies change.

Effects of chronic alcohol exposure on dopamine uptake in rat nucleus accumbens and caudate putamen

RATIONALE

Existing data strongly suggest that alcohol affects dopamine (DA) neurotransmission in the brain. However, many questions remain about the effects of alcohol on the delicate equilibrium between such neurochemical processes as DA release and uptake. Dysregulation of these processes in the mesolimbic and nigrostriatal systems after chronic alcohol ingestion could be a neuroadaptation contributing to dependence.

OBJECTIVES

In the present study, we have employed an alcohol vapor inhalation model to characterize the effects of chronic alcohol exposure on DA dynamics in rat nucleus accumbens (NAc) and caudate putamen (CP) using fast-scan cyclic voltammetry (FSCV) in brain slices. This method provides a unique view of real-time, spatially resolved changes in DA concentration.

RESULTS

We found that chronic alcohol exposure enhanced DA uptake rates in rat NAc and CP. These changes would have the effect of down-regulating extracellular DA levels, presumably a compensatory effect related to increased DA release by repeated alcohol exposure. The sensitivity of terminal release-regulating DA autoreceptors was not different in alcohol-exposed rats compared with alcohol-naïve animals.

CONCLUSIONS

The DA uptake changes after chronic alcohol exposure documented here using FSCV may be associated with a compensatory response of the DA system aimed at decreasing DA signaling. Alterations in autoreceptor function may require relatively long lasting alcohol exposure.

Impulsivity and chronic stress are associated with amphetamine-induced striatal dopamine release

A challenging question that continues to plague the field of addiction is why some individuals are more vulnerable for substance use disorders than others. Several important risk factors for substance abuse have been identified in clinical studies, including trait impulsivity and environmental stress. However, the neurobiological mechanisms that underlie the relationships remain poorly understood. The purpose of this study was to examine associations among impulsivity, stress, and striatal dopamine (DA) responses to amphetamine (AMPH) in humans. Forty healthy M, F adults, ages 18-29 years, completed self-report measures of trait impulsivity, life events stress, and perceived stress. Subjects subsequently underwent two consecutive 90-min positron emission tomography (PET) studies with high specific activity [11C]raclopride. The first scan was preceded by an intravenous injection of saline; the second was preceded by 0.3 mg/kg AMPH. Findings showed that high impulsivity was associated with blunted right ventral striatal DA release. However, effects were modified by a significant interaction with life events stress. Dopamine release was greater in low vs. high impulsivity subjects under conditions of low or moderate stress. Under conditions of high stress, both groups had low DA release. Subjects with high impulsivity reported more pleasant effects with AMPH than subjects with low impulsivity. In contrast, stress was negatively associated with pleasant drug effects. No associations were observed between impulsivity or stress and cortisol responses to AMPH. The findings are consistent with notions that blunted DA responses represent an endophenotype for substance use disorders.

Polyvagal Theory and developmental psychopathology: emotion dysregulation and conduct problems from preschool to adolescence

In science, theories lend coherence to vast amounts of descriptive information. However, current diagnostic approaches in psychopathology are primarily atheoretical, emphasizing description over etiological mechanisms. We describe the importance of Polyvagal Theory toward understanding the etiology of emotion dysregulation, a hallmark of psychopathology. When combined with theories of social reinforcement and motivation, Polyvagal Theory specifies etiological mechanisms through which distinct patterns of psychopathology emerge. In this paper, we summarize three studies evaluating autonomic nervous system functioning in children with conduct problems, ages 4-18. At all age ranges, these children exhibit attenuated sympathetic nervous system responses to reward, suggesting deficiencies in approach motivation. By middle school, this reward insensitivity is met with inadequate vagal modulation of cardiac output, suggesting additional deficiencies in emotion regulation. We propose a biosocial developmental model of conduct problems in which inherited impulsivity is amplified through social reinforcement of emotional lability. Implications for early intervention are discussed.

A genetic association study of dopamine metabolism-related genes and chronic headache with drug abuse

To assess the role of dopamine metabolism-related genes in the genetic liability to chronic headache with drug abuse (DA). We performed a genetic association study using four functional polymorphisms of the dopamine receptor 4 (DRD4), dopamine transporter (DAT), mono-amino-oxidase A (MAOA) and cathecol-O-methyl-transferase (COMT) genes in 103 patients with chronic daily headache associated with DA (CDHDA). Control samples were 117 individuals without headache or DA (controls) and 101 patients with episodic migraine without aura and without DA (MO). No differences were found at the COMT and MAOA genes among the three groups investigated. Allele 4 of DRD4 was significantly overrepresented in patients with MO compared with both controls and CDHDA. Allele 10 of the DAT gene was significantly underrepresented in patients with CDHDA when compared with the MO group. Genetic variability at the DRD4 gene is involved in the predisposition to episodic MO but not to DA, while liability to CDHDA may involve genetic variability at the DAT gene in comparison with episodic MO.

Temperament characteristics, as assessed by the tridimensional personality questionnaire, moderate the response to sertraline in depressed opiate-dependent methadone patients

During a randomized, double-blind, placebo controlled study of the effects of sertraline in depressed methadone-maintained patients, 82 completed the tridimensional personality questionnaire (TPQ) to assess whether temperament dimensions can affect treatment-related changes in mood and drug use. Mood outcome significantly differed according to scores on the reward dependence scale (RD). Low RD participants displayed a significantly better mood response to sertraline than high RD participants. Participants with high harm avoidance (HA) scores were more likely to be abstinent at the end of the 12 week trial of sertraline than low HA participants. High persistence (P) participants were less likely to be abstinent at the end of the 12-week trial. These results suggest that temperament dimensions may be important for identifying substance dependent patients more likely to benefit from pharmacological interventions for comorbid depressive disorders.

Allelic association of a dopamine transporter gene polymorphism with antisocial behaviour in heroin-dependent patients

Polymorphism of a variable number of tandem repeats (VNTR) in the 3' untranslated region of exon 15 of the SLC6A3 gene, coding for the dopamine transporter (DAT), was analysed to test whether length variation contributes to differences in the individual susceptibility to aggressive - criminal behaviour and liability to heroin dependence. The repeat number of the DAT polymorphism was assessed in 125 healthy subjects and 104 heroin-dependent subjects (including 52 addicted individuals with violent behaviour and criminal records). There was no significant difference in the frequencies of genotypes and alleles between heroin-dependent subjects and control subjects. On the contrary, there was a significant difference between offenders and non-offenders, p = 0.004 and p = 0.002, respectively, among heroin-dependent subjects. No association was found between DAT polymorphism and history of suicide. Buss - Durkee Hostility Inventory (BDHI) mean total scores were significantly higher in heroin addicts than in controls (p < 0.001) and in antisocial - violent heroin addicts in comparison with addicted individuals without antisocial behaviour (p < 0.005). The regression analysis of BDHI subscales, performed to provide an estimate of the magnitude of any potential effect on the risk of aggressiveness associated with the variants in DAT VNTR, showed that the presence of the 9 - 9 genotype significantly increases the risk of irritability and direct aggressiveness more than six and 10 times with respect to the 9 - 10 genotype. Our findings suggest that the 9-repeat allele of the DAT polymorphism confers increased susceptibility to antisocial - violent behaviour and aggressiveness, rather than drug dependence per se in heroin-dependent males.

Human dopamine transporter gene variation: effects of protein coding variants V55A and V382A on expression and uptake activities

The human dopamine transporter (DAT, SLC6A3) is an important 15 exon gene for dopamine neurotransmission and dopamine recycling. Common exon 15 variable number tandem repeat variants can be associated with attention deficit/hyperactivity disorder. Rarer single nucleotide polymorphisms produce missense variants including V55A and V382A. We now report studies of the functional influences of these DAT protein-coding variants. In COS cell transient-expression assays, V382A displays about half of the dopamine uptake velocity Vmax and cocaine analog binding Bmax values of wildtype DAT. V382A lowers dopamine's potency in inhibiting cocaine analog binding by six-fold. Cells expressing V382A or mixtures of V382A and wildtype DAT both display reduced plasma membrane and increased perinuclear expression, consistent with dominant effects of V328A on expression. V55A expresses normally but reveals a 1.7-fold-lower Km for dopamine uptake. Individuals with these human DAT protein variants could display altered dopamine systems.

Sex-dependent modulation of ethanol consumption in vesicular monoamine transporter 2 (VMAT2) and dopamine transporter (DAT) knockout mice

Several lines of evidence suggest that monoaminergic systems, especially dopaminergic and serotoninergic systems, modulate ethanol consumption. Humans display significant differences in expression of the vesicular and plasma membrane monoamine transporters important for monoaminergic functions, including the vesicular monoamine transporter (VMAT2, SLC18A2) and dopamine transporter (DAT, SLC6A3). In addition, many ethanol effects differ by sex in both humans and animal models. Therefore, ethanol consumption and preference were compared in male and female wild-type mice, and knockout (KO) mice with deletions of genes for DAT and VMAT2. Voluntary ethanol (2-32% v/v) and water consumption were compared in two-bottle preference tests in wild-type (+/+) vs heterozygous VMAT2 KO mice (+/-) and in wild-type (+/+) vs heterozygous (+/-) or homozygous (-/-) DAT KO mice. Deletions of either the DAT or VMAT2 genes increased ethanol consumption in male KO mice, although these effects were highly dependent on ethanol concentration, while female DAT KO mice had higher ethanol preferences. Thus, lifetime reductions in the expression of either DAT or VMAT2 increase ethanol consumption, dependent on sex.

Relationship between personality trait and regional cerebral glucose metabolism assessed with positron emission tomography

There have been no studies systematically investigating relationships between biogenetic temperament dimensions and patterns of brain glucose metabolism. Nineteen healthy subjects were evaluated regarding the biogenetic temperament using Cloninger's Temperament and Character Inventory (TCI). In addition, [18F] fluorodeoxyglucose (FDG) positron emission tomography (PET) was used to measure regional brain glucose metabolism. Voxel-based correlation analysis was used to test correlations between regional brain glucose metabolism and scores on the TCI. We identified that each temperament dimension, such as Novelty Seeking, Harm Avoidance, and Reward Dependence, was significantly correlated with specific brain regions. The majority of correlations were observed in the areas of paralimbic regions and temporal lobes. The current study provides evidence linking each biogenetic temperament dimension with specific brain areas and provides a promising base for future personality research.