ADHD: increased dopamine receptor availability linked to attention deficit and low neonatal cerebral blood flow

Consumption of commonly used artificial food dyes increases activity and oxidative stress in the animal model Caenorhabditis elegans

In recent decades, the consumption of artificial colorants in foods and beverages has increased despite of concerns in the general population raised by studies that have shown possible injurious effects. In this study, tartrazine, sunset yellow, quinoline yellow, ponceau 4R, carmoisine and allura red were employed as pure compounds to explore their effects in vivo in the animal model Caenorhabditis elegans. The exposition of C. elegans to these artificial dyes produced damage related with aging such as oxidative stress and lipofuscin accumulation, as well as a heavy shortening of lifespan, alterations in movement patterns and alterations in the production of dopamine receptors. Besides, microarray analysis performed with worms treated with tartrazine and ponceau 4R showed how the consumption of synthetic colorants is able to alter the expression of genes involved in resistance to oxidative stress and neurodegeneration.

Modelling Autism Spectrum Disorder (ASD) and Attention-Deficit/Hyperactivity Disorder (ADHD) Using Mice and Zebrafish

Autism spectrum disorders (ASD) and attention-deficit/hyperactivity disorder (ADHD) are two debilitating neurodevelopmental disorders. The former is associated with social impairments whereas the latter is associated with inattentiveness, hyperactivity, and impulsivity. There is recent evidence that both disorders are somehow related and that genes may play a large role in these disorders. Despite mounting human and animal research, the neurological pathways underlying ASD and ADHD are still not well understood. Scientists investigate neurodevelopmental disorders by using animal models that have high similarities in genetics and behaviours with humans. Mice have been utilized in neuroscience research as an excellent animal model for a long time; however, the zebrafish has attracted much attention recently, with an increasingly large number of studies using this model. In this review, we first discuss ASD and ADHD aetiology from a general point of view to their characteristics and treatments. We also compare mice and zebrafish for their similarities and discuss their advantages and limitations in neuroscience. Finally, we summarize the most recent and existing research on zebrafish and mouse models of ASD and ADHD. We believe that this review will serve as a unique document providing interesting information to date about these models, thus facilitating research on ASD and ADHD.

ADHD – What Is the Meaning of Sex-dependent Incidence Differences?

There is a clear experience in clinical practice: boys with a diagnosis of ADHD are clearly in greater numbers than girls. It is noteworthy that even in the “older” review articles, the cause of sex-dependent incidence is not mentioned. If we accept the neurodevelopmental hypothesis of such disorder, then the possible genetic predisposition breaks down into two separate groups. On the genome of an individual with ADHD and on the genome of the parents. However, it cannot be overlooked that the incidence of ADHD (3–7%) corresponds to the incidence and sex differences of the number of newborns born at a certain risk (premature birth, immaturity, hypotrophy, hypoxic-ischemic syndrome, low birth weight, etc.). This association of possible genetic predisposition with “external” risks in the genesis of ADHD raises the question of whether a higher incidence of ADHD, as well as higher morbidity and mortality in males, are a) the norm and the female is privileged, or b) the female is the norm and the male is handicapped. The picture of ADHD includes various cognitive dysfunctions with one possible cause in norepinephrine and dopamine insufficiency. Experimental work shows that in response to stress females release more catecholamines in the CNS than males. Since catecholamines stimulate membrane Na+ K+ ATPase activity, this means both the value of the membrane potential and the threshold for activation is increased. Females are more successful in responding to and adapting to a stressful situation due to their higher production of noradrenaline in the CNS.

The behavioral neuroendocrinology of dopamine systems in differently reared juvenile male rhesus monkeys (Macaca mulatta)

Dopamine (DA) is a critical neuromodulator of behavior. With propensities for addiction, hyper-activity, cognitive impairment, aggression, and social subordinance, monkeys enduring early maternal deprivation evoke human disorders involving dopaminergic dysfunction. To examine whether DA system alterations shape the behavioral correlates of adverse rearing, male monkeys (Macaca mulatta) were either mother-reared (MR: N = 6), or separated from their mothers at birth and nursery-reared (NR: N = 6). Behavior was assessed during 20-minute observations of subjects interacting with same- or differently-reared peers. Cerebrospinal fluid (CSF) biogenic amines, and serum testosterone (T), cortisol (CORT), and prolactin (PRL) were collected before and after pharmacologic challenge with saline or the DA receptor-2 (DRD2) antagonist Raclopride (RAC). Neuropeptide correlations observed in MR were non-existent in NR monkeys. Compared to MR, NR showed reduced DA tone; higher basal serum T; and lower CSF serotonin (5-HT). RAC increased PRL, T and CORT, but the magnitude of responses varied as a function of rearing. Levels of PRL significantly increased following RAC in MR, but not NR. Elevations in T following RAC were only significant among MR. Contrastingly, the net change (RAC CORT - saline CORT) in CORT was greater in NR than MR. Finally, observations conducted during the juvenile phase in a novel play-arena revealed more aggressive, self-injurious, and repetitive behaviors, which negatively correlated with indexes of dopaminergic tone in NR monkeys. In conclusion, early maternal deprivation alters brain DA systems, and thus may be associated with characteristic cognitive, social, and addiction outcomes.

DNA methylome perturbations: an epigenetic basis for the emergingly heritable neurodevelopmental abnormalities associated with maternal smoking and maternal nicotine exposure†

Maternal smoking during pregnancy is associated with an ensemble of neurodevelopmental consequences in children and therefore constitutes a pressing public health concern. Adding to this burden, contemporary epidemiological and especially animal model research suggests that grandmaternal smoking is similarly associated with neurodevelopmental abnormalities in grandchildren, indicative of intergenerational transmission of the neurodevelopmental impacts of maternal smoking. Probing the mechanistic bases of neurodevelopmental anomalies in the children of maternal smokers and the intergenerational transmission thereof, emerging research intimates that epigenetic changes, namely DNA methylome perturbations, are key factors. Altogether, these findings warrant future research to fully elucidate the etiology of neurodevelopmental impairments in the children and grandchildren of maternal smokers and underscore the clear potential thereof to benefit public health by informing the development and implementation of preventative measures, prophylactics, and treatments. To this end, the present review aims to encapsulate the burgeoning evidence linking maternal smoking to intergenerational epigenetic inheritance of neurodevelopmental abnormalities, to identify the strengths and weaknesses thereof, and to highlight areas of emphasis for future human and animal model research therein.

Investigating interactive effects of worry and the catechol-o-methyltransferase gene (COMT) on working memory performance

Extant research indicates that worry is associated with reduced working memory. It remains unclear, however, what mechanisms contribute to impaired performance in worriers. Critically, dopamine in the prefrontal cortex heavily influences the stability of mental representations during working memory tasks, yet no research has probed its role in associations between worry and working memory. To address this gap, the current study was designed to examine the moderating role of dopamine on the association between worry and working memory, using the catechol-o-methyltransferase (COMT) gene as a proxy for basal levels of dopamine. Across four assessments, we examined within- and between-person variation in worry and its interactive effects with COMT to predict working memory performance. Within-person variation in worry interacted with COMT to predict accuracy, such that higher worry across time predicted less accuracy for homozygous Val carriers but not Met carriers. Our findings demonstrate that basal dopamine plays an important role in how increases in worry across time for an individual negatively impact working memory performance.

Perinatal Dietary Polyunsaturated Fatty Acids in Brain Development, Role in Neurodevelopmental Disorders

n-3 and n-6 polyunsaturated fatty acids (PUFAs) are essential fatty acids that are provided by dietary intake. Growing evidence suggests that n-3 and n-6 PUFAs are paramount for brain functions. They constitute crucial elements of cellular membranes, especially in the brain. They are the precursors of several metabolites with different effects on inflammation and neuron outgrowth. Overall, long-chain PUFAs accumulate in the offspring brain during the embryonic and post-natal periods. In this review, we discuss how they accumulate in the developing brain, considering the maternal dietary supply, the polymorphisms of genes involved in their metabolism, and the differences linked to gender. We also report the mechanisms linking their bioavailability in the developing brain, their transfer from the mother to the embryo through the placenta, and their role in brain development. In addition, data on the potential role of altered bioavailability of long-chain n-3 PUFAs in the etiologies of neurodevelopmental diseases, such as autism, attention deficit and hyperactivity disorder, and schizophrenia, are reviewed.

Maternal Opioid Exposure Culminates in Perturbed Murine Neurodevelopment and Hyperactive Phenotype in Adolescence

Opioid use by women during pregnancy has risen dramatically since 2004, accompanied by a striking increase in the prevalence of neonatal opioid withdrawal syndrome (NOWS) and other long-term neurological deficits. However, the mechanisms underlying the impact of prenatal opioid exposure on fetal neurodevelopment are largely unknown. To translate from the clinical presentation, we developed a novel mouse model to study the neurodevelopmental consequences of maternal opioid use and management. Female mice were treated with oxycodone (OXY) before mating to mimic opioid use disorder (OUD) in humans. Following pregnancy confirmation, dams were switched to buprenorphine (BUP) via oral administration, simulating medication management of OUD (MOUD) in pregnant women. Here, we document critical changes in fetal brain development including reduced cortical thickness, altered corticogenesis, and ventriculomegaly in embryos from dams that were treated with opioids before and throughout pregnancy. Maternal care giving behavior was slightly altered without affecting gross growth of offspring. However, adolescent offspring exposed to maternal opioid use during pregnancy exhibited hyperactivity in late adolescence. Remarkably, we also show increased generation of dopaminergic neurons within the ventral tegmental area (VTA) of mice exposed to prenatal opioids. These data provide critical evidence of teratogenic effects of opioid use during pregnancy and suggest a causal relationship between maternal opioid use and neurodevelopmental/behavioral anomalies in adolescence.

Design and validation of a mechanically flexible and ultra-lightweight high-density diffuse optical tomography system for functional neuroimaging of newborns

Significance: Neonates are a highly vulnerable population. The risk of brain injury is greater during the first days and weeks after birth than at any other time of life. Functional neuroimaging that can be performed longitudinally and at the cot-side has the potential to improve our understanding of the evolution of multiple forms of neurological injury over the perinatal period. However, existing technologies make it very difficult to perform repeated and/or long-duration functional neuroimaging experiments at the cot-side. Aim: We aimed to create a modular, high-density diffuse optical tomography (HD-DOT) technology specifically for neonatal applications that is ultra-lightweight, low profile and provides high mechanical flexibility. We then sought to validate this technology using an anatomically accurate dynamic phantom. Approach: An advanced 10-layer rigid-flexible printed circuit board technology was adopted as the basis for the DOT modules, which allows for a compact module design that also provides the flexibility needed to conform to the curved infant scalp. Two module layouts were implemented: dual-hexagon and triple-hexagon. Using in-built board-to-board connectors, the system can be configured to provide a vast range of possible layouts. Using epoxy resin, thermochromic dyes, and MRI-derived 3D-printed moulds, we constructed an electrically switchable, anatomically accurate dynamic phantom. This phantom was used to quantify the imaging performance of our flexible, modular HD-DOT system. Results: Using one particular module configuration designed to cover the infant sensorimotor system, the device provided 36 source and 48 detector positions, and over 700 viable DOT channels per wavelength, ranging from 10 to ∼ 45    mm over an area of approximately 60    cm 2 . The total weight of this system is only 70 g. The signal changes from the dynamic phantom, while slow, closely simulated real hemodynamic response functions. Using difference images obtained from the phantom, the measured 3D localization error provided by the system at the depth of the cortex was in the of range 3 to 6 mm, and the lateral image resolution at the depth of the neonatal cortex is estimated to be as good as 10 to 12 mm. Conclusions: The HD-DOT system described is ultra-low weight, low profile, can conform to the infant scalp, and provides excellent imaging performance. It is expected that this device will make functional neuroimaging of the neonatal brain at the cot-side significantly more practical and effective.

High long-term test-retest reliability for extrastriatal 11C-raclopride binding in healthy older adults

In vivo dopamine D2-receptor availability is frequently assessed with ¹¹C-raclopride and positron emission tomography. Due to low signal-to-noise ratios for ¹¹C-raclopride in areas with low D2 receptor densities, the ligand has been considered unreliable for measurements outside the dopamine-dense striatum. Intriguingly, recent studies show that extrastriatal ¹¹C-raclopride binding potential (BP_ND) values are (i) reliably higher than in the cerebellum (where D2-receptor levels are negligible), (ii) correlate with behavior in the expected direction, and (iii) showed good test-retest reliability in a sample of younger adults. The present work demonstrates high seven-month test-retest reliability of striatal and extrastriatal ¹¹C-raclopride BP_ND values in healthy, older adults (n = 27, age: 64-78 years). Mean ¹¹C-raclopride BP_ND values were stable between test sessions in subcortical nuclei, and in frontal and temporal cortices (p > 0.05). Across all structures analyzed, intraclass correlation coefficients were high (0.85-0.96), absolute variability was low (mean: 4-8%), and coefficients of variance ranged between 9 and 25%. Furthermore, regional ¹¹C-raclopride BP_ND values correlated with previously determined ¹⁸F-fallypride BP_ND values (ρ = 0.97 and 0.92 in correlations with and without striatal values, respectively, p < 0.01) and postmortem determined D2-receptor densities (including striatum: ρ = 0.92; p < 0.001; excluding striatum: ρ = 0.75; p = 0.067). These observations suggest that extrastriatal ¹¹C-raclopride measurements represent a true D2 signal.

Latent-Profile Analysis Reveals Behavioral and Brain Correlates of Dopamine-Cognition Associations

Evidence suggests that associations between the neurotransmitter dopamine and cognition are nonmonotonic and open to modulation by various other factors. The functional implications of a given level of dopamine may therefore differ from person to person. By applying latent-profile analysis to a large (n = 181) sample of adults aged 64-68 years, we probabilistically identified 3 subgroups that explain the multivariate associations between dopamine D2/3R availability (probed with 11C-raclopride-PET, in cortical, striatal, and hippocampal regions) and cognitive performance (episodic memory, working memory, and perceptual speed). Generally, greater receptor availability was associated with better cognitive performance. However, we discovered a subgroup of individuals for which high availability, particularly in striatum, was associated with poor performance, especially for working memory. Relative to the rest of the sample, this subgroup also had lower education, higher body-mass index, and lower resting-state connectivity between caudate nucleus and dorsolateral prefrontal cortex. We conclude that a smaller subset of individuals induces a multivariate non-linear association between dopamine D2/3R availability and cognitive performance in this group of older adults, and discuss potential reasons for these differences that await further empirical scrutiny.

Availability of Striatal Dopamine Transporter in Healthy Individuals With and Without a Family History of ADHD

OBJECTIVE

ADHD is the most prevalent neurodevelopmental disorder. It is highly heritable and multifactorial, but the definitive causes remain unknown. Abnormal dopamine transporter (DAT) availability has been reported, but the data are inconsistent. The aim of this study was to examine whether DAT availability differs between healthy parents with and without ADHD offspring.

METHOD

Eleven healthy parents with ADHD offspring and 11 age- and sex-matched healthy controls without ADHD offspring were recruited. The availability of DAT was approximated using single-photon emission computed tomography, with [^99mTc] TRODAT-1 as the ligand.

RESULTS

DAT availability in the basal ganglia, caudate nucleus, and putamen was significantly lower in the parents with ADHD offspring than in the healthy controls without ADHD offspring.

CONCLUSION

The results suggest that ADHD could be heritable via abnormal DAT activities.

C957T-mediated Variation in Ligand Affinity Affects the Association between 11C-raclopride Binding Potential and Cognition

The dopamine (DA) system plays an important role in cognition. Accordingly, normal variation in DA genes has been found to predict individual differences in cognitive performance. However, little is known of the impact of genetic differences on the link between empirical indicators of the DA system and cognition in humans. The present work used PET with 11C-raclopride to assess DA D2-receptor binding potential (BP) and links to episodic memory, working memory, and perceptual speed in 179 healthy adults aged 64–68 years. Previously, the T-allele of a DA D2-receptor single-nucleotide polymorphism, C957T, was associated with increased apparent affinity of 11C-raclopride, giving rise to higher BP values despite similar receptor density values between allelic groups. Consequently, we hypothesized that 11C-raclopride BP measures inflated by affinity rather than D2-receptor density in T-allele carriers would not be predictive of DA integrity and therefore prevent finding an association between 11C-raclopride BP and cognitive performance. In accordance with previous findings, we show that 11C-raclopride BP was increased in T-homozygotes. Importantly, 11C-raclopride BP was only associated with cognitive performance in groups with low or average ligand affinity (C-allele carriers of C957T, n = 124), but not in the high-affinity group (T-homozygotes, n = 55). The strongest 11C-raclopride BP–cognition associations and the highest level of performance were found in C-homozygotes. These findings show that genetic differences modulate the link between BP and cognition and thus have important implications for the interpretation of DA assessments with PET and 11C-raclopride in multiple disciplines ranging from cognitive neuroscience to psychiatry and neurology.

The Association Between Prenatal Stress and Externalizing Symptoms in Childhood: Evidence From the Avon Longitudinal Study of Parents and Children

BACKGROUND

It has been suggested that prenatal maternal stress may increase the risk of childhood externalizing disorders, yet no large cohort study has investigated this association across a large range of acute stressors. Our objective was to estimate the association between prenatal stressful events and risk of offspring conduct disorder and hyperactivity.

METHODS

We used data from 10,184 mother-offspring pairs from the United Kingdom-based Avon Longitudinal Study of Parents and Children. Mothers self-reported 42 prenatal stressful life events at 18 weeks' gestation. Symptoms of conduct disorder and hyperactivity in their offspring were measured at 6, 9, 11, 13, and 16 years of age using the Strengths and Difficulties Questionnaire. The primary outcome was membership in high-symptom trajectories of 1) conduct disorder and 2) hyperactivity throughout childhood, identified using latent class growth modeling. Multinomial logistic regression models estimated the association between prenatal stress and both conduct disorder and hyperactivity, after adjusting for sex, parental education, low birth weight, preterm birth, parental social class, maternal smoking and drinking, maternal mental health, offspring stressful life events, and offspring depressive and anxious symptoms.

RESULTS

Those exposed to the highest quartile of prenatal stress were more likely to belong to the high symptom trajectory for hyperactivity (B = 0.46, p < .05) and conduct disorder (B = 0.88, p < .01), respectively. Prenatal stress further demonstrated a positive, dose-response relationship with symptoms of externalizing disorders at independent time points.

CONCLUSIONS

The findings suggest that prenatal stressful events may be an independent risk factor for offspring externalizing symptoms, regardless of maternal mental health and offspring internalizing.

ADHD Among Rural Southeastern Nigerian Primary School Children: Prevalence and Psychosocial Factors

OBJECTIVE

To determine the prevalence of ADHD among primary school pupils in a rural community in Southeastern Nigeria and to determine the psychosocial factors associated with the condition.

METHOD

One hundred eighty-one randomly selected participants had their teachers complete the school version of ADHD Rating Scale-IV. Their parents also completed a sociodemographic questionnaire, the clinical interview form for the child and adolescent ADHD patients, and home version of the ADHD Rating Scale-IV.

RESULTS

Twelve (6.6%) of the children met the criteria for diagnosis. A history of prolonged labor (odds ratio [OR] = 14.1; 95% confidence interval [CI] = [2.13, 93.1]), and parents' negative assessment of their marriages (OR = 0.1; CI = [0.017, 0.567]) were the most predominant factors which independently associated with the ADHD in the children.

CONCLUSION

There is, therefore, a need for the care of rural dwelling African children, who otherwise would have difficulties accessing health care that is concentrated in the cities.

Angiogenic, neurotrophic, and inflammatory system SNPs moderate the association between birth weight and ADHD symptom severity

Low birth weight is associated with increased risk for Attention-Deficit/Hyperactivity Disorder (ADHD); however, the etiological underpinnings of this relationship remain unclear. This study investigated if genetic variants in angiogenic, dopaminergic, neurotrophic, kynurenine, and cytokine-related biological pathways moderate the relationship between birth weight and ADHD symptom severity. A total of 398 youth from two multi-site, family-based studies of ADHD were included in the analysis. The sample consisted of 360 ADHD probands, 21 affected siblings, and 17 unaffected siblings. A set of 164 SNPs from 31 candidate genes, representing five biological pathways, were included in our analyses. Birth weight and gestational age data were collected from a state birth registry, medical records, and parent report. Generalized Estimating Equations tested for main effects and interactions between individual SNPs and birth weight centile in predicting ADHD symptom severity. SNPs within neurotrophic (NTRK3) and cytokine genes (CNTFR) were associated with ADHD inattentive symptom severity. There was no main effect of birth weight centile on ADHD symptom severity. SNPs within angiogenic (NRP1 & NRP2), neurotrophic (NTRK1 & NTRK3), cytokine (IL16 & S100B), and kynurenine (CCBL1 & CCBL2) genes moderate the association between birth weight centile and ADHD symptom severity. The SNP main effects and SNP × birth weight centile interactions remained significant after adjusting for multiple testing. Genetic variability in angiogenic, neurotrophic, and inflammatory systems may moderate the association between restricted prenatal growth, a proxy for an adverse prenatal environment, and risk to develop ADHD.

ADHD, altered dopamine neurotransmission, and disrupted reinforcement processes: implications for smoking and nicotine dependence

Attention deficit hyperactivity disorder (ADHD) is a common and impairing disorder affecting millions of children, adolescents, and adults. Individuals with ADHD smoke cigarettes at rates significantly higher than their non-diagnosed peers and the disorder also confers risk for a number of related adverse smoking outcomes including earlier age of initiation, faster progression to regular use, heavier smoking/greater dependence, and more difficulty quitting. Progress in our understanding of dopamine neurotransmission and basic behavioral reinforcement processes in ADHD may help increase our understanding of the ADHD-smoking comorbidity. This review will examine how these areas have been studied and how further work may aid in the development of better prevention and treatment for smoking in those with ADHD.

Amphetamine-induced dopamine release and neurocognitive function in treatment-naive adults with ADHD

Converging evidence from clinical, preclinical, neuroimaging, and genetic research implicates dopamine neurotransmission in the pathophysiology of attention deficit hyperactivity disorder (ADHD). The in vivo neuroreceptor imaging evidence also suggests alterations in the dopamine system in ADHD; however, the nature and behavioral significance of those have not yet been established. Here, we investigated striatal dopaminergic function in ADHD using [(11)C]raclopride PET with a d-amphetamine challenge. We also examined the relationship of striatal dopamine responses to ADHD symptoms and neurocognitive function. A total of 15 treatment-free, noncomorbid adult males with ADHD (age: 29.87 ± 8.65) and 18 healthy male controls (age: 25.44 ± 6.77) underwent two PET scans: one following a lactose placebo and the other following d-amphetamine (0.3 mg/kg, p.o.), administered double blind and in random order counterbalanced across groups. In a separate session without a drug, participants performed a battery of neurocognitive tests. Relative to the healthy controls, the ADHD patients, as a group, showed greater d-amphetamine-induced decreases in striatal [(11)C]raclopride binding and performed more poorly on measures of response inhibition. Across groups, a greater magnitude of d-amphetamine-induced change in [(11)C]raclopride binding potential was associated with poorer performance on measures of response inhibition and ADHD symptoms. Our findings suggest an augmented striatal dopaminergic response in treatment-naive ADHD. Though in contrast to results of a previous study, this finding appears consistent with a model proposing exaggerated phasic dopamine release in ADHD. A susceptibility to increased phasic dopamine responsivity may contribute to such characteristics of ADHD as poor inhibition and impulsivity.

Dissociable and common effects of methylphenidate, atomoxetine and citalopram on response inhibition neural networks

Response inhibition is an executive function that allows the detection and modification of unwanted actions. Its underlying neurochemistry and neurobiology have been explored by combining classic neuropsychological paradigms, such as the go/no-go task (GNG), with targeted pharmacology and functional neuroimaging. We sought to further this literature by using single doses of methylphenidate (30 mg), atomoxetine (60 mg), citalopram (30 mg) and placebo to probe dopaminergic, noradrenergic and serotonergic aspects of response inhibition. Twenty-seven (27) healthy, right-handed males participated in a randomised, double blind, placebo-controlled, within subject, crossover fMRI study to examine stop-related BOLD activation correlates of a modified GNG task. Methylphenidate demonstrated activation versus placebo in the pregenual cingulate (dorsal anterior cingulate), right inferior frontal, left middle frontal, left angular and right superior temporal gyri and right caudate. Atomoxetine demonstrated activation versus placebo across a broad network of cortical regions. Both methylphenidate and atomoxetine, but not citalopram, activated superior temporal, right inferior frontal and left middle frontal clusters. Citalopram only activated the left inferior occipital lobe. Taking the above as functionally defined regions of interest, we examined the specificity of stop-related drug activity by comparing mean activations across the four conditions. Only methylphenidate demonstrated drug-specific effects with increased activation of the pregenual cingulate and decreased activation of the caudate. Direct comparison of methylphenidate and atomoxetine showed broad recruitment of prefrontal regions but specific effects of methylphenidate in the pregenual cingulate and caudate revealing dissociable modulations of response inhibition networks.

Attention deficit/hyperactivity disorder after neonatal surgery: review of the pathophysiology and risk factors

There are many factors that influence the long-term neurological outcomes in children following cardiac surgery. Because there is also complex interaction between these many factors, it is difficult to assess which are primary and modifiable and which can be used to make improvements in outcomes. As survival after complex neonatal heart surgery has increased, the number of children with long-term neurological deficits is becoming more evident and this affects quality of life for children and their families.

One area of long-term assessment is the incidence of attention deficit/hyperactivity disorder (ADHD). The incidence rate for ADHD following pediatric cardiac surgery is significantly higher than the normal rate for children of the same age. Because this is a measureable long-term outcome, it can be used to evaluate methods for cerebral protection during surgery as well as the timing of surgical procedures to maximize cerebral oxygen levels.

This paper will review the pathophysiological basis for ADHD in this population, based on the similarities between neonatal cardiac surgical patients and pre-term infants. Both populations have an increased risk for ADHD and the etiology and pathological changes in pre-term infants have been widely investigated over the past 25 years. The rate of ADHD in this population is a window into the effects of these pathological changes on long-term outcomes.

Reducing the incidence of ADHD in the future in this population should be a primary goal in developing and assessing new cerebral protective strategies during cardiac surgery.

Preterm birth: neuropsychological profiles and atypical developmental pathways

Preterm birth is characterized by multiple interacting atypical constraints affecting different aspects of neuropsychological development. In the first years of life, perceptual, motor, and communicative-linguistic abilities, as well as attention, processing speed, and memory are affected by preterm birth resulting in cascading effects on later development. From school age to adolescence, a catch-up of simpler competencies (i.e., receptive lexicon) along with a more selective effect on more complex competencies (i.e., complex linguistic functions, math, motor, and executive functions) are observed, as well as a relevant incidence of behavioral outcomes. A wide heterogeneity in preterm children's neuropsychological profiles is described depending on the interaction among the degree of neonatal immaturity, medical complications, neurological damages/alterations, environmental and social factors. Severe neuromotor and sensory damages are not frequent, while low severity impairments are common among preterm children. It is argued that developmental pathways of preterm children are atypical, and not merely delayed, and are characterized by different developmental patterns and relationships among competencies.

The roles of dopamine and noradrenaline in the pathophysiology and treatment of attention-deficit/hyperactivity disorder

Through neuromodulatory influences over fronto-striato-cerebellar circuits, dopamine and noradrenaline play important roles in high-level executive functions often reported to be impaired in attention-deficit/hyperactivity disorder (ADHD). Medications used in the treatment of ADHD (including methylphenidate, dextroamphetamine and atomoxetine) act to increase brain catecholamine levels. However, the precise prefrontal cortical and subcortical mechanisms by which these agents exert their therapeutic effects remain to be fully specified. Herein, we review and discuss the present state of knowledge regarding the roles of dopamine (DA) and noradrenaline in the regulation of corticostriatal circuits, with a focus on the molecular neuroimaging literature (both in ADHD patients and in healthy subjects). Recent positron emission tomography evidence has highlighted the utility of quantifying DA markers, at baseline or following drug administration, in striatal subregions governed by differential cortical connectivity. This approach opens the possibility of characterizing the neurobiological underpinnings of ADHD (and associated cognitive dysfunction) and its treatment by targeting specific neural circuits. It is anticipated that the application of refined and novel positron emission tomography methodology will help to disentangle the overlapping and dissociable contributions of DA and noradrenaline in the prefrontal cortex, thereby aiding our understanding of ADHD and facilitating new treatments.

Behavioural symptoms of attention deficit/hyperactivity disorder in preterm and term children born small and appropriate for gestational age: a longitudinal study

Background

It remains unclear whether it is more detrimental to be born too early or too small in relation to symptoms of attention deficit/hyperactivity disorder (ADHD). Thus, we tested whether preterm birth and small body size at birth adjusted for gestational age are independently associated with symptoms of ADHD in children.

Methods

A longitudinal regional birth cohort study comprising 1535 live-born infants between 03/15/1985 and 03/14/1986 admitted to the neonatal wards and 658 randomly recruited non-admitted infants, in Finland. The present study sample comprised 828 children followed up to 56 months. The association between birth status and parent-rated ADHD symptoms of the child was analysed with multiple linear and logistic regression analyses.

Results

Neither prematurity (birth < 37 weeks of gestation) nor lower gestational age was associated with ADHD symptoms. However, small for gestational age (SGA < -2 standard deviations [SD] below the mean for weight at birth) status and lower birth weight SD score were significantly, and independently of gestational age, associated with higher ADHD symptoms. Those born SGA, relative to those born AGA, were also 3.60-times more likely to have ADHD symptoms scores above the clinical cut-off. The associations were not confounded by factors implicated as risks for pregnancy and/or ADHD.

Conclusions

Intrauterine growth restriction, reflected in SGA status and lower birth weight, rather than prematurity or lower gestational age per se, may increase risk for symptoms of ADHD in young children.

Perfusion magnetic resonance imaging in psychiatry

INTRODUCTION

Cerebral perfusion imaging using magnetic resonance imaging (MRI) is widely used in the research and clinical fields to assess the profound changes in blood flow related to ischemic events such as acute stroke, chronic steno-occlusive disease, vasospasm, and abnormal vessel formations from congenital conditions or tumoral neovascularity. With continuing improvements in the precision of MRI-based perfusion techniques, it is increasingly feasible to use this tool in the study of the subtle brain perfusion changes occurring in psychiatric illnesses. This article aims to review the existing literature on applications of perfusion MRI in psychiatric disorder and substance abuse research. The article also provides a brief introductory overview of dynamic susceptibility contrast MRI and arterial spin labeling techniques. An outlook of necessary steps to bring perfusion MRI into the realm of clinical psychiatry as a diagnostic tool is brought forth. Opportunities for research in unexplored disorders and with higher field strengths are briefly examined.

METHODS

PubMed, ISI Web of Knowledge & Scopus were used to search the literature and cross reference several neuropsychiatric disorders with a search term construct, including "magnetic resonance imaging," "dynamic susceptibility contrast," "arterial spin labeling," perfusion or "cerebral blood flow" or "cerebral blood volume" or "mean transit time." The list of disorders used in the search included schizophrenia, depression and bipolar disorder, dementia and Alzheimer's disease, Parkinson's disease, posttraumatic stress disorder, autism, Asperger disease, attention deficit, Tourette syndrome, obsessive-compulsive disorder, Huntington's disease, bulimia nervosa, anorexia nervosa, and substance abuse. For each disorder for which perfusion MRI studies were found, a brief overview of the disorder symptoms, treatment, prevalence, and existing models is provided, and previous findings from nuclear medicine-based perfusion imaging are overviewed. Findings of perfusion MRI studies are then summarized, and overlap of findings are discussed. Overarching conclusions are made, or an outlook for future work in the area is offered, where appropriate.

RESULTS

Despite the now fairly broad availability of perfusion MRI, only a limited number of studies were found using this technology. The search produced 13 studies of schizophrenia, 7 studies in major depression, 12 studies in Alzheimer's disease, and 2 studies in Parkinson's disease. Drug abuse and other disorders have mainly been studied with nuclear medicine-based perfusion imaging. The literature concerning the use of perfusion imaging in psychiatry has not been reviewed in the last 5 years or more. The use of MRI for perfusion measurements in psychiatry has not been reviewed in 10 years.

CONCLUSIONS

Although MRI-based perfusion imaging in psychiatry has mainly been used as a research tool, a path is progressively being cleared for its application in clinical diagnostic and treatment monitoring. The precision of perfusion MRI methods now rivals that of nuclear medicine-based perfusion imaging techniques. Because of their noninvasive nature, arterial spin labeling methods have gained popularity in studies of neuropsychiatric disorders such as schizophrenia, depression, Alzheimer's, and Parkinson's diseases. Perfusion imaging measurements have yet to be included within the diagnostic criteria of neuropsychiatric disorders despite having shown to have great discriminant power in specific disorders. As this young methodology continues to improve and research studies demonstrate the correlation of measured perfusion abnormalities to microcirculatory abnormalities and neuropsychiatric symptomatology, the idea of including such a test within diagnostic criteria for certain mental illnesses becomes increasingly plausible.

Neuroimaging of response interference in twins concordant or discordant for inattention and hyperactivity symptoms

Attention deficit hyperactivity disorder (ADHD) is to a large extent influenced by genetic factors, but environmental influences are considered important as well. To distinguish between functional brain changes underlying primarily genetically and environmentally mediated ADHD, we used functional magnetic resonance imaging (fMRI) to compare response interference in monozygotic twins highly concordant or discordant for attention problems (AP). AP scores were assessed longitudinally with the Child Behavior Check List attention problem scale (CBCL-AP). Response interference was measured during two executive function paradigms; a color-word Stroop and a flanker task. The neuroimaging results indicated that, across the entire sample, children with high CBCL-AP scores, relative to children with low CBCL-AP scores, showed decreased activation to response interference in dorsolateral prefrontal, parietal and temporal brain regions. Increased activation was noted in the premotor cortex and regions associated with visual selective attention processing, possibly reflecting compensatory mechanisms to maintain task performance. Specific comparisons of high and low scoring concordant twin pairs suggest that AP of genetic origin was characterized by decreased activation of the left dorsolateral prefrontal cortex during the Stroop task and right parietal lobe during the flanker task. In contrast, comparison of twins from discordant monozygotic pairs, suggests that AP of environmental origin was characterized by decreased activation in left and right temporal lobe areas, but only during Stroop interference. The finding of distinct brain activation changes to response interference in inattention/hyperactivity of "genetic" versus "environmental" origin, indicates that genetic and environmental risk factors for attention/hyperactivity problems affect the brain in different ways.

Dopaminergic dysfunction in attention deficit hyperactivity disorder (ADHD), differences between pharmacologically treated and never treated young adults: a 3,4-dihdroxy-6-[18F]fluorophenyl-l-alanine PET study

The dopaminergic system plays a key role in attention-deficit/hyperactivity disorder (ADHD). Methylphenidate (MP), a dopamine (DA) reuptake inhibitor, is a drug of first choice for treating ADHD. This cross-over study investigated alterations in DA metabolism in young males with ADHD who had never been pharmacologically treated and MP-treated patients in comparison to healthy subjects. Dynamic 3,4-dihdroxy-6-[18F]fluorophenyl-L-alanine (FDOPA) PET scans were carried out on 20 male patients with ADHD and 18 healthy men. Eight ADHD patients had never been treated with psychostimulants, the rest had received MP. Based on the tissue-slope-intercept plot parametric images of FDOPA influx rate constant (Ki) were generated for each subject from dynamic 3D FDOPA datasets and transformed into standard stereotactic space. First a volume of interest analysis was performed on each single subject. In a second step data were introduced to a SPM2 analysis to detect significant changes in mean voxel Ki values between the normal control group and each patient group. In comparison to controls, ADHD patients as a group (irrespective of treatment status) showed a lower Ki in bilateral putamen, amygdala and dorsal midbrain. There was a lower Ki in the left putamen, right amygdala and right dorsal midbrain in untreated patients compared to controls together with a relative higher influx in the left amygdala and right anterior cingulate cortex. In contrast, methylphenidate treatment was associated with a significantly lower Ki in the striatum and amygdala bilaterally, and in the right dorsal midbrain. Untreated young adult ADHD patients showed a dopamine dysfunction that might be partly due to compensatory mechanisms. MP seems to down-regulate dopamine turnover. This effect might be one component in the mechanism of action of this drug in ADHD treatment.

Etiologic classification of attention-deficit/hyperactivity disorder

Attention-deficit/hyperactivity disorder is a neurobiological syndrome with an estimated prevalence among children and adolescents of 5%. It is a highly heritable disorder, but acquired factors in etiology are sometimes uncovered that may be amenable to preventive measures or specific therapy. Early reports have described symptoms similar to attention-deficit/hyperactivity disorder that followed brain trauma or viral encephalitis, and recent MRI studies have demonstrated brain volumetric changes that may be involved in the pathophysiology of the syndrome. The American Psychiatric Association's Diagnostic Statistical Manual, introduced in 1968, emphasizes symptomatic criteria in diagnosis. Here, an overview of environmental factors in the etiology of attention-deficit/hyperactivity disorder is presented to encourage more emphasis and research on organic causal factors, preventive intervention, and specific therapies. An organic theory and the genetic and biochemical basis of attention-deficit/hyperactivity disorder are briefly reviewed, and an etiologic classification is suggested. Environmental factors are prenatal, perinatal, and postnatal in origin. Pregnancy- and birth-related risk factors include maternal smoking and alcohol ingestion, prematurity, hypoxic-ischemic encephalopathy, and thyroid deficiency. Childhood illnesses associated with attention-deficit/hyperactivity disorder include virus infections, meningitis, encephalitis, head injury, epilepsy, toxins, and drugs. More controversial factors discussed are diet-related sensitivities and iron deficiency. Early prenatal recognition, prevention, and treatment of environmental etiologies of attention-deficit/hyperactivity disorder may reduce physician reliance on symptomatic modification with medication, a frequent reason for parental concern.

Nuclear Medicine in Pediatric Neurology and Neurosurgery: Epilepsy and Brain Tumors

In pediatric drug-resistant epilepsy, nuclear medicine can provide important additional information in the presurgical localization of the epileptogenic focus. The main modalities used are interictal (18)F-fluorodeoxyglucose positron emission tomography (FDG-PET) and ictal regional cerebral perfusion study with single-photon emission computed tomography (SPECT). Nuclear medicine techniques have a sensitivity of approximately 85% to 90% in the localization of an epileptogenic focus in temporal lobe epilepsy; however, in this clinical setting, they are not always clinically indicated because other techniques (eg, icterictal and ictal electroencephalogram, video telemetry, magnetic resonance imaging [MRI]) may be successful in the identification of the epileptogenic focus. Nuclear medicine is very useful when MRI is negative and/or when electroencephalogram and MRI are discordant. A good technique to identify the epileptogenic focus is especially needed in the setting of extra-temporal lobe epilepsy; however, in this context, identification of the epileptogenic focus is more difficult for all techniques and the sensitivity of the isotope techniques is only 50% to 60%. This review article discusses the clinical value of the different techniques in the clinical context; it also gives practical suggestions on how to acquire good ictal SPECT and interictal FDG-PET scans. Nuclear medicine in pediatric brain tumors can help in differentiating tumor recurrence from post-treatment sequelae, in assessing the response to treatment, in directing biopsy, and in planning therapy. Both PET and SPECT tracers can be used. In this review, we discuss the use of the different tracers available in this still very new, but promising, application of radioisotope techniques.

Birth weight and attention-deficit/hyperactivity symptoms in childhood and early adolescence: a prospective Swedish twin study

OBJECTIVE

To determine whether low birth weight increases the risk of attention-deficit/hyperactivity disorder (ADHD) in childhood and early adolescence.

METHOD

In a population-based sample of 1,480 twin pairs born in the period 1985-1986 ascertained from the Swedish Twin Registry, birth weight was collected prospectively through the Medical Birth Registry. ADHD symptoms were measured with a 14-item checklist covering DSM-III-R criteria (parental rating) at age 8 to 9 years and 13 to 14 years. We used both a dichotomous approach for birth weight (>400 g or 15% weight difference) and ADHD (eight or more symptoms) and continuous measures to investigate between- and within-twin pair effects.

RESULTS

Our results showed that low birth weight was a risk factor for symptoms of ADHD and the associations did not diminish when we controlled for genetic influence. The lighter twin in birth weight-discordant pairs had on average 13% higher ADHD symptom score at age 8 to 9 years (p = .006) and 12% higher ADHD score at age 13 to 14 years (p = .018) compared with the heavier twin. The genetic correlations suggest modest or no genetic overlap between birth weight and ADHD.

CONCLUSIONS

The hypothesis that low birth weight is associated with the development of ADHD symptoms was supported in this prospective twin study. Fetal growth restriction seems to represent a modest but fairly consistent environmental influence on the development of ADHD symptoms.

A structural MRI study in monozygotic twins concordant or discordant for attention/hyperactivity problems: evidence for genetic and environmental heterogeneity in the developing brain

Several structural brain abnormalities have been reported in patients with Attention Deficit Hyperactivity Disorder (ADHD). However, the etiology of these brain changes is still unclear. To investigate genetic and environmental influences on ADHD related neurobiological changes, we performed Voxel-Based Morphometry on MRI scans from monozygotic (MZ) twins selected from a large longitudinal population database to be highly concordant or highly discordant for ratings on the Child Behavior Checklist Attention Problem scale (CBCL-AP). Children scoring low on the CBCL-AP are at low risk for ADHD, whereas children scoring high on this scale are at high-risk for ADHD. Brain differences between concordant high-risk twin pairs and concordant low-risk twin pairs likely reflect the genetic risk for ADHD; brain differences between the low-risk and high-risk twins from discordant MZ twin pairs reflect the environmental risk for ADHD. A major difference between comparisons of high and low-risk twins from concordant pairs and high/low twins from discordant pairs was found for the prefrontal lobes. The concordant high-risk pairs showed volume loss in orbitofrontal subdivisions. High-risk members from the discordant twin pairs exhibited volume reduction in the right inferior dorsolateral prefontal cortex. In addition, the posterior corpus callosum was compromised in concordant high-risk pairs, only. Our findings indicate that inattention and hyperactivity symptoms are associated with anatomical abnormalities of a distributed action-attentional network. Different brain areas of this network appear to be affected in inattention/hyperactivity caused by genetic (i.e., high concordant MZ pairs) vs. environmental (i.e., high-low discordant MZ pairs) risk factors. These results provide clues that further our understanding of brain alterations in ADHD.

Brain dopamine transporter levels in treatment and drug naïve adults with ADHD

Attention deficit hyperactivity disorder (ADHD) is the most frequent psychiatric disorder in children, yet data are sparse on its pathophysiology. Particularly relevant are the dopamine transporters since these are the main targets of stimulant medications used for ADHD treatment. Though some imaging studies have shown increases in dopamine transporters in ADHD others have not and their role in the neurobiology of ADHD remains unclear. Here we investigate dopamine transporters in ADHD subjects with control of potentially confounding factors (previous medication and/or drug histories, comorbidity) and their association with clinical symptoms. Positron emission tomography and [11C]cocaine were used to measure dopamine transporters in 20 never medicated adults with ADHD and 25 controls. Dopamine transporters were lower in left caudate (13%, p < 0.05) and in left nucleus accumbens (p < 0.005) in ADHD subjects than in controls. In putamen dopamine transporters did not differ between groups but were associated with scores of inattention (Conners Adult Attention Rating Scale) both in ADHD subjects (p < 0.005) and in controls (p < 0.005). Thus, for a given transporter level the scores for inattention were on average five times greater in ADHD subjects than in controls. These results do not corroborate increases in dopamine transporters in ADHD subjects and show that in some they are reduced. It also provides evidence that dopamine transporter levels modulate attention but suggest that additional pathology (e.g., prefrontal or cingulostriatal pathways, noradrenergic neurotransmission) is necessary to account for the large differences in inattention observed between controls and ADHD subjects.

D2-like dopamine receptors mediate the response to amphetamine in a mouse model of ADHD

The mechanisms underlying the effects of psychostimulants in attention deficit hyperactivity disorder (ADHD) are not well understood, but indirect evidence implicates D2 dopamine receptors. Here we dissect the components of dopaminergic neurotransmission in the hyperactive mouse mutant coloboma to identify pre- and postsynaptic elements essential for the effects of amphetamine in these mice. Amphetamine treatment reduced locomotor activity in coloboma mice, but induced a robust increase in dopamine overflow suggesting that abnormal regulation of dopamine efflux does not account for the behavioral effect. However, the D2-like dopamine receptor antagonists haloperidol and raclopride, but not the D1-like dopamine receptor antagonist SCH23390, blocked the amphetamine-induced reduction in locomotor activity in coloboma mice, providing direct evidence that D2-like dopamine receptors mediate the effect of amphetamine in these mice. With the precedent established that it is possible to directly antagonize this response, this strategy should prove useful for identifying novel therapeutics in ADHD.

Attention deficit disorders: are we barking up the wrong tree?

Attention deficit disorder (AAD) and attention deficit/hyperactivity disorder (ADHD) are very frequent and protean developmental disorders without a definite biologic marker. This review proposes a framework to understand the enlarged spectrum of its manifestations based on current knowledge of the mechanisms underlying arousal and attention variations during sleep/wake cycle. The neuro-modulation's pivotal role in this process as well as in the fine tuning of synaptic architecture during development must be taken into account when trying to understand the marked fuzziness of the symptoms and the very high prevalence of reported co-morbidities. The series of related interactions includes a cyclic deactivation of the dorso-lateral portion of the prefrontal cortex (DLPFC) during sleep, suspending executive functions, co-occurring with rhythmic periods of decreased noradrenergic tonus. A protracted unbalance in modulation, with catecholaminergic relative deficiency, could explain less-than-optimum waking DLPFC activation and the most important manifestations of ADD. Beside the well documented dopaminergic effects of stimulant medication used in ADD and ADHD, a more important role must be assigned to noradrenaline (NA). At this light hyperactivity and impulsivity are less important dimensions. Rather, an attention deficit spectrum disorder should probably be regarded as a complication of a core defect in prefrontal cortex dependent inhibitory control, underlying inattention.

Moderate-level prenatal alcohol exposure alters striatal dopamine system function in rhesus monkeys

BACKGROUND

Moderate prenatal alcohol exposure can cause impairments even in the absence of gross morphological defects associated with fetal alcohol syndrome. The basal ganglia, which include the dopamine-rich striatum, are sensitive to fetal alcohol-induced injury. In this study, we manipulated the timing of moderate-level alcohol exposure and compared the risk of adverse effects on striatal dopamine (DA) system function in rhesus monkeys.

METHODS

Thirty-five young adult rhesus monkeys (Macaca mulatta) from four groups of females were assessed: (1) an early alcohol-exposed group (n=9), in which mothers voluntarily consumed 0.6 g/kg alcohol solution on gestational days 0 through 50; (2) a middle-to-late gestation alcohol-exposed group (n=7), in which mothers voluntarily consumed 0.6 g/kg alcohol solution on gestational days 50 through 135; (3) a continuous-exposure group (n=9), in which mothers voluntarily consumed 0.6 g/kg alcohol solution on days 0 through 135; and (4) controls (n=10), in which mothers voluntarily consumed an isocaloric control solution on gestational days 0 through 50, 50 through 135, or 0 through 135. We studied striatal DA system function by positron emission tomography in separate scans for trapping of [(18)F]fallypride and 6-[(18)F]fluoro-m-tyrosine to assess striatal DA D2 receptor (D2R) binding and DA synthesis, respectively, via dopadecarboxylase activity.

RESULTS

Moderate-level alcohol exposure during early gestation and continuous exposure throughout gestation (early + middle-to-late exposure) reduced the striatal D2R binding to DA synthesis ratio, whereas middle-to-late alcohol gestation exposure increased the striatal D2R binding to DA synthesis ratio. The continuous-exposure group showed the largest effect. Moreover, the D2R binding/DA synthesis ratio was related to neonatal neurobehavior measures in control monkeys, but these relationships were disrupted in the fetal alcohol-exposed monkeys.

CONCLUSION

These results suggest that the vulnerability of the DA system to the effects of moderate doses of alcohol during gestation depend on the timing of the alcohol exposure. Early-gestation moderate alcohol exposure resulted in a reduction or blunting of dopaminergic function in adulthood, whereas middle to late exposure (without early exposure) either induced the opposite pattern or heightened dopaminergic function. Continuously exposed monkeys showed the largest effect, suggesting that the sooner women stop drinking, the better it is for the fetus.

Increased dopamine D2/D3 receptor binding after recovery from anorexia nervosa measured by positron emission tomography and [11c]raclopride

BACKGROUND

Several lines of evidence support the possibility that disturbances of dopamine (DA) function could contribute to alterations of weight, feeding, motor activity, and reward in anorexia nervosa (AN).

METHODS

To assess possibly trait-related disturbances but avoid confounding effects of malnutrition, 10 women who were recovered from AN (REC AN) were compared with 12 healthy control women (CW). Positron emission tomography with [(11)C]raclopride was used to assess DA D2/D3 receptor binding.

RESULTS

The women who were recovered from AN had significantly higher [(11)C]raclopride binding potential in the antero-ventral striatum than CW. For REC AN, [(11)C]raclopride binding potential was positively related to harm avoidance in the dorsal caudate and dorsal putamen.

CONCLUSIONS

These data lend support for the possibility that decreased intrasynaptic DA concentration or increased D2/D3 receptor density or affinity is associated with AN and might contribute to the characteristic harm avoidance or increased physical activity found in AN. Most intriguing is the possibility that individuals with AN might have a DA related disturbance of reward mechanisms contributing to altered hedonics of feeding behavior and their ascetic, anhedonic temperament.

Antenatal maternal anxiety and stress and the neurobehavioural development of the fetus and child: links and possible mechanisms. A review

A direct link between antenatal maternal mood and fetal behaviour, as observed by ultrasound from 27 to 28 weeks of gestation onwards, is well established. Moreover, 14 independent prospective studies have shown a link between antenatal maternal anxiety/stress and cognitive, behavioural, and emotional problems in the child. This link generally persisted after controlling for post-natal maternal mood and other relevant confounders in the pre- and post-natal periods. Although some inconsistencies remain, the results in general support a fetal programming hypothesis. Several gestational ages have been reported to be vulnerable to the long-term effects of antenatal anxiety/stress and different mechanisms are likely to operate at different stages. Possible underlying mechanisms are just starting to be explored. Cortisol appears to cross the placenta and thus may affect the fetus and disturb ongoing developmental processes. The development of the HPA-axis, limbic system, and the prefrontal cortex are likely to be affected by antenatal maternal stress and anxiety. The magnitude of the long-term effects of antenatal maternal anxiety/stress on the child is substantial. Programs to reduce maternal stress in pregnancy are therefore warranted.

Methylphenidate-evoked changes in striatal dopamine correlate with inattention and impulsivity in adolescents with attention deficit hyperactivity disorder

Abnormal central dopamine (DA) neurotransmission has been implicated in the impulsivity, inattention, and hyperactivity of attention deficit hyperactivity disorder (ADHD). We hypothesized that a pharmacological challenge with methylphenidate (MP) at a therapeutic dose increases extracellular DA concentrations in proportion to the severity of these specific ADHD symptoms. To test this hypothesis, we measured by PET the effect of acute challenge with MP on the availability of striatal binding sites for [11C]raclopride (pB), an index of altered interstitial DA concentration, in nine unmedicated adolescents (1 female, 8 males; age 13.7 +/- 1.8 years) with a current diagnosis of ADHD. We estimated the pB of [11C]raclopride for brain dopamine D2/3 receptors first in a baseline resting condition, and again after an acute challenge with MP (0.3 mg/kg, p.o.), and calculated the percentage change in (%DeltapB) in left and right striatum. On another day, measurements of impulsivity and inattention were performed using a computerized continuous performance test. There was a significant correlation between the magnitude of %DeltapB in the right striatum and the severity of inattention and impulsivity. MP-evoked %DeltapB correlated with standard scores for impulse control (r = 0.68; P = 0.02), attention (r = 0.81; P = 0.005), information processing (r = 0.66; P = 0.02), and consistency of attention, or variability (r = 0.60; P = 0.04). In conclusion, the results link inattention and impulsivity with sensitivity of brain DA receptor availability to an MP challenge, corroborating the hypothesis that MP serves to potentiate decreased DA neurotransmission in ADHD.

Effect of moderate hypercapnic hypoxia on cerebral dopaminergic activity and brain O2 uptake in intrauterine growth-restricted newborn piglets

There is evidence that intrauterine growth restriction (IUGR) is associated with altered dopaminergic function in the immature brain. Compelling evidence exists that in the newborn brain, specific structures are especially vulnerable to O2 deprivation. The dopaminergic system is shown to be sensitive to O2 deprivation in the immature brain. However, the respective enzyme activities have not been measured in the living neonatal brain after IUGR under hypercapnic hypoxia (H/H). Therefore, 18F-labeled 6-fluoro-L-3,4-dihydroxyphenylalanine (FDOPA) together with positron emission tomography was used to estimate the aromatic amino acid decarboxylase activity of the brain of seven normal weight (body weight 2078 +/- 434 g) and seven IUGR newborn piglets (body weight 893 +/- 109 g). Two positron emission tomography scans were performed in each piglet. All animals underwent a period of normoxia and moderate H/H. Simultaneously, cerebral blood flow was measured with colored microspheres and cerebral metabolic rate of O2 was determined. In newborn normal-weight piglets, the rate constant for FDOPA decarboxylation was markedly increased in mesostriatal regions during H/H, whereas brain oxidative metabolism remained unaltered. In contrast, moderate H/H induced in IUGR piglets a marked reduction of clearance rates for FDOPA metabolites (p <0.05), which was accompanied by a tendency of lowering the rate constant for FDOPA conversion. Furthermore, IUGR piglets maintained cerebral O2 uptake in the early period of H/H, but during the late period of H/H, a significantly reduced cerebral metabolic rate of O2 occurred (p <0.05). Thus, IUGR is accompanied by a missing activation of dopaminergic activity and attenuated brain oxidative metabolism during moderate H/H. This may indicate endogenous brain protection against O2 deprivation.

Reduced midbrain dopamine transporter binding in male adolescents with attention-deficit/hyperactivity disorder: association between striatal dopamine markers and motor hyperactivity

BACKGROUND

The hypothesis that altered dopamine transmission underlies hyperactive-inattentive behavior in children with attention-deficit/hyperactivity disorder (ADHD) is based on genetic studies and the efficacy of psychostimulants. Most of previous positron emission tomography (PET) and single photon emission tomography (SPET) studies have shown altered binding of dopamine markers in the basal ganglia. Yet, the functional role of the neurochemical disturbances are poorly understood. The purpose of our study was to examine dopamine transporter (DAT) and dopamine D2 receptor (D2R) binding in adolescents with ADHD and to search for its relationship with cognitive functions as well as locomotor hyperactivity.

METHODS

Twelve adolescents with ADHD and 10 young adults were examined with PET using the selective radioligands [11C]PE2I and [11C]raclopride, indexing DAT and D2R density. The simplified reference tissue model was used to calculate binding potential (BP) values. Attention and motor behavior were investigated with a continuous performance task (CPT) and motion measurements.

RESULTS

The BP value for [11C]PE2I and [11C]raclopride in the striatum of children with ADHD did not differ from that of the young adult control subjects. In the midbrain, however, the BP values for DAT were significantly lower (16%; p = .03) in children with ADHD. Dopamine D2 receptor binding in the right caudate nucleus correlated significantly with increased motor activity (r = .70, p = .01).

CONCLUSIONS

The lower BP values for DAT in the midbrain suggest that dopamine signaling in subjects with ADHD is altered. Altered dopamine signaling might have a causal relationship to motor hyperactivity and might be considered as a potential endophenotype of ADHD.