The dopamine transporter and neuroimaging in attention deficit hyperactivity disorder

Exploring transgenerational inheritance in epigenotypes of DAT heterozygous rats: Circadian anomalies and attentional vulnerability

Dopamine (DA) is mainly involved in locomotor activity, reward processes and maternal behaviors. Rats with KO gene for dopamine transporter (DAT), coding for a truncated DAT protein, are in hyperdopaminergic conditions and thus develop stereotyped behaviors and hyperactivity. Our aim was to test the prior transgenerational modulation of wild and truncated alleles as expressed in heterozygous DAT rats: specifically, we addressed the possible sequelae due to genotype and gender of the ancestors, with regard to behavioral differences in F1, F2, F3 rats. We studied non-classical DAT heterozygotes (HETs) based on two specular lines, with putative grand-maternal vs. grand-paternal imprinting. MAT females (F1; offspring of KO male and WT female) mated with a KO male to generate MIX offspring (F2). Specularly, PAT females (F1; offspring of KO female and WT male) mated with a KO male to generate PIX offspring (F2). Similarly to PAT, we obtained MUX (F2; HET offspring of MAT sire and KO dam); we also observed the F3 (MYX: HET offspring of KO male and MUX female, thus with DAT-KO maternal grandmother like also for PIX). We studied their circadian cycle of locomotor activity and their behavior in the elevated-plus-maze (EPM). Locomotor hyper-activity occurs in F1, the opposite occurs in F2, with MYX rats appearing undistinguishable from WT ones. Open-arm preference emerged in PIX and MIX rats. Only MAT and MYX rats showed a significant vulnerability for ADHD-like inattentive symptoms (duration of rearing in the EPM; Viggiano et al., 2002). A risk-taking profile is evident in the F2 phenotype, while inattentiveness from F1 progeny tends to be transferred to F3. We hypothesize that DAT-related phenotypes result from effective inheritance through pedigree of imprints that are dependent on grandparents, suggesting a protective role for gestation within a hyperdopaminergic uterus. For major features, similar odd (F1, F3) generations appear opposed to even (F2) ones; for minor specific features, the phenotype transfer may affect the progenies with a male but not a female DAT-KO ancestor.

The mesocortical dopaminergic system cannot explain hyperactivity in an animal model of attention deficit hyperactivity disorder (ADHD)- Spontaneously hypertensive rats (SHR)

BACKGROUND

Attention deficit hyperactivity disorder (ADHD) is one of the most prevalent neuropsychiatric disorders with morphological brain abnormalities. There is a growing body of evidence that abnormalities in the dopaminergic system may account for ADHD pathogenesis. However, it is not clear whether the dopaminergic system is hyper or hypoactive. To determine whether the DA neurons and/or axons deficiency might be the cause of the postulated dopaminergic hypofunction in spontaneously hypertensive rats (SHR, animal model of ADHD), this study examined the dopaminergic neurons and fibers in the brain tissues of SHRs and Wistar Kyoto rats (WKY, control animals). Here, we performed immunohistochemical tyrosine hydroxylase (TH) and dopamine-beta-hydroxylase (DBH) staining on brain sections collected on juveniles from SHR and WKY. Moreover, behavioral testing to examine the hyperactivity in the open field area was also elucidated.

RESULTS

The mesocortical dopaminergic system appears to be normal in juvenile SHR, as suggested by (i) no alteration in the area density of TH-immunoreactive (TH-ir) dopaminergic neurons in the ventral tegmental area (VTA), (ii) no alterations in the volume density of TH-ir fibers in layer I of the prelimbic (PrL) subregion of medial PFC (mPFC), (iii) no alteration in the percentage of TH-ir dopaminergic fibers in layer I of the PrL subregion of mPFC as revealed by TH and/or DBH immunoreactivity. Furthermore, the SHR showed increased locomotor activity than WKY in the open field test.

CONCLUSIONS

The demonstration of no alteration in mesocortical dopaminergic neurons and fiber in SHR raises some concern about the position of SHR as an animal model of the inattentive subtype of ADHD. However, these results strengthen this strain as an animal model of hyperactive/impulsive subtype ADHD for future studies that may elucidate the underlying mechanism mediating hyperactivity and test various treatment strategies.

Polyunsaturated fatty acids (PUFA) for attention deficit hyperactivity disorder (ADHD) in children and adolescents

BACKGROUND

Attention deficit hyperactivity disorder (ADHD) is a major problem in children and adolescents, characterised by age-inappropriate levels of inattention, hyperactivity, and impulsivity, and is associated with long-term social, academic, and mental health problems. The stimulant medications methylphenidate and amphetamine are the most frequently used treatments for ADHD, but these are not always effective and can be associated with side effects. Clinical and biochemical evidence suggests that deficiencies of polyunsaturated fatty acids (PUFA) could be related to ADHD. Research has shown that children and adolescents with ADHD have significantly lower plasma and blood concentrations of PUFA and, in particular, lower levels of omega-3 PUFA. These findings suggest that PUFA supplementation may reduce the attention and behaviour problems associated with ADHD. This review is an update of a previously published Cochrane Review. Overall, there was little evidence that PUFA supplementation improved symptoms of ADHD in children and adolescents.

OBJECTIVES

To compare the efficacy of PUFA to other forms of treatment or placebo in treating the symptoms of ADHD in children and adolescents.

SEARCH METHODS

We searched 13 databases and two trials registers up to October 2021. We also checked the reference lists of relevant studies and reviews for additional references.

SELECTION CRITERIA

We included randomised and quasi-randomised controlled trials that compared PUFA with placebo or PUFA plus alternative therapy (medication, behavioural therapy, or psychotherapy) with the same alternative therapy alone in children and adolescents (aged 18 years and under) diagnosed with ADHD.

DATA COLLECTION AND ANALYSIS

We used standard Cochrane methods. Our primary outcome was severity or improvement of ADHD symptoms. Our secondary outcomes were severity or incidence of behavioural problems; quality of life; severity or incidence of depressive symptoms; severity or incidence of anxiety symptoms; side effects; loss to follow-up; and cost. We used GRADE to assess the certainty of evidence for each outcome.

MAIN RESULTS

We included 37 trials with more than 2374 participants, of which 24 trials were new to this update. Five trials (seven reports) used a cross-over design, while the remaining 32 trials (52 reports) used a parallel design. Seven trials were conducted in Iran, four each in the USA and Israel, and two each in Australia, Canada, New Zealand, Sweden, and the UK. Single studies were conducted in Brazil, France, Germany, India, Italy, Japan, Mexico, the Netherlands, Singapore, Spain, Sri Lanka, and Taiwan. Of the 36 trials that compared a PUFA to placebo, 19 used an omega-3 PUFA, six used a combined omega-3/omega-6 supplement, and two used an omega-6 PUFA. The nine remaining trials were included in the comparison of PUFA to placebo, but also had the same co-intervention in the PUFA and placebo groups. Of these, four trials compared a combination of omega-3 PUFA plus methylphenidate to methylphenidate. One trial each compared omega-3 PUFA plus atomoxetine to atomoxetine; omega-3 PUFA plus physical training to physical training; and an omega-3 or omega-6 supplement plus methylphenidate to methylphenidate; and two trials compared omega-3 PUFA plus dietary supplement to dietary supplement. Supplements were given for a period of between two weeks and six months. Although we found low-certainty evidence that PUFA compared to placebo may improve ADHD symptoms in the medium term (risk ratio (RR) 1.95, 95% confidence interval (CI) 1.47 to 2.60; 3 studies, 191 participants), there was high-certainty evidence that PUFA had no effect on parent-rated total ADHD symptoms compared to placebo in the medium term (standardised mean difference (SMD) -0.08, 95% CI -0.24 to 0.07; 16 studies, 1166 participants). There was also high-certainty evidence that parent-rated inattention (medium-term: SMD -0.01, 95% CI -0.20 to 0.17; 12 studies, 960 participants) and hyperactivity/impulsivity (medium-term: SMD 0.09, 95% CI -0.04 to 0.23; 10 studies, 869 participants) scores were no different compared to placebo. There was moderate-certainty evidence that overall side effects likely did not differ between PUFA and placebo groups (RR 1.02, 95% CI 0.69 to 1.52; 8 studies, 591 participants). There was also moderate-certainty evidence that medium-term loss to follow-up was likely similar between groups (RR 1.03, 95% CI 0.77 to 1.37; 13 studies, 1121 participants).

AUTHORS' CONCLUSIONS

Although we found low-certainty evidence that children and adolescents receiving PUFA may be more likely to improve compared to those receiving placebo, there was high-certainty evidence that PUFA had no effect on total parent-rated ADHD symptoms. There was also high-certainty evidence that inattention and hyperactivity/impulsivity did not differ between PUFA and placebo groups. We found moderate-certainty evidence that overall side effects likely did not differ between PUFA and placebo groups. There was also moderate-certainty evidence that follow-up was similar between groups. It is important that future research addresses the current weaknesses in this area, which include small sample sizes, variability of selection criteria, variability of the type and dosage of supplementation, and short follow-up times.

Consequences of Acute or Chronic Methylphenidate Exposure Using Ex Vivo Neurochemistry and In Vivo Electrophysiology in the Prefrontal Cortex and Striatum of Rats

Methylphenidate (MPH) is among the main drugs prescribed to treat patients with attention-deficit and hyperactivity disease (ADHD). MPH blocks both the norepinephrine and dopamine reuptake transporters (NET and DAT, respectively). Our study was aimed at further understanding the mechanisms by which MPH could modulate neurotransmitter efflux, using ex vivo radiolabelled neurotransmitter assays isolated from rats. Here, we observed significant dopamine and norepinephrine efflux from the prefrontal cortex (PFC) after MPH (100 µM) exposure. Efflux was mediated by both dopamine and norepinephrine terminals. In the striatum, MPH (100 µM) triggered dopamine efflux through both sodium- and vesicular-dependent mechanisms. Chronic MPH exposure (4 mg/kg/day/animal, voluntary oral intake) for 15 days, followed by a 28-day washout period, increased the firing rate of PFC pyramidal neurons, assessed by in vivo extracellular single-cell electrophysiological recordings, without altering the responses to locally applied NMDA, via micro-iontophoresis. Furthermore, chronic MPH treatment resulted in decreased efficiency of extracellular dopamine to modulate NMDA-induced firing activities of medium spiny neurons in the striatum, together with lower MPH-induced (100 µM) dopamine outflow, suggesting desensitization to both dopamine and MPH in striatal regions. These results indicate that MPH can modulate neurotransmitter efflux in brain regions enriched with dopamine and/or norepinephrine terminals. Further, long-lasting alterations of striatal and prefrontal neurotransmission were observed, even after extensive washout periods. Further studies will be needed to understand the clinical implications of these findings.

Dopamine-transporter heterozygous rats carrying maternal wild-type allele are more vulnerable to the development of compulsive behavior

Compulsivity is defined as an unstoppable tendency towards repetitive and habitual actions, which are reiterated despite negative consequences. Polydipsia is induced preclinically by intermittent reward leading rodents to ingest large amounts of fluids. We focused on the role of dopamine transporter (DAT) and inheritance factors in compulsive behavior. Our sample consisted of DAT heterozygous (HET) rats with different genetic inheritance (MAT-HET, born from WT-dams x KO-fathers; MIX-HET, born from HET-dams x KO-fathers). As controls, we used both wild-type (WT) rats and their socially-isolated (WTi) siblings. We ran the schedule-induced polydipsia (SIP) protocol, to induce compulsive behavior; then the Y-maze and marble-burying tests, to verify its actual development. Only MAT-HET (who inherited the functional DAT allele from the WT mother) is vulnerable to developing compulsive behavior. MAT-HET rats drank increasingly more water during SIP and showed significant perseverance in the Y-maze test and exhibited compulsive actions in the marble-burying test. Interestingly, compulsive behaviors of MAT-HET rats correlate with expression ex-vivo of different genes in different areas. Regarding the prefrontal cortex (PFC), D2R correlates with Y-maze "perseverance" in addition to BDNF; considering the amygdala (AMY), both D3R and OXTR correlate with SIP "licks". Indeed, compulsivity may be linked to D2R and BDNF in PFC, while extreme anxiety in MAT-HET rats may be associated with D3R and OXTR in the amygdala. These results confirm some similarities between MAT-HET and DAT-KO subjects and link the epigenetic context of the DAT gene to the development of compulsive behavior. This article is protected by copyright. All rights reserved.

Antagonization of monoamine reuptake transporters by agmatine improves anxiolytic and locomotive behaviors commensurate with fluoxetine and methylphenidate

Background

Agmatine (AGM) is known for its protective effects including neuroprotection, nephroprotection, gastroprotection, cardioprotection, and glucoprotection. Studies have validated the neuroprotective role of AGM as antidepressant, anxiolytic, locomotive, and antipsychotic agent in psychopathologies. Fluoxetine (FLX) is the most extensively prescribed antidepressant while methylphenidate (MPD) is the most frequently prescribed psychoactive stimulant for ADHD (attention deficit hyperactivity disorder) treatment worldwide. The mechanism of action of FLX and MPD involves reuptake inhibition of serotonin and dopamine and norepinephrine at presynaptic transporters. Present study was designed to determine the safety and efficacy of AGM administration along with conventional antidepressant and psychostimulative drugs. The study also aimed to establish underlying mechanism of action of AGM at monoamine reuptake transporters.

Results

AGM significantly ameliorated locomotion in activity box and open field while anxiolytic behaviors in light/dark transition box and EPM were also improved (p<0.01). The growth and appetite of animals were enhanced along with antidepressive behavior in FST (p<0.01). Moreover, co-administration of AGM with FLX or MPD improved rats’ behaviors as compared to single AGM administration.

Conclusion

Present study determined the significant anxiolytic, locomotor, and antidepressive effects of AGM compared with FLX and MPD. The study also showed improved behaviors of rats treated with combined doses of AGM with FLX or MPD along with food intake and body weights. This study has also proposed the potential mechanism of action of AGM at monoamine receptors that may lead to inhibition of monoamine reuptake transporters that may lead to increase in 5-HT, D, and NE concentrations at synaptic level.

Prevalence of cocaine use and cocaine use disorder among adult patients with attention-deficit/hyperactivity disorder: A systematic review and meta-analysis

We conducted this systematic review and meta-analysis (registered with PROSPERO CRD42020142039) of the literature to estimate the lifetime prevalence of cocaine use and cocaine use disorder among adult patients with attention-deficit/hyperactivity disorder (ADHD). The literature search was performed on the electronic databases PubMed and PsychINFO without date or language restrictions. Additional studies were identified by hand searching of citations. Inclusion criteria were: studies involving adult patients with ADHD and reporting cocaine use and/or cocaine use disorders. Data were pooled in the meta-analyses using a generalized linear mixed model with random effects. Statistical heterogeneity was assessed using the Cochran Q test. Sensitivity analyses were conducted. Twelve studies were included in the review: six in the meta-analysis of cocaine use and nine in the meta-analysis of cocaine use disorder. The estimated prevalence of cocaine use was 26.0% (95% CI 0.18-0.35) and the estimated prevalence of cocaine use disorder was 10.0% (95% CI 0.08-0.13). Heterogeneity in both meta-analyses was high but decreased to non-significance in the meta-analysis on cocaine use disorder after excluding the outlier study. In conclusion, one out of four adult patients with ADHD use cocaine and one out of ten develop a lifetime cocaine use disorder. Since cocaine use can lead to more severe and complex disorders of impaired systemic functioning, adult patients with ADHD should be assessed for cocaine use disorder and promptly referred for treatment.

High impulsive choice is accompanied by an increase in dopamine release in rat dorsolateral striatum

Dopamine neurotransmission has been consistently associated with individual differences in impulsive choice. Clinical and preclinical evidence suggests that low striatal dopamine D₂ signaling predisposes to engage in impulsive behaviors. Although dopamine D₂ signaling controls dopamine (DA) extracellular levels, the relationship between striatal dopamine extracellular levels and impulsive choice remains poorly understood. Using quantitative microdialysis, we investigated whether extracellular DA levels in rat dorsolateral striatum (DLS) correlates with preference for an immediate small reward or for a delayed larger reward. Rats were tested in a delay-discounting task and classified as high impulsive (HI) or low impulsive (LI) according to the area under the discounting curve (AUC). No-net flux microdialysis experiments, assessing basal DA release, DA-uptake, and DA extracellular concentration (DA C_ext), were carried out in dorsolateral striatum (DLS) of urethane-anesthetized rats. Rats classified as HI showed a higher DA release compared with LI rats. Differences in DLS DA-uptake and DA C_ext were non-significant. Importantly, a significant negative correlation was observed between AUC and DA release, indicating that the lower the AUC, the higher the DLS DA release. This finding shows that DA release is augmented in the DLS of rats classified as HI, suggesting that a hyper-activated nigro-striatal pathway contributes to impulsive choice.

Chronic Physical Activity for Attention Deficit Hyperactivity Disorder and/or Autism Spectrum Disorder in Children: A Meta-Analysis of Randomized Controlled Trials

Purpose: To explore the effects of physical activity (PA) intervention on executive function (EF) and motor skills (MS) among children with attention deficit hyperactivity disorder and/or autism spectrum disorder (ASD).

Methods: Relevant studies were sourced from PubMed, Web of Science, EMBASE, Cochrane Library, CNKI and Wanfang Data. Only randomized controlled trials (RCT) were included based upon the following criteria: (1) participants were children and clinically diagnosed with ADHD/ASD, (2) intervention strategies were identified as chronic physical activity, and (3) EF (e.g., cognitive flexibility) and/or MS (e.g., gross motor skills) were measured at baseline and post-intervention and compared with an eligible control group.

Results: Eleven studies involving 346 participants were finally identified. PA elicited significant improvements in EF and MS in children with ADHD/ASD. Regarding changes in the EF of participants, PA showed a great improvement in overall EF [standardized mean difference (SMD): 0.90, 95% confidence interval (CI) 0.49–1.30, p < 0.00001], inhibitory control (SMD: 1.30, 95% CI 0.58–2.02, p = 0.0004) and cognitive flexibility (SMD: 0.85, 95% CI 0.42–1.29, p = 0.0001), but no significant improvement in working memory (SMD: 0.28, 95% CI −0.15–0.71, p = 0.20). Significant improvements were also found with respect to gross motor skills (SMD: 0.80, 95% CI 0.30–1.30, p = 0.002), but no significant changes were found in fine motor skills (SMD: 0.30, 95% CI −0.91–1.52, p = 0.62).

Conclusion: Chronic PA interventions may promote EF and MS in children with ADHD/ASD, especially in inhibitory control, cognitive flexibility, and gross motor skills. However, PA interventions seemed to have insignificant effects on working memory and fine motor skills to children with ADHD/ASD.

PROSPERO registration number: CRD42019118622

The association between the Lie scale of the Maudsley personality inventory and striatal dopamine D2/D3 receptor availability of healthy Chinese community subjects

The present study examined the relationship between the Lie scale scores and striatal D2/D3 receptor availability with respect to the cerebellum in 42 healthy community volunteers in Taiwan using single photon emission computed tomography (SPECT) with [123I]iodo-benzoaminde (IBZM). Even after controlling of age and educational level, subjects' Lie scale scores of the Maudsley personality inventory correlate negatively with D2/D3 receptor availability. Individual with higher Lie scale scores may have higher impulsivity due to lower dopaminergic availability.

Lower Attentional Skills predict increased exploratory foraging patterns

When engaged in a search task, one needs to arbitrate between exploring and exploiting the environment to optimize the outcome. Many intrinsic, task and environmental factors are known to influence the exploration/exploitation balance. Here, in a non clinical population, we show that the level of inattention (assessed as a trait) is one such factor: children with higher scores on an ADHD (Attention Deficit/Hyperactivity Disorder) questionnaire exhibited longer transitions between consecutively retrieved items, in both a visual and a semantic search task. These more frequent exploration behaviours were associated with differential performance patterns: children with higher levels of ADHD traits performed better in semantic search, while their performance was unaffected in visual search. Our results contribute to the growing literature suggesting that ADHD should not be simply conceived as a pure deficit of attention, but also as a specific cognitive strategy that may prove beneficial in some contexts.

Investigating possible causal effects of externalizing behaviors on tobacco initiation: A Mendelian randomization analysis

Observational studies suggest childhood externalizing disorders are associated with increased smoking and earlier initiation. However, causality cannot be inferred from observational data alone. The current study uses two-sample MR to examine the causal relationship between externalizing behaviors and tobacco use. Single nucleotide polymorphisms (SNPs) associated with aggression were obtained from the Early Life Epidemiology Consortium (mean age 8), ADHD from the Integrative Psychiatric Research and Psychiatric Genomics Consortiums (age range 6-18), and tobacco initiation and age of onset from the Tobacco and Genetics Consortium. SNPs were combined using the inverse variance weighted approach, weighted median approach, and MR-Egger regression. There was no clear evidence of an effect of aggression on tobacco initiation or age of onset for childhood aggression (initiation: β -0.002, 95% CI -0.005, 0.001, P = 0.286; age: β -0.001 95% CI -0.002, 0.000, P = 0.310) or adolescent aggression (initiation: β -0.001, 95% CI -0.006, 0.003, P = 0.610; age: β 0.000, 95% CI 0.000, 0.001, P = 0.183)]. However, there was some evidence of an association of ADHD on tobacco initiation (OR 1.23, 95% CI 1.10, 1.35, P = 0.016), although no clear evidence of an effect of ADHD on age of onset (OR = 1.022, 95% CI 0.992, 1.052, P = 0.215). Our results provide some evidence that genetic risk of childhood ADHD is causally related to increased risk of tobacco initiation; however, the causal estimate is relatively small. We found no clear evidence that genetic risk of childhood aggression is causally related to the risk of tobacco initiation or age of onset.

Genetic imaging study with [Tc-99m] TRODAT-1 SPECT in adolescents with ADHD using OROS-methylphenidate

AIM

To examine theeffects on the brain of 2-month treatment withamethylphenidate extended-release formulation (OROS-MPH) using [Tc-^99m] TRODAT-1SPECT in a sample of treatment-naïve adolescents with Attention Deficit/Hyperactivity Disorder (ADHD). In addition, to assess whether risk alleles (homozygosity for 10-repeat allele at the DAT1 gene were associated with alterations in striatal DAT availability.

METHODS

Twenty adolescents with ADHD underwent brain single-photon emission computed tomography (SPECT) scans with [Tc-^99m] TRODAT-1 at baseline and two months after starting OROS-MPH treatment with dosages up to 1 mg/kg/day. Severity of illness was estimated using the Clinical Global Impression Scale (CGI-S) and DuPaul ADHD Rating Scale-Clinician version (ARS) before treatment,1 month and 2 months after initiating OROS-MPH treatment.

RESULTS

Decreased DAT availability was found in both the right caudate (pretreatment DAT binding: 224.76 ± 33.77, post-treatment DAT binding: 208.86 ± 28.75, p = 0.02) and right putamen (pre-treatment DAT binding: 314.41 ± 55.24, post-treatment DAT binding: 285.66 ± 39.20, p = 0.05) in adolescents with ADHD receiving OROS-MPH treatment. Adolescents with ADHD who showed a robust response to OROS-MPH (n = 7) had significantly greater reduction of DAT density in the right putamen than adolescents who showed less robust response to OROS-MPH (n = 13) (p = 0.02). However, between-group differences by treatment responses were not related with DAT density in the right caudate. Risk alleles (homozygosity for the 10-repeat allele of DAT1 gene) in the DAT1 gene were not associated with alterations in striatal DAT availability.

CONCLUSION

Two months of OROS-MPH treatment decreased DAT availability in both the right caudate and putamen. Adolescents with ADHD who showed a robust response to OROS-MPH had greater reduction of DAT density in the right putamen. However,our findings did not support an association between homozygosity for a 10-repeat allele in the DAT1 gene and DAT density, assessedusing[Tc-^99m] TRODAT-1SPECT.

Influence of the SLC6A3-DAT1 Gene on Multifaceted Measures of Self-regulation in Preschool Children

Development of self-regulation, the capacity to voluntarily modulate thoughts, emotions and actions is strongly related to the maturation of the dopamine-mediated executive attention network (EAN). The attention control processes associated with the EAN greatly overlap with efficiency of the executive functions and are correlated with measures of effortful control. Regulation of dopamine levels within the EAN, particularly in the basal ganglia is carried out by the action of dopamine transporters. In humans, the SLC6A3/DAT1 gene carries out the synthesis of the DAT protein. The 10-repeat allele has been associated with an enhanced expression of the gene and has been related to ADHD symptoms. Little is known about the impact of DAT1 variations on children's capacity to self-regulate in contexts that impose particular demands of regulatory control such as the school or home. This study defines a multi-domain phenotype of self-regulation and examines whether variations of the DAT1 gene accounts for individual differences in performance in 4–5 year old children. Results show that presence of the 10r allele is related to a diminished ability to exert voluntary regulation of reactivity. These findings shed light on the neurobiological mechanisms underlying individual differences in self-regulation during childhood.

Characterization of VNTRs Within the Entire Region of SLC6A3 and Its Association with Hypertension

The dopamine transporter SLC6A3 (DAT1) mediates uptake of dopamine into presynaptic terminals. In addition, in previous reports, hypertensive rats were associated with DAT gene, but the genetic association with SLC6A3 and hypertension is still unknown. We examined the distribution of variable number of tandem repeats (VNTRs) and conducted polymorphic analysis of the entire region of SLC6A3. Ten VNTR regions (MS1-10) were revealed throughout the intronic and UTRs; seven VNTR regions were newly isolated and three VNTRs were previously reported. Four VNTR regions (SLC6A3-MS1, -MS4, -MS8 [rs3836790], and -MS9 [rs28363170]) showed polymorphism and these loci were found to be transmitted through meiosis following Mendelian inheritance. These VNTR polymorphisms may be useful markers for paternity mapping and DNA fingerprinting. Furthermore, we also conducted a case-control study between the controls and essential hypertensive cases. Analysis of the genotypes of SLC6A3-MS8 (rs3836790) revealed that having an 8/6-repeat allele, which was only detected in hypertensive cases, was associated with hypertension (p < 0.05). Additional significant association was identified between the short 7-repeat allele of SLC6A3-MS9 (rs28363170) and the occurrence of hypertension (odds ratio 2.02; p < 0.05). These results revealed the genetic association between SLC6A3 and hypertension, and the specific VNTR alleles of SLC6A3 may be a risk factor for hypertension.

Attenuated Tonic and Enhanced Phasic Release of Dopamine in Attention Deficit Hyperactivity Disorder

It is unclear whether attention deficit hyperactive disorder (ADHD) is a hypodopaminergic or hyperdopaminergic condition. Different sets of data suggest either hyperactive or hypoactive dopamine system. Since indirect methods used in earlier studies have arrived at contradictory conclusions, we directly measured the tonic and phasic release of dopamine in ADHD volunteers. The tonic release in ADHD and healthy control volunteers was measured and compared using dynamic molecular imaging technique. The phasic release during performance of Eriksen's flanker task was measured in the two groups using single scan dynamic molecular imaging technique. In these experiments volunteers were positioned in a positron emission tomography (PET) camera and administered a dopamine receptor ligand (11)C-raclopride intravenously. After the injection PET data were acquired dynamically while volunteers either stayed still (tonic release experiments) or performed the flanker task (phasic release experiments). PET data were analyzed to measure dynamic changes in ligand binding potential (BP) and other receptor kinetic parameters. The analysis revealed that at rest the ligand BP was significantly higher in the right caudate of ADHD volunteers suggesting reduced tonic release. During task performance significantly lower ligand BP was observed in the same area, indicating increased phasic release. In ADHD tonic release of dopamine is attenuated and the phasic release is enhanced in the right caudate. By characterizing the nature of dysregulated dopamine neurotransmission in ADHD, the results explain earlier findings of reduced or increased dopaminergic activity.

Association of adult attention deficit hyperactivity disorder subtypes and response to methylphenidate HCL treatment: A magnetic resonance spectroscopy study

The effects of methylphenidate (MPH) treatment on N-acetyl aspartate (NAA), choline and creatine are being examined in individuals with different subtypes of attention deficit hyperactivity disorder (ADHD). Sixty ADHD subjects were included into the study aging between 18 and 60 years. Levels of NAA, creatine and choline in anterior cingulate cortex, cerebellum, striatum and dorsolateral prefrontal cortex were measured with magnetic resonance spectroscopy. Then, 10mg oral MPH was given to the subjects and the same metabolite levels were measured after an interval of 30min. Distribution of the patients according to the ADHD subtypes was as follows: 21 of them (35.0%) were in the inattentive type, 11 of them (18.3%) were in the hyperactive type and 28 of them were (46.7%) in the combined type. Changes of brain metabolite levels after MPH were found not to be statistically significantly different between the subtypes. The increase of choline levels after MPH compared to the levels of choline before MPH in striatum in the combined type patients were statistically significant. No clear association was found between ADHD subtypes and changes of brain metabolites with use of MPH in adult ADHD.

Increased dopamine transporter function as a mechanism for dopamine hypoactivity in the adult infralimbic medial prefrontal cortex following adolescent social stress

Being bullied during adolescence is associated with later mental illnesses characterized by deficits in cognitive tasks mediated by prefrontal cortex (PFC) dopamine (DA). Social defeat of adolescent male rats, as a model of teenage bullying victimization, results in medial PFC (mPFC) dopamine (DA) hypofunction in adulthood that is associated with increased drug seeking and working memory deficits. Increased expression of the DA transporter (DAT) is also seen in the adult infralimbic mPFC following adolescent defeat. We propose the functional consequence of this increased DAT expression is enhanced DA clearance and subsequently decreased infralimbic mPFC DA availability. To test this, in vivo chronoamperometry was used to measure changes in accumulation of the DA signal following DAT blockade, with increased DAT-mediated clearance being reflected by lower DA signal accumulation. Previously defeated rats and controls were pre-treated with the norepinephrine transporter (NET) inhibitor desipramine (20 mg/kg, ip.) to isolate infralimbic mPFC DA clearance to DAT, then administered the selective DAT inhibitor GBR-12909 (20 or 40 mg/kg, sc.). Sole NET inhibition with desipramine produced no differences in DA signal accumulation between defeated rats and controls. However, rats exposed to adolescent social defeat demonstrated decreased DA signal accumulation compared to controls in response to both doses of GBR-12909, indicating greater DAT-mediated clearance of infralimbic mPFC DA. These results suggest that protracted increases in infralimbic mPFC DAT function represent a mechanism by which adolescent social defeat stress produces deficits in adult mPFC DA activity and corresponding behavioral and cognitive dysfunction.

Prefrontal cortical α2A-adrenoceptors and a possible primate model of attention deficit and hyperactivity disorder

Attention deficit and hyperactivity disorder (ADHD), a prevalent syndrome in children worldwide, is characterized by impulsivity, inappropriate inattention, and/or hyperactivity. It seriously afflicts cognitive development in childhood, and may lead to chronic under-achievement, academic failure, problematic peer relationships, and low self-esteem. There are at least three challenges for the treatment of ADHD. First, the neurobiological bases of its symptoms are still not clear. Second, the commonly prescribed medications, most showing short-term therapeutic efficacy but with a high risk of serious side-effects, are mainly based on a dopamine mechanism. Third, more novel and efficient animal models, especially in nonhuman primates, are required to accelerate the development of new medications. In this article, we review research progress in the related fields, focusing on our previous studies showing that blockade of prefrontal cortical α2A-adrenoceptors in monkeys produces almost all the typical behavioral symptoms of ADHD.

Thyrotoropin receptor knockout changes monoaminergic neuronal system and produces methylphenidate-sensitive emotional and cognitive dysfunction

Attention deficit/hyperactivity disorder (ADHD) has been reported in association with resistance to thyroid hormone, a disease caused by a mutation in the thyroid hormone receptor β (TRβ) gene. TRβ is a key protein mediating down-regulation of thyrotropin (TSH) expression by 3,3',5-tri-iodothyronine (T3), an active form of thyroid hormone. Dysregulation of TSH and its receptor (TSHR) is implicated in the pathophysiology of ADHD but the role of TSHR remains elusive. Here, we clarified a novel role for TSHR in emotional and cognitive functions related to monoaminergic nervous systems. TSHR knockout mice showed phenotypes of ADHD such as hyperactivity, impulsiveness, a decrease in sociality and increase in aggression, and an impairment of short-term memory and object recognition memory. Administration of methylphenidate (1, 5 and 10mg/kg) reversed impulsiveness, aggression and object recognition memory impairment. In the knockout mice, monoaminergic changes including decrease in the ratio of 3-methoxy-4-hydroxyphenylglycol/noradrenaline and increase in the ratio of homovanillic acid/dopamine were observed in some brain regions, accompanied by increase in the expression of noradrenaline transporter in the frontal cortex. When TSH was completely suppressed by the supraphysiological administration of T3 to the adult mice, some behavioral and neurological changes in TSHR KO mice were also observed, suggesting that these changes were not due to developmental hypothyroidism induced by the inactivation of TSHR but to the loss of the TSH-TSHR pathway itself. Taken together, the present findings suggest a novel role for TSHR in behavioral and neurological phenotypes of ADHD.

Aberrant glutamate signaling in the prefrontal cortex and striatum of the spontaneously hypertensive rat model of attention-deficit/hyperactivity disorder

RATIONALE

Attention-deficit/hyperactivity disorder (ADHD) is thought to involve hypofunctional catecholamine systems in the striatum, nucleus accumbens, and prefrontal cortex (PFC); however, recent clinical evidence has implicated glutamate dysfunction in the pathophysiology of ADHD. Recent studies show that increased stimulation of dopamine D2 and D4 receptors causes inhibition of N-methyl-D-aspartate and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors, respectively. The spontaneously hypertensive rat (SHR) model of ADHD combined type (C) has been found to have a hypofunctional dopamine system in the ventral striatum, nucleus accumbens, and PFC compared to the control Wistar Kyoto (WKY) strain.

OBJECTIVES

Based on the current understanding of typical dopamine-glutamate interactions, we hypothesized that the SHR model of ADHD would have a hyperfunctional glutamate system terminating in the striatum, nucleus accumbens, and PFC.

RESULTS

High-speed amperometric recordings combined with four-channel microelectrode arrays to directly measure glutamate dynamics showed increased evoked glutamate release in the PFC (cingulate and infralimbic cortices, p < 0.05) and also in the striatum (p < 0.05) of the SHR (ADHD-C) as compared to the WKY. Finally, glutamate uptake was discovered to be aberrant in the PFC, but not the striatum, of the SHR when compared to the control WKY strain.

CONCLUSIONS

These results suggest that the glutamatergic system in the PFC of the SHR model of ADHD is hyperfunctional and that targeting glutamate in the PFC could lead to the development of novel therapeutics for the treatment of ADHD.

Dopamine system genes are associated with orienting bias among healthy individuals

Healthy individuals display subtle orienting bias, manifested as a tendency to direct greater attention toward one hemispace, and evidence suggests that this bias reflects an individual trait, which may be modulated by asymmetric dopamine signaling in striatal and frontal regions. The current study examined the hypothesis that functional genetic variants within dopaminergic genes (DAT1 3' VNTR, dopamine D2 receptor Taq1A (rs1800497) and COMT Val158Met (rs4680)) contribute to individual differences in orienting bias, as measured by the greyscales paradigm, in a sample of 197 young healthy Israeli Jewish participants. For the Taq1A variant, homozygous carriers of the A2 allele displayed significantly increased leftward orienting bias compared to the carriers of the A1 allele. Additionally, and as previously reported by others, we found that bias towards leftward orienting of attention was significantly greater among carriers of the 9-repeat allele of the DAT1 3' VNTR as compared to the individuals who were homozygous for the 10-repeat allele. No significant effect of the COMT Val158Met on orienting bias was found. Taken together, our findings support the potential influence of genetic variants on inter-individual differences in orienting bias, a phenotype relevant to both normal and impaired cognitive processes.

Does adult ADHD interact with COMT val (158) met genotype to influence working memory performance?

Both attention-deficit/hyperactivity disorder (ADHD) and catechol-O-methyltransferase (COMT) genotype have been linked to altered dopaminergic transmission and possible impairment in frontal lobe functioning. This study offers an investigation of a possible interaction between ADHD diagnosis and COMT genotype on measures of working memory and executive function. Thirty-five adults with ADHD, who were recruited from the ADHD outpatient clinic at the Department of Psychiatry, Psychosomatics and Psychotherapy, University of Würzburg, and thirty-five matched healthy controls completed the Digit Span test and the Stroop Color Word Test. While there were no main effects of ADHD or COMT, the two factors interacted on both Digit Span subtests with the two groups' met/met carriers showing significantly different performance on the Digit Span Forward subtest and the val/val carriers showing significantly different performance on the Digit Span Backward subtest. Findings provide preliminary support for a differential impact of COMT genotype on working memory measures in adult patients with ADHD compared to healthy controls.

New neurotechnologies for the diagnosis and modulation of brain dysfunctions

This is a major review article to acquaint psychologists with new neurotechnologies for the diagnosis and modulation of brain abnormalities. While psychometrics measures brain functions in terms of behavioral parameters, a recently emerged branch of neuroscience called neurometrics relies on measuring the electrophysiological parameters of brain functioning. There are two approaches in neurometrics. The first relies on the spectral characteristics of spontaneous electroencephalograms (EEG) and measures deviations from normality in EEG recorded in the resting state. The second approach relies on event-related potentials (ERPs) that measure the electrical responses of the brain to stimuli and actions in behavioral tasks. The present study reviews recent research on the application of ERPs for the discrimination of different types of brain dysfunction. Attention deficit-hyperactivity disorder (ADHD) is used as an example. It is shown that the diagnostic power of ERPs is enhanced by the recent emergence of new methods of analysis, such as independent component analysis (ICA) and low resolution electromagnetic tomography (LORETA).

Influence of the COMT val(108/158)met polymorphism on continuous performance task indices

The Continuous Performance Task (CPT) is a widely-used measure of sustained attention and impulsivity. Deficits in CPT performance have been found in several psychiatric disorders, such as Attention-Deficit/Hyperactivity Disorder (ADHD) and schizophrenia. Molecular genetic studies of CPT performance are currently limited and have generally revealed inconsistent findings. The current study tested the associations of the COMT val(108/158)met polymorphism with AX-CPT indices (i.e., omission and commission errors, d׳, and lnβ), as well as the variability of these indices across blocks, in a sample of clinic-referred and non-referred children (N=380). We found significant associations between COMT and variability in the Signal Detection Theory (SDT) indices d׳ and lnβ across blocks, as well as a statistical trend for association between COMT and commission errors. Higher externalizing psychopathology was associated with general impairment on AX-CPT performance, and for some indices (i.e., d׳ variability and lnβ variability) the effect of COMT was stronger at higher levels of psychopathology. Our findings support the role of COMT in components of CPT performance and highlight the potential utility of using SDT indices, particularly in relation to variability in performance. Moreover, our results suggest that for some indices the effect of COMT is stronger at higher levels of externalizing psychopathology. Our study yields some preliminary insights regarding the neurobiology of CPT performance, which may elucidate the mechanisms by which specific genes confer risk for various cognitive deficits, as well as relevant disorders characterized by these deficits.

Methylphenidate HCl: therapy for attention deficit hyperactivity disorder

Methylphenidate is a first-line therapy for attention deficit hyperactivity disorder, the most prevalent neuropsychiatric disorder of childhood. The compound is a piperidine and the D-threo-isomer is considered the biologically active form. The compound is available in multiple short- and long-acting preparations, having different delivery systems leading to varying kinetics without clear superiority in efficacy or tolerability at the group level. Common adverse effects are insomnia, appetite disturbance, stomach ache, headache and dizziness. Its mechanism of action is linked to the monoamines dopamine and norepinephrine. The compound appears to predominantly increase the synaptic concentration of dopamine, presumably via inhibition of the dopamine transporter DAT1. There also appears to be effects on presynaptic vesicular trafficking and distribution of dopamine. Both immediate- and sustained-release preparations of methylphenidate have proven efficacy in children and adults with attention deficit hyperactivity disorder. Analysis of the National Institutes of Health-sponsored multimodal treatment study of attention deficit hyperactivity disorder supports a combined medication and behavioral therapy approach.

Association between phthalates and attention deficit disorder and learning disability in U.S. children, 6-15 years

OBJECTIVE

This study investigates the association between urinary phthalate metabolite levels and attention deficit disorder (ADD), learning disability (LD), and co-occurrence of ADD and LD in 6-15-year-old children.

METHODS

We used cross-sectional data from the National Health and Nutrition Examination Survey (NHANES, 2001-2004). Phthalate metabolites with ≥75% detection in urine samples were examined. The study population comprised 1493 children with parent-reported information on ADD or LD diagnosis and phthalate concentrations in urine. Phthalate concentrations were creatinine-adjusted and log10-transformed for analysis. All models controlled for child sex, age, race, household income, blood lead, and maternal smoking during pregnancy.

RESULTS

There were 112 ADD cases, 173 LD cases, and 56 ADD and LD cases in the sample. After adjusting for potential confounders, we found increased odds of ADD with increasing urinary concentration of di-2-ethylhexyl phthalates (OR: 2.1; 95% CI: 1.1, 3.9) and high molecular weight phthalates (OR: 2.7; 95% CI: 1.2, 6.1). In addition, dibutyl phthalates (OR: 3.3; 95% CI: 0.9, 12.7) and high molecular weight phthalates (OR: 3.7; 95% CI: 0.9, 14.8) were marginally associated with increased odds of co-occurring ADD and LD. We did not find associations for any phthalate and LD alone. We observed stronger associations between phthalates and ADD and both ADD and LD in girls than boys in some models.

CONCLUSIONS

We found cross-sectional evidence that certain phthalates are associated with increased odds of ADD and both ADD and LD. Further investigations with longitudinal data are needed to confirm these results.

Association between the DAT1 gene and spatial working memory in attention deficit hyperactivity disorder

An association between attention deficit hyperactivity disorder (ADHD) and the dopamine transporter gene (DAT1) was reported in clinical samples. This study aimed to explore whether there was an association between DAT1 and spatial working memory (SWM), a promising endophenotype for ADHD. This family-based association sample consisted of 382 probands with DSM-IV ADHD and their family members (n = 1298) in Taiwan. The SWM task of the Cambridge Neuropsychological Test Automated Battery (CANTAB) was used to measure SWM of all participants. We screened 15 polymorphisms across the DAT1 gene, including 14 single nucleotide polymorphisms (SNPs) and the variable number of tandem repeat polymorphism in the 3'-untranslated region. We used the Family-Based Association Test (FBAT) to test the associations of genetic polymorphisms with the SWM measures. In single locus association analyses, two SNPs (rs2617605 and rs37020) were significantly associated with the double errors (adjusted p = 0.03 and 0.03, respectively) after adjustment for multiple testing. In haplotype analyses, a haplotype rs403636 (G)/rs463379 (C)/rs393795 (C)/rs37020 (G) was significantly associated with total within-search errors (minimal p = 0.001), within-search errors in eight boxes (minimal p = 0.002), total double errors (minimal p = 0.001) and double errors in eight boxes (minimal p = 0.004). Our finding of the haplotype rs403636 (G)/rs463379 (C)/rs393795 (C)/rs37020 (G) as a novel genetic marker for spatial working memory suggests that variation in DAT1 may provide insight into the pathways leading from genotype to phenotype of ADHD.

Enhanced prepulse inhibition and low sensitivity to a dopamine agonist in HESR1 knockout mice

Transcription factor Hesr family genes are important in neuronal development. We demonstrated previously that HESR1 and HESR2 modified expression of the dopamine transporter (DAT) reporter gene. HESR-family genes have been investigated in development, but their functions, especially in relation to behaviors regulated by dopamine, in adult animals remain unclear. In the present study, we investigated the effects of Hesr1 and Hesr2 on behavior. A behavioral test battery to examine spontaneous activity, anxiety-like behavior, aggressive behavior, pain sensitivity, and sensorimotor gating was conducted in Hesr1 and Hesr2 knockout (KO) mice. Enhanced prepulse inhibition (PPI), which is a form of sensorimotor gating, was observed in only Hesr1 KO mice; other behavioral traits were mostly comparable to wild-type animals in both the Hesr1 and the Hesr2 KO lines. Next, we used a dopamine agonist, apomorphine, to confirm the involvement of the dopaminergic system. Injection of apomorphine reduced the enhanced PPI in Hesr1 KO mice. Additionally, dose-dependent sensitivity to the agonist was lower in the Hesr1 KO mice than in wild-type mice, suggesting that the enhanced PPI resulted from this alteration in dopamine sensitivity. Furthermore, DAT mRNA was downregulated in Hesr1 KO mice, whereas the dopamine D1 and D2 receptors were comparable. These findings suggest Hesr1 to be a novel factor that affects dopamine sensitivity and the sensorimotor gating system.

The effect of different stimulus attributes on the attentional performance of children with attention deficit/hyperactivity disorder and dyslexia

While teachers have traditionally used the interesting objects to increase student attention in the classroom, evidence supporting the effectiveness of this method is lacking. The present study investigated the influence of different stimulus attributes for typical developing students and for students with attention deficit/hyperactivity disorder (ADHD) and dyslexia. Thirty children with ADHD, 30 children with dyslexia, and 30 typical developing students were tested using a measuring tool that was constructed by the authors to assess their sustained attention and selective attention on the geometric-figure assessment and the interesting-figure assessment. The geometric-figure assessment included a square, circle, trapezium, and triangle; and the interesting-figure assessment included a house, cat, hand, and tree. While the typical developing group showed better selective attention on the geometric-figure assessment, there was no difference between the dyslexic group and the ADHD group with respect to selective attention. Furthermore, the typical developing and dyslexic groups did not differ in the geometric-figure assessment in sustained attention and were both better in this area than the ADHD group. In the interesting-figure assessment, the typical developing and dyslexic groups performed similarly in sustained attention, but selective attention of the dyslexic group improved more than the ADHD group, similar to the typical developing group. Both selective attention of the dyslexic group and sustained attention of the ADHD group showed positive significant differences in the interesting-figure assessment, but sustained attention of the dyslexic group and selective attention of the ADHD group showed little difference in the interesting-figure assessment. Surprisingly, the typical developing group did not show any significant difference in the interesting-figure assessment, possibly because they had previously demonstrated a ceiling effect in the geometric-figure assessment.

Animal foraging and the evolution of goal-directed cognition

Foraging- and feeding-related behaviors across eumetazoans share similar molecular mechanisms, suggesting the early evolution of an optimal foraging behavior called area-restricted search (ARS), involving mechanisms of dopamine and glutamate in the modulation of behavioral focus. Similar mechanisms in the vertebrate basal ganglia control motor behavior and cognition and reveal an evolutionary progression toward increasing internal connections between prefrontal cortex and striatum in moving from amphibian to primate. The basal ganglia in higher vertebrates show the ability to transfer dopaminergic activity from unconditioned stimuli to conditioned stimuli. The evolutionary role of dopamine in the modulation of goal-directed behavior and cognition is further supported by pathologies of human goal-directed cognition, which have motor and cognitive dysfunction and organize themselves, with respect to dopaminergic activity, along the gradient described by ARS, from perseverative to unfocused. The evidence strongly supports the evolution of goal-directed cognition out of mechanisms initially in control of spatial foraging but, through increasing cortical connections, eventually used to forage for information.

Emerging association between addictive gaming and attention-deficit/hyperactivity disorder

Children's and adolescent's use of computer games and videogames is becoming highly popular and has increased dramatically over the last decade. There is growing evidence of high prevalence of addiction to computer games and videogames among children, which is causing concern because of its harmful consequences. There is also emerging evidence of an association between computer game and videogame addiction and attention deficit/hyperactivity disorder (ADHD). This is indicated by the occurrence of gaming addiction as a co-morbid disorder of ADHD, common physiological and pharmacological mechanisms, and potential genetic association between the two disorders. A proper understanding of the psychological and neurotransmitter mechanisms underlying both disorders is important for appropriate diagnostic classification of both disorders. Furthermore, it is important for development of potential pharmacological treatment of both disorders. Relatively few studies have investigated the common mechanisms for both disorders. This paper reviews new findings, trends, and developments in the field. The paper is based on a literature search, in Medline and PUBMED, using the keywords addictive gaming and ADHD, of articles published between 2000 and 2012.

The spontaneously hypertensive and Wistar Kyoto rat models of ADHD exhibit sub-regional differences in dopamine release and uptake in the striatum and nucleus accumbens

The most widely used animal model of attention-deficit/hyperactivity disorder (ADHD) is the spontaneously hypertensive rat (SHR/NCrl), which best represents the combined subtype (ADHD-C). Recent evidence has revealed that a progenitor strain, the Wistar Kyoto from Charles River Laboratories (WKY/NCrl), is useful as a model of the inattentive subtype (ADHD-PI) and the Wistar Kyoto from Harlan Laboratories (WKY/NHsd) and the Sprague Dawley (SD) have been suggested as controls. Dopamine (DA) dysfunction in the striatum (Str) and nucleus accumbens core (NAc) is thought to play a significant role in the pathophysiology of ADHD but data obtained with the SHR is equivocal. Using high-speed chronoamperometric recordings with carbon fiber microelectrodes, we found that the SHR/NCrl displayed decreased KCl-evoked DA release versus the WKY/NCrl model of ADHD-PI in the dorsal Str. The WKY/NCrl and the WKY/NHsd control did not differ from each other; however, the control SD released less DA than the WKY/NCrl model of ADHD-PI in the dorsal Str and less than the control WKY/NHsd in the intermediate Str. The SHR/NCrl had faster DA uptake in the ventral Str and NAc versus both control strains, while the WKY/NCrl model of ADHD-PI exhibited faster DA uptake in the NAc versus the SD control. These results suggest that increased surface expression of DA transporters may explain the more rapid uptake of DA in the Str and NAc of these rodent models of ADHD.

Dopamine transporter genotype predicts attentional asymmetry in healthy adults

A number of recent studies suggest that DNA variation in the dopamine transporter gene (DAT1) influences spatial attention asymmetry in clinical populations such as ADHD, but confirmation in non-clinical samples is required. Since non-spatial factors such as attentional load have been shown to influence spatial biases in clinical conditions, here we sought to determine whether any association between DAT1 genotype and spatial bias might be moderated by non-spatial attentional load. Healthy adults were asked to react to sudden onset peripheral targets while demand on non-spatial attention was manipulated via a central task. Participants were genotyped for a DAT1 variable number of tandem repeat (VNTR) polymorphism. The 10-repeat allele of this variant is a replicated susceptibility allele for ADHD and has been shown to associate with spatial bias. As expected, an overall leftward asymmetry/pseudoneglect was observed when the data were averaged across the entire sample. When data were stratified by DAT1 genotype, individuals lacking homozygosity for the 10-repeat DAT1 allele (non-10/10) showed a pronounced leftward bias that was significantly different from zero. In line with past reports from children with ADHD, this leftward bias was attenuated in individuals who were homozygous for the DAT1 10-repeat allele (10/10), suggestive of relatively weaker right hemisphere dominance for spatial attention. This effect of DAT1 genotype on spatial bias was not modulated by non-spatial attention load. These data confirm in healthy adult participants both the existence and the direction of the relationship previously reported between DAT1 genotype and spatial bias in children with ADHD. These data add to a growing body of evidence showing that spatial attentional asymmetry is a stable quantitative trait, with individual differences in this trait significantly predicted by common DNA variation in the DAT1 gene.

The androgen receptor facilitates inhibition of human dopamine transporter (DAT1) reporter gene expression by HESR1 and HESR2 via the variable number of tandem repeats

A functional genetic polymorphism in the 3'-untranslated region (UTR) within exon 15 of the human DAT gene (DAT1) has been described. This 3'-UTR contains a variable number of tandem repeats (VNTR) 40 bp in length; many association studies of psychiatric or developmental disorders with this VNTR have been conducted. We previously demonstrated that HESR1 (the Hairy/enhancer of split related transcriptional factor 1 with YRPW motif) and HESR2 reduced DAT reporter gene expression via this 3'-UTR. VNTR allele-dependent altered reporter gene expression was also observed. In the present study, we wanted to clarify the molecular characterization of HESR1 and HESR2, focusing on its cis-element and co-factor. Deletion of the VNTR domain increased reporter gene expression both with and without transfection of HESRs, suggesting that the VNTR inhibits DAT expression, and is responsive to HESRs. In the presence of transfected androgen receptor (AR), activity of the luciferase reporter with the nine-repeat allele (9r) decreased, while that with the ten-repeat allele (10r), the most frequent in the population, increased significantly. Furthermore, co-expression of HESR1 or HESR2 with AR increased the inhibitory effect of the HESRs. Our data indicate that a functional modification occurs when the HESRs are coupled with AR. This HESR-AR interaction could be the molecular basis of sexual dimorphisms in DAT expression, or other dopamine-related behavioral traits.

Polyunsaturated fatty acids (PUFA) for attention deficit hyperactivity disorder (ADHD) in children and adolescents

BACKGROUND

Attention deficit hyperactivity disorder (ADHD) is a major problem in children and adolescents, characterised by age-inappropriate levels of inattention, hyperactivity and impulsivity, and is associated with long-term social, academic and mental health problems. The stimulant medications methylphenidate and amphetamine are the most frequently used treatments for ADHD, but these are not always effective and can be associated with side effects. Clinical and biochemical evidence suggests that deficiencies of polyunsaturated fatty acids (PUFA) could be related to ADHD. Children and adolescents with ADHD have been shown to have significantly lower plasma and blood concentrations of PUFA and, in particular, lower levels of omega-3 PUFA. These findings suggest that PUFA supplementation may reduce the attention and behaviour problems associated with ADHD.

OBJECTIVES

To compare the efficacy of PUFA to other forms of treatment or placebo in treating the symptoms of ADHD in children and adolescents.

SEARCH METHODS

We searched the following databases in August 2011: CENTRAL (The Cochrane Library 2011, Issue 2), MEDLINE (1948 to July Week 3, 2011), EMBASE (1980 to 2011 Week 29), PsycINFO (1806 to current), CINAHL (1937 to current), BIOSIS (1969 to 30 July 2011), Science Citation Index (1970 to 30 July 2011), Social Science Citation Index (1970 to 30 July 2011), Conference Proceedings Citation Index - Science (1990 to 30 July 2011), Conference Proceedings Citation Index - Social Science and Humanities (1990 to 30 July 2011), Cochrane Database of Systematic Reviews (2011, Issue 7), DARE (2011 Issue 2), Dissertation Abstracts (via Dissertation Express) and the metaRegister of Controlled Trials (mRCT). In addition, we searched the following repositories for theses on 2 August 2011: DART, NTLTD and TROVE. We also checked reference lists of relevant studies and reviews for additional references.

SELECTION CRITERIA

Two review authors independently assessed the results of the database searches. We resolved any disagreements regarding the selection of studies through consensus or, if necessary, by consultation with a third member of the review team.

DATA COLLECTION AND ANALYSIS

Two members of the review team independently extracted details of participants and setting, interventions, methodology and outcome data. If differences were identified, we resolved them by consensus or referral to a third member of the team. We made all reasonable attempts to contact the authors where further clarification or missing data were needed.

MAIN RESULTS

We included 13 trials with 1011 participants in the review. After screening 366 references, we considered 23 relevant and obtained the full text for consideration. We excluded five papers and included 18 papers describing the 13 trials. Eight of the included trials had a parallel design: five compared an omega-3 PUFA supplement to placebo; two compared a combined omega-3 and omega-6 supplement to placebo, and one compared an omega-3 PUFA to a dietary supplement. Five of the included trials had a cross-over design: two compared combined omega-3/6 PUFA to placebo; two compared omega-6 PUFA with placebo; one compared omega-3 to omega-6 PUFA, and one compared omega-6 PUFA to dexamphetamine. Supplements were given for a period of between four and 16 weeks.There was a significantly higher likelihood of improvement in the group receiving omega-3/6 PUFA compared to placebo (two trials, 97 participants; risk ratio (RR) 2.19, 95% confidence interval (CI) 1.04 to 4.62). However, there were no statistically significant differences in parent-rated ADHD symptoms (five trials, 413 participants; standardised mean difference (SMD) -0.17, 95% CI -0.38 to 0.03); inattention (six trials, 469 participants; SMD -0.04, 95% CI -0.29 to 0.21) or hyperactivity/impulsivity (five trials, 416 participants; SMD -0.04, 95% CI -0.25 to 0.16) when all participants receiving PUFA supplements were compared to those receiving placebo.There were no statistically significant differences in teacher ratings of overall ADHD symptoms (four trials, 324 participants; SMD 0.05, 95% CI -0.18 to 0.27); inattention (three trials, 260 participants; SMD 0.26, 95% CI -0.22 to 0.74) or hyperactivity/impulsivity (three trials, 259 participants; SMD 0.10, 95% CI -0.16 to 0.35).There were also no differences between groups in behaviour, side effects or loss to follow-up.Overall, there were no other differences between groups for any other comparison.

AUTHORS' CONCLUSIONS

Overall, there is little evidence that PUFA supplementation provides any benefit for the symptoms of ADHD in children and adolescents. The majority of data showed no benefit of PUFA supplementation, although there were some limited data that did show an improvement with combined omega-3 and omega-6 supplementation.It is important that future research addresses current weaknesses in this area, which include small sample sizes, variability of selection criteria, variability of the type and dosage of supplementation, short follow-up times and other methodological weaknesses.

Recent advances in imaging of dopaminergic neurons for evaluation of neuropsychiatric disorders

Dopamine is the most intensely studied monoaminergic neurotransmitter. Dopaminergic neurotransmission plays an important role in regulating several aspects of basic brain function, including motor, behavior, motivation, and working memory. To date, there are numerous positron emission tomography (PET) and single photon emission computed tomography (SPECT) radiotracers available for targeting different steps in the process of dopaminergic neurotransmission, which permits us to quantify dopaminergic activity in the living human brain. Degeneration of the nigrostriatal dopamine system causes Parkinson's disease (PD) and related Parkinsonism. Dopamine is the neurotransmitter that has been classically associated with the reinforcing effects of drug abuse. Abnormalities within the dopamine system in the brain are involved in the pathophysiology of attention deficit hyperactivity disorder (ADHD). Dopamine receptors play an important role in schizophrenia and the effect of neuroleptics is through blockage of dopamine D₂ receptors. This review will concentrate on the radiotracers that have been developed for imaging dopaminergic neurons, describe the clinical aspects in the assessment of neuropsychiatric disorders, and suggest future directions in the diagnosis and management of such disorders.

Methylphenidate, interstimulus interval, and reaction time performance of children with attention deficit/hyperactivity disorder: a pilot study

Thirteen children with attention deficit/hyperactivity disorder (ADHD: DSM-IV-TR) participated in the pilot study. They carried out a Go/No-Go test with a short (2 seconds) and long (6 seconds) interstimulus interval (ISI) when on placebo and a therapeutic dose of methylphenidate (MPH). For the long-ISI placebo condition the responses were slow and inaccurate. This pattern of response may be due to underactivation of the readiness-to-respond state that is not fully controlled by effort allocation. Speed of response and accuracy were enhanced during the short-ISI placebo condition and the long-ISI MPH condition. However, the combined effect (short ISI and MPH) resulted in a fast but inaccurate response style. This pattern of response may be due to overactivation of the readiness-to-respond state. The data of the pilot study support the stimulus shift hypothesis: MPH administration result in deterioration on tests on which children had previously done well (short ISI plus placebo versus short ISI plus MPH). In addition, the data support the idea that ADHD is associated with poor state regulation rather than motivational (delay aversion) theories or temporal-processing/time-estimation theories of ADHD. The pilot study defined empirically an issue for further study with the larger controlled sample.

Neuropsychological endophenotypes in attention-deficit/hyperactivity disorder: a review of genetic association studies

As a relatively large body of research has been published up to now, it may be informative to explore whether the use of endophenotypes has produced consistent findings in attention-deficit hyperactivity disorder (ADHD). We reviewed the results of genetic studies investigating associations between putative susceptibility genes for ADHD and neuropsychological traits relevant for this disorder. A PubMed database search identified 47 studies. Most of them (n = 36) examined a single candidate gene, while seven studies examined two or three genes and only four studies examined 10 genes or more. The most investigated genes were DRD4, DAT1, COMT, MAOA, and DBH. Regarding DRD4, association of high reaction time variability with the 7-R allele absence appears to be the most consistent result. Speed of processing, set shifting, and cognitive impulsiveness were less frequently investigated, but seem to be altered in the 7-R allele carriers. Regarding DAT1, majority of studies reported negative results indicating that this gene may have a modulating effect rather than direct influence on cognitive functioning. The other genes were investigated in fewer studies, and the reported findings need to be replicated. The principal methodological issues that could represent confounding factors and may explain conflicting results are discussed.

Psychopathological aspects of dopaminergic gene polymorphisms in adolescence and young adulthood

Dopamine hypotheses of several psychiatric disorders are based upon the clinical benefits of drugs affecting dopamine transporter or receptors, and have prompted intensive candidate gene research within the dopaminergic system during the last two decades. The aim of this review is to survey the most important findings concerning dopaminergic gene polymorphisms in attention deficit hyperactivity disorder (ADHD), Tourette syndrome (TS), obsessive compulsive disorder, and substance abuse. Also, genetic findings of related phenotypes, such as inattention, impulsivity, aggressive behavior, and novelty seeking personality trait are presented, because recent studies have applied quantitative trait measures using questionnaires, symptom scales, or other objective endophenotypes. Unfortunately, genetic variants with minor effects are problematic to detect in these complex inheritance disorders, often leading to contradictory results. The most consistent association findings relate to ADHD and the dopamine transporter and the dopamine D4 receptor genes. Meta-analyses also support the association between substance abuse and the D2 receptor gene. The dopamine catabolizing enzyme genes, such as monoamine oxidase (MAO) A and catechol-O-methyltransferase (COMT) genes, have been linked to aggressive behaviors.

Lack of association between a 3'UTR VNTR polymorphism of dopamine transporter gene (SLC6A3) and ADHD in a Brazilian sample of adult patients

OBJECTIVE

To investigate a possible association between a 3'UTR VNTR polymorphism of the dopamine transporter gene (SLC6A3) and ADHD in a Brazilian sample of adult patients.

METHOD

Study Case-control with 102 ADHD adult outpatients ( DSM-IV criteria) and 479 healthy controls. The primers' sequence used were: 3'UTR-Forward: 5' TGT GGT GAT GGG AAC GGC CTG AG 3' and 3'UTR-Reverse: 5' CTT CCT GGA GGT CAC GGC TCA AGG 3'. Alleles of the 3'UTR were coded according to their number of repeats: 6- repeat 320 bp (allele 6), 8- repeat 400 bp (allele 8), 9- repeat 440 bp (allele 9), 10- repeat 480 bp (allele 10), and 11- repeat 520 bp (allele 11).

RESULTS

There were no allelic (χ(2) = 2.67, 5df, p = .75) and genotypic (χ(2) = 7.20, 1 df, p = .61) association between adult ADHD and VNTR 3'UTR polymorphism of SLC6A3.

CONCLUSION

Our findings do not support SLC6A3 as marker genetic susceptibility factor in adult ADHD. More comprehensive polymorphism coverage within the SLC6A3 region should be conducted in larger samples, including comparisons in clinical subgroups, and in samples with different ethnic backgrounds.

The moderating role of the dopamine transporter 1 gene on P50 sensory gating and its modulation by nicotine

Although schizophrenia has been considered primarily a disease of dopaminergic neurotransmission, the role of dopamine in auditory sensory gating deficits in this disorder and their amelioration by smoking/nicotine is unclear. Hypothesizing that individual differences in striatal dopamine levels may moderate auditory gating and its modulation by nicotine, this preliminary study used the mid-latency (P50) auditory event-related potential (ERP) to examine the single dose (6 mg) effects of nicotine (vs. placebo) gum on sensory gating in 24 healthy nonsmokers varying in the genetic expression of the dopamine transporter (DAT). Consistent with an inverted-U relationship between dopamine level and the drug effects, individuals carrying the 9R (lower gene expression) allele, which is related to greater striatal dopamine levels, tended to evidence increased baseline gating compared to 10R (higher gene expression) allele carriers and showed a reduction in gating with acute nicotine. The present results may help to understand the link between excessive smoking and sensory gating deficits in schizophrenia and to explain the potential functional implications of genetic disposition on nicotinic treatment in schizophrenia.

Noise benefit in prepulse inhibition of the acoustic startle reflex

RATIONALE

Under some conditions, external sensory noise enhances cognitive functions, a phenomenon possibly involving stochastic resonance and/or enhanced central dopamine transmission. Prepulse inhibition (PPI) of the startle reflex is a robust measure of sensorimotor gating and can be modulated by activity in the cortex and basal ganglia, including the central dopamine pathways.

OBJECTIVES

Previous empirical studies suggest a differential effect of acoustic noise in normal children and children with attention-deficit hyperactivity disorder (ADHD). This study investigated the effect of acoustic noise on PPI and if dopamine transmission interacts with acoustic noise effects in a rat ADHD model.

METHODS

The effect of background acoustic noise on acoustic startle response and PPI were measured with a constant prepulse to background noise ratio of 9 dB(A). Spontaneously hypertensive (SH) rats were used as the ADHD model and compared with Wistar and Sprague-Dawley rats. Microdialysis, methylphenidate treatment and 6-OHDA lesions were used to investigate interaction with dopamine transmission.

RESULTS

Background noise facilitated PPI differently in SH rats and controls. The prefrontal cortex in SH rats had low basal dopamine concentrations, a high DOPAC/dopamine ratio and blunted dopamine release during PPI testing. Methylphenidate had small, but strain-specific, effects on startle and PPI. Bilateral 6-hydroxydopamine lesions did not alter startle or PPI.

CONCLUSIONS

Prefrontal dopamine transmission is altered in SH rats during the sensorimotor gating task of PPI of the acoustic startle, indicating increased dopamine reuptake in this ADHD rat model. We propose that noise benefit could be explored as a non-pharmacological alternative for treating neuropsychiatric disorders.

Association between the dopamine transporter gene and the inattentive subtype of attention deficit hyperactivity disorder in Taiwan

Attention deficit hyperactivity disorder (ADHD) is a common heritable childhood psychiatric disorder. Since methylphenidate, one of the main drugs used to treat ADHD, targets the dopamine transporter, this study examined the linkage disequilibrium (LD) structure of the dopamine transporter gene (DAT1) and investigated whether the DAT1 gene was associated with ADHD. This Chinese family-based association sample consisted of 273 DSM-IV diagnosed ADHD probands and their family members (n=906). We screened 15 polymorphisms across the DAT1 gene, including 14 single nucleotide polymorphism (SNP) markers and the variable number of tandem repeat (VNTR) polymorphism in 3'-untranslated region (3'UTR). Calculations of pairwise LD revealed three main haplotype blocks (HBs): HB1 (intron 2 through intron 6), HB2 (intron 8 through intron 11), and HB3 (3'UTR). Family-Based Association Tests showed that no allele was significantly more transmitted than expected to the ADHD children for these 15 markers. Haplotype-Based Association Tests showed that a haplotype rs27048 (C)/rs429699 (T) was significantly associated with the inattentive subtype (P=0.008). In quantitative analyses, this haplotype also demonstrated significant association with the inattention severity (P=0.012). Our finding of the haplotype rs27048 (C)/rs429699 (T) as a novel genetic marker in the inattentive ADHD subtype suggests that variation in the DAT1 gene may primarily affect the inattentive subtype of ADHD.