Linking ADHD, impulsivity, and drug abuse: a neuropsychological perspective

The Role of Alpha-Synuclein in Neurodevelopmental Diseases

Neurodevelopmental disorders are a group of diseases with cognitive, motor, and emotional development deficits. Alpha-synuclein (α-syn) is a synaptic protein involved in transmission and neurodevelopment. This protein was previously shown to be associated with several disorders, including Parkinson's disease. Furthermore, a close link between neurodevelopmental disorders and Parkinson's has also been found. Changes in synaptic function have been noticed in neurodevelopmental disorders, including autism spectrum disorder. Impaired neurogenesis and related cognitive problems have been associated with altered expression of α-syn. Various studies reported α-syn in different body fluids and tissues such as blood and serum. Alpha-synuclein can help in better understanding the pathogenesis of neurodevelopmental diseases and facilitating their early diagnosis. This review aims to go over the recent advances in the role of α-syn in the pathophysiology of neurodevelopmental disorders, including autism spectrum disorder, attention deficit hyperactivity disorder, and motor and social impairment, and its value as a diagnostic biomarker.

Attention Deficit Hyperactivity Disorder: A Risk Factor for Premature Discontinuation of Inpatient Opioid Withdrawal Treatment

Background: Substance use disorders present a tremendous challenge within contemporary healthcare systems. Specifically, in the domain of opioid use disorders (OUDs), several foundational elements are crucial for the efficacious management of afflicted individuals. Regrettably, the premature discontinuation of inpatient opioid withdrawal treatment is a prevalent phenomenon. This study aims to elucidate the prevalence of the premature termination of inpatient opioid withdrawal treatment among patients with comorbid ADHD. Methods: We conducted a comprehensive assessment of all participants currently undergoing inpatient opioid withdrawal treatment. Our assessment protocol included the administration of the ADHD Self-Report Scale (ADHD-SR) and the Wender Utah Rating Scale (WURS-k). Additionally, participants who met the thresholds on one or both questionnaires underwent further evaluation using the Diagnostic Interview for ADHD in Adults (DIVA-2.0). Results: The prevalence of individuals diagnosed with ADHD within the studied cohort was determined to be 29.3%. Among the subset of participants identified as ADHD-positive, a notable 54.5% prematurely ceased therapy. In contrast, among those identified as ADHD-negative, the premature discontinuation rate was substantially lower at 28.3%. Conclusions: In summary, the impact of ADHD as a comorbid condition on the efficacy of inpatient opioid withdrawal treatment has been underscored. By identifying comorbid ADHD early in the treatment process, tailored therapeutic approaches may help to maximize the effectiveness of interventions and may improve patient outcomes. This underscores the importance of proactive screening for ADHD as a psychiatric comorbidity in optimizing the management of individuals undergoing inpatient opioid withdrawal treatment.

[Spectrum of Complex Partial Performance Disorders in Patients with Mental Illnesses]

INTRODUCTION

Recent research highlights a high prevalence of minimal cerebral dysfunctions (MCD) in patients with mental disorders. Nonetheless, empirical understanding of minimal cerebral dysfunctions and diffuse neuropsychological impairments in adult patients remains limited.

METHOD

In our study, we examined 399 patients with diverse common mental disorders on minimal cerebral dysfunctions. 329 patients were in psychosomatic rehabilitation, 40 in forensic psychiatry, and 30 in an addiction ward of a psychiatric hospital at the time of the study. Symptom patterns and anamnesis of MCD and sociodemographic characteristics of the patients were recorded using structured questionnaires.

RESULTS

Overall, about 29% of all patients reported MCD symptoms. Patients with MCD reported greater problem burden in everyday coping (attention, arithmetic, memory, sensitivity to noise, orientation) and social interaction (outsider, excitability) than patients without partial performance disorders.

CONCLUSIONS

Patients with mental illness reported a heterogeneous pattern of minimal cerebral dysfunctions. These frequent disorders should be recognized in diagnostics and treatment. Further studies should investigate therapeutic approaches for MCD according to Baltes' Selective Optimization and Compensation model.

Motor impulsivity but not risk-related impulsive choice is associated to drug intake and drug-primed relapse

Introduction

Motor impulsivity and risk-related impulsive choice have been proposed as vulnerability factors for drug abuse, due to their high prevalence in drug abusers. However, how these two facets of impulsivity are associated to drug abuse remains unclear. Here, we investigated the predictive value of both motor impulsivity and risk-related impulsive choice on characteristics of drug abuse including initiation and maintenance of drug use, motivation for the drug, extinction of drug-seeking behavior following drug discontinuation and, finally, propensity to relapse.

Methods

We used the Roman High- (RHA) and Low- Avoidance (RLA) rat lines, which display innate phenotypical differences in motor impulsivity, risk-related impulsive choice, and propensity to self-administer drugs. Individual levels of motor impulsivity and risk-related impulsive choice were measured using the rat Gambling task. Then, rats were allowed to self-administer cocaine (0.3 mg/kg/infusion; 14 days) to evaluate acquisition and maintenance of cocaine self-administration, after which motivation for cocaine was assessed using a progressive ratio schedule of reinforcement. Subsequently, rats were tested for their resistance to extinction, followed by cue-induced and drug-primed reinstatement sessions to evaluate relapse. Finally, we evaluated the effect of the dopamine stabilizer aripiprazole on reinstatement of drug-seeking behaviors.

Results

We found that motor impulsivity and risk-related impulsive choice were positively correlated at baseline. Furthermore, innate high levels of motor impulsivity were associated with higher drug use and increased vulnerability to cocaine-primed reinstatement of drug-seeking. However, no relationships were observed between motor impulsivity and the motivation for the drug, extinction or cue-induced reinstatement of drug-seeking. High levels of risk-related impulsive choice were not associated to any aspects of drug abuse measured in our study. Additionally, aripiprazole similarly blocked cocaine-primed reinstatement of drug-seeking in both high- and low-impulsive animals, suggesting that aripiprazole acts as a D_2/3R antagonist to prevent relapse independently of the levels of impulsivity and propensity to self-administer drugs.

Discussion

Altogether, our study highlights motor impulsivity as an important predictive factor for drug abuse and drug-primed relapse. On the other hand, the involvement of risk-related impulsive choice as a risk factor for drug abuse appears to be limited.

Quality of life implications for elevated trait impulsivity in people with Parkinson's disease

BACKGROUND

Several non-motor features of Parkinson's disease (PD) are known to adversely affect patient health-related quality of life (HRQL). However, the specific impact of neuropsychiatric complications, such as impulsive behaviour, is yet to be elucidated.

OBJECTIVES

The present cross-sectional, observational study aimed to investigate the effects of heightened trait impulsivity on HRQL in individuals with PD.

METHODS

A total of 322 people with idiopathic PD were sequentially recruited from Movement Disorder clinics across Australia. Trait impulsivity in patients was determined by Barratt's Impulsiveness Scale Version 11 (BIS-11), and grouped into tertiles (low, medium, and high). Patient HRQL was determined by the 39-item Parkinson's Disease Questionnaire (PDQ-39), complemented by the Cambridge Behavioural Inventory-Revised (CBI-R) indicating caregivers' perception of patient HRQL.

RESULTS

When total BIS-11 scores were grouped into tertiles, patient perceived and caregiver-perceived HRQL were 1.7-fold (p < .001) and 2.2-fold (p < .001) worse in the high BIS-11 group when compared to patients in the low group. Univariate analysis revealed significant associations between second-order attentional (p < .001) and non-planning (p < .001) impulsivity domains with PDQ-39 scores. When controlling for confounding demographic and clinical variables, a multivariate linear regression model revealed second-order attentional impulsivity was independently predictive of poor patient perceived HRQL (p < .001).

CONCLUSION

These findings suggest that increasing trait impulsivity is significantly associated with patient perceived HRQL in PD. Improved knowledge and recognition of subclinical impulsivity may guide clinicians' treatment and reduce disease burden for patients experiencing PD symptoms.

Internet Gaming Disorder in Children and Adolescents with Attention Deficit Hyperactivity Disorder

Although Attention Deficit Hyperactivity Disorder (ADHD) has been related to an increased risk for behavioral addictions, the relationship between ADHD and Internet Gaming Disorder (IGD) is still debated. The aim of this study is to address this topic by exploring the prevalence of IGD in a consecutive sample of ADHD youth, compared to a normal control group, and by assessing selected psychopathological and cognitive features in ADHD patients with and without IGD. One hundred and eight patients with ADHD (mean age 11.7 ± 2.6 years, 96 males) and 147 normal controls (NC) (mean age 13.9 ± 3.0 years, 114 males) were included in the study and received structured measures for IGD. In the ADHD group, 44% of the sample were above the IGD cut-off, compared to 9.5% in the NC group. ADHD patients with IGD presented with greater severity and impairment, more severe ADHD symptomatology, more internalizing symptoms, particularly withdrawal/depression and socialization problems, and more prominence of addiction and evasion dimensions. A binary logistic regression showed that the degree of inattention presented a greater weight in determining IGD. These findings may be helpful for identifying, among ADHD patients, those at higher risk for developing a superimposed IGD.

Sign tracking predicts suboptimal behavior in a rodent gambling task

RATIONALE

Reward-associated cues can promote maladaptive behavior, including risky decision-making in a gambling setting. A propensity for sign tracking over goal tracking-i.e., interaction with a reward-predictive cue rather than the site of reward-demonstrates an individual's tendency to transfer motivational value to a cue. However, the relationship of sign tracking to risky decision-making remains unclear.

OBJECTIVES

To determine whether sign tracking predicts risky choice, we used a Pavlovian conditioned approach task to evaluate the tendency of male rats to sign track to a lever cue and then trained rats on a rodent gambling task (rGT) with win-associated cues. We also tested the effects of D-amphetamine, quinpirole (a D₂/D₃ receptor agonist), and PD128907 (a D₃ receptor agonist) on gambling behavior in sign tracker and goal tracker individuals.

RESULTS

Increased sign tracking relative to goal tracking was associated with suboptimal performance on the rGT, including decreased selection of the optimal choice, increased selection of a high-risk/high-reward option, and increased impulsive premature choices. Amphetamine increased choices of a low-risk/low-reward option at the expense of optimal and high-risk choices, whereas quinpirole and PD128907 had little effect on choice allocation, but reduced impulsivity. Drug effects were similar across sign tracker and goal tracker individuals.

CONCLUSIONS

Cue reactivity, as measured by sign tracking, is predictive and may be an important driver of risky and impulsive choices in a gambling setting laden with salient audiovisual cues. Evaluating an individual's sign tracking behavior may be an avenue to predict vulnerability to pathological gambling and the efficacy of treatments.

Intact Context-Dependent Modulation of Conflict Monitoring in Childhood ADHD

Objective: Conflict monitoring is well known to be modulated by context. This is known as the Gratton effect, meaning that the degree of interference is smaller when a stimulus-response conflict had been encountered previously. It is unclear to what extent these processes are changed in ADHD. Method: Children with ADHD (combined subtype) and healthy controls performed a modified version of the sequence flanker task. Results: Patients with ADHD made significantly more errors than healthy controls, indicating general performance deficits. However, there were no differences regarding reaction times, indicating an intact Gratton effect in ADHD. These results were supported by Bayesian statistics. Conclusion: The results suggest that the ability to take contextual information into account during conflict monitoring is preserved in patients with ADHD despite this disorder being associated with changes in executive control functions overall. These findings are discussed in light of different theoretical accounts on contextual modulations of conflict monitoring.

The neurobehavioral mechanisms of motivational control in attention-deficit/hyperactivity disorder

Attention-deficit/hyperactivity disorder (ADHD) poses debilitating impairments in the neurobehavioral systems governing reward-related processes-key to the control of motivated behaviors. Individuals with ADHD may rely on a motivational control system that favors cue-driven habits-rooted in the posterior putamen-over caudate and prefrontal cortex-driven goal-directed behaviors. We examined the neurobehavioral correlates of motivational control in ADHD. Twenty-five adults with ADHD and 25 neurotypicals underwent fMRI while training on two stimulus-response-outcome associations. A devaluation procedure followed, whereby they were selectively satiated on one of the snack outcomes, decreasing its value. A subsequent extinction test determined outcome-sensitivity (i.e., whether responses towards devalued snack diminished). Despite behavioral similarities, the ADHD group displayed a distinct neural signature marked by enhanced posterior putamen activation as a function of training. This region also displayed diminished functional connectivity with the dorsal anterior cingulate cortex, which is associated with top-down control. Our whole-brain analysis yielded ADHD-specific posterior putamen and opercular/insular cortex activity over the course of training-regions associated with stimulus-sensitivity and maladaptively rigid behaviors, respectively. Neural comparisons also identified hyper-recruitment of the hippocampus in the ADHD group. These results highlight corticostriatal discrepancies in ADHD, possibly serving as a biomarker of the disorder.

Intact Stimulus-Response Conflict Processing in ADHD-Multilevel Evidence and Theoretical Implications

Attention-deficit-hyperactivity disorder (ADHD) is closely associated with deficits in cognitive control. It seems, however, that the degree of deficits strongly depends on the examined subprocess, with the resolution of stimulus–stimulus conflicts being particularly difficult for patients with ADHD. The picture is far less clear regarding stimulus–response conflicts. The current study provides multi-level behavioural and neurophysiological data on this type of conflict monitoring in children with ADHD compared to healthy controls. To account for the potentially strong effects of intra-individual variability, electroencephalogram (EEG) signal decomposition methods were used to analyze the data. Crucially, none of the analyses (behavioural, event-related potentials, or decomposed EEG data) show any differences between the ADHD group and the control group. Bayes statistical analysis confirmed the high likelihood of the null hypothesis being true in all cases. Thus, the data provide multi-level evidence showing that conflict monitoring processes are indeed partly intact in ADHD, even when eliminating possible biasing factors such as intra-individual variability. While stimulus–stimulus conflict processing has been shown to be consistently dysfunctional in ADHD, the resolution of stimulus–response conflicts is not deficient in this patient group. In comparison to other studies, the results provide novel theoretical insights into the nature of conflict control deficits in childhood ADHD.

Personality Traits or Genetic Determinants-Which Strongly Influences E-Cigarette Users?

Presently, a growing popularity of electronic cigarettes may be observed. Used as a means of obtaining nicotine they allow to substitute traditional cigarettes. The origins of substance use disorders are conditioned by dopaminergic signaling which influences motivational processes being elementary factors conditioning the process of learning and exhibiting goal-directed behaviors. The study concentrated on analysis of three polymorphisms located in the dopamine receptor 2 (DRD2) gene—rs1076560, rs1799732 and rs1079597 using the PCR method, personality traits determined with the Big Five Questionnaire, and anxiety measured with the State Trait Anxiety Inventory. The study was conducted on a group of 394 volunteers, consisting e-cigarette users (n = 144) and controls (n = 250). Compared to the controls the case group subjects achieved significantly higher scores in regard to the STAI state and the trait scale, as well as the NEO-FFI Neuroticism and Openness scale. Likewise, in the case of the STAI state for DRD2 rs1076560 significant differences were found. Furthermore, while comparing the groups (e-cigarette users vs. controls) we noticed interactions for the NEO FFI Neuroticism and DRD2 rs1076560. The same was observed in the case of interactions significance while comparing groups (e-cigarette users vs. controls) for the STAI trait/scale and DRD2 rs1799732. Findings from this study demonstrate that psychological factors and genetic determinants should be analyzed simultaneously and comprehensively while considering groups of addicted patients. Since the use, and rapid increase in popularity, of electronic cigarettes has implications for public health, e-cigarette users should be studied holistically, especially younger groups of addicted and experimenting users.

The Ankyrin Repeat and Kinase Domain Containing 1 Gene Polymorphism (ANKK1 Taq1A) and Personality Traits in Addicted Subjects

The Taq1A polymorphism located in the ANKK1 gene is one of the most widely studied polymorphisms in regards to the genetics of behavior and addiction. The aim of our study was to analyze this polymorphism with regard to personality characteristics and anxiety measured by means of the Personality Inventory—(NEO Five-Factor Inventory—NEO—FFI) and the State-Trait Anxiety Inventory (STAI) in polysubstance addicted subjects. The study group consisted of 600 male volunteers, including 299 addicted subjects and 301 controls. Psychiatrists recruited members for both groups. Addiction was diagnosed in the case group. In the control group mental illness was excluded. The same psychometric test and genotyping using the real-time PCR (polymerase chain reaction) method was performed for both groups. The results were investigated by means of multivariate analysis of the main effects Multi-factor ANOVA. Significantly higher scores on the scale of STAI state and Neuroticism and Openness traits, as well as lower scores on the scales of Extraversion, Agreeability, and Conscientiousness, were found in the case group subjects, compared to the controls. Differences in frequency of genotypes and alleles of Taq1A polymorphism between the studied groups were not found. Multi-factor ANOVA of addicted subjects and control subjects and the ANKK1 Taq1A variant interaction approximated the statistical significance for the STAI state. The main effects ANOVA of both subjects’ groups were found for the STAI state and trait, the Neuroticism scale, the Extraversion scale, and the Agreeability scale. The ANKK1 Taq1A main effects approximated the statistical significance of the STAI trait. Our study shows not only differences in personality traits between addicted and non-addicted subjects, but also the possible impact of ANKK1 on given traits and on addiction itself.

Brain circuitry associated with the development of substance use in bipolar disorder and preliminary evidence for sexual dimorphism in adolescents

Substance use disorders and mood disorders are highly comorbid and confer a high risk for adverse outcomes. However, data are limited on the neurodevelopmental basis of this comorbidity. Substance use initiation typically occurs during adolescence, and sex-specific developmental mechanisms are implicated. In this preliminary study, we review the literature and investigate regional gray matter volume (GMV) associated with subsequent substance use problems in adolescents with bipolar disorder (BD) and explore these associations for females and males. Thirty adolescents with DSM-IV-diagnosed BD and minimal alcohol/substance exposure completed baseline structural magnetic resonance imaging scans. At follow-up (on average 6 years post baseline), subjects were administered the CRAFFT interview and categorized into those scoring at high ( ≥ 2: CRAFFT_HIGH ) vs. low ( < 2: CRAFFT_LOW ) risk for alcohol/substance problems. Lower GMV in prefrontal, insular, and temporopolar cortices were observed at baseline among adolescents with BD reporting subsequent alcohol and cannabis use compared to adolescents with BD who did not (P < 0.005, clusters ≥ 20 voxels). Lower dorsolateral prefrontal GMV was associated with future substance use in both females and males. In females, lower orbitofrontal and insula GMV was associated with future substance use, while in males, lower rostral prefrontal GMV was associated with future use. Lower orbitofrontal, insular, and temporopolar GMV was observed in those who transitioned to smoking tobacco. Findings indicate that GMV development is associated with risk for future substance use problems in adolescents with BD, with results implicating GMV development in regions subserving emotional regulation in females and regions subserving executive processes and attention in males. © 2016 Wiley Periodicals, Inc.

Difference in Perseverative Errors during a Visual Attention Task with Auditory Distractors in Alpha-9 Nicotinic Receptor Subunit Wild Type and Knock-Out Mice

The auditory efferent system is a neural network that originates in the auditory cortex and projects to the cochlear receptor through olivocochlear (OC) neurons. Medial OC neurons make cholinergic synapses with outer hair cells (OHCs) through nicotinic receptors constituted by α9 and α10 subunits. One of the physiological functions of the α9 nicotinic receptor subunit (α9-nAChR) is the suppression of auditory distractors during selective attention to visual stimuli. In a recent study we demonstrated that the behavioral performance of alpha-9 nicotinic receptor knock-out (KO) mice is altered during selective attention to visual stimuli with auditory distractors since they made less correct responses and more omissions than wild type (WT) mice. As the inhibition of the behavioral responses to irrelevant stimuli is an important mechanism of the selective attention processes, behavioral errors are relevant measures that can reflect altered inhibitory control. Errors produced during a cued attention task can be classified as premature, target and perseverative errors. Perseverative responses can be considered as an inability to inhibit the repetition of an action already planned, while premature responses can be considered as an index of the ability to wait or retain an action. Here, we studied premature, target and perseverative errors during a visual attention task with auditory distractors in WT and KO mice. We found that α9-KO mice make fewer perseverative errors with longer latencies than WT mice in the presence of auditory distractors. In addition, although we found no significant difference in the number of target error between genotypes, KO mice made more short-latency target errors than WT mice during the presentation of auditory distractors. The fewer perseverative error made by α9-KO mice could be explained by a reduced motivation for reward and an increased impulsivity during decision making with auditory distraction in KO mice.

Intrinsic Network Connectivity Patterns Underlying Specific Dimensions of Impulsiveness in Healthy Young Adults

Impulsiveness is a central human personality trait and of high relevance for the development of several mental disorders. Impulsiveness is a multidimensional construct, yet little is known about dimension-specific neural correlates. Here, we address the question whether motor, attentional and non-planning components, as measured by the Barratt Impulsiveness Scale (BIS-11), are associated with distinct or overlapping neural network activity. In this study, we investigated brain activity at rest and its relationship to distinct dimensions of impulsiveness in 30 healthy young adults (m/f = 13/17; age mean/SD = 26.4/2.6 years) using resting-state functional magnetic resonance imaging at 3T. A spatial independent component analysis and a multivariate model selection strategy were used to identify systems loading on distinct impulsivity domains. We first identified eight networks for which we had a-priori hypotheses. These networks included basal ganglia, cortical motor, cingulate and lateral prefrontal systems. From the eight networks, three were associated with impulsiveness measures (p < 0.05, FDR corrected). There were significant relationships between right frontoparietal network function and all three BIS domains. Striatal and midcingulate network activity was associated with motor impulsiveness only. Within the networks regionally confined effects of age and gender were found. These data suggest distinct and overlapping patterns of neural activity underlying specific dimensions of impulsiveness. Motor impulsiveness appears to be specifically related to striatal and midcingulate network activity, in contrast to a domain-unspecific right frontoparietal system. Effects of age and gender have to be considered in young healthy samples.

Transitions and Motivations for Substance Misuse in Prison Inmates With ADHD and Conduct Disorder: Validation of a New Instrument

OBJECTIVE

There is a reasonable theoretical base for understanding the possible causes and motivations behind substance misuse and its dependency. There is a need for a reliable and valid measure that delineates the markers of substance use from its initiation and identifies different motivations for drug use transitioning, maintenance, and dependency. We addressed this gap in the United Kingdom by examining and validating the Substance Transitions in Addiction Rating Scale (STARS).

METHODS

For this review, 390 male prisoners were screened for conduct disorder and assessed with a clinical diagnostic interview for attention deficit/hyperactivity disorder (ADHD). They completed the four STARS subscales regarding their substance use. Exploratory structural equation modeling was performed to assess the STARS structure and to derive factors to assess validity against ADHD and conduct disorder diagnostic categories.

RESULTS

Each of the subscales produced meaningful and reliable factors that supported the self-medication and behavioral disinhibition hypotheses of substance use motivation. The findings robustly show that ADHD is significantly associated with the need for coping as a way of managing primary and comorbid symptoms, but not conduct disorder. The findings were strongest for the combined ADHD type.

DISCUSSION

STARS has a great potential to further the understanding of the motivation behind substance use and its dependency in different populations.

Association between risky behaviors in adolescents and altered psychophysiological emotional responses

Introducción. La psicofisiología de la respuesta emocional en la adolescencia es un factor clave en la comprensión de conductas de riesgo y desadaptación.Objetivo. Comparar especificidades de la reacción psicofisiológica emocional entre adolescentes con y sin conductas de riesgo.Materiales y métodos. Las medidas consistieron en la caracterización de conductas de riesgo (CR), variaciones en la frecuencia cardiaca (FC) electromiografía (EMG), conductancia de la piel (CP) y temperatura durante la presentación de estímulos emocionales visuales, así como la calificación en parámetros de valencia emocional, activación y dominancia de dichos estímulos.Resultados. Se encontraron diferencias significativas entre los adolescentes con CR comparados con aquellos que no las presentaban: se detectaron signos de mayor reacción psicofisiológica a los estímulos emocionales.Conclusiones. El grupo control se caracterizó por una bradicardia inicial más expresiva en comparación con el grupo con CR, ambos grupos mostraron desaceleración cardíaca más pronunciada ante estímulos desagradables, niveles más altos en EMG ante estímulos agradables en el grupo con RB e indicadores más elevados de CP ante los tres tipos de estímulo. Se requiere un estudio de cohorte a fin de comparar los hallazgos actuales en CR frente a la reacción fisiológica emocional entre los grupos de adolescentes.

α2A -Adrenergic receptor polymorphisms and mRNA expression levels are associated with delay discounting in cocaine users

Cocaine users characteristically display preferences for smaller immediate rewards over larger delayed rewards, and this delay discounting (DD) has been proposed as an endophenotype of cocaine addiction. Recent evidence suggests that the norepinephrine system and more specifically the α_2A -adrenergic receptor (ADRA2A) are impacted by chronic cocaine use while also being potentially involved in the neural mechanisms underlying DD. Hence, we investigated the effects of ADRA2A polymorphisms and ADRA2A mRNA expression levels on DD of cocaine users and stimulant-naïve controls. Two hundred and twenty-three participants (129 cocaine users and 94 stimulant-naïve healthy controls) completed a computerized DD paradigm and were genotyped for three single nucleotide polymorphisms (SNPs; rs1800544, rs521674 and rs602618) in the ADRA2A gene, while their peripheral ADRA2A mRNA expression was quantified in whole blood samples. The three SNPs were in near-perfect linkage disequilibrium. Accordingly, significant group*genotype interactions were found for all three ADRA2A variants revealing steeper DD in cocaine users (but not in controls) carrying the G-allele of SNP rs1800544, the T-allele of rs521674 and the C-allele of rs602618. Similarly, high ADRA2A mRNA expression levels were significantly associated with a reduced tendency to choose smaller more immediate rewards (over larger delayed rewards) in cocaine users but not in controls. As the relationship between DD and cocaine use was moderated by ADRA2A SNPs and by peripheral ADRA2A gene expression, we propose that the norepinephrine system is involved in DD deficits observed in cocaine using individuals. Consequently, pharmacological compounds targeting ADRA2As might be considered for the symptom-specific treatment of delay aversion in stimulant addiction.

Association between Internet gaming disorder and adult attention deficit and hyperactivity disorder and their correlates: Impulsivity and hostility

Internet gaming disorder (IGD) and attention deficit and hyperactivity disorder (ADHD) are associated with impulsivity and hostility. This study evaluated the associations among ADHD, impulsivity, hostility, and IGD. We recruited 87 individuals with IGD and 87 controls without a history of IGD. All participants underwent a diagnostic interview based on the DSM-5 IGD criteria and DSM-IV-TR ADHD criteria and completed a questionnaire regarding impulsivity and hostility. The information from the diagnostic interviews was assessed using the clinical global impression scale. The results suggested that IGD is associated with ADHD among young adults and that young adults with both IGD and ADHD have higher impulsivity and hostility. Furthermore, impulsivity and hostility mediate the association between ADHD and IGD. Thus, ADHD is a common comorbidity of IGD among young adults, and impulsivity and hostility are major factors involved in comorbid ADHD and IGD. Young adults with ADHD should be thoroughly assessed, particularly for their impulsivity and hostility, and interventions for IGD should be developed.

Cross-generational transmission from drug abuse in parents to attention-deficit/hyperactivity disorder in children

BACKGROUND

Attention-deficit/hyperactivity disorder (ADHD) predisposes to drug abuse (DA) and twin studies suggest shared genetic effects. We here seek to determine, using adoption and adoption-like samples, the magnitude of the cross-generational transmission from DA in parents to ADHD in their children and clarify the degree to which this arises from genetic v. rearing effects.

METHOD

We ascertained ADHD and DA from multiple Swedish registries. Statistical analysis was performed by Cox and path models.

RESULTS

Risk for ADHD was significantly and similarly increased in the offspring of biological mothers and fathers with DA who did v. did not rear their offspring. Risk for ADHD was not elevated in the offspring of adoptive or step-parents with DA.

CONCLUSIONS

Cross-generational transmission was observed from DA in parents to ADHD in their children. An analysis of adoptive and adoptive-like parent-offspring relationships suggested that this transmission results from genetic and not from rearing effects.

Developmental role of acetylcholinesterase in impulse control in zebrafish

Cellular and molecular processes that mediate individual variability in impulsivity, a key behavioral component of many neuropsychiatric disorders, are poorly understood. Zebrafish heterozygous for a nonsense mutation in ache (ache^sb55/+) showed lower levels of impulsivity in a 5-choice serial reaction time task (5-CSRTT) than wild type and ache^+∕+. Assessment of expression of cholinergic (nAChR), serotonergic (5-HT), and dopamine (DR) receptor mRNA in both adult and larval (9 dpf) ache^sb55/+ revealed significant downregulation of chrna2, chrna5, and drd2 mRNA in ache^sb55/+ larvae, but no differences in adults. Acute exposure to cholinergic agonist/antagonists had no effect on impulsivity, supporting the hypothesis that behavioral effects observed in adults were due to lasting impact of developmental alterations in cholinergic and dopaminergic signaling. This shows the cross-species role of cholinergic signaling during brain development in impulsivity, and suggests zebrafish may be a useful model for the role of cholinergic pathways as a target for therapeutic advances in addiction medicine.

Serotonin: waiting but not rewarding

A new study in mice demonstrates that stimulating dorsal raphe serotonin boosts patient waiting but stimulation itself is not rewarding. Dorsal raphe serotonin's unique contribution provides a neural locus for impulsivity and related failures of patience.

The neurometabolic fingerprint of excessive alcohol drinking

'Omics' techniques are widely used to identify novel mechanisms underlying brain function and pathology. Here we applied a novel metabolomics approach to further ascertain the role of frontostriatal brain regions for the expression of addiction-like behaviors in rat models of alcoholism. Rats were made alcohol dependent via chronic intermittent alcohol vapor exposure. Following a 3-week abstinence period, rats had continuous access to alcohol in a two-bottle, free-choice paradigm for 7 weeks. Nontargeted flow injection time-of-flight mass spectrometry was used to assess global metabolic profiles of two cortical (prelimbic and infralimbic) and two striatal (accumbens core and shell) brain regions. Alcohol consumption produces pronounced global effects on neurometabolomic profiles leading to a clear separation of metabolic phenotypes between treatment groups, particularly. Further comparisons of regional tissue levels of various metabolites, most notably dopamine and Met-enkephalin, allow the extrapolation of alcohol consumption history. Finally, a high-drinking metabolic fingerprint was identified indicating a distinct alteration of central energy metabolism in the accumbens shell of excessively drinking rats that could indicate a so far unrecognized pathophysiological mechanism in alcohol addiction. In conclusion, global metabolic profiling from distinct brain regions by mass spectrometry identifies profiles reflective of an animal's drinking history and provides a versatile tool to further investigate pathophysiological mechanisms in alcohol dependence.

Attention-deficit/hyperactivity disorder and risk for drug use disorder: a population-based follow-up and co-relative study

BACKGROUND

Although the association between attention-deficit/hyperactivity disorder (ADHD) and drug use disorder (DUD) is well documented, it is unclear whether it is causal or results from familial confounding.

METHOD

In this study we included all 551 164 individuals born in Sweden between 1991 and 1995 and used linked data from multiple nationwide registries to identify those with ADHD prior to age 15 years (1.71%). We used Cox proportional hazards models to investigate the future risk for DUD as a function of an ADHD registration and then compared the results from the entire population with the results from a co-relative design. Using the Swedish Multi-Generation Register, we identified all full-sibling, half-sibling and first-cousin pairs discordant for ADHD.

RESULTS

In the population sample, ADHD had a substantially increased risk for future DUD with a hazard ratio (HR) of 3.34 after accounting for gender and parental education. Examining discordant cousin pairs, discordant half-siblings and discordant siblings, those with ADHD had HRs for DUD of 3.09, 2.10 and 2.38 respectively. Controlling for the number of ADHD registrations, ADHD patients with and without stimulant treatment were similarly associated with later DUD risk.

CONCLUSIONS

ADHD diagnosed before 15 years of age was strongly related to future risk for DUD. The magnitude of this association was modestly reduced in relative pairs discordant for ADHD, suggesting that the ADHD-DUD association is partly causal and partly a result of familial confounding. We found no evidence to suggest that this association resulted from stimulant treatment.

Molecular psychiatry of zebrafish

Due to their well-characterized neural development and high genetic homology to mammals, zebrafish (Danio rerio) have emerged as a powerful model organism in the field of biological psychiatry. Here, we discuss the molecular psychiatry of zebrafish, and its implications for translational neuroscience research and modeling central nervous system (CNS) disorders. In particular, we outline recent genetic and technological developments allowing for in vivo examinations, high-throughput screening and whole-brain analyses in larval and adult zebrafish. We also summarize the application of these molecular techniques to the understanding of neuropsychiatric disease, outlining the potential of zebrafish for modeling complex brain disorders, including attention-deficit/hyperactivity disorder (ADHD), aggression, post-traumatic stress and substance abuse. Critically evaluating the advantages and limitations of larval and adult fish tests, we suggest that zebrafish models become a rapidly emerging new field in modern molecular psychiatry research.

The four causes of ADHD: a framework

In addition to the symptoms singled out by the diagnostic criteria for Attention-Deficit Hyperactivity Disorder (ADHD), a comprehensive definition should inform us of the events that trigger ADHD in both its acute and chronic manifestations; the neurobiology that underlies it; and the evolutionary forces that have kept it in the germ line of our species. These factors are organized in terms of Aristotle's four kinds of "causes," or explanations: formal, efficient, material, and final. This framework systematizes the nosology, biology, psychology, and evolutionary pressures that cause ADHD.

Pharmacological treatment of attention deficit hyperactivity disorder with co-morbid drug dependence

BACKGROUND

Drug dependence is frequent in patients with attention deficit hyperactivity disorder (ADHD). Nevertheless, the efficacy and safety of pharmacological treatments in this population are unclear.

METHODS

A systematic review with meta-analysis was performed. Randomised placebo-controlled clinical trials investigating the efficacy of pharmacological treatment in patients with co-occurring ADHD and substance use disorder (SUD) were included. ADHD symptom severity, drug abstinence and all-cause treatment discontinuation were the primary study endpoints. The effects of patient-, intervention- and study-related covariates over the primary outcomes were investigated by means of meta-regression.

RESULTS

Thirteen studies were included, enrolling a total of 1,271 patients. A small to moderate reduction of ADHD symptoms was found. Meta-regression analysis identified the presence of a lead-in period as a covariate associated with reduced efficacy. Conversely, no beneficial effect was observed either on drug abstinence or treatment discontinuation. The efficacy on ADHD symptoms was smaller in studies with a lead-in period. A positive correlation between the efficacy for ADHD and that for SUD was found.

CONCLUSIONS

The efficacy of pharmacological interventions for co-occurring ADHD and SUD has been little investigated. Mixed results were obtained: while pharmacological interventions improved ADHD symptoms, no beneficial effect on drug abstinence or on treatment discontinuation was noted. The strength of the recommendation of pharmacological treatment for co-occurring ADHD and SUD is therefore modest. The study was registered with the international prospective register of systematic reviews (PROSPERO): CRD 4212003414.

Prevalence of purging at age 16 and associations with negative outcomes among girls in three community-based cohorts

BACKGROUND

The comorbidity of purging behaviours, such as vomiting, inappropriate use of laxatives, diuretics or slimming medications, has been examined in literature. However, most studies do not include adolescents, individuals who purge in the absence of binge eating, or those purging at subclinical frequency. This study examines the prevalence of purging among 16-year-old girls across three countries and their association with substance use and psychological comorbidity.

METHODS

Data were obtained by questionnaire in 3 population-based cohorts (Avon Longitudinal Study of Parents and Children (ALSPAC), United Kingdom, n = 1,608; Growing Up Today Study (GUTS), USA, n = 3,504; North Finland Birth Cohort (NFBC85/86), Finland, n = 2,306). Multivariate logistic regressions were employed to estimate associations between purging and outcomes. Four models were fit adjusting for binge eating and potential confounders of these associations.

RESULTS

In ALSPAC, 9.7% of girls reported purging in the 12-months prior to assessment, 7.3% in GUTS, and 3.5% in NFBC. In all 3 cohorts, purging was associated with adverse outcomes such as binge drinking (ALSPAC: odds ratio (OR) = 2.0, 95% confidence interval (CI) = 1.4-2.9; GUTS: OR = 2.5, 95% CI = 1.5-4.0; NFBC: OR = 1.7, 95% CI = 1.0-2.8), drug use (ALSPAC: OR = 2.9, 95% CI = 1.8-4.7; GUTS: OR = 4.5, 95% CI = 2.8-7.3; NFBC: OR = 4.1, 95% CI = 2.6-6.6), depressive symptoms in ALSPAC (OR = 2.2, 95% CI = 1.5-3.1) and GUTS(OR = 3.7, 95% CI = 2.2-6.3), and several psychopathology measures including clinical anxiety/depression in NFBC (OR = 11.2, 95% CI = 3.9, 31.7).

CONCLUSIONS

Results show a higher prevalence of purging behaviours among girls in the United Kingdom compared to those in the United States and Finland. Our findings support evidence highlighting that purging in adolescence is associated with negative outcomes, independent of its frequency and binge eating.

Relationship between impulsivity, prefrontal anticipatory activation, and striatal dopamine release during rewarded task performance

Impulsivity, and in particular the negative urgency aspect of this trait, is associated with poor inhibitory control when experiencing negative emotion. Individual differences in aspects of impulsivity have been correlated with striatal dopamine D2/D3 receptor availability and function. This multi-modal pilot study used both positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) to evaluate dopaminergic and neural activity, respectively, using modified versions of the monetary incentive delay task. Twelve healthy female subjects underwent both scans and completed the NEO Personality Inventory Revised to assess Impulsiveness (IMP). We examined the relationship between nucleus accumbens (NAcc) dopaminergic incentive/reward release, measured as a change in D2/D3 binding potential between neutral and incentive/reward conditions with [(11)C]raclopride PET, and blood oxygen level-dependent (BOLD) activation elicited during the anticipation of rewards, measured with fMRI. Left NAcc incentive/reward dopaminergic release correlated with anticipatory reward activation within the medial prefrontal cortex (mPFC), left angular gyrus, mammillary bodies, and left superior frontal cortex. Activation in the mPFC negatively correlated with IMP and mediated the relationship between IMP and incentive/reward dopaminergic release in left NAcc. The mPFC, with a regulatory role in learning and valuation, may influence dopamine incentive/reward release.

Pharmacological and clinical dilemmas of prescribing in co-morbid adult attention-deficit/hyperactivity disorder and addiction

The present article reviews whether available efficacy and safety data support the pharmacological treatment of adult attention-deficit/hyperactivity disorder (ADHD) in patients with concurrent substance use disorders (SUD). Arguments for and against treating adult ADHD with active SUD are discussed. Findings from 19 large open studies and controlled clinical trials show that the use of atomoxetine or extended-release methylphenidate formulations, together with psychological therapy, yield promising though inconclusive results about short term efficacy of these drugs in the treatment of adult ADHD in patients with SUD and no other severe mental disorders. However, the efficacy of these drugs is scant or lacking for treating concurrent SUD. No serious safety issues have been associated with these drugs in patients with co-morbid SUD-ADHD, given their low risk of abuse and favourable side effect and drug-drug interaction profile. The decision to treat adult ADHD in the context of active SUD depends on various factors, some directly related to SUD-ADHD co-morbidity (e.g. degree of diagnostic uncertainty for ADHD) and other factors related to the clinical expertise of the medical staff and availability of adequate resources (e.g. the means to monitor compliance with pharmacological treatment). Our recommendation is that clinical decisions be individualized and based on a careful analysis of the advantages and disadvantages of pharmacological treatment for ADHD on a case-by-case basis in the context of active SUD.

Atomoxetine reduces anticipatory responding in a 5-choice serial reaction time task for adult zebrafish

Deficits in impulse control are related to a number of psychiatric diagnoses, including attention deficit hyperactivity disorder, addiction, and pathological gambling. Despite increases in our knowledge about the underlying neurochemical and neuroanatomical correlates, understanding of the molecular and cellular mechanisms is less well established. Understanding these mechanisms is essential in order to move towards individualized treatment programs and increase efficacy of interventions. Zebrafish are a very useful vertebrate model for exploring molecular processes underlying disease owing to their small size and genetic tractability. Their utility in terms of behavioral neuroscience, however, hinges on the validation and publication of reliable assays with adequate translational relevance. Here, we report an initial pharmacological validation of a fully automated zebrafish version of the commonly used five-choice serial reaction time task using a variable interval pre-stimulus interval. We found that atomoxetine reduced anticipatory responses (0.6 mg/kg), whereas a high-dose (4 mg/kg) methylphenidate increased anticipatory responses and the number of trials completed in a session. On the basis of these results, we argue that similar neurochemical processes in fish as in mammals may control impulsivity, as operationally defined by anticipatory responses on a continuous performance task such as this, making zebrafish potentially a good model for exploring the molecular basis of impulse control disorders and for first-round drug screening.

Alpha-synuclein deletion decreases motor impulsivity but does not affect risky decision making in a mouse Gambling Task

RATIONALE

There is evidence to support the role of alpha-synuclein in motor impulsivity, but the extrapolation of this finding to other types of impulsivity remains to be elucidated.

OBJECTIVE

This study aims to investigate the role of alpha-synuclein in choice impulsivity/risky decision-making by means of a mouse version of the Iowa Gambling Task (mIGT).

METHODS

Two strains of mice that differ in the expression of the alpha-synuclein gene, the C57BL/6JOlaHsd (HA) and C57BL/6J (CR), were tested in the mIGT. HA mice differ from their CR ancestors in possessing a chromosomal deletion resulting in the loss of two genes: snca, encoding alpha-synuclein and mmrn1, encoding multimerin-1. Mice were trained in the mIGT until a stable pattern of responding was achieved and then the acute effects of ethanol and cocaine in choice preference were investigated.

RESULTS

No differences between the strains were evident in risky decision-making in any of the experiments, but HA mice showed consistently reduced levels of premature responding in comparison with CR mice, confirming the reduced motor impulsivity found in a previous study. Ethanol did not modify the percentage of advantageous choices in either strain, while cocaine increased the risky choice behaviour by increasing the percentage of disadvantageous choices in both strains.

CONCLUSIONS

We provide further evidence for the involvement of alpha-synuclein in motor impulsivity and suggest that alpha-synuclein does not play a role in risky decision-making as evaluated in the mIGT.

Effects of acute and sub-chronic nicotine on impulsive choice in rats in a probabilistic delay-discounting task

RATIONALE

Cigarette smokers typically display impulsivity by preferring immediate rewards over larger, delayed rewards at shorter delays than do non-smokers. Suggesting causality, nicotine injections in rats increase the choice for an immediate reward over a larger, delayed reward.

OBJECTIVES

To examine the generality of this latter effect, the present study employed a delay-discounting task to determine if acute and sub-chronic nicotine will also increase impulsive choice when subjective reward value is manipulated by changes in the probability, rather than magnitude, of reward.

MATERIALS AND METHODS

Rats were presented with two levers, one of which delivered an immediate water reward on half of the trials, while the other lever delivered the same reward on every trial, but only after one of five increasing delays.

RESULTS

Acute injections of 1.2 mg/kg, but not 0.8 mg/kg, of nicotine increased the preference for the immediate (but less certain) reward lever at intermediate delays. Moreover, twice-daily injections of 0.8 mg/kg of nicotine for 6 days progressively increased the preference for the immediate reward. Latency to make the first response on each trial was not affected by nicotine.

CONCLUSIONS

The similar increases in impulsive choice produced by both acute and sub-chronic nicotine in delay-discounting paradigms whether subjective reward value is manipulated by changes in reward magnitude or probability suggests that nicotine may be increasing what is common to these paradigms, namely delay discounting. Whatever the mechanism, these data indicate that both acute and sub-chronic nicotine may help develop and maintain an addiction by increasing impulsivity.

Are executive function and impulsivity antipodes? A conceptual reconstruction with special reference to addiction

RATIONALE

Although there is considerable interest in how either executive function (EF) or impulsivity relate to addiction, there is little apparent overlap between these research areas.

OBJECTIVES

The present paper aims to determine if components of these two constructs are conceptual antipodes--widely separated on a shared continuum.

METHODS

EFs and impulsivities were compared and contrasted. Specifically, the definitions of the components of EF and impulsivity, the methods used to measure the various components, the populations of drug users that show deficits in these components, and the neural substrates of these components were compared and contrasted.

RESULTS

Each component of impulsivity had an antipode in EF. EF, however, covered a wider range of phenomena, including compulsivity.

CONCLUSIONS

Impulsivity functions as an antipode of certain components of EF. Recognition of the relationship between EF and impulsivity may inform the scientific inquiry of behavioral problems such as addiction. Other theoretical implications are discussed.

Deletion of alpha-synuclein decreases impulsivity in mice

The presynaptic protein alpha-synuclein, associated with Parkinson's Disease (PD), plays a role in dopaminergic neurotransmission and is implicated in impulse control disorders (ICDs) such as drug addiction. In this study we investigated a potential causal relationship between alpha-synuclein and impulsivity, by evaluating differences in motor impulsivity in the 5-choice serial reaction time task (5-CSRTT) in strains of mice that differ in the expression of the alpha-synuclein gene. C57BL/6JOlaHsd mice differ from their C57BL/6J ancestors in possessing a chromosomal deletion resulting in the loss of two genes, snca, encoding alpha-synuclein, and mmrn1, encoding multimerin-1. C57BL/6J mice displayed higher impulsivity (more premature responding) than C57BL/6JOlaHsd mice when the pre-stimulus waiting interval was increased in the 5-CSRTT. In order to ensure that the reduced impulsivity was indeed related to snca, and not adjacent gene deletion, wild type (WT) and mice with targeted deletion of alpha-synuclein (KO) were tested in the 5-CSRTT. Similarly, WT mice were more impulsive than mice with targeted deletion of alpha-synuclein. Interrogation of our ongoing analysis of impulsivity in BXD recombinant inbred mouse lines revealed an association of impulsive responding with levels of alpha-synuclein expression in hippocampus. Expression of beta- and gamma-synuclein, members of the synuclein family that may substitute for alpha-synuclein following its deletion, revealed no differential compensations among the mouse strains. These findings suggest that alpha-synuclein may contribute to impulsivity and potentially, to ICDs which arise in some PD patients treated with dopaminergic medication.

Do executive and reactive disinhibition mediate the effects of familial substance use disorders on adolescent externalizing outcomes?

The present study examined the potential mediating roles of executive and reactive disinhibition in predicting conduct problems, attention-deficit/hyperactivity disorder (ADHD) symptoms, and substance use among adolescents with and without a family history of substance use disorders. Using data from 247 high-risk adolescents, parents, and grandparents, structural equation modeling indicated that reactive disinhibition, as measured by sensation seeking, mediated the effect of familial drug use disorders on all facets of the adolescent externalizing spectrum. Executive disinhibition, as measured by response disinhibition, spatial short term memory, and "trait" impulsivity, was associated with ADHD symptoms. Moreover, although executive functioning weakness were unrelated to familial substance use disorders, adolescents with familial alcohol use disorders were at risk for "trait" impulsivity marked by a lack of planning. These results illustrate the importance of "unpacking" the broad temperament style of disinhibition and of studying the processes that underlie the commonality among facets of the externalizing spectrum and processes that predict specific externalizing outcomes.