Targeting the dopamine system in the treatment of attention-deficit/hyperactivity disorder

A longitudinal study of the gut microbiota during the first three years of life: Links with problem behavior and executive functions at preschool age

Early life is a sensitive period when microbiota-gut-brain interactions may have important impact on development. This study investigated the associations of the gut microbiota in the first three years of life (two, six, and 12 weeks, and one and three years) with problem behavior and executive functions in N = 64 three-year-old children. Higher relative abundance of Streptococcus at the age of two weeks, as well as its trajectory over time (including ages two, six and 12 weeks, and one and three years), was related to worse executive functions. Higher relative abundance of [Ruminococcus] torques group at the age of three years, as well as its trajectory from one to three years, was associated with less internalizing behavior. Besides, several robust age-specific associations were identified: higher Bifidobacterium relative abundance (age three years) was associated with more internalizing and externalizing issues; higher Blautia relative abundance (age three years) was linked to less internalizing behavior; and increased relative abundance of an unidentified Enterobacteriaceae genus (age two weeks) was related to more externalizing behavior. Our findings provide important longitudinal evidence that early-life gut microbiota may be linked to behavioral and cognitive development in low-risk children.

Molecular Characterisation of the Mechanism of Action of Stimulant Drugs Lisdexamfetamine and Methylphenidate on ADHD Neurobiology: A Review

Attention-deficit/hyperactivity disorder (ADHD) is a common childhood-onset neurodevelopmental disorder characterised by persistent inattention, hyperactivity and impulsivity. Moreover, ADHD is commonly associated with other comorbid diseases (depression, anxiety, bipolar disorder, etc.). The ADHD symptomatology interferes with subject function and development. The treatment of ADHD requires a multidisciplinary approach based on a combination of non-pharmacological and pharmacological treatments with the aim of ameliorating the symptomatology; among first-line pharmacological treatments are stimulants [such as methylphenidate (MPH) and lisdexamfetamine dimesylate (LDX)]. In this review we explored recent ADHD- and stimulants-related literature, with the aim of compiling available descriptions of molecular pathways altered in ADHD, and molecular mechanisms of current first-line stimulants MPH and LDX. While conducting the narrative review, we applied structured search strategies covering PubMed/MEDLINE database and performed handsearching of reference lists on the results of those searches. The aetiology and pathophysiology of ADHD are incompletely understood; both genetic and environmental factors have been associated with the disorder and its grade of burden, and also the relationship between the molecular mechanisms of pharmacological treatments and their clinical implications. The lack of comprehensive understanding of the underlying molecular pathology makes both the diagnosis and treatment difficult. Few published studies evaluating molecular data on the mechanism of action (MoA) of MPH and LDX on ADHD are available and most of them are based on animal models. Further studies are necessary to improve the knowledge of ADHD pathophysiology and how the MoAs of MPH and LDX differentially modulate ADHD pathophysiology and control ADHD symptomatology.

Concurrent water- and foodborne exposure to microplastics leads to differential microplastic ingestion and neurotoxic effects in zebrafish

Organisms constantly ingest microplastics directly from the environment or indirectly via trophic transfer due to the pervasiveness of microplastic pollution. However, most previous studies have only focused on waterborne exposure at the individual level, while few studies have investigated the contribution of trophic transfer to the exposure in organisms. We comprehensively evaluated the differences in microplastic ingestion and toxic effects in zebrafish exposed to microplastics via two concurrent routes (waterborne and foodborne). The polyethylene microplastics (40-47 μm, 0.1-10 mg/L) concentration used here was set in a range closed to the environmentally relevant microplastic concentrations, especially considering the extreme high concentration scenarios in wastewater. The concentration of microplastics resulting from foodborne exposure (0.01±0.01 μg/mg; 0.1±0.1 particles/mg) was significantly lower than that through waterborne exposure (0.06±0.02 μg/mg; 0.8±0.3 particles/mg), suggesting the ingestion of microplastics in their tissues occurs mainly through direct environmental uptake rather than food chain transfer (though the initial microplastic concentration was 1000 folds lower). However, more sublethal impacts, including the significant abnormal hyperactive swimming behaviour (107±5% induction; p< 0.05), were observed in the foodborne group than waterborne group. Additionally, ingenuity pathway analysis predicted both exposure routes caused obvious nervous system interference but through opposite modes of action. This was further verified by the alteration of neurotransmitter biomarkers that neurotoxicity mechanisms were completely different for the two exposure routes. The neurotoxic effects of microplastics are non-negligible and can exert together through both water- and foodborne exposure routes, which deserves further attention.

Gut microbiome in ADHD and its relation to neural reward anticipation

BACKGROUND

Microorganisms in the human intestine (i.e. the gut microbiome) have an increasingly recognized impact on human health, including brain functioning. Attention-deficit/hyperactivity disorder (ADHD) is a neurodevelopmental disorder associated with abnormalities in dopamine neurotransmission and deficits in reward processing and its underlying neuro-circuitry including the ventral striatum. The microbiome might contribute to ADHD etiology via the gut-brain axis. In this pilot study, we investigated potential differences in the microbiome between ADHD cases and undiagnosed controls, as well as its relation to neural reward processing.

METHODS

We used 16S rRNA marker gene sequencing (16S) to identify bacterial taxa and their predicted gene functions in 19 ADHD and 77 control participants. Using functional magnetic resonance imaging (fMRI), we interrogated the effect of observed microbiome differences in neural reward responses in a subset of 28 participants, independent of diagnosis.

RESULTS

For the first time, we describe gut microbial makeup of adolescents and adults diagnosed with ADHD. We found that the relative abundance of several bacterial taxa differed between cases and controls, albeit marginally significant. A nominal increase in the Bifidobacterium genus was observed in ADHD cases. In a hypothesis-driven approach, we found that the observed increase was linked to significantly enhanced 16S-based predicted bacterial gene functionality encoding cyclohexadienyl dehydratase in cases relative to controls. This enzyme is involved in the synthesis of phenylalanine, a precursor of dopamine. Increased relative abundance of this functionality was significantly associated with decreased ventral striatal fMRI responses during reward anticipation, independent of ADHD diagnosis and age.

CONCLUSIONS

Our results show increases in gut microbiome predicted function of dopamine precursor synthesis between ADHD cases and controls. This increase in microbiome function relates to decreased neural responses to reward anticipation. Decreased neural reward anticipation constitutes one of the hallmarks of ADHD.

Tributyltin affects shoaling and anxiety behavior in female rare minnow (Gobiocypris rarus)

Effects of tributyltin (TBT) on reproduction are well established in many fish species. However, few studies report the effects of TBT on non-reproductive behaviors, which is a novel aspect of endocrine disruption in fish. Thus, the present study used rare minnow (Gobiocypris rarus) to investigate the effects of TBT, at environmental concentrations of 1, 10 and 100ng/L, on shoaling and anxiety behaviors. The results showed that fish exposed to TBT had less group cohesion during the course of the 10-min observation period as compared with the control fish. Further, TBT altered the shoaling in the Novel tank test, where shoaling is determined as the tendency to leave a shoal of littermates trapped behind a Plexiglas barrier at one end of the test tank. Fish exposed to TBT had shorter latency before leaving shoal mates and spent more time away from shoal than control fish. In addition, we also used Novel tanks to study the anxiety behavior as the tendency to stay at the bottom when introduced into an unfamiliar environment. The fish exposed to TBT showed increased anxiety, manifested as increased latency to enter the upper half and decreased time in upper half when compared with the control fish. TBT exposure increased the levels of dopamine and its metabolite 3,4-dihydroxyphenylacetic acid, and decreased the levels of 5-hydroxytryptamine and its metabolite 5-hydroxy indole acetic acid in the brain. Thus, the hypofunction of the dopaminergic system or of the serotoninergic system or the combination of the two may underlie the observed behavioral change, which might affect the fitness of fish in their natural environment.

Cytotoxic, genotoxic, and neurotoxic effects of Mg, Pb, and Fe on pheochromocytoma (PC-12) cells

Metals such as lead (Pb), magnesium (Mg), and iron (Fe) are ubiquitous in the environment as a result of natural occurrence and anthropogenic activities. Although Mg, Fe, and others are considered essential elements, high level of exposure has been associated with severe adverse health effects including cardiovascular, hematological, nephrotoxic, hepatotoxic, and neurologic abnormalities in humans. In the present study we hypothesized that Mg, Pb, and Fe are cytotoxic, genotoxic and neurotoxic, and their toxicity is mediated through oxidative stress and alteration in protein expression. To test the hypothesis, we used the pheochromocytoma (PC-12) cell line as a neuro cell model and performed the LDH assay for cell viability, Comet assay for DNA damage, Western blot for oxidative stress, and HPLC-MS to assess the concentration levels of neurological biomarkers such as glutamate, dopamine (DA), and 3-methoxytyramine (3-MT). The results of this study clearly show that Mg, Pb, and Fe, respectively in the form of MgSO4 , Pb(NO3 )2 , FeCl2 , and FeCl3 induce cytotoxicity, oxidative stress, and genotoxicity in PC-12 cells. In addition, exposure to these metallic compounds caused significant changes in the concentration levels of glutamate, dopamine, and 3-MT in PC-12 cells. Taken together the findings suggest that MgSO4 , Pb(NO3 )2 , FeCl2 , and FeCl3 have the potential to induce substantial toxicity to PC-12 cells.

Dual regulating effects of gastrodin on extracellular dopamine concentration in rats models of Tourette's syndrome

PURPOSE

Evaluate the dual regulating effects of gastrodin on striatal extracellular dopamine (DA) concentration in Tourette's syndrome (TS) rat models, and explore the underlying pharmacological mechanisms.

MATERIALS AND METHODS

Seventy Wistar rats were randomly divided into control group and TS model group. The former was intraperitoneally injected with saline (0.9%), while in the later, the rats were injected with Apomorphine (Apo) and 3,3'-iminodipropionitrile (IDPN) respectively to manipulate two kinds of TS rat models. Both Apo and IDPN induced rats were further assigned to three conditions, and the related rats were treated respectively by oral gavage with saline, gastrodin and Haloperidol (Hal). Data of stereotypy of the rats were collected. After 8 weeks, the extracellular content of DA and HVA in striatum were examined by intracerebral microdialysis and follow-up high-performance liquid chromatography (HPLC), and the expression of dopamine transporter (DAT) was probed by Western blot.

RESULTS

Gastrodin improved the stereotyped behaviors in TS rats. Furthermore, it down-regulated the elevated striatal extracellular DA concentration in Apo-induced rats and up-regulated the decreased DA content in the rats exposed to IDPN. Meanwhile, a dramatic down-regulation was detected in DAT protein expression in Apo + GAS group, while an opposite profile was showed in the IDPN + GAS group.

CONCLUSIONS

The dual regulating effects of gastrodin on extracellular DA level have been established, and the related mechanisms would be the dual regulating effects of gastrodin on the expression of DAT, a glycoprotein in the regulation of the extracellular DA concentration.

Candidate genetic pathways for attention-deficit/hyperactivity disorder (ADHD) show association to hyperactive/impulsive symptoms in children with ADHD

OBJECTIVE

Because multiple genes with small effect sizes are assumed to play a role in attention-deficit/hyperactivity disorder (ADHD) etiology, considering multiple variants within the same analysis likely increases the total explained phenotypic variance, thereby boosting the power of genetic studies. This study investigated whether pathway-based analysis could bring scientists closer to unraveling the biology of ADHD.

METHOD

The pathway was described as a predefined gene selection based on a well-established database or literature data. Common genetic variants in pathways involved in dopamine/norepinephrine and serotonin neurotransmission and genes involved in neuritic outgrowth were investigated in cases from the International Multicentre ADHD Genetics (IMAGE) study. Multivariable analysis was performed to combine the effects of single genetic variants within the pathway genes. Phenotypes were DSM-IV symptom counts for inattention and hyperactivity/impulsivity (n = 871) and symptom severity measured with the Conners Parent (n = 930) and Teacher (n = 916) Rating Scales.

RESULTS

Summing genetic effects of common genetic variants within the pathways showed a significant association with hyperactive/impulsive symptoms ((p)empirical = .007) but not with inattentive symptoms ((p)empirical = .73). Analysis of parent-rated Conners hyperactive/impulsive symptom scores validated this result ((p)empirical = .0018). Teacher-rated Conners scores were not associated. Post hoc analyses showed a significant contribution of all pathways to the hyperactive/impulsive symptom domain (dopamine/norepinephrine, (p)empirical = .0004; serotonin, (p)empirical = .0149; neuritic outgrowth, (p)empirical = .0452).

CONCLUSION

The present analysis shows an association between common variants in 3 genetic pathways and the hyperactive/impulsive component of ADHD. This study demonstrates that pathway-based association analyses, using quantitative measurements of ADHD symptom domains, can increase the power of genetic analyses to identify biological risk factors involved in this disorder.

Tributyltin exposure influences predatory behavior, neurotransmitter content and receptor expression in Sebastiscus marmoratus

Tributyltin (TBT) is a ubiquitous marine contaminant due to its extensive use as a biocide, fungicide and antifouling agent. However, the neurotoxic effect of TBT has not been extensively studied, especially in marine fish. This study was conducted to investigate the effects of TBT (10, 100 and 1000 ng/L) on the predatory behavior of Sebastiscus marmoratus and to look into the mechanism involved. The results showed that TBT exposure depressed predatory activity after 50 days exposure. Dopamine levels in the fish brains increased in a dose-dependent manner, while 5-hydroxytryptamine and norepinephrine levels decreased significantly in the TBT exposure group compared to the control. The mRNA levels of dopamine receptors, which have functions such as cognition, motor activity, motivation and reward, mood, attention and learning, were significantly down-regulated by TBT exposure. Although the levels of amino acid neurotransmitters, including glutamate, did not show marked alteration, the expression of the glutamatergic signaling pathway such as N-methyl-D-aspartate receptors, a-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptor, calmodulin, Ca(2+)/calmodulin-dependent protein kinases-II and cyclic adenosine monophosphate responsive element binding protein, was significantly reduced by TBT exposure, which indicated that central nerve activities were in a state of depression, thus affecting the predatory activities of the fish.

Sensory and sensorimotor gating in adult attention-deficit/hyperactivity disorder (ADHD)

Even though there is an impaired perceptual capacity in attention-deficit/hyperactivity disorder (ADHD) patients, psychophysiological alterations, such as impaired gating as indexed by prepulse inhibition (PPI) or suppression of P50 auditory event-related potentials, have not been found in patients with ADHD. Hence, potential relationships of psychophysiological measures of gating to psychopathology and cognitive performance remain unclear. The present study investigates two distinct operational measures of gating as well as cognitive performance within adult ADHD patients in order to assess the relationship of these measures to psychopathology. PPI, P50 suppression, cognitive performance, and psychopathologic symptoms were assessed in 26 ADHD patients and 26 healthy control subjects. ADHD patients compared to healthy control subjects exhibited impaired P50 suppression, performed worse in cognitive tasks, and reported more psychopathological symptoms, but were normal in the test of PPI. Thus, P50 gating deficits are not specific to schizophrenia-spectrum disorders. These findings highlight the differences between P50 gating and PPI as measures of the gating construct. In keeping with the lack of correlations between these two putative operational measures of gating seen in both humans and animals, adult ADHD patients exhibit deficient P50 suppression and poor cognitive performance, despite exhibiting normal levels of PPI.

The dopamine receptor D4 7-repeat allele influences neurocognitive functioning, but this effect is moderated by age and ADHD status: an exploratory study

OBJECTIVES

Evidence suggests the involvement of the dopamine D4 receptor gene (DRD4) in the pathogenesis of ADHD, but the exact mechanism is not well understood. Earlier reports on the effects of DRD4 polymorphisms on neurocognitive and neuroimaging measures are inconsistent. This study investigated the functional consequences of the 7-repeat allele of DRD4 on neurocognitive endophenotypes of ADHD in the Dutch subsample of the International Multicenter ADHD Genetics study.

METHODS

Participants were 350 children (5-11.5 years) and adolescents (11.6-19 years) with ADHD and their 195 non-affected siblings. An overall measure of neuropsychological functioning was derived by principal component analysis from five neurocognitive and five motor tasks. The effects of DRD4 and age were examined using Linear Mixed Model analyses.

RESULTS

The analyses were stratified for affected and non-affected participants after finding a significant three-way interaction between ADHD status, age and the 7-repeat allele. Apart from a main effect of age, a significant interaction effect of age and DRD4 was found in non-affected but not in affected participants, with non-affected adolescent carriers of the 7-repeat allele showing worse neuropsychological performance. In addition, carrying the 7-repeat allele of DRD4 was related to a significantly worse performance on verbal working memory in non-affected siblings, independent of age.

CONCLUSIONS

These results might indicate that the effect of the DRD4 7-repeat allele on neuropsychological functioning is dependent on age and ADHD status.

Adults with attention-deficit/hyperactivity disorder - a diffusion-tensor imaging study of the corpus callosum

The objective of the present study was to investigate the microstructure and the macrostructure of the corpus callosum (CC) in adults with Attention-Deficit/Hyperactivity Disorder (ADHD) by means of magnetic resonance imaging (MRI). Twenty-nine participants with ADHD and 37 controls were included from the Norwegian ADHD project in Bergen. We measured the fractional anisotropy (FA) values, as well as the size of different subdivisions of the CC, using diffusion tensor imaging (DTI) and anatomical MRI. The isthmus/splenium part of the CC in the ADHD group showed reduced FA values compared to the control group, whereas the size of the CC did not differ across groups. Our findings thus demonstrate a divergence between microstructural and macrostructural measures in the CC of adults with ADHD. This contrasts with findings in children demonstrating callosal abnormalities in both microstructure and macrostructure. Our results may indicate that adults with ADHD in part have succeeded in passing by an earlier developmental delay of the CC, resulting in a normalization of callosal macrostructure into adulthood. However, microstructural differences are still present in adults, which may point to an abnormal lateralization in adults with ADHD, or could be a sign of a persisting impairment.

Ningdong granule: a complementary and alternative therapy in the treatment of attention deficit/hyperactivity disorder

BACKGROUND

Attention deficit/hyperactivity disorder (ADHD) is a common neurobehavioral and neuropsychiatric disorder in school-age children, and recent studies provide evidence implicating the metabolic abnormalities of dopamine (DA) for its pathophysiology. Methylphenidate, a kind of psychostimulant, is widely used in the treatment of ADHD, but some patients do not respond to it or cannot bear its side effects. As a traditional Chinese medicine preparation, Ningdong granule (NDG) has been used in the treatment of ADHD for several years in China. However, a systematical pharmacological study on its safety and mechanism still remains obscure.

OBJECTIVE

This paper aims to evaluate the efficiency, safety, and possible mechanism of NDG on ADHD children compared to methylphenidate.

METHODS

Seventy-two ADHD children were recruited to perform an 8-week, randomized, methylphenidate-controlled, doubled-blinded trial. The subjects were equally assigned to two groups receiving either NDG 5 mg/kg/day or methylphenidate 1 mg/kg/day for 8 weeks. The efficiency was assessed by the Teacher and Parent ADHD Rating Scales every 2 weeks for a total of 8 weeks. The side effects were recorded during the study. Blood, urine, and stool routine samples, liver and renal function test, and DA and homovanillic acid (HVA) concentration in sera were tested at the beginning and end of the trial.

RESULTS

NDG ameliorated ADHD symptoms after an 8-week medication with fewer side effects compared to methylphenidate (P < 0.05). The result also showed NDG to be safe and tolerable for ADHD children as monitored by the blood, urine, and stool analysis and liver and renal function for 8 weeks (P < 0.05). Moreover, the level of HVA in sera increased in NDG-treated group (P < 0.05), while the content of DA had no significant change during the study. An analysis of Pearson correlation coefficients also showed that the increased content of HVA in sera was associated with the improved scores of Teacher and Parent ADHD Rating Scales.

CONCLUSIONS

Compared to methylphenidate, NDG is effective and safe for ADHD children in the short term, increases the HVA concentration in sera to regulate DA metabolism, and promises to be an alternative medication, safely and effectively.

Methylphenidate normalizes frontocingulate underactivation during error processing in attention-deficit/hyperactivity disorder

BACKGROUND

Children with attention-deficit/hyperactivity disorder (ADHD) have deficits in performance monitoring often improved with the indirect catecholamine agonist methylphenidate (MPH). We used functional magnetic resonance imaging to investigate the effects of single-dose MPH on activation of error processing brain areas in medication-naive boys with ADHD during a stop task that elicits 50% error rates.

METHODS

Twelve medication-naive boys with ADHD were scanned twice, under either a single clinical dose of MPH or placebo, in a randomized, double-blind design while they performed an individually adjusted tracking stop task, designed to elicit 50% failures. Brain activation was compared within patients under either drug condition. To test for potential normalization effects of MPH, brain activation in ADHD patients under either drug condition was compared with that of 13 healthy age-matched boys.

RESULTS

During failed inhibition, boys with ADHD under placebo relative to control subjects showed reduced brain activation in performance monitoring areas of dorsomedial and left ventrolateral prefrontal cortices, thalamus, cingulate, and parietal regions. MPH, relative to placebo, upregulated activation in these brain regions within patients and normalized all activation differences between patients and control subjects. During successful inhibition, MPH normalized reduced activation observed in patients under placebo compared with control subjects in parietotemporal and cerebellar regions.

CONCLUSIONS

MPH normalized brain dysfunction in medication-naive ADHD boys relative to control subjects in typical brain areas of performance monitoring, comprising left ventrolateral and dorsomedial frontal and parietal cortices. This could underlie the amelioration of MPH of attention and academic performance in ADHD.

Methylphenidate normalizes fronto-striatal underactivation during interference inhibition in medication-naïve boys with attention-deficit hyperactivity disorder

Youth with attention deficit hyperactivity disorder (ADHD) have deficits in interference inhibition, which can be improved with the indirect catecholamine agonist methylphenidate (MPH). Functional magnetic resonance imaging was used to investigate the effects of a single dose of MPH on brain activation during interference inhibition in medication-naïve ADHD boys. Medication-naïve boys with ADHD were scanned twice, in a randomized, double-blind design, under either a single clinical dose of MPH or placebo, while performing a Simon task that measures interference inhibition and controls for the oddball effect of low-frequency appearance of incongruent trials. Brain activation was compared within patients under either drug condition. To test for potential normalization effects of MPH, brain activation in ADHD patients under either drug condition was compared with that of healthy age-matched comparison boys. During incongruent trials compared with congruent-oddball trials, boys with ADHD under placebo relative to controls showed reduced brain activation in typical areas of interference inhibition, including right inferior prefrontal cortex, left striatum and thalamus, mid-cingulate/supplementary motor area, and left superior temporal lobe. MPH relative to placebo upregulated brain activation in right inferior prefrontal and premotor cortices. Under the MPH condition, patients relative to controls no longer showed the reduced activation in right inferior prefrontal and striato-thalamic regions. Effect size comparison, furthermore, showed that these normalization effects were significant. MPH significantly normalized the fronto-striatal underfunctioning in ADHD patients relative to controls during interference inhibition, but did not affect medial frontal or temporal dysfunction. MPH therefore appears to have a region-specific upregulation effect on fronto-striatal activation.

Adults with attention-deficit/hyperactivity disorder - a brain magnetic resonance spectroscopy study

BACKGROUND

Impaired cognitive control in individuals with attention-deficit/hyperactivity disorder (ADHD) may be related to a prefrontal cortical glutamatergic deficit. We assessed the glutamate level in the left and the right midfrontal region including the anterior cingulate cortex in adults with ADHD and healthy controls.

METHODS

Twenty-nine adults with ADHD and 38 healthy controls were included. We used Proton Magnetic Resonance Imaging with single voxel point-resolved spectroscopy to measure the ratio of glutamate to creatine (Glu/Cre) in the left and the right midfrontal region in the two groups.

RESULTS

The ADHD group showed a significant reduction of Glu/Cre in the left midfrontal region compared to the controls.

CONCLUSION

The reduction of Glu/Cre in the left midfrontal region in the ADHD group may reflect a glutamatergic deficit in prefrontal neuronal circuitry in adults with ADHD, resulting in problems with cognitive control.

Intra-individual variability in genetic and environmental models of attention-deficit/hyperactivity disorder

The frequent observation of intra-individual variability (IIV) in the expression of ADHD symptoms suggest that IIV is an integral component of the disorder. We tested IIV in ADHD-like phenotype from five different studies of rodent models of ADHD, including studies with Spontaneous Hypertensive Rats (SHR/NCrl and SHR/N), Wistar-Kyoto Hyperactive Rats (WKHA/N), Wistar-Kyoto Hypertensive rat (WKHT), PCB-126 and -153-treated Lewis rats and behaviorally normal Wistar/Mol, Wistar-Kyoto (WKY/N and WKY/NMol), and untreated Lewis rats. Averages of the absolute residual deviation of ADHD-like behavior from individual means ("individual phenotypic dispersion," PD(i)) were used to represent IIV in the fixed-interval (FI) and extinction (EXT) phases of operant behavioral activity. Across all studies, SHR rats had higher PD(i) than WKY rats (P < 0.0001) for all ADHD-like traits, and higher PD(i) for hyperactivity than WKHT and WKHA/N rats. Male SHR rats in particular had higher PD(i) for hyperactivity than male or female WKYs, SHR females for EXT hyperactivity, and higher dispersion for inattention than WKY females. These findings strongly suggest the genetic control of IIV, and suggest that the SHR may be a useful model for the identification of genes for IIV in human ADHD. These findings also obliquely support the SHR as a useful model for ADHD overall.

Does the difference between physically active and couch potato lie in the dopamine system?

Obesity and other inactivity related diseases are increasing at an alarming rate especially in Western societies. Because of this, it is important to understand the regulating mechanisms involved in physical activity behavior. Much research has been done in regard to the psychological determinants of physical activity behavior; however, little is known about the underlying genetic and biological factors that may contribute to regulation of this complex trait. It is true that a significant portion of any trait is regulated by genetic and biological factors. In the case of voluntary physical activity behavior, these regulating mechanisms appear to be concentrated in the central nervous system. In particular, the dopamine system has been shown to regulate motor movement, as well as motivation and reward behavior. The pattern of regulation of voluntary physical activity by the dopamine system is yet to be fully elucidated. This review will summarize what is known about the dopamine system and regulation of physical activity, and will present a hypothesis of how this signaling pathway is mechanistically involved in regulating voluntary physical activity behavior. Future research in this area will aid in developing personalized strategies to prevent inactivity related diseases.

Trauma and posttraumatic stress disorder in South African adolescents: a case-control study of cognitive deficits

Despite the prominence of neuropsychological deficits in memory, attention and learning in adults exposed to trauma and those who develop posttraumatic stress disorder (PTSD), few studies have explored these cognitive deficits in adolescents. This study aimed to assess the impact of PTSD on various neurocognitive functions in South African adolescents. In a case-control study, 40 traumatized adolescents (20 with PTSD and 20 without) were evaluated for the presence of PTSD and were then referred for neuropsychological evaluation using a standardized neuropsychological test battery. The presence of PTSD itself, rather than trauma exposure, was associated with cognitive deficiencies in attention, visual memory and nonverbal concept formation. This study highlights the impact of PTSD itself-and particularly current symptoms-on the cognitive development of adolescents. As this effect appears to be stronger than the impact of trauma alone, more studies on the long-term consequences of PTSD on youth cognitive development are crucial.

Prepulse inhibition of startle in adults with ADHD

Prepulse inhibition of startle (PPI) is a measure of sensorimotor gating, a pre-conscious regulator of attention. PPI is impaired in adults with schizophrenia and several other neuropsychiatric disorders associated with attentional abnormalities. The core feature of ADHD involves deficits in attention and, like schizophrenia, ADHD is associated with dysregulation of cortical-striatal circuits and dopamine transmission. Therefore, PPI may be disrupted in ADHD. While ADHD persists into adulthood in approximately half the children with ADHD, there has not been any published report of PPI in ADHD adults. In this study, PPI was measured in a sample of ADHD adults and compared to a sample of healthy comparison (HC) subjects. Twenty unmedicated adults with ADHD (11 inattentive subtype, 9 combined subtype) and 17 HC subjects were administered an eyeblink startle PPI paradigm. The PPI of ADHD adults was not significantly different from that of HC subjects in any of the PPI conditions. There was no significant effect of ADHD subtype nor of gender. The lack of PPI deficits in ADHD adults has important implications and suggests that, despite the presence of PPI dysregulation in a large number of disparate neuropsychiatric disorders, it is not a general feature of all neuropsychiatric disorders with attention abnormalities. Furthermore, the attentional deficiency in ADHD may have a neurobiological substrate somewhat distinct from schizophrenia and other neuropsychiatric disorders that are associated with PPI deficits. This distinction may be related to a relative sparing of pre-conscious attentional functions in ADHD compared to other disorders with PPI impairment.

The dopamine receptor D4 7-repeat allele and prenatal smoking in ADHD-affected children and their unaffected siblings: no gene-environment interaction

BACKGROUND

The dopamine receptor D4 (DRD4) 7-repeat allele and maternal smoking during pregnancy are both considered as risk factors in the aetiology of attention deficit hyperactivity disorder (ADHD), but few studies have been conducted on their interactive effects in causing ADHD. The purpose of this study is to examine the gene by environment (GxE) interaction of the DRD4 7-repeat allele and smoking during pregnancy on ADHD and oppositional behavior in families from the International Multicenter ADHD Genetics project; and further, to test the hypothesis that the direction of effect of the DRD4 7-repeat allele differs between ADHD affected and unaffected children.

METHODS

Linear mixed models were used to assess main and interactive effects of the DRD4 7-repeat allele and smoking during pregnancy in 539 ADHD-affected children and their 407 unaffected siblings, aged 6-17 years.

RESULTS

There was some evidence pointing to differential effects of the DRD4 7-repeat allele on ADHD and oppositional symptoms in the affected (fewer symptoms) and unaffected children (increasing ADHD symptoms of teacher ratings). Affected children were more often exposed to prenatal smoking than unaffected children. There were limited main effects of prenatal smoking on severity of symptoms. Given the number of tests performed, no indication was found for GxE interactions.

CONCLUSION

Despite the large sample size, no GxE interactions were found. The impact of the DRD4 7-repeat allele might differ, depending on affected status and rater. This finding is discussed in terms of differences in the activity of the dopaminergic system and of different genes involved in rater-specific behaviors.

Oxidative imbalance in adult attention deficit/hyperactivity disorder

OBJECTIVE

There are few studies evaluating the biochemical basis of adult attention deficit/hyperactivity disorder (A-ADHD). In the present study, we evaluated whether nitric oxide (NO), an oxidant, level and superoxide dismutase (SOD), an antioxidant, activity are associated with A-ADHD or not.

METHODS

Twenty A-ADHD patients from Gaziantep University Sahinbey Research Hospital, Psychiatry Clinic, diagnosed according to The Turkish version of Adult ADD/ADHD DSM IV-Based Diagnostic Screening and Rating Scale by two psychiatrists (H.A.S. and S.S.), and twenty-one healthy volunteer controls were included. Blood samples were collected; NO levels and SOD activities were measured.

RESULTS

The mean NO levels in patients were significantly higher than those of controls and SOD activity of patients was significantly lower than controls.

CONCLUSIONS

Remarkable high levels of oxidant NO, and low SOD activities suggest an oxidative imbalance in A-ADHD. This is the first study evaluating the oxidative metabolism in A-ADHD.

What are the key directions in the genetics of attention deficit hyperactivity disorder?

PURPOSE OF REVIEW

The aim of this review is to describe the considerable advances in consolidating the empirical evidence on several key topics in the genetics of attention deficit hyperactivity disorder, namely the quantitative genetic studies of the nature of attention deficit hyperactivity disorder and its comorbidities, the molecular genetic studies that show modest but consistent effects of specific genotypes, and the growing recognition of genotype by environment interaction. Such interactions are studied to explain what happens when individuals with a susceptible genotype are exposed to a particular environment.

RECENT FINDINGS

There have been a significant number of twin studies that have examined different models of the symptomatology of attention deficit hyperactivity disorder and how these symptoms are reported. Similarly, molecular genetic research is complicated by very different outcome measures, and study across the whole field is made more problematic by genotype by environment interaction effects. One of the most interesting areas of development is that of psychopharmacogenetics.

SUMMARY

Two key developments have been integrative models of the genetics of attention deficit hyperactivity disorder and brain structure, which may have implications for future attention deficit hyperactivity disorder subtyping, and collaboration. This is not just within attention deficit hyperactivity disorder as in the IMAGE study, but also across disciplines.

Effects of low to moderate acute doses of pramipexole on impulsivity and cognition in healthy volunteers

The neurotransmitter dopamine is integrally involved in the rewarding effects of drugs, and it has also been thought to mediate impulsive behaviors in animal models. Most of the studies of drug effects on impulsive behaviors in humans have involved drugs with complex actions on different transmitter systems and different receptor subtypes. The present study was designed to characterize the effect of single doses of pramipexole, a D2/D3 agonist, on measures of cognitive and impulsive behavior, as well as on mood in healthy volunteers. Healthy men and women (N = 10) received placebo and 2 doses of pramipexole, 0.25 and 0.50 mg, in a within-subject, double-blinded study. Outcome measures included changes in cognitive performance, assessed by the Automated Neuropsychological Assessment Metrics, several behavioral measures related to impulsive behavior, including the Balloon Analogue Risk Task, Delay Discounting Task, Go/No-Go Task, Card Perseveration Task, and subjective ratings of mood assessed by Addiction Research Center Inventory, Profile of Mood States, and Drug Effects Questionnaire. Pramipexole decreased positive ratings of mood (euphoria, intellectual efficiency, and energy) and increased both subjectively reported sedation and behavioral sedation indicated by impaired cognitive performance on several measures of the Automated Neuropsychological Assessment Metrics. Single low to medium doses of this drug did not produce a decrease in impulsive responding on behavioral measures included in this study. The sedative-like effects observed in this study may reflect presynaptic actions of the drug. Higher doses with postsynaptic actions may be needed to produce either behavioral or subjective stimulant-like effects.

Personality characteristics associated with persistent ADHD in late adolescence

This study focused on the personality characteristics associated with Attention-deficit/Hyperactivity disorder (ADHD) in a longitudinal sample of youth, with a particular focus on differences between those with and without persisting ADHD symptoms. Participants with ADHD (n = 90) were initially evaluated when they were 7-11 years old, and re-assessed at 16-22 years of age. Matched control subjects (n = 80) were recruited at the time of the follow-up evaluation. At follow-up, the Kiddie-SADS-PL, a semi-structured psychiatric interview, and the NEO-PI, a self-report personality inventory, were administered. Data were analyzed using multivariate analyses of variance (MANOVA). Results indicate that childhood ADHD is associated with lower scores on the NEO Conscientiousness subscale in adolescents/young adults--irrespective of the degree of ADHD persistence. In contrast, ratings of Neuroticism and Agreeableness appear to be more closely linked to adolescent status; those with persisting symptoms only exhibited increased Neuroticism and decreased Agreeableness. These results suggest that ADHD, and the degree to which symptoms persist into adolescence, may be closely linked to personality structure.