Reduced striatal GABA in unmedicated children with ADHD at 7T

Differential effects of perigestational consumption of sucrose-sweetened beverages on anxiety and depression-related behaviors in adult offspring: Sex disparity in a mouse model

Consumption of sucrose-sweetened drinks (SSDs) during pregnancy and breastfeeding can lead to various health and metabolism issues, but the potential impact on neurodevelopment and long-term effects remains unclear. This study aims to examine how maternal consumption of SSDs during gestation and lactation influences anxiety and depression-related behavior in adult offspring. Adult female CD-1 mice were randomly assigned to a control group (CG) or a sucrose group (SG) 2 weeks before gestation. The SG had 2 h of access to an SSD (15% w/w, 0.6 kcal/ml) for 2 weeks before mating, during pregnancy, and throughout lactation, totaling 8 weeks. Adult offspring were then evaluated for depressive-related behaviors and anxiety-related behaviors. Our findings reveal that perigestational consumption of SSDs does not lead to offspring presenting behaviors related to depression, but it does increase swimming behavior. However, maternal consumption of SSDs could impact the fighting response due to a diminished motivational component. In contrast, perigestational consumption of SSDs has apparent effects on anxiety-related behavior. Furthermore, female offspring appeared to be particularly vulnerable, exhibiting a higher anxiety index compared with controls. These findings indicate that females could be more vulnerable to the effects of maternal consumption of SSDs, being more susceptible to the presence of anxiety-related behaviors.

Novel pharmacological targets for GABAergic dysfunction in ADHD

Attention deficit/hyperactivity disorder (ADHD) is a neurodevelopment disorder that affects approximately 5% of the population. The disorder is characterized by impulsivity, hyperactivity, and deficits in attention and cognition, although symptoms vary across patients due to the heterogenous and polygenic nature of the disorder. Stimulant medications are the standard of care treatment for ADHD patients, and their effectiveness has led to the dopaminergic hypothesis of ADHD in which deficits in dopaminergic signaling, especially in cortical brain regions, mechanistically underly ADHD pathophysiology. Despite their effectiveness in many individuals, almost one-third of patients do not respond to stimulant treatments and the long-term negative side effects of these medications remain unclear. Emerging clinical evidence is beginning to highlight an important role of dysregulated excitatory/inhibitory (E/I) balance in ADHD. These deficits in E/I balance are related to functional abnormalities in glutamate and Gamma-Aminobutyric Acid (GABA) signaling in the brain, with increasing emphasis placed on GABAergic interneurons driving specific aspects of ADHD pathophysiology. Recent genome-wide association studies (GWAS) have also highlighted how genes associated with GABA function are mutated in human populations with ADHD, resulting in the generation of several new genetic mouse models of ADHD. This review will discuss how GABAergic dysfunction underlies ADHD pathophysiology, and how specific receptors/proteins related to GABAergic interneuron dysfunction may be pharmacologically targeted to treat ADHD in subpopulations with specific comorbidities and symptom domains. This article is part of the Special Issue on "PFC circuit function in psychiatric disease and relevant models".

Parvalbumin interneuron deficiency in the prefrontal and motor cortices of spontaneously hypertensive rats: an attention-deficit hyperactivity disorder animal model insight

Background

Attention deficit hyperactivity disorder (ADHD) is characterized by impairments in developmental-behavioral inhibition, resulting in impulsivity and hyperactivity. Recent research has underscored cortical inhibition deficiencies in ADHD via the gamma-aminobutyric acid (GABA)ergic system, which is crucial for maintaining excitatory-inhibitory balance in the brain. This study explored postnatal changes in parvalbumin (PV) immunoreactivity, indicating GABAergic interneuron types, in the prefrontal (PFC) and motor (MC) cortices of spontaneously hypertensive rats (SHRs), an ADHD animal model.

Methods

Examining PV- positive (PV+) cells associated with dopamine D2 receptors (D2) and the impact of dopamine on GABA synthesis, we also investigated changes in the immunoreactivity of D2 and tyrosine hydroxylase (TH). Brain sections from 4- to 10-week-old SHRs and Wistar Kyoto rats (WKYs) were immunohistochemically analyzed, comparing PV+, D2+ cells, and TH+ fiber densities across age-matched SHRs and WKYs in specific PFC/MC regions.

Results

The results revealed significantly reduced PV+ cell density in SHRs: prelimbic (~20% less), anterior cingulate (~15% less), primary (~15% less), and secondary motor (~17% less) cortices. PV+ deficits coincided with the upregulation of D2 in prepubertal SHRs and the downregulation of TH predominantly in pubertal/postpubertal SHRs.

Conclusion

Reduced PV+ cells in various PFC regions could contribute to inattention/behavioral alterations in ADHD, while MC deficits could manifest as motor hyperactivity. D2 upregulation and TH deficits may impact GABA synthesis, exacerbating behavioral deficits in ADHD. These findings not only shed new light on ADHD pathophysiology but also pave the way for future research endeavors.

Chronic Methylphenidate Effects on Brain Gene Expression: An Exploratory Review

Methylphenidate (MP) is a psychostimulant commonly prescribed for individuals with attention deficit hyperactivity disorder (ADHD) but it is also taken with and without a prescription for performance enhancement. Prior research has characterized the effects of MP on behavior, cognition, and neurochemistry. This exploratory review covers the uses of MP and examined the effects of MP on gene expression in the brain following exposure. Overall, MP causes a wide-spread potentiation of genes, in a region-specific manner; consequently, inducing neuronal alterations, such as synaptic plasticity and transmission, resulting in observed behaviors and affects. Monoamine neurotransmitters and post-synaptic density protein genes generally had a potentiating effect in gene expression after exposure to MP.

The contributions of neonatal inhalation of copper to air pollution-induced neurodevelopmental outcomes in mice

Exposures to ambient ultrafine particle (UFP) air pollution (AP) during the early postnatal period in mice (equivalent to human third trimester brain development) produce male-biased changes in brain structure, including ventriculomegaly, reduced brain myelination, alterations in neurotransmitters and glial activation, as well as impulsive-like behavioral characteristics, all of which are also features characteristic of male-biased neurodevelopmental disorders (NDDs). The purpose of this study was to ascertain the extent to which inhaled Cu, a common contaminant of AP that is also dysregulated across multiple NDDs, might contribute to these phenotypes. For this purpose, C57BL/6J mice were exposed from postnatal days 4-7 and 10-13 for 4 hr/day to inhaled copper oxide (CuxOy) nanoparticles at an environmentally relevant concentration averaging 171.9 ng/m3. Changes in brain metal homeostasis and neurotransmitter levels were determined following termination of exposure (postnatal day 14), while behavioral changes were assessed in adulthood. CuxOy inhalation modified cortical metal homeostasis and produced male-biased disruption of striatal neurotransmitters, with marked increases in dopaminergic function, as well as excitatory/inhibitory imbalance and reductions in serotonergic function. Impulsive-like behaviors in a fixed ratio (FR) waiting-for-reward schedule and a fixed interval (FI) schedule of food reward occurred in both sexes, but more prominently in males, effects which could not be attributed to altered locomotor activity or short-term memory. Inhaled Cu as from AP exposures, at environmentally relevant levels experienced during development, may contribute to impaired brain function, as shown by its ability to disrupt brain metal homeostasis and striatal neurotransmission. In addition, its ability to evoke impulsive-like behavior, particularly in male offspring, may be related to striatal dopaminergic dysfunction that is known to mediate such behaviors. As such, regulation of air Cu levels may be protective of public health.

Evaluation of electroretinography (ERG) parameters as a biomarker for ADHD

BACKGROUND

The retina is recognized as an accessible part of the brain due to their common embryonic origin. The electroretinogram (ERG) has proven to be a valuable tool for detecting schizophrenia and bipolarity. We therefore investigated its ability to detect ADHD.

METHODS

The cone and rod luminance response functions of the ERG were recorded in 26 ADHD subjects (17 women and 9 men) and 25 controls (16 women and 9 men).

RESULTS

No significant differences were found between the mixed groups, but sexual dysmorphia was observed in the significant results. In males, a significant prolonged cone a-wave latency was observed in the ADHD group. In females, we observed a significant decrease in the cone a- and b-wave amplitudes and a trend for a prolonged cone b-wave latency as well as a higher scotopic mixed rod-cone a-wave in the ADHD group.

CONCLUSION

The data obtained in this study show the potential of the ERG to detect ADHD, warranting further large-scale studies.

Molecular Mechanisms Underlying NMDARs Dysfunction and Their Role in ADHD Pathogenesis

Attention deficit hyperactivity disorder (ADHD) is one of the most common neurodevelopmental disorders, although the aetiology of ADHD is not yet understood. One proposed theory for developing ADHD is N-methyl-D-aspartate receptors (NMDARs) dysfunction. NMDARs are involved in regulating synaptic plasticity and memory function in the brain. Abnormal expression or polymorphism of some genes associated with ADHD results in NMDAR dysfunction. Correspondingly, NMDAR malfunction in animal models results in ADHD-like symptoms, such as impulsivity and hyperactivity. Currently, there are no drugs for ADHD that specifically target NMDARs. However, NMDAR-stabilizing drugs have shown promise in improving ADHD symptoms with fewer side effects than the currently most widely used psychostimulant in ADHD treatment, methylphenidate. In this review, we outline the molecular and genetic basis of NMDAR malfunction and how it affects the course of ADHD. We also present new therapeutic options related to treating ADHD by targeting NMDAR.

Viloxazine extended-release capsules for the treatment of attention-deficit/ hyperactivity disorder in adult patients

INTRODUCTION

Attention-deficit/hyperactivity disorder (ADHD) is a common neurobehavioral disorder with symptoms that may persist in up to 90% of adults diagnosed during childhood and continue to cause significant impairment throughout the lifespan. In the United States (US), amphetamine and methylphenidate formulations have been available to treat ADHD for several decades. Only one nonstimulant, atomoxetine, was available for the treatment of ADHD in adults until recently. In April 2022, a second nonstimulant, viloxazine extended-release (VLX-ER), became available in the US for the treatment of adult ADHD. Efficacy was previously established in placebo-controlled trials in children and adolescents.

AREAS COVERED

VLX-ER is a norepinephrine reuptake inhibitor with serotonin activity. The efficacy in adults, adverse event profile, pharmacokinetics, drug-drug interactions, and metabolism of VLX-ER are reviewed.

EXPERT OPINION

Despite the availability of effective pharmacological treatments for ADHD, many patients discontinue treatment in less than 1 year. Stimulants are effective in more than 80% of patients; however, some may have difficulty tolerating them. Although there were no head-to-head studies, the effect size of VLX-ER in an adult efficacy trial was lower than has been shown for stimulants. Nevertheless, the approval of VLX-ER adds another effective ADHD treatment option for adults.

Multinuclear Magnetic Resonance Spectroscopy at Ultra-High-Field: Assessing Human Cerebral Metabolism in Healthy and Diseased States

The brain is a highly energetic organ. Although the brain can consume metabolic substrates, such as lactate, glycogen, and ketone bodies, the energy metabolism in a healthy adult brain mainly relies on glucose provided via blood. The cerebral metabolism of glucose produces energy and a wide variety of intermediate metabolites. Since cerebral metabolic alterations have been repeatedly implicated in several brain disorders, understanding changes in metabolite levels and corresponding cell-specific neurotransmitter fluxes through different substrate utilization may highlight the underlying mechanisms that can be exploited to diagnose or treat various brain disorders. Magnetic resonance spectroscopy (MRS) is a noninvasive tool to measure tissue metabolism in vivo. ¹H-MRS is widely applied in research at clinical field strengths (≤3T) to measure mostly high abundant metabolites. In addition, X-nuclei MRS including, ¹³C, ²H, ¹⁷O, and ³¹P, are also very promising. Exploiting the higher sensitivity at ultra-high-field (>4T; UHF) strengths enables obtaining unique insights into different aspects of the substrate metabolism towards measuring cell-specific metabolic fluxes in vivo. This review provides an overview about the potential role of multinuclear MRS (¹H, ¹³C, ²H, ¹⁷O, and ³¹P) at UHF to assess the cerebral metabolism and the metabolic insights obtained by applying these techniques in both healthy and diseased states.

Changes in brain metabolite levels across childhood

Metabolites play important roles in brain development and their levels change rapidly in the prenatal period and during infancy. Metabolite levels are thought to stabilize during childhood, but the development of neurochemistry across early-middle childhood remains understudied. We examined the developmental changes of key metabolites (total N-acetylaspartate, tNAA; total choline, tCho; total creatine, tCr; glutamate+glutamine, Glx; and myo-inositol, mI) using short echo-time magnetic resonance spectroscopy (MRS) in the anterior cingulate cortex (ACC) and the left temporo-parietal cortex (LTP) using a mixed cross-sectional/longitudinal design in children aged 2-11 years (ACC: N=101 children, 112 observations; LTP: N=95 children, 318 observations). We found age-related effects for all metabolites. tNAA increased with age in both regions, while tCho decreased with age in both regions. tCr increased with age in the LTP only, and mI decreased with age in the ACC only. Glx did not show linear age effects in either region, but a follow-up analysis in only participants with ≥3 datapoints in the LTP revealed a quadratic effect of age following an inverted U-shape. These substantial changes in neurochemistry throughout childhood likely underlie various processes of structural and functional brain development.

Cerebellar gamma-aminobutyric acid: Investigation of group effects in neurodevelopmental disorders

Neurodevelopmental disorders (NDDs) including autism spectrum disorder (ASD), attention-deficit hyperactivity disorder (ADHD) and obsessive-compulsive disorder (OCD) are thought to arise in part from the disruption in the excitatory/inhibitory balance of gamma-aminobutyric acid (GABA) and glutamate in the brain. Recent evidence has shown the involvement of the cerebellum in cognition and affect regulation, and cerebellar atypical function or damage is reported frequently in NDDs. Magnetic resonance spectroscopy studies have reported decreases in GABA in cortical brain areas in the NDDs, however, GABA levels in the cerebellum have not been examined. To determine possible group effects, we used a MEGA-PRESS acquisition to investigate GABA+ levels in a cerebellar voxel in 343 individuals (aged 2.5-22 years) with ASD, ADHD, OCD and controls. Using a mixed effects model, we found no significant differences between groups in GABA+ concentration. Our findings suggest that cerebellar GABA+ levels do not differentiate NDD groups.

Mapping the cortico-striatal transcriptome in attention deficit hyperactivity disorder

Despite advances in identifying rare and common genetic variants conferring risk for ADHD, the lack of a transcriptomic understanding of cortico-striatal brain circuitry has stymied a molecular mechanistic understanding of this disorder. To address this gap, we mapped the transcriptome of the caudate nucleus and anterior cingulate cortex in post-mortem tissue from 60 individuals with and without ADHD. Significant differential expression of genes was found in the anterior cingulate cortex and, to a lesser extent, the caudate. Significant downregulation emerged of neurotransmitter gene pathways, particularly glutamatergic, in keeping with models that implicate these neurotransmitters in ADHD. Consistent with the genetic overlap between mental disorders, correlations were found between the cortico-striatal transcriptomic changes seen in ADHD and those seen in other neurodevelopmental and mood disorders. This transcriptomic evidence points to cortico-striatal neurotransmitter anomalies in the pathogenesis of ADHD, consistent with current models of the disorder.

Low serum allopregnanolone levels in children with attention deficit hyperactivity disorder

Attention deficit hyperactivity disorder (ADHD) has increasing evidence for the role of neurohormones in its etiopathogenesis. It has been suggested that the effects of neurosteroids on the brain in the early developmental period may predispose to neurodevelopmental pathologies. In our study, we examined serum dehydroepiandrosterone (DHEA), dehydroepiandrosterone sulfate (DHEA-S), and allopregnanolone levels in children with ADHD and whether these neurosteroids differ in the presence of specific learning disorder (SLD) and oppositional defiant disorder (ODD) comorbidities (ADHD+SLD and ADHD+ODD). We also investigated the relationship between neurosteroid levels and the severity of ADHD symptoms. Thirty-five prepubertal children with ADHD and 33 prepubertal healthy children, all aged 6-10 years, were included in this study. The severity of ADHD symptoms was assessed with the parent-rated and teacher-rated Turgay DSM-IV Disruptive Behavior Disorders Rating Scale (T-DSM-IV-S). Serum allopregnanolone levels were significantly lower in the ADHD group compared to healthy controls. When analyzed according to comorbidity status, serum allopregnanolone levels were lower in ADHD+SLD and ADHD+ODD groups compared to healthy controls. However, when compared to healthy children, serum DHEA and DHEA-S levels in children with ADHD were not significantly different. Serum allopregnanolone levels were negatively associated with teacher-rated T-DSM-IV-S hyperactivity/impulsivity scores for all participants only. These findings suggest that allopregnanolone may play a role in the pathophysiology of ADHD, especially in the presence of ODD and SLD comorbidities.

Emerging findings of glutamate-glutamine imbalance in the medial prefrontal cortex in attention deficit/hyperactivity disorder: systematic review and meta-analysis of spectroscopy studies

One of the main challenges in investigating the neurobiology of ADHD is our limited capacity to study its neurochemistry in vivo. Magnetic resonance spectroscopy (MRS) estimates metabolite concentrations within the brain, but approaches and findings have been heterogeneous. To assess differences in brain metabolites between patients with ADHD and healthy controls, we searched 12 databases screening for MRS studies. Studies were divided into 'children and adolescents' and 'adults' and meta-analyses were performed for each brain region with more than five studies. The quality of studies was assessed by the Newcastle-Ottawa Scale. Thirty-three studies met our eligibility criteria, including 874 patients with ADHD. Primary analyses revealed that the right medial frontal area of children with ADHD presented higher concentrations of a composite of glutamate and glutamine (p = 0.02, SMD = 0.53). Glutamate might be implicated in pruning and neurodegenerative processes as an excitotoxin, while glutamine excess might signal a glutamate depletion that could hinder neurotrophic activity. Both neuro metabolites could be implicated in the differential cortical thinning observed in patients with ADHD across all ages. Notably, more homogeneous designs and reporting guidelines are the key factors to determine how suitable MRS is for research and, perhaps, for clinical psychiatry. Results of this meta-analysis provided an overall map of the brain regions evaluated so far, addressed the role of glutamatergic metabolites in the pathophysiology of ADHD, and pointed to new perspectives for consistent use of the tool in the field.

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.

S-ketamine administration in pregnant mice induces ADHD- and depression-like behaviors in offspring mice

BACKGROUND

Anesthesia and psychotropic drugs in pregnant women may cause long-term effects on the brain development of unborn babies. The authors set out to investigate the neurotoxicity of S-ketamine, which possesses anesthetic and antidepressant effects and may cause attention deficit hyperactivity disorder (ADHD)- and depression-like behaviors in offspring mice.

METHODS

Pregnant mice were administered with low-, medium-, and high-dose S-ketamine (15, 30, and 60 mg/kg) by intraperitoneal injection for 5 days from gestational day 14-18. At 21 days after birth, an elevated plus-maze test, fear conditioning, open field test, and forced swimming test were used to assess ADHD- and depression-like behaviors. Neuronal amount, glial activation, synaptic function indicated by ki67, and inhibitory presynaptic proteins revealed by GAD2 in the hippocampus, amygdala, habenula nucleus, and lateral hypothalamus (LHA) were determined by immunofluorescence assay.

RESULTS

All the pregnant mice exposed to high-dose S-ketamine administration had miscarriage after the first injection. Both low-dose and medium-dose S-ketamine administration significantly increased the open-arm time and attenuated frozen time in the fear conditioning, which indicates impulsivity and memory dysfunction-like behaviors. Medium-dose S-ketamine administration reduced locomotor activity in the open field and increased immobility time in the forced swimming test, indicating depression-like behaviors. Changes in astrocytic activation, synaptic dysfunction, and decreased inhibitory presynaptic proteins were found in the hippocampus, amygdala, and habenula nucleus.

CONCLUSIONS

These results demonstrate that S-ketamine may lead to detrimental effects, including ADHD-and depression-like behaviors in offspring mice. More studies should be promoted to determine the neurotoxicity of S-ketamine in the developing brain.

The metacontrol hypothesis as diagnostic framework of OCD and ADHD: A dimensional approach based on shared neurobiological vulnerability

Obsessive-compulsive disorder (OCD) and attention-deficit hyperactivity disorder (ADHD) are multi-faceted neuropsychiatric conditions that in many aspects appear to be each other's antipodes. We suggest a dimensional approach, according to which these partially opposing disorders fall onto a continuum that reflects variability regarding alterations of cortico-striato-thalamo-cortical (CSTC) circuits and of the processing of neural noise during cognition. By using theoretical accounts of human cognitive metacontrol, we develop a framework according to which OCD can be characterized by a chronic bias towards exaggerated cognitive persistence, equivalent to a high signal-to-noise ratio (SNR)-which facilitates perseverative behaviour but impairs mental flexibility. In contrast, ADHD is characterized by a chronic bias towards inflated cognitive flexibility, equivalent to a low SNR-which increases behavioural variability but impairs the focusing on one goal and on relevant information. We argue that, when pharmacology is not feasible, novel treatments of these disorders may involve methods to manipulate the signal-to-noise ratio via non-invasive brain stimulation techniques, in order to normalize the situational imbalance between cognitive persistence and cognitive flexibility.

Neuroimaging at 7 Tesla: a pictorial narrative review

Neuroimaging using the 7-Tesla (7T) human magnetic resonance (MR) system is rapidly gaining popularity after being approved for clinical use in the European Union and the USA. This trend is the same for functional MR imaging (MRI). The primary advantages of 7T over lower magnetic fields are its higher signal-to-noise and contrast-to-noise ratios, which provide high-resolution acquisitions and better contrast, making it easier to detect lesions and structural changes in brain disorders. Another advantage is the capability to measure a greater number of neurochemicals by virtue of the increased spectral resolution. Many structural and functional studies using 7T have been conducted to visualize details in the white matter and layers of the cortex and hippocampus, the subnucleus or regions of the putamen, the globus pallidus, thalamus and substantia nigra, and in small structures, such as the subthalamic nucleus, habenula, perforating arteries, and the perivascular space, that are difficult to observe at lower magnetic field strengths. The target disorders for 7T neuroimaging range from tumoral diseases to vascular, neurodegenerative, and psychiatric disorders, including Alzheimer's disease, Parkinson's disease, multiple sclerosis, epilepsy, major depressive disorder, and schizophrenia. MR spectroscopy has also been used for research because of its increased chemical shift that separates overlapping peaks and resolves neurochemicals more effectively at 7T than a lower magnetic field. This paper presents a narrative review of these topics and an illustrative presentation of images obtained at 7T. We expect 7T neuroimaging to provide a new imaging biomarker of various brain disorders.

Reduced Glx and GABA Inductions in the Anterior Cingulate Cortex and Caudate Nucleus Are Related to Impaired Control of Attention in Attention-Deficit/Hyperactivity Disorder

Attention-deficit/hyperactivity disorder (ADHD) is a neurodevelopmental disorder that impairs the control of attention and behavioral inhibition in affected individuals. Recent genome-wide association findings have revealed an association between glutamate and GABA gene sets and ADHD symptoms. Consistently, people with ADHD show altered glutamate and GABA content in the brain circuitry that is important for attention control function. Yet, it remains unknown how glutamate and GABA content in the attention control circuitry change when people are controlling their attention, and whether these changes can predict impaired attention control in people with ADHD. To study these questions, we recruited 18 adults with ADHD (31-51 years) and 16 adults without ADHD (28-54 years). We studied glutamate + glutamine (Glx) and GABA content in the fronto-striatal circuitry while participants performed attention control tasks. We found that Glx and GABA concentrations at rest did not differ between participants with ADHD or without ADHD. However, while participants were performing the attention control tasks, participants with ADHD showed smaller Glx and GABA increases than participants without ADHD. Notably, smaller GABA increases in participants with ADHD significantly predicted their poor task performance. Together, these findings provide the first demonstration showing that attention control deficits in people with ADHD may be related to insufficient responses of the GABAergic system in the fronto-striatal circuitry.

Relationship between sleep problems and chronotypes of children and adolescents with attention deficit and hyperactivity disorder and serum GABA, glutamate and homocysteine levels

In this study, we aimed to determine the relationship between chronotype, sleep problems and serum levels of GABA (gamma amminobutyric acid), glutamate and homocysteine in children and adolescents diagnosed with attention deficit and hyperactivity disorder (ADHD) as well as factors affecting this relationship. Sleep problems of 46 children and adolescents aged 7-18 years diagnosed with ADHD and 30 healthy volunteers aged 7-18 years were evaluated with Children's Sleep Habits Questionnaire (CSHQ) while chronotypes were evaluated with Children's Chronotype Questionnaire (CCQ). Serum glutamate, GABA and homocysteine levels were measured using immunosorbent test (ELISA) kits. Sleep problems were significantly more common in the ADHD group compared to the control group (p < .001). Serum GABA, glutamate and homocysteine levels were found to be predictor biomarkers for ADHD, independent of total sleep problem score. When the homocysteine levels were above the cut-off point of 9.445 µmol/L, the sensitivity in early diagnosis of ADHD was 84.8% and the specificity was 70.0%. Although ADHD is a disorder in which sleep problems are common, increased serum GABA, glutamate and homocysteine are important in diagnosing ADHD independent of ADHD-related sleep problems. Homocysteine levels may be an important predictor for the presence of ADHD.

Ultra-High-Field Imaging of the Pediatric Brain and Spinal Cord

Neuroimaging with ultra-high field magnets (≥7T) provides superior signal-to-noise, spatial resolution and tissue contrast; but also greater safety concerns, longer scanning times, and increased distortion and field inhomogeneity. Brain and spinal cord anatomic microstructure and function imaged in greater detail offers improved lesion detection, delineation, and characterization. The ongoing development of novel imaging contrasts and translation of cutting-edge sequences will aid more accurate, sensitive, and precise diagnosis, interventional planning, and follow-up for a variety of pathologic conditions.

Increased locomotor activity via regulation of GABAergic signalling in foxp2 mutant zebrafish-implications for neurodevelopmental disorders

Recent advances in the genetics of neurodevelopmental disorders (NDDs) have identified the transcription factor FOXP2 as one of numerous risk genes, e.g. in autism spectrum disorders (ASD) and attention-deficit/hyperactivity disorder (ADHD). FOXP2 function is suggested to be involved in GABAergic signalling and numerous studies demonstrate that GABAergic function is altered in NDDs, thus disrupting the excitation/inhibition balance. Interestingly, GABAergic signalling components, including glutamate-decarboxylase 1 (Gad1) and GABA receptors, are putative transcriptional targets of FOXP2. However, the specific role of FOXP2 in the pathomechanism of NDDs remains elusive. Here we test the hypothesis that Foxp2 affects behavioural dimensions via GABAergic signalling using zebrafish as model organism. We demonstrate that foxp2 is expressed by a subset of GABAergic neurons located in brain regions involved in motor functions, including the subpallium, posterior tuberculum, thalamus and medulla oblongata. Using CRISPR/Cas9 gene-editing we generated a novel foxp2 zebrafish loss-of-function mutant that exhibits increased locomotor activity. Further, genetic and/or pharmacological disruption of Gad1 or GABA-A receptors causes increased locomotor activity, resembling the phenotype of foxp2 mutants. Application of muscimol, a GABA-A receptor agonist, rescues the hyperactive phenotype induced by the foxp2 loss-of-function. By reverse translation of the therapeutic effect on hyperactive behaviour exerted by methylphenidate, we note that application of methylphenidate evokes different responses in wildtype compared to foxp2 or gad1b loss-of-function animals. Together, our findings support the hypothesis that foxp2 regulates locomotor activity via GABAergic signalling. This provides one targetable mechanism, which may contribute to behavioural phenotypes commonly observed in NDDs.

A role for GABA in the modulation of striatal and hippocampal systems under stress

Previous research has demonstrated that stress modulates the competitive interaction between the hippocampus and striatum, two structures known to be critically involved in motor sequence learning. These earlier investigations, however, have largely focused on blood oxygen-level dependent (BOLD) responses. No study to date has examined the link between stress, motor learning and levels of striatal and hippocampal gamma-aminobutyric acid (GABA). This knowledge gap is surprising given the known role of GABA in neuroplasticity subserving learning and memory. The current study thus examined: a) the effects of motor learning and stress on striatal and hippocampal GABA levels; and b) how learning- and stress-induced changes in GABA relate to the neural correlates of learning. To do so, fifty-three healthy young adults were exposed to a stressful or non-stressful control intervention before motor sequence learning. Striatal and hippocampal GABA levels were assessed at baseline and post-intervention/learning using magnetic resonance spectroscopy. Regression analyses indicated that stress modulated the link between striatal GABA levels and functional plasticity in both the hippocampus and striatum during learning as measured with fMRI. This study provides evidence for a role of GABA in the stress-induced modulation of striatal and hippocampal systems.

Neuroimaging in Attention-Deficit/Hyperactivity Disorder: Recent Advances

Attention-deficit/hyperactivity disorder (ADHD) is a common neurodevelopmental condition, leading to impaired attention and impulsive behaviors diagnosed in, but not limited to, children. ADHD can cause symptoms throughout life. This article summarizes structural (conventional, volumetric, and diffusion tensor imaging MRI) and functional [task-based functional MRI (fMRI), resting state fMRI, PET, and MR spectroscopy] brain findings in patients with ADHD. Consensus is lacking regarding altered anatomic or functional imaging findings of the brain in children with ADHD, likely because of the disorder's heterogeneity. Most anatomic studies report abnormalities in the frontal lobes, basal ganglia, and corpus callosum; decreased surface area in the left ventral frontal and right prefrontal cortex; thinner medial temporal lobes; and smaller caudate nuclei. Using fMRI, researchers have focused on the prefrontal and temporal regions, reflecting perception-action mapping alterations. Artificial intelligence models evaluating brain anatomy have highlighted changes in cortical thickness and shape of the inferior frontal cortex, bilateral sensorimotor cortex, left temporal lobe, and insula. Early intervention and/or normal brain maturation can alter imaging patterns and convert functional imaging studies to a normal pattern. While the imaging findings provide insight into the disease's neuropathophysiology, no definitive structural or functional pattern defines the disorder from a neuroradiologic perspective.

Ultrahigh field in vivo characterization of microstructural abnormalities in the orbitofrontal cortex and amygdala in autism

There are currently no biomarkers for autism spectrum disorder (ASD). This neurodevelopmental condition has previously been associated with histopathological findings, including increased neuronal packing density in the amygdala, abnormal laminar cytoarchitecture and increased average neuronal density in the prefrontal cortex. The present study examined whether new brain imaging technologies could reveal in vivo, in adults with ASD, the manifestation of previously described histopathological changes. Using quantitative mapping at ultrahigh field (7 Tesla), we show that we can observe microstructural alterations in the right lateral orbitofrontal cortex and the bilateral amygdala in adult individuals with ASD in vivo. These imaging alterations point to an abnormal laminar cytoarchitecture and to an increased neuronal density, similar to what has been previously described in post-mortem data in ASD. Our data demonstrate that it is possible to visualize, in vivo and at the individual level, alterations of cortical and subcortical microstructure in ASD. Future studies will be needed to extend these findings to a larger group of individuals and evaluate their association with symptomatology as well as their specificity among the different neurodevelopmental disorders.

Monoaminergic hypo- or hyperfunction in adolescent and adult attention-deficit hyperactivity disorder?

Disturbances of dopamine (DA), serotonin (5-HT) and/or norepinephrine (NE) functions are implied in attention-deficit hyperactivity disorder (ADHD). However, the precise cortical and subcortical mechanisms are still not fully understood. In the present survey, we conducted a PUBMED search, which provided 37 in vivo investigations with PET and SPECT on 419 ADHD patients and 490 controls. The retrospective analysis revealed increased striatal DA transporter (DAT) in adolescent as well as adult medication-naïve and not acutely medicated patients. In acutely medicated adults, DAT was not different from controls. Midbrain DAT was normal in adults, but decreased in adolescents. Striatal D₂ receptor (R) binding was normal in both adolescents (not acutely medicated) and adults (acutely medicated and not acutely medicated). In medication-naïve adults, DA synthesis was decreased in putamen and amygdala, but normal in the whole striatum and midbrain. In not acutely medicated adults, DA synthesis was reduced in putamen, whole striatum, prefrontal cortex, frontal cortex, amygdala and midbrain, whereas, in adolescents, no regional differences were observed. In adult (not acutely medicated) subjects, cingulate D₁R was reduced. 5-HT transporter (SERT) binding was decreased in striatum and thalamus, but normal in midbrain, neocortex and limbic regions, whereas, in medication-naïve adults, SERT was diminished in striatum and midbrain, but normal in thalamus and neocortex. The findings suggest transient stages of synaptic DA shortage as well as DA surplus in individual brain regions, which elicit presynaptic as well as postsynaptic compensatory mechanisms, striving to attain functional homeostasis. Thereby, it remains a matter of debate, whether ADHD may be characterized by a general hypo- or hyperactivity of DA and/or 5-HT function.

Transcutaneous vagus nerve stimulation in patients with attention-deficit/hyperactivity disorder: A viable option?

Individuals with attention-deficit/hyperactivity disorder (ADHD) suffer from a range of cognitive and behavioral problems that severely impair their educational and occupational attainment. ADHD symptoms have been linked to structural and functional changes within and between different brain regions, particularly the prefrontal cortex. At the system level, reduced availability of the neurotransmitters dopamine (DA) and norepinephrine (NE) but also γ-aminobutyric acid (GABA) have been repeatedly demonstrated. Recently, non-invasive brain stimulation (NIBS) techniques have been explored as treatment alternatives to alter dysfunctional activation patterns in specified brain areas or networks. In the current paper, we introduce transcutaneous vagus nerve stimulation (tVNS) as a systemic approach to directly affect NE and GABA neurotransmission. TVNS is a non-drug intervention with low risk and proven efficacy in improving cognitive particularly executive functions. It is easy to apply and therefore well-suited to provide home-based or mobile treatment options allowing a significant increase in treatment intensity and providing easier access to medical care for individuals who are unable to regularly visit a clinician. We describe in detail the underlying mechanisms of tVNS and current fields of application and discuss its potential as an adjuvant treatment for ADHD.

Precision Medicine Care in ADHD: The Case for Neural Excitation and Inhibition

Attention-deficit/hyperactivity disorder (ADHD) is a neurodevelopmental disorder that has become increasingly prevalent worldwide. Its core symptoms, including difficulties regulating attention, activity level, and impulses, appear in early childhood and can persist throughout the lifespan. Current pharmacological options targeting catecholamine neurotransmissions have effectively alleviated symptoms in some, but not all affected individuals, leaving clinicians to implement trial-and-error approach to treatment. In this review, we discuss recent experimental evidence from both preclinical and human studies that suggest imbalance of excitation/inhibition (E/I) in the fronto-striatal circuitry during early development may lead to enduring neuroanatomical abnormality of the circuitry, causing persistence of ADHD symptoms in adulthood. We propose a model of precision medicine care that includes E/I balance as a candidate biomarker for ADHD, development of GABA-modulating medications, and use of magnetic resonance spectroscopy and scalp electrophysiology methods to monitor the effects of treatments on shifting E/I balance throughout the lifespan.

Neuron-Glia Interactions in Neurodevelopmental Disorders

Recent studies have revealed synaptic dysfunction to be a hallmark of various psychiatric diseases, and that glial cells participate in synapse formation, development, and plasticity. Glial cells contribute to neuroinflammation and synaptic homeostasis, the latter being essential for maintaining the physiological function of the central nervous system (CNS). In particular, glial cells undergo gliotransmission and regulate neuronal activity in tripartite synapses via ion channels (gap junction hemichannel, volume regulated anion channel, and bestrophin-1), receptors (for neurotransmitters and cytokines), or transporters (GLT-1, GLAST, and GATs) that are expressed on glial cell membranes. In this review, we propose that dysfunction in neuron-glia interactions may contribute to the pathogenesis of neurodevelopmental disorders. Understanding the mechanisms of neuron-glia interaction for synapse formation and maturation will contribute to the development of novel therapeutic targets of neurodevelopmental disorders.

Effects of 12-Week Methylphenidate Treatment on Neurometabolism in Adult Patients with ADHD: The First Double-Blind Placebo-Controlled MR Spectroscopy Study

Attention deficit hyperactivity disorder (ADHD) is a frequent neurodevelopmental disorder that often persists into adulthood. Methylphenidate (MPH) is the first-line treatment for ADHD; however, despite its wide usage, little is known about its neurometabolic effects. Until now, no randomized and blinded clinical trials have been conducted addressing the neurometabolic signals of MPH administration in adults with ADHD. In the current study, the authors investigated how MPH intake and group psychotherapy (GPT) influence brain neurometabolism over the course of three months. The authors hypothesized a decrease in the anterior cingulate cortex (ACC) glutamate concentration following MPH administration. This study was part of a double-blind multicenter trial (Comparison of Methylphenidate and Psychotherapy in Adult ADHD Study (COMPAS)) investigating the effects of MPH and GPT in patients with adult ADHD. Using single-voxel magnetic resonance spectroscopy (MRS) of the pregenual ACC and the left cerebellar hemisphere (CHL), we investigated the concentration of glutamate plus glutamine (Glx), N-acetyl-aspartate, creatine, total choline containing compounds, and myo-inositol in patients before and after 12 weeks of treatment. Neither MPH nor GPT significantly influenced the Glx concentration or any of the other metabolite concentrations in the ACC and CHL after 12 weeks. Therefore, contrary to the hypothesis, no change in the prefrontal Glx signal was detected after MPH treatment. Given that MRS does not differentiate between glutamate in the synaptic cleft and in neuronal tissue, MPH-induced down-regulation of glutamatergic neurotransmission in the ACC might only affect the concentration of glutamate in the synaptic cleft, while the general availability of glutamate in the respective neuronal tissue might be unaffected by MPH intake. The observed lack of any MPH-induced normalization in metabolite concentrations is less surprising, considering that the baseline sample did not significantly differ from a healthy control group. Future studies of other regions, such as the basal ganglia, and the use of novel methods, such as whole brain MRS and multimodal imaging approaches, are necessary.