Family-based association analysis of serotonin genes in pathological gambling disorder: evidence of vulnerability risk in the 5HT-2A receptor gene

Molecular mechanisms underlying resting-state brain functional correlates of behavioral inhibition

Previous literature has established the presence of sex differences in behavioral inhibition as well as its neural substrates and related disease risk. However, there is limited evidence that speaks directly to the question of whether or not there are sex-dependent associations between behavioral inhibition and resting-state brain function and, if so, how they are modulated by the underlying molecular mechanisms. We computed functional connectivity density (FCD) using resting-state functional MRI data to examine their associations with behavioral inhibition ability measured using a Go/No-Go task across a large cohort of 510 healthy young adults. Then, we examined the spatial relationships of the FCD correlates of behavioral inhibition with gene expression and neurotransmitter atlases to explore their potential genetic architecture and neurochemical basis. A significant negative correlation between behavioral inhibition and FCD in the left superior parietal lobule was found in females but not males. Further spatial correlation analyses demonstrated that the identified neural correlates of behavioral inhibition were associated with expression of gene categories predominantly implicating essential components of the cerebral cortex (glial cell, neuron, axon, dendrite, and synapse) and ion channel activity, as well as were linked to the serotonergic system. Our findings may not only yield important insights into the molecular mechanisms underlying the female-specific neural substrates of behavioral inhibition, but also provide a critical context for understanding how biological sex might contribute to variation in behavioral inhibition and its related disease risk.

Brain 5-HT2A receptor binding and its neural network related to behavioral inhibition system

The tendency to avoid punishment, called behavioral inhibition system, is an essential aspect of motivational behavior. Behavioral inhibition system is related to negative affect, such as anxiety, depression and pain, but its neural basis has not yet been clarified. To clarify the association between individual variations in behavioral inhibition system and brain 5-HT_2A receptor availability and specify which brain networks were involved in healthy male subjects, using [¹⁸F]altanserin positron emission tomography and resting-state functional magnetic resonance imaging. Behavioral inhibition system score negatively correlated with 5-HT_2A receptor availability in anterior cingulate cortex. A statistical model indicated that the behavioral inhibition system score was associated with 5-HT_2A receptor availability, which was mediated by the functional connectivity between anterior cingulate cortex and left middle frontal gyrus, both of which involved in the cognitive control of negative information processing. Individuals with high behavioral inhibition system displays low 5-HT_2A receptor availability in anterior cingulate cortex and this cognitive control network links with prefrontal-cingulate integrity. These findings have implications for underlying the serotonergic basis of physiologies in aversion.

Understanding the genetics and neurobiological pathways behind addiction (Review)

The hypothesis issued by modern medicine states that many diseases known to humans are genetically determined, influenced or not by environmental factors, which is applicable to most psychiatric disorders as well. This article focuses on two pending questions regarding addiction: Why do some individuals become addicted while others do not? along with Is it a learned behavior or is it genetically predefined? Recent data suggest that addiction is more than repeated exposure, it is the synchronicity between intrinsic factors (genotype, sex, age, preexisting addictive disorder, or other mental illness), extrinsic factors (childhood, level of education, socioeconomic status, social support, entourage, drug availability) and the nature of the addictive agent (pharmacokinetics, path of administration, psychoactive properties). The dopamine-mesolimbic motivation-reward-reinforcement cycle remains the most coherent physiological theory in addiction. While the common property of addictive substances is that they are dopamine-agonists, each class has individual mechanisms, pharmacokinetics and psychoactive potentials.

Genome-wide association study of pathological gambling

Background

Pathological gambling is a behavioural addiction with negative economic, social, and psychological consequences. Identification of contributing genes and pathways may improve understanding of aetiology and facilitate therapy and prevention. Here, we report the first genome-wide association study of pathological gambling. Our aims were to identify pathways involved in pathological gambling, and examine whether there is a genetic overlap between pathological gambling and alcohol dependence.

Methods

Four hundred and forty-five individuals with a diagnosis of pathological gambling according to the Diagnostic and Statistical Manual of Mental Disorders were recruited in Germany, and 986 controls were drawn from a German general population sample. A genome-wide association study of pathological gambling comprising single marker, gene-based, and pathway analyses, was performed. Polygenic risk scores were generated using data from a German genome-wide association study of alcohol dependence.

Results

No genome-wide significant association with pathological gambling was found for single markers or genes. Pathways for Huntington's disease (P-value = 6.63 × 10−3); 5′-adenosine monophosphate-activated protein kinase signalling (P-value = 9.57 × 10−3); and apoptosis (P-value = 1.75 × 10−2) were significant. Polygenic risk score analysis of the alcohol dependence dataset yielded a one-sided nominal significant P-value in subjects with pathological gambling, irrespective of comorbid alcohol dependence status.

Conclusions

The present results accord with previous quantitative formal genetic studies which showed genetic overlap between non-substance- and substance-related addictions. Furthermore, pathway analysis suggests shared pathology between Huntington's disease and pathological gambling. This finding is consistent with previous imaging studies.

Neural and neurocognitive markers of vulnerability to gambling disorder: a study of unaffected siblings

Psychological and neurobiological markers in individuals with gambling disorder (GD) could reflect transdiagnostic vulnerability to addiction or neuroadaptive consequences of long-term gambling. Using an endophenotypic approach to identify vulnerability markers, we tested the biological relatives of cases with GD. Male participants seeking treatment for GD (n = 20) were compared with a male control group (n = 18). Biological siblings of cases with GD (n = 17, unrelated to the current GD group) were compared with a separate control group (n = 19) that overlapped partially with the GD control group. Participants completed a comprehensive assessment of clinical scales, neurocognitive functioning, and fMRI of unexpected financial reward. The GD group displayed elevated levels of self-report impulsivity and delay discounting, and increased risk-taking on the Cambridge Gamble Task. We did not observe impaired motor impulsivity on the stop-signal task. Siblings of GD showed some overlapping effects; namely, elevated impulsivity (negative urgency) and increased risk-taking on the Cambridge Gamble Task. We did not observe any differences in the neural response to win outcomes, either in the GD or sibling analysis compared with their control group. Within the GD group, activity in the thalamus and caudate correlated negatively with gambling severity. Increased impulsivity and risk-taking in GD are present in biological relatives of cases with GD, suggesting these markers may represent pre-existing vulnerability to GD.

Fractionating impulsivity: neuropsychiatric implications

The ability to make decisions and act quickly without hesitation can be advantageous in many settings. However, when persistently expressed, impulsive decisions and actions are considered risky, maladaptive and symptomatic of such diverse brain disorders as attention-deficit hyperactivity disorder, drug addiction and affective disorders. Over the past decade, rapid progress has been made in the identification of discrete neural networks that underlie different forms of impulsivity - from impaired response inhibition and risky decision making to a profound intolerance of delayed rewards. Herein, we review what is currently known about the neural and psychological mechanisms of impulsivity, and discuss the relevance and application of these new insights to various neuropsychiatric disorders.

Gambling disorder: an integrative review of animal and human studies

Gambling disorder (GD), previously called pathological gambling and classified as an impulse control disorder in DSM-III and DSM-IV, has recently been reclassified as an addictive disorder in the DSM-5. It is widely recognized as an important public health problem associated with substantial personal and social costs, high rates of psychiatric comorbidity, poor physical health, and elevated suicide rates. A number of risk factors have been identified, including some genetic polymorphisms. Animal models have been developed in order to study the underlying neural basis of GD. Here, we discuss recent advances in our understanding of the risk factors, disease course, and pathophysiology. A focus on a phenotype-based dissection of the disorder is included in which known neural correlates from animal and human studies are reviewed. Finally, current treatment approaches are discussed, as well as future directions for GD research.

Biochemical Diagnosis in Substance and Non-substance Addiction

An optimal biochemical marker for addiction would be some easily traced molecules in body specimens, which indicates indulgent addictive behaviors, or susceptibility to certain addictive stimuli. In this chapter, we discussed existing literature about possible biomarkers, and classified them into three categories: origin forms and metabolites of substances, markers from biochemical responses to certain addiction, and genetic and epigenetic biomarkers suggesting susceptibility to addiction. In every category, we examined studies concerning certain type of addiction one by one, with focuses mainly on opiates, psychostimulants, and pathological gambling. Several promising molecules were highlighted, including those of neurotrophic factors, inflammatory factors, and indicators of vascular injury, and genetic and epigenetic biomarkers such as serum miRNAs. DNA methylation signatures and signal nucleotide polymorphism of candidate gene underlying the addiction.

Neural and psychological underpinnings of gambling disorder: A review

Gambling disorder affects 0.4 to 1.6% of adults worldwide, and is highly comorbid with other mental health disorders. This article provides a concise primer on the neural and psychological underpinnings of gambling disorder based on a selective review of the literature. Gambling disorder is associated with dysfunction across multiple cognitive domains which can be considered in terms of impulsivity and compulsivity. Neuroimaging data suggest structural and functional abnormalities of networks involved in reward processing and top-down control. Gambling disorder shows 50-60% heritability and it is likely that various neurochemical systems are implicated in the pathophysiology (including dopaminergic, glutamatergic, serotonergic, noradrenergic, and opioidergic). Elevated rates of certain personality traits (e.g. negative urgency, disinhibition), and personality disorders, are found. More research is required to evaluate whether cognitive dysfunction and personality aspects influence the longitudinal course and treatment outcome for gambling disorder. It is hoped that improved understanding of the biological and psychological components of gambling disorder, and their interactions, may lead to improved treatment approaches and raise the profile of this neglected condition.

Behavioral addictions in addiction medicine: from mechanisms to practical considerations

Recent progress has been made in our understanding of nonsubstance or "behavioral" addictions, although these conditions and their most appropriate classification remain debated and the knowledge basis for understanding the pathophysiology of and treatments for these conditions includes important gaps. Recent developments include the classification of gambling disorder as a "Substance-Related and Addictive Disorder" in the 5th edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) and proposed diagnostic criteria for Internet Gaming Disorder in Section 3 of DSM-5. This chapter reviews current neuroscientific understandings of behavioral addictions and the potential of neurobiological data to assist in the development of improved policy, prevention, and treatment efforts.

Addiction-related genes in gambling disorders: new insights from parallel human and pre-clinical models

Neurobiological research supports the characterization of disordered gambling (DG) as a behavioral addiction. Recently, an animal model of gambling behavior was developed (rat gambling task, rGT), expanding the available tools to investigate DG neurobiology. We investigated whether rGT performance and associated risk gene expression in the rat's brain could provide cross-translational understanding of the neuromolecular mechanisms of addiction in DG. We genotyped tagSNPs (single-nucleotide polymorphisms) in 38 addiction-related genes in 400 DG and 345 non-DG subjects. Genes with P<0.1 in the human association analyses were selected to be investigated in the animal arm to determine whether their mRNA expression in rats was associated with the rat's performance on the rGT. In humans, DG was significantly associated with tagSNPs in DRD3 (rs167771) and CAMK2D (rs3815072). Our results suggest that age and gender might moderate the association between CAMK2D and DG. Moderation effects could not be investigated due to sample power. In the animal arm, only the association between rGT performance and Drd3 expression remained significant after Bonferroni correction for 59 brain regions. As male rats were used, gender effects could not be investigated. Our results corroborate previous findings reporting the involvement of DRD3 receptor in addictions. To our knowledge, the use of human genetics, pre-clinical models and gene expression as a cross-translation paradigm has not previously been attempted in the field of addictions. The cross-validation of human findings in animal models is crucial for improving the translation of basic research into clinical treatments, which could accelerate neurobiological and pharmacological investigations in addictions.

Gambling in Brazil: a call for an open debate

AIMS

To provide an overview of gambling in Brazil, including historical background, past and current legislation, gamblers' profile, treatment and research initiatives.

METHODS

Review of the published literature and research reports.

RESULTS

Gambling is deeply rooted in Brazilian history and culture, but gambling regulation historically alternates between legalization and banning. Currently, only state lotteries, horse betting and poker-playing are allowed. There is pressure to widen the games repertoire, but efforts at full legalization and commercial exploration of gambling have receded. Despite the barriers to gambling access, Brazil has prevalence rates similar to other countries: 1.0 and 1.3% life-time prevalence for pathological and problem gambling. A faster progression from regular to problem gambling was found among middle-aged women in clinical samples and for adolescent male gamblers in a population-based sample. Youth gambling is associated with severe forms of gambling and other risk-taking behaviours. Treatment options are scarce, and the public health system is unprepared to support gambling patients. Ongoing incipient efforts are being made to establish a treatment model combining psychotherapy and psychiatric comorbidity treatment with promotion of quality of life.

CONCLUSION

Life-time incidence of pathological gambling in Brazil appears similar to many other countries, at approximately 1%. Arguably, there is a need to develop a more coherent regulatory and treatment response to this societal problem.

Genetic factors in exercise adoption, adherence and obesity

Physical activity and exercise play critical roles in energy balance. While many interventions targeted at increasing physical activity have demonstrated efficacy in promoting weight loss or maintenance in the short term, long term adherence to such programmes is not frequently observed. Numerous factors have been examined for their ability to predict and/or influence physical activity and exercise adherence. Although physical activity has been demonstrated to have a strong genetic component in both animals and humans, few studies have examined the association between genetic variation and exercise adherence. In this review, we provide a detailed overview of the non-genetic and genetic predictors of physical activity and adherence to exercise. In addition, we report the results of analysis of 26 single nucleotide polymorphisms in six candidate genes examined for association to exercise adherence, duration, intensity and total exercise dose in young adults from the Training Interventions and Genetics of Exercise Response (TIGER) Study. Based on both animal and human research, neural signalling and pleasure/reward systems in the brain may drive in large part the propensity to be physically active and to adhere to an exercise programme. Adherence/compliance research in other fields may inform future investigation of the genetics of exercise adherence.

[Gambling addiction]

Extensive coherent clinical, psychopathological, neurobiological and genetic similarities with substance-related addictions justify the forthcoming classification of gambling addiction under the new category "Substance Use and Addictive Disorders" in the DSM-5. Thus, gambling addiction can be regarded as the prototype of behavioral addiction. In general it should be kept in mind that isolated gambling forms are associated with varying addictive potential due to specific situational and structural game characteristics. High rates of indebtedness, suicidality, social isolation and gambling-related crime often accompany pathological gambling. As a consequence gambling addiction represents a mental disorder with a significant economic burden. In Germany 12-month prevalence rates for problem gambling in adulthood range from 0.24 % to 0.64  % and for pathological gambling from 0.20 % to 0.56 %. Because gambling products rank among the so-called demeriting (i.e. potentially harmful) social activities, player and youth protection measures to prevent gambling disorders and associated crime should be best regulated as a state monopoly.

Genetics of impulse control disorders in Parkinson's disease

Impulse control disorders (ICD) have been recognised in Parkinson's disease (PD) as adverse effects of dopamine replacement therapy, particularly with dopamine agonists. Although virtually all PD patients are treated with dopaminergic drugs, only a minority will develop hyperdopaminergic states, suggesting predisposing and/or protecting factors. The age at onset, the sex and the dose or type of dopaminergic drugs have been identified as clinical predictive factors. Recent genetic studies have investigated associations between ICD and polymorphisms of genes involved in the dopamine metabolism pathway (COMT, DAT), dopamine receptors (DRD1, DRD2, DRD3, DRD4), serotonin receptors and its transporter (HTR2A, 5HTT), and glutamate receptors (GRIN2B). Although validation in larger and independent cohorts is needed, the results from these studies give us some insights into the pathophysiology of hyperdopaminergic states and may be useful, at term, in personalising antiparkinsonian treatment in clinical practice.