NMDA receptor function in the prefrontal cortex of a rat model for attention-deficit hyperactivity disorder

Aberrant glutamatergic systems underlying impulsive behaviors: Insights from clinical and preclinical research

Impulsivity is a broad construct that often refers to one of several distinct behaviors and can be measured with self-report questionnaires and behavioral paradigms. Several psychiatric conditions are characterized by one or more forms of impulsive behavior, most notably the impulsive/hyperactive subtype of attention-deficit/hyperactivity disorder (ADHD), mood disorders, and substance use disorders. Monoaminergic neurotransmitters are known to mediate impulsive behaviors and are implicated in various psychiatric conditions. However, growing evidence suggests that glutamate, the major excitatory neurotransmitter of the mammalian brain, regulates important functions that become dysregulated in conditions like ADHD. The purpose of the current review is to discuss clinical and preclinical evidence linking glutamate to separate aspects of impulsivity, specifically motor impulsivity, impulsive choice, and affective impulsivity. Hyperactive glutamatergic activity in the corticostriatal and the cerebro-cerebellar pathways are major determinants of motor impulsivity. Conversely, hypoactive glutamatergic activity in frontal cortical areas and hippocampus and hyperactive glutamatergic activity in anterior cingulate cortex and nucleus accumbens mediate impulsive choice. Affective impulsivity is controlled by similar glutamatergic dysfunction observed for motor impulsivity, except a hyperactive limbic system is also involved. Loss of glutamate homeostasis in prefrontal and nucleus accumbens may contribute to motor impulsivity/affective impulsivity and impulsive choice, respectively. These results are important as they can lead to novel treatments for those with a condition characterized by increased impulsivity that are resistant to conventional treatments.

Thymol as a Potential Neuroprotective Agent: Mechanisms, Efficacy, and Future Prospects

Neurodegenerative diseases pose a growing global health challenge, with limited effective therapeutic options. Mitochondrial dysfunction, oxidative stress, neuroinflammation, apoptosis, and autophagy are common underlying mechanisms in these diseases. Thymol is a phenolic monoterpene compound that has gained attention for its diverse biological properties, including antioxidant, anti-inflammatory, and immunomodulatory activities. Thymol supplementation could provide potential neuroprotection and improve cognitive deficits, depressant-like effects, learning, and memory impairments in rodents. Mechanistic investigations reveal that the neuroprotective effects of thymol involve the improvement of oxidative stress, mitochondrial dysfunction, and inflammatory response. Several signaling pathways, including mitochondrial apoptotic, NF-κB, AKT, Nrf2, and CREB/BDNF pathways are also involved. In this review, the neuroprotective effects of thymol, the potential molecular mechanisms, safety, applications, and current challenges toward development as a neuroprotective agent were summarized and discussed. We hope that this review provides valuable insights for the further development of this promising natural product as a promising neuroprotective agent.

Glutamate receptor genetic variants affected peripheral glutamatergic transmission and treatment induced improvement of Indian ADHD probands

Attention deficit hyperactivity disorder (ADHD), a childhood-onset neurobehavioral disorder, often perturbs scholastic achievement and peer-relationship. The pivotal role of glutamate (Glu) in learning and memory indicated an influence of Glu in ADHD, leading to the exploration of Glu in different brain regions of ADHD subjects. We for the first time analyzed GluR genetic variations, Glu levels, as well as expression of Glu receptors (GluR) in the peripheral blood of eastern Indian ADHD probands to find out the relevance of Glu in ADHD prognosis. After obtaining informed written consent for participation, peripheral blood was collected for analyzing the genetic variants, Glu level, and expression of target genes. Since ADHD probands are often treated with methylphenidate or atomoxetine for providing symptomatic remediation, we have also tested post-therapeutic improvement in the ADHD trait scores in the presence of different GluR genotypes. Two variants, GRM7 rs3749380 "T" and GRIA1 rs2195450 "C", exhibited associations with ADHD (P ≤ 0.05). A few GluR genetic variants showed significant association with higher trait severity, low IQ, lower plasma Glu level, down-regulated GluR mRNA expression, and poor response to medications. This indicates that down-regulated glutamatergic system may have an effect on ADHD etiology and treatment efficacy warranting further in-depth investigation.

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.

Methyl Palmitate Modulated NMDA-Induced Cerebral Hyperemia in Hypertensive Rats

N-methyl-D-aspartate (NMDA) receptors were found to be dysfunctional in hypertensive rats. Methyl palmitate (MP) has been shown to diminish the nicotine-induced increase in blood flow in the brainstem. The aim of this study was to determine how MP modulated NMDA-induced increased regional cerebral blood flow (rCBF) in normotensive (WKY), spontaneously hypertensive (SHR), and renovascular hypertensive (RHR) rats. The increase in rCBF after the topical application of experimental drugs was measured using laser Doppler flowmetry. Topical NMDA application induced an MK-801-sensitive increase in rCBF in anesthetized WKY rats, which was inhibited by MP pretreatments. This inhibition was prevented by pretreatment with chelerythrine (a PKC inhibitor). The NMDA-induced increase in rCBF was also inhibited by the PKC activator in a concentration-dependent manner. Neither MP nor MK-801 affected the increase in rCBF induced by the topical application of acetylcholine or sodium nitroprusside. Topical application of MP to the parietal cortex of SHRs, on the other hand, increased basal rCBF slightly but significantly. MP enhanced the NMDA-induced increase in rCBF in SHRs and RHRs. These results suggested that MP had a dual effect on the modulation of rCBF. MP appears to play a significant physiological role in CBF regulation.

The protective effect of thymoquinone or/and thymol against monosodium glutamate-induced attention-deficit/hyperactivity disorder (ADHD)-like behavior in rats: Modulation of Nrf2/HO-1, TLR4/NF-κB/NLRP3/caspase-1 and Wnt/β-Catenin signaling pathways in rat model

Both thymoquinone (TQ) and thymol (T) have been proved to possess a positive impact on human health. In this research, we aimed to investigate the effect of these compounds separately and together on the Attention-deficit/hyperactivity disorder (ADHD)-like behavior induced by monosodium glutamate (MSG) in rats. Forty male, Spargue Dawley rat pups (postnatal day 21), were randomly allocated into five groups: Normal saline (NS), MSG, MSG+TQ, MSG+T, and MSG+TQ+T. MSG (0.4 mg/kg/day), TQ (10 mg/kg/day) and T (30 mg/kg/day) were orally administered for 8 weeks. The behavioral tests proved that rats treated with TQ and/or T showed improved locomotor, attention and cognitive functions compared to the MSG group with more pronounced effect displayed with their combination. All treated groups showed improvement in MSG-induced aberrations in brain levels of GSH, IL-1β, TNF-α, GFAP, glutamate, calcium, dopamine, norepinephrine, Wnt3a, β-Catenin and BDNF. TQ and/or T treatment also enhanced the mRNA expression of Nrf2, HO-1 and Bcl2 while reducing the protein expression of TLR4, NFκB, NLRP3, caspase 1, Bax, AIF and GSK3β as compared to the MSG group. However, the combined therapy showed more significant effects in all measured parameters. All of these findings were further confirmed by the histopathological examinations. Current results concluded that the combined therapy of TQ and T had higher protective effects than their individual supplementations against MSG-induced ADHD-like behavior in rats.

Omega-3 Rich Oils Attenuate ADHD-Like Behaviour Induced by Dietary Monosodium Glutamate in Rats

<b>Background and Objective:</b> Attention Deficit Hyperactivity Disorder (ADHD) is a neurodevelopmental disorder characterized by inattention, hyperactivity and cognitive dysfunction. The present study was designed to examine the possible modulatory effect of Fish, Walnuts or Fenugreek Oils against Attention Deficit Hyperactivity Disorder (ADHD)-like Behavior induced by Monosodium Glutamate (MSG) in Rats. <b>Materials and Methods:</b> Fifty weaning rats were divided into five groups, (each group contain 10 rats) as follows: Group 1: Normal control rats were fed on a balanced diet. Groups from 2-5 rats were fed on a balanced diet+MSG (0.4 g kg<sup></sup><sup>1</sup> diet), Group 2 served as a positive control group whereas group 3, 4 and 5 treated with Fish, Walnuts and Fenugreek oil, respectively, (200 mg kg<sup></sup><sup>1</sup> b.wt.) by intra-gastric tube. Biochemical and behavioural parameters were tested as well as microscopic examination of brain tissue was done. <b>Results:</b> MSG ingestion caused marked disruption in locomotors activity, memory function and brain tissue structure along with significant abnormalities in some bio-markers and reduction in the gene expression level of Bcl-2 in brain tissue. However, treatment with the tested oils showed remarkable effect by reversing the condition. <b>Conclusion:</b> Dietary supplementation with walnut; fenugreek or fish oils at the tested dose could modulate the condition of ADHD in rats.

Association of Gene Variations in Ionotropic Glutamate Receptor and Attention-Deficit/Hyperactivity Disorder in the Chinese Population: A Two-Stage Case-Control Study

Objective: The aim of this study was to comprehensively explore the relationship between genetic variations within GRIN2A, GRIN2B, GRIK1, GRIK4, GRID2, and ADHD. Method: Genotyping was performed with the Sequenom MassARRAY system in a two-stage case-control study. ADHD symptoms were assessed using the Swanson, Nolan, and Pelham version IV scale and the Integrated Visual and Auditory Continuous Performance Test. In silico analysis was performed with website resources. Results: GRID2 rs1385405 showed a significant association with ADHD risk in the codominant model (OR = 2.208, 95% CI = [1.387, 3.515]) in the first stage and in the codominant model (OR = 1.874, 95% CI = [1.225, 2.869]) and recessive model (OR = 1.906, 95% CI = [1.265, 2.873]) in the second stage and related to inattention and hyperactivity symptom. In addition, rs1385405 disturbed the activity of exonic splicing enhancer and mediated GRID2 gene expression in the frontal cortex. Conclusion: our data provided evidence for the participation of GRID2 variants in conferring the risk of ADHD.

Categorizing SHR and WKY rats by chi2 algorithm and decision tree

Classifying mental disorder is a big issue in psychology in recent years. This article focuses on offering a relation between decision tree and encoding of fMRI that can simplify the analysis of different mental disorders and has a high ROC over 0.9. Here we encode fMRI information to the power-law distribution with integer elements by the graph theory in which the network is characterized by degrees that measure the number of effective links exceeding the threshold of Pearson correlation among voxels. When the degrees are ranked from low to high, the network equation can be fit by the power-law distribution. Here we use the mentally disordered SHR and WKY rats as samples and employ decision tree from chi2 algorithm to classify different states of mental disorder. This method not only provides the decision tree and encoding, but also enables the construction of a transformation matrix that is capable of connecting different metal disorders. Although the latter attempt is still in its fancy, it may have a contribution to unraveling the mystery of psychological processes.

Role of Neuropeptide S on Behavioural and Neurochemical Changes of an Animal Model of Attention-Deficit/Hyperactivity Disorder

Neuropeptide S (NPS) is a recently discovered peptide signalling through its receptor NPSR, which is expressed throughout the brain. Since NPSR activation increases dopaminergic transmission, we now tested if NPSR modulates behavioural and neurochemical alterations displayed by an animal model of attention-deficit/hyperactivity disorder (ADHD), Spontaneous Hypertensive Rats (SHR), compared to its control strain, Wistar Kyoto rats (WKY). NPS (0.1 and 1 nmol, intracerebroventricularly (icv)) did not modify the performance in the open field test in both strains; however, NPSR antagonism with [^tBu-d-Gly⁵]NPS (3 nmol, icv) increased, per se, the total distance travelled by WKY. In the elevated plus-maze, NPS (1 nmol, icv) increased the percentage of entries in the open arms (%EO) only in WKY, an effect prevented by pretreatment with [^tBu-d-Gly⁵]NPS (3 nmol, icv), which decreased per se the %EO in WKY and increased their number of entries in the closed arms. Immunoblotting of frontal cortical extracts showed no differences of NPSR density, although SHR had a lower NPS content than WKY. SHR showed higher activity of dopamine uptake than WKY, and NPS (1 nmol, icv) did not change this profile. Overall, the present work shows that the pattern of functioning of the NPS system is distinct in WKY and SHR, suggesting that this system may contribute to the pathophysiology of ADHD.

Prenatal nicotine exposure in mice induces sex-dependent anxiety-like behavior, cognitive deficits, hyperactivity, and changes in the expression of glutamate receptor associated-genes in the prefrontal cortex

In rodents, prenatal nicotine exposure (PNE) has been associated with increased risk for development of cognitive and emotional disturbances, but the findings are somewhat conflicting. Lack of behavioral alterations following PNE could be due to the variety of methods available for nicotine delivery, exposure time and species used, with inbred strains being mostly employed. Such differences suggest the need to investigate the behavioral phenotype in each PNE model available if we are to find models with enhanced translational value. In this study, we assessed sex-dependent effects of PNE on ADHD-related behaviors and on the levels of mRNA coding for glutamate receptor subunits within the prefrontal cortex in the outbred NMRI mice exposed to nicotine via maternal drinking water during gestation. Cotinine levels were assessed in newborn pups. Behaviors related to anxiety, compulsivity, working memory, and locomotion were evaluated in both sexes of young adult offspring using the elevated zero maze, marble burying, spontaneous alternation behavior, and locomotor activity tests. Expression of mRNA coding for different glutamate receptors subunits within the prefrontal cortex (PFC) was measured using RT-qPCR. Cotinine levels in the serum of newborns confirmed fetal nicotine exposure. Both male and female offspring showed ADHD-like behaviors, such as deficit in the SAB test and hyperactivity. In addition, PNE male mice displayed anxiety- and compulsive-like behaviors, effects that were absent in female offspring. Finally, PNE reduced the mRNA expression of GluN1-, GluN2B-, and mGluR2-related genes within the PFC of male offspring, whereas it reduced the expression of mRNA coding for GluA2 subunit in female mice. PNE in NMRI mice induced sex-dependent behavioral changes, which parallels clinical findings following maternal cigarette smoke exposure. Alterations detected in PFC mRNA glutamate receptor proteins could contribute to the abnormal behavioral responses observed, but other signaling pathways or brain regions are likely involved in the behavioral susceptibility of PNE individuals.

The role of glutamate receptors in attention-deficit/hyperactivity disorder: From physiology to disease

Attention-deficit hyperactivity disorder (ADHD) is the most common psychiatric disorder in children and adolescents, which is characterized by behavioral problems such as attention deficit, hyperactivity, and impulsivity. As the receptors of the major excitatory neurotransmitter in the mammalian central nervous system (CNS), glutamate receptors (GluRs) are strongly linked to normal brain functioning and pathological processes. Extensive investigations have been made about the structure, function, and regulation of GluR family, describing evidences that support the disruption of these mechanisms in mental disorders, including ADHD. In this review, we briefly described the family and function of GluRs in the CNS, and discussed what is recently known about the role of GluRs in ADHD, that including GluR genes, animal models, and the treatment, which would help us further elucidate the etiology of ADHD.

Altered α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor function and expression in hippocampus in a rat model of attention-deficit/hyperactivity disorder (ADHD)

Glutamatergic α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs) carry the bulk of excitatory synaptic transmission. Their modulation plays key roles in synaptic plasticity, which underlies hippocampal learning and memory. A dysfunctional glutamatergic system may negatively affect learning abilities and underlie symptoms of attention-deficit/hyperactivity disorder (ADHD). The aim of this study was to investigate whether the expression and function of AMPARs were altered in ADHD. We recorded AMPAR mediated synaptic transmission at hippocampal excitatory synapses and quantified immunogold labelling density of AMPAR subunits GluA1 and GluA2/3 in a rat model for ADHD; the spontaneously hypertensive rat (SHR). Electrophysiological recordings showed significantly reduced AMPAR mediated synaptic transmission at the CA3-to-CA1 pyramidal cell synapses in stratum radiatum and stratum oriens in SHRs compared to control rats. Electronmicroscopic immunogold quantifications did not show any statistically significant changes in labelling densities of the GluA1 subunit of the AMPAR on dendritic spines in stratum radiatum or in stratum oriens. However, there was a significant increase of the GluA2/3 subunit intracellularly in stratum oriens in SHR compared to control, interpreted as a compensatory effect. The proportion of synapses lacking AMPAR subunit labelling was the same in the two genotypes. In addition, electronmicroscopic examination of tissue morphology showed the density of this type of synapse (i.e., asymmetric synapses on spines), and the average size of the synaptic membranes, to be the same. AMPAR dysfunction, possibly involving molecular changes, in hippocampus may in part reflect altered learning in individuals with ADHD.

Genetic Insights Into ADHD Biology

ADHD is a neurobiological disorder with a large worldwide prevalence causing significant impairment in children, adolescents, and adults. While there is general agreement about genetic contributions toward the disorder, progress in leveraging genetics to learn more about the biology and risk factors for ADHD has been limited. In this perspective, we identified 105 genes from the literature showing at least nominal statistical significance in association with ADHD. We analyzed these genes for enrichment in biological pathways and in known interacting biological networks. We also analyzed the expression patterns of candidate genes across brain regions and across periods of human development. From our analysis, we identify 14 genes that cluster within an interactive gene network, with enrichment in nitric oxide synthase and alpha-1 adrenergic pathways. Furthermore, these genes show enrichment for expression in the cerebellum during childhood through young adulthood, and in the cortex in adolescence and young adulthood. Gene discovery holds great potential for elucidating the unknown biological underpinnings of ADHD. Genome-wide sequencing efforts are underway and are likely to provide important insights that can be leveraged for new treatments and interventions.

l-Carnosine as Adjunctive Therapy in Children and Adolescents with Attention-Deficit/Hyperactivity Disorder: A Randomized, Double-Blind, Placebo-Controlled Clinical Trial

OBJECTIVES

This study aimed to investigate the efficacy and tolerability of l-carnosine as an add-on to methylphenidate in management of children with attention-deficit/hyperactivity disorder (ADHD).

METHODS

This was an 8-week, randomized, double-blind placebo-controlled study. Fifty-six drug-free children and adolescents aged 6-17 years old with a diagnosis of ADHD entered the study. The patients were randomly assigned to l-carnosine (800 mg/d in two divided doses) or placebo plus methylphenidate (0.5-1.5 mg/kg/d) for 8 weeks. Children were assessed using the Teacher and Parent ADHD Rating Scale-IV (ADHD-RS-IV) at baseline and at weeks 4 and 8 postbaseline.

RESULTS

Fifty patients completed the study, and all had two postbaseline measurements. Using the general linear model repeated measures, significant effect was observed for time × treatment interaction on total and inattention subscales of the Parent ADHD-RS (Greenhouse-Geisser corrected: F = 3.783, df = 1.444, p = 0.041 and F = 4.032, df = 1.600, p = 0.030). Improvements in the Teacher ADHD-RS were not significantly different between the two groups in total (Greenhouse-Geisser corrected: F = 0.200, df = 1.218, p = 0.705), as well as inattention and hyperactivity subscale scores (p = 0.956 and 0.281, respectively). The frequency of side effects was not significantly different between the two treatment arms.

CONCLUSIONS

l-carnosine, as a supplementary medication, might be beneficial in treatment of children with ADHD. However, further investigations and different doses of l-carnosine are required to replicate these findings in children with ADHD.

Increased store-operated Ca2+ entry mediated by GNB5 and STIM1

Recent human genetic studies have shown that Gβ5 is related to various clinical symptoms, such as sinus bradycardia, cognitive disability, and attention deficit hyperactivity disorder. Although the calcium signaling cascade is closely associated with a heterotrimeric G-protein, the function of Gβ5 in calcium signaling and its relevance to clinical symptoms remain unknown. In this study, we investigated the in vitro changes of store-operated calcium entry (SOCE) with exogenous expression of Gβ5. The cells expressing Gβ5 had enhanced SOCE after depletion of calcium ion inside the endoplasmic reticulum. Gβ5 also augmented Stim1- and Orai1-dependent SOCE. An ORAI1 loss-of-function mutant did not show inhibition of Gβ5-induced SOCE, and a STIM1-ERM truncation mutant showed no enhancement of SOCE. These results suggested a novel role of GNB5 and Stim1, and provided insight into the regulatory mechanism of SOCE.

Chronic Methylphenidate Alters Tonic and Phasic Glutamate Signaling in the Frontal Cortex of a Freely-Moving Rat Model of ADHD

Glutamate dysfunction has been implicated in a number of substance of abuse studies, including cocaine and methamphetamine. Moreover, in attention-deficit/hyperactivity disorder (ADHD), it has been discovered that when the initiation of stimulant treatment occurs during adolescence, there is an increased risk of developing a substance use disorder later in life. The spontaneously hypertensive rat (SHR) serves as a phenotype for ADHD and studies have found increased cocaine self-administration in adult SHRs when treated with the stimulant methylphenidate (MPH) during adolescence. For this reason, we wanted to examine glutamate signaling in the pre-limbic frontal cortex, a region implicated in ADHD and drug addiction, in the SHR and its progenitor control strain, the Wistar Kyoto (WKY). We chronically implanted glutamate-selective microelectrode arrays (MEAs) into 8-week-old animals and treated with MPH (2 mg/kg, s.c.) for 11 days while measuring tonic and phasic extracellular glutamate concentrations. We observed that intermediate treatment with a clinically relevant dose of MPH increased tonic glutamate levels in the SHR but not the WKY compared to vehicle controls. After chronic treatment, both the SHR and WKY exhibited increased tonic glutamate levels; however, only the SHR was found to have decreased amplitudes of phasic glutamate signaling following chronic MPH administration. The findings from this study suggest that the MPH effects on extracellular glutamate levels in the SHR may potentiate the response for drug abuse later in life. Additionally, these data illuminate a pathway for investigating novel therapies for the treatment of ADHD and suggest that possibly targeting the group II metabotropic glutamate receptors may be a useful therapeutic avenue for adolescents diagnosed with ADHD.

Risk of ADHD After Multiple Exposures to General Anesthesia: A Nationwide Retrospective Cohort Study

OBJECTIVE

To study the association between general anesthesia exposure before age 3 years and having a later ADHD diagnosis.

METHOD

In a birth cohort, data were collected from a nationwide population database for children born between 1997 and 1999 who were exposed to general anesthesia before their third birthday. Age- and gender-matched enrollees without general anesthesia exposure were taken as the comparison. Groups were compared to identify the incidence of ADHD after age 4 and anesthesia-related predictive factors.

RESULTS

Among the 1,146 exposed children, 74 ADHD cases were identified, and 158 ADHD cases were identified in 3,438 matched controls. After adjusting for comorbid conditions and possible confounding factors, if exposure on more than one occasion or ≥3 hr, an increased likelihood of having a later ADHD diagnosis was found (HR, 1.71 and 2.43, respectively).

CONCLUSION

Children with multiple or ≥3 hr general anesthesia exposures before age 3 years have an increased likelihood of a later ADHD diagnosis.

DLGAP1 and NMDA receptor-associated postsynaptic density protein genes influence executive function in attention deficit hyperactivity disorder

Objective

To explore the association of DLGAP1 gene with executive function (EF) in attention deficit hyperactivity disorder (ADHD) children.

Method

A total of 763 ADHD children and 140 healthy controls were enrolled. The difference of EF between ADHD and controls was analyzed using the analysis of covariance (ANCOVA), with IQ, sex, and age as covariates. Both the associations of SNPs with EF and three symptom traits of ADHD were conducted using an additive linear regression model by PLINK with the same covariates as ANCOVA.

Results

Compared with controls, children with ADHD showed poorer cognitive flexibility and inhibition. Two SNPs (rs2049161, p-value = 5.08e-7, adjusted p-value = 1.63e-4, rs16946051, p-value = 5.18e-7, adjusted p-value = 1.66e-4) survived multiple tests in Trail Making Test. Both SNPs also showed association with TOH (rs2049161, p = 6.82e-4, rs16946051, p = 7.91e-4). Set-based analysis for gene DLGAP1 and its functional pathway DLGAP1-DLG4-NMDA showed they were associated with cognitive flexibility at both gene (p = .0057) and pathway level (p = .0321). Furthermore, the gene and pathway also showed association with ADHD symptom score. The associated SNPs and their LD proxies were related to the expression of DLGAP1 in medulla and frontal cortex.

Conclusion

Children with ADHD showed deficit in EF, especially, cognitive flexibility and inhibition. DLGAP1 was associated with cognitive flexibility and plan, and the role of DLGAP1 might be implemented through the complex of DLGAP1-DLG4-NMDA.

Sarcosine treatment for oppositional defiant disorder symptoms of attention deficit hyperactivity disorder children

Methylphenidate, a stimulant that activates dopaminergic and noradrenergic function, is an important agent in the treatment of attention deficit hyperactivity disorder (ADHD). Sarcosine, a glycine transporter-1 inhibitor, may also play a role in treating ADHD by modulating the glutamatergic neurotransmission system through activating N-methyl-D-aspartate type glutamate receptors. This study aimed to assess the efficacy of sarcosine in treating children with ADHD. We conducted a six-week, randomized, double-blind, placebo-controlled clinical trial. The primary outcome measures were those on the Inattention, Hyperactivity/impulsivity, and oppositional defiant disorder (ODD) subscales of the Swanson, Nolan, and Pelham, version IV scale. Efficacy and safety were measured bi-weekly. A total of 116 children with ADHD were enrolled. Among them, 48 (83%) of the 58 sarcosine recipients and 44 (76%) of the 58 placebo recipients returned for the first post-treatment visit. The missing data values were imputed by the last observation carry forward method. From a multiple linear regression analysis, using the generalized estimating equation approach, and an intention to treat analysis, the efficacy of sarcosine marginally surpassed that of placebo at weeks 2, 4, and 6, with p-values=0.01, 0.026, and 0.012, respectively, although only for ODD symptoms. Treatment of ADHD by sarcosine (0.03 g/kg/day) was well tolerated. Sarcosine could possibly be a novel agent for managing ODD symptoms in the context of ADHD. However, future larger-scale studies are warranted to optimize its dosage.

Influence of pharmacological manipulations of NMDA and cholinergic receptors on working versus reference memory in a dual component odor span task

Developed as a tool to assess working memory capacity in rodents, the odor span task (OST) has significant potential to advance drug discovery in animal models of psychiatric disorders. Prior investigations indicate OST performance is impaired by systemic administration of N-methyl-d-aspartate receptor (NMDA-r) antagonists and is sensitive to cholinergic manipulations. The present study sought to determine whether an impairment in OST performance can be produced by systemic administration of the competitive NMDA-r antagonist 3-(2-carboxypiperazin-4-yl)propyl-1-phosphonic acid (CPP; 3, 10, 17 mg/kg i.p.) in a unique dual-component variant of the OST, and whether this impairment is ameliorated by nicotine (0.75 mg/kg i.p.). Male Sprague-Dawley rats were trained to asymptotic level of performance on a 24-trial two-comparison incrementing nonmatching to sample OST. In addition, rats were administered a two-comparison olfactory reference memory (RM) task, which was integrated into the OST. The RM task provided an assessment of the effects of drug administration on global behavioral measures, long-term memory and motivation. Several measures of working memory (span, longest run, and accuracy) were dose dependently impaired by CPP without adversely affecting RM. Analysis of drug effects across trial blocks demonstrated a significant impairment of performance even at low memory loads, suggesting a CPP-induced deficit of olfactory short-term memory that is not load-dependent. Although nicotine did not ameliorate CPP-induced impairments in span or accuracy, it did block the impairment in longest run produced by the 10 mg/kg dose of CPP. Overall, our results indicate that performance in our 24 odor two-comparison OST is capacity dependent and that CPP impaired OST working, but not reference, memory.

Genetic predisposition and early life experience interact to determine glutamate transporter (GLT1) and solute carrier family 12 member 5 (KCC2) levels in rat hippocampus

Attention-deficit/hyperactivity disorder (ADHD) is one of the most common child psychiatric disorders. While it is typically treated with medications that target dopamine and norepinephrine transmission, there is increasing evidence that other neurotransmitter systems, such as glutamate and GABA, may be involved. The aetiology of ADHD is unknown; however, there is evidence that early life stress may contribute to the development of the disorder. In the present study we used proteomic analysis (iTRAQ) followed by sodium dodecyl sulfate polyacrylamide gel electrophoresis and Western blot analysis to investigate hippocampal protein profiles of three rat strains: an animal model of ADHD, spontaneously hypertensive rats (SHR), their control Wistar-Kyoto rats (WKY), and Sprague-Dawley rats (SD). We additionally investigated how these protein profiles are affected by maternal separation, a model of early life stress. Our findings show that solute carrier family 12 member 5 (KCC2) is increased in SHR hippocampus. The glutamate transporter GLT1 splice variant, GLT1b, was increased (proteomic analysis) while total GLT1 (comprised mostly of GLT1a splice variant) was reduced (Western blot analysis) in SHR hippocampus, compared to WKY and SD--a pattern that is consistent with elevated extracellular glutamate levels. Maternal separation increased total GLT1 in hippocampi of SHR, WKY, and SD, and reduced GLT1b in SHR hippocampus. Together these findings provide evidence for disturbed glutamatergic and GABAergic transmission in SHR hippocampus, maternal separation effects on glutamate uptake in hippocampi of all three strains, as well a unique effect of maternal separation on GLT1b levels in SHR hippocampus. These data suggest significant involvement of glutamatergic and GABAergic transmission in the neuropathophysiology of ADHD, and implicates changes in glutamatergic transmission as a result of early life stress.

Glyphosate Use Predicts ADHD Hospital Discharges in the Healthcare Cost and Utilization Project Net (HCUPnet): A Two-Way Fixed-Effects Analysis

There has been considerable international study on the etiology of rising mental disorders, such as attention-deficit hyperactivity disorder (ADHD), in human populations. As glyphosate is the most commonly used herbicide in the world, we sought to test the hypothesis that glyphosate use in agriculture may be a contributing environmental factor to the rise of ADHD in human populations. State estimates for glyphosate use and nitrogen fertilizer use were obtained from the U.S. Geological Survey (USGS). We queried the Healthcare Cost and Utilization Project net (HCUPNET) for state-level hospitalization discharge data in all patients for all-listed ADHD from 2007 to 2010. We used rural-urban continuum codes from the USDA-Economic Research Service when exploring the effect of urbanization on the relationship between herbicide use and ADHD. Least squares dummy variable (LSDV) method and within method using two-way fixed effects was used to elucidate the relationship between glyphosate use and all-listed ADHD hospital discharges. We show that a one kilogram increase in glyphosate use, in particular, in one year significantly positively predicts state-level all-listed ADHD discharges, expressed as a percent of total mental disorders, the following year (coefficient = 5.54E-08, p<.01). A study on the effect of urbanization on the relationship between glyphosate and ADHD indicates that the relationship is marginally significantly positive after multiple comparison correction only in urban U.S. counties (p<.025). Furthermore, total glyphosate use is strongly positively associated with total farm use of nitrogen fertilizers from 1992 to 2006 (p<.001). We present evidence from the biomedical research literature of a plausible link among glyphosate, nitrogen dysbiosis and ADHD. Glyphosate use is a significant predictor of state hospitalizations for all-listed ADHD hospital discharges, with the effect concentrated in urban U.S. counties. This effect is seen even after controlling for individual state characteristics, strong correlations over time, and other significant associations with ADHD in the literature. We draw upon the econometric results to propose unique mechanisms, borrowing principles from soil and atmospheric sciences, for how glyphosate-based herbicides may be contributing to the rise of ADHD in all populations.

Common prefrontal cortical gene expression profiles between adolescent SHR/NCrl and WKY/NCrl rats which showed inattention behavior

Factor analyses of attention-deficit/hyperactivity (ADHD) symptoms divide the behavioral symptoms of ADHD into two separate domains, one reflecting inattention and the other, a combination of hyperactivity and impulsivity. Identifying domain-specific genetic risk variants may aid in the discovery of specific biological risk factors for ADHD. In contrast with data available on genes involved in hyperactivity and impulsivity, there is limited information on the genetic influences of inattention. Transcriptional profiling analysis in animal models of disorders may provide an important tool to identify genetic involvement in behavioral phenotypes. To explore some of the potential genetic underpinnings of ADHD inattention, we examined common differentially expressed genes (DEGs) in the prefrontal cortex of SHR/NCrl, the most validated animal model of ADHD and WKY/NCrl, animal model of ADHD-inattentive type. In contrast with Wistar rats, strain representing the "normal" heterogeneous population, SHR/NCrl and WKY/NCrl showed inattention behavior in the Y-maze task. The common DEGs in the PFC of SHR/NCrl and WKY/NCrl vs. Wistar rats are those involved in transcription (e.g. Creg1, Thrsp, Zeb2), synaptic transmission (e.g. Atp2b2, Syt12, Chrna5), neurological system process (e.g. Atg7, Cacnb4, Grin3a), and immune response (e.g. Atg7, Ip6k2, Mx2). qRT-PCR analyses validated expression patterns of genes representing the major functional gene families among the DEGs (Grin3a, Thrsp, Vof-16 and Zeb2). Although further studies are warranted, the present findings indicate novel genes associated with known functional pathways of relevance to ADHD which are assumed to play important roles in the etiology of ADHD-inattentive subtype.

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

RATIONALE

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

OBJECTIVES

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

RESULTS

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

CONCLUSIONS

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

Behavioral changes following PCB 153 exposure in the spontaneously hypertensive rat - an animal model of Attention-Deficit/Hyperactivity Disorder

Background

Attention-Deficit/Hyperactivity Disorder (ADHD) is a behavioral disorder affecting 3-5% of children. Although ADHD is highly heritable, environmental factors like exposure during early development to various toxic substances like polychlorinated biphenyls (PCBs) may contribute to the prevalence. PCBs are a group of chemical industrial compounds with adverse effects on neurobiological and cognitive functioning, and may produce behavioral impairments that share significant similarities with ADHD. The present study examined the relation between exposure to PCB 153 and changes in ADHD-like behavior in an animal model of ADHD, the spontaneously hypertensive rats (SHR/NCrl), and in Wistar Kyoto (WKY/NHsd) controls.

Methods

SHR/NCrl and WKY/NHsd, males and females, were orally given PCB 153 dissolved in corn oil at around postnatal day (PND) 8, 14, and 20 at a dosage of 1, 3 or 6 mg/kg bodyweight at each exposure. The control groups were orally administered corn oil only. The animals were behaviorally tested for exposure effects from PND 37 to 64 using an operant procedure.

Results

Exposure to PCB 153 was associated with pronounced and long-lasting behavioral changes in SHR/NCrl. Exposure effects in the SHR/NCrl depended on dose, where 1 mg/kg tended to reduce ADHD-like behaviors and produce opposite behavioral effects compared to 3 mg/kg and 6 mg/kg, especially in the females. In the WKY/NHsd controls and for the three doses tested, PCB 153 exposure produced a few specific behavioral changes only in males. The data suggest that PCB 153 exposure interacts with strain and sex, and also indicate a non-linear dose–response relation for the behaviors observed.

Conclusions

Exposure to PCB 153 seems to interact with several variables including strain, sex, dose, and time of testing. To the extent that the present findings can be generalized to humans, exposure effects of PCB 153 on ADHD behavior depends on amount of exposure, where high doses may aggravate ADHD symptoms in genetically vulnerable individuals. In normal controls, exposure may not constitute an environmental risk factor for developing the full range of ADHD symptoms, but can produce specific behavioral changes.

Utilizing Focus Groups with Potential Participants and Their Parents: An Approach to Inform Study Design in a Large Clinical Trial

BACKGROUND

In the recent literature, there has been some evidence that exposure of children to anesthetic procedures during the first two years of life may impair cognitive function and learning in later life. We planned a clinical study to quantify this risk, a study involving testing 1,000 children for neurodevelopmental deficits. As a part of this planning, we conducted focus groups involving potential participants and their parents to elicit information regarding three issues: communications with the community and potential participants, recruitment and consent processes, and the return of neurodevelopmental testing results.

METHODS

Three focus groups were conducted with the parents of potential participants and one focus group was conducted with an 18-19 year old group; each group consisted of 6-10 participants. The moderated discussions had questions about recruitment, consenting issues, and expectations from the study about return of both overall trial findings and individual research test results.

RESULTS

The focus group data gave us an insight on potential participants' views on recruitment, consenting, communications about the study, and expectations about return of both overall trial findings and individual research test results. The concerns expressed were largely addressable. In addition, the concern we had about some parents enrolling their children in the study solely for the sake of getting their child's cognitive function results was dispelled.

CONCLUSIONS

We found that the individuals participating in our focus groups were generally enthusiastic about the large clinical study and could see the value in answering the study question. The data from the focus groups were used to inform changes to the recruitment and consent process. Focus group input was also instrumental in affirming the study design regarding return of results. Our experience suggests that the approach we used may serve as a model for other investigators to help inform the various elements of clinical study design, in particular the recruitment and consenting processes and expectations of potential participants regarding the return of individual research findings.

A translational approach to evaluate the efficacy and safety of the novel AMPA receptor positive allosteric modulator org 26576 in adult attention-deficit/hyperactivity disorder

BACKGROUND

It has been posited that glutamate dysregulation contributes to the pathophysiology of attention-deficit/hyperactivity disorder (ADHD). Modulation of glutamate neurotransmission may provide alternative therapeutic options. The novel 2-amino-3-(5-methyl-3-oxo-1,2-oxazol-4-yl)propanoic acid receptor positive allosteric modulator Org 26576 was investigated with a translational approach including preclinical and clinical testing.

METHODS

Neonatal rat 6-hydroxydopamine lesion-induced hyperactivity was used as preclinical model. Seventy-eight ADHD adults entered a multicenter, double-blind, placebo-controlled, two-period crossover trial. After 1 week placebo lead-in, 67 subjects were randomized into one of four treatment sequences: sequence A (n = 15) Org 26576 (100 mg b.i.d.) for 3 weeks, followed by a 2-week placebo crossover and 3 weeks placebo; sequence B (n = 16) 5 weeks placebo followed by 3 weeks Org 26576 (100 mg b.i.d.); sequence C (n = 18) Org 26576 flexible dose (100-300 mg b.i.d.) for 3 weeks, then 5 weeks placebo; sequence D (n = 18) 5 weeks placebo followed by 3 weeks Org 26576 (100-300 mg b.i.d.). The Adult ADHD Investigator Symptom Rating Scale was used to assess changes in ADHD symptomatology.

RESULTS

Org 26576 (1, 3, 10 mg/kg intraperitoneal) produced dose-dependent inhibition of locomotor hyperactivity in 6-hydroxydopamine-lesioned rats. Org 26576 (100 mg b.i.d.) was superior to placebo in treating symptoms of adult ADHD subjects. The primary Adult ADHD Investigator Symptom Rating Scale results were supported by some secondary analyses. However, Org 26576 (100-300 mg b.i.d.) did not confirm these results. Most frequently reported adverse events were nausea, dizziness, and headache.

CONCLUSIONS

These preclinical and clinical findings suggest that Org 25676 may have utility in the treatment of ADHD.

The role of memantine in the treatment of psychiatric disorders other than the dementias: a review of current preclinical and clinical evidence

Memantine, a non-competitive NMDA receptor antagonist approved for Alzheimer's disease with a good safety profile, is increasingly being studied in a variety of non-dementia psychiatric disorders. We aimed to critically review relevant literature on the use of the drug in such disorders. We performed a PubMed search of the effects of memantine in animal models of psychiatric disorders and its effects in human studies of specific psychiatric disorders. The bulk of the data relates to the effects of memantine in major depressive disorder and schizophrenia, although more recent studies have provided data on the use of the drug in bipolar disorder as an add-on. Despite interesting preclinical data, results in major depression are not encouraging. Animal studies investigating the possible usefulness of memantine in schizophrenia are controversial; however, interesting findings were obtained in open studies of schizophrenia, but negative placebo-controlled, double-blind studies cast doubt on their validity. The effects of memantine in anxiety disorders have been poorly investigated, but data indicate that the use of the drug in obsessive-compulsive disorder and post-traumatic stress disorder holds promise, while findings relating to generalized anxiety disorder are rather disappointing. Results in eating disorders, catatonia, impulse control disorders (pathological gambling), substance and alcohol abuse/dependence, and attention-deficit hyperactivity disorder are inconclusive. In most psychiatric non-Alzheimer's disease conditions, the clinical data fail to support the usefulness of memantine as monotherapy or add-on treatment However, recent preclinical and clinical findings suggest that add-on memantine may show antimanic and mood-stabilizing effects in treatment-resistant bipolar disorder.

ADHD: current and future therapeutics

The stimulants, amphetamine and methylphenidate, have long been the mainstay of attention-deficit hyperactivity disorder (ADHD) therapy. They are rapidly effective and are generally the first medications selected by physicians. In the development of alternative pharmacological approaches, drug candidates have been evaluated with a wide diversity of mechanisms. All of these developments have contributed real progress in the field, but there is still much room for improvement and unmet clinical need in ADHD pharmacotherapy. The availability of a wide range of compounds with a high degree of specificity for individual monoamines (dopamine and noradrenaline) and/or different pharmacological mechanisms has refined our understanding of the essential elements for optimum pharmacological effect in managing ADHD. In this chapter, we review the pharmacology of the different classes of drug used to treat ADHD and provide a neurochemical rationale, predominantly from the use of in vivo microdialysis experiments, to explain their relative efficacy and potential to elicit side effects. In addition, we will consider how predictions based on results from animal models translate into clinical outcomes. The treatment of ADHD is also described from the perspective of the physician. Finally, the new research development for drugs to treat ADHD is discussed.

Forebrain NR2B overexpression facilitating the prefrontal cortex long-term potentiation and enhancing working memory function in mice

Prefrontal cortex plays an important role in working memory, attention regulation and behavioral inhibition. Its functions are associated with NMDA receptors. However, there is little information regarding the roles of NMDA receptor NR2B subunit in prefrontal cortical synaptic plasticity and prefrontal cortex-related working memory. Whether the up-regulation of NR2B subunit influences prefrontal cortical synaptic plasticity and working memory is not yet clear. In the present study, we measured prefrontal cortical synaptic plasticity and working memory function in NR2B overexpressing transgenic mice. In vitro electrophysiological data showed that overexpression of NR2B specifically in the forebrain region resulted in enhancement of prefrontal cortical long-term potentiation (LTP) but did not alter long-term depression (LTD). The enhanced LTP was completely abolished by a NR2B subunit selective antagonist, Ro25-6981, indicating that overexpression of NR2B subunit is responsible for enhanced LTP. In addition, NR2B transgenic mice exhibited better performance in a set of working memory paradigms including delay no-match-to-place T-maze, working memory version of water maze and odor span task. Our study provides evidence that NR2B subunit of NMDA receptor in prefrontal cortex is critical for prefrontal cortex LTP and prefrontal cortex-related working memory.

Overview of animal models of attention deficit hyperactivity disorder (ADHD)

Attention-deficit/hyperactivity disorder (ADHD) is a heterogeneous, highly heritable, behavioral disorder that affects ∼5% to 10% of children worldwide. Although animal models cannot truly reflect human psychiatric disorders, they can provide insight into the disorder that cannot be obtained from human studies because of the limitations of available techniques. Genetic models include the spontaneously hypertensive rat (SHR), the Naples High Excitability (NHE) rat, poor performers in the 5-choice serial reaction time (5-CSRT) task, the dopamine transporter (DAT) knock-out mouse, the SNAP-25 deficient mutant coloboma mouse, mice expressing a human mutant thyroid hormone receptor, a nicotinic receptor knock-out mouse, and a tachykinin-1 (NK1) receptor knock-out mouse. Chemically induced models of ADHD include prenatal or early postnatal exposure to ethanol, nicotine, polychlorinated biphenyls, or 6-hydroxydopamine (6-OHDA). Environmentally induced models have also been suggested; these include neonatal anoxia and rat pups reared in social isolation. The major insight provided by animal models was the consistency of findings regarding the involvement of dopaminergic, noradrenergic, and sometimes also serotonergic systems, as well as more fundamental defects in neurotransmission.

Cortical and hippocampal EEG effects of neurotransmitter agonists in spontaneously hypertensive vs. kainate-treated rats

To analyze mediatory mechanisms underlying attention-deficit hyperactivity disorder (ADHD) and their association with epilepsy, the electroencephalogram (EEG) responses to various centrally applied neurotransmitter agonists were studied in spontaneously hypertensive (SH), kainate-treated (KA), and normotensive (control) rats, with chronically implanted electrodes into the frontal cortex and hippocampus and a cannula into the lateral cerebral ventricle. In SH rats, the baseline EEG showed increased delta and beta2 activity in the hippocampus and decreased alpha/beta1 activity in both brain areas. In KA rats, these delta and alpha/beta1 effects were observed 2 weeks post-kainate, while the beta2 activity increase occurred after 5 weeks in the hippocampus and, to a greater extent, 9 weeks post-injection in both brain areas. In SH rats, NMDA increased delta and decreased alpha/beta1 activity, similar to KA rats 5 weeks post-injection. In SH rats, clonidine augmented theta/beta2 increase in the cortex and alpha suppression in both brain areas, in parallel with induction of beta2 activity in the hippocampus. These beta2 effects were observed 5 and 9 weeks post-kainate. In SH rats, baclofen produced robust delta/theta enhancement and alpha/beta1 suppression in both brain areas, with additional beta2 activity increase in the hippocampus, while muscimol was ineffective in both groups of rats. In KA rats, EEG responses to GABA agonists were similar to those in control. Our results demonstrate sensitization of NMDA receptors and α2-adrenoceptors both in SH and KA rats and that of GABAb receptors specifically in SH rats.

Investigation of post-transcriptional gene regulatory networks associated with autism spectrum disorders by microRNA expression profiling of lymphoblastoid cell lines

Background

Autism spectrum disorders (ASD) are neurodevelopmental disorders characterized by abnormalities in reciprocal social interactions and language development and/or usage, and by restricted interests and repetitive behaviors. Differential gene expression of neurologically relevant genes in lymphoblastoid cell lines from monozygotic twins discordant in diagnosis or severity of autism suggested that epigenetic factors such as DNA methylation or microRNAs (miRNAs) may be involved in ASD.

Methods

Global miRNA expression profiling using lymphoblasts derived from these autistic twins and unaffected sibling controls was therefore performed using high-throughput miRNA microarray analysis. Selected differentially expressed miRNAs were confirmed by quantitative reverse transcription-polymerase chain reaction (qRT-PCR) analysis, and the putative target genes of two of the confirmed miRNA were validated by knockdown and overexpression of the respective miRNAs.

Results

Differentially expressed miRNAs were found to target genes highly involved in neurological functions and disorders in addition to genes involved in gastrointestinal diseases, circadian rhythm signaling, as well as steroid hormone metabolism and receptor signaling. Novel network analyses of the putative target genes that were inversely expressed relative to the relevant miRNA in these same samples further revealed an association with ASD and other co-morbid disorders, including muscle and gastrointestinal diseases, as well as with biological functions implicated in ASD, such as memory and synaptic plasticity. Putative gene targets (ID3 and PLK2) of two RT-PCR-confirmed brain-specific miRNAs (hsa-miR-29b and hsa-miR-219-5p) were validated by miRNA overexpression or knockdown assays, respectively. Comparisons of these mRNA and miRNA expression levels between discordant twins and between case-control sib pairs show an inverse relationship, further suggesting that ID3 and PLK2 are in vivo targets of the respective miRNA. Interestingly, the up-regulation of miR-23a and down-regulation of miR-106b in this study reflected miRNA changes previously reported in post-mortem autistic cerebellum by Abu-Elneel et al. in 2008. This finding validates these differentially expressed miRNAs in neurological tissue from a different cohort as well as supports the use of the lymphoblasts as a surrogate to study miRNA expression in ASD.

Conclusions

Findings from this study strongly suggest that dysregulation of miRNA expression contributes to the observed alterations in gene expression and, in turn, may lead to the pathophysiological conditions underlying autism.

Region-specific alteration in brain glutamate: possible relationship to risk-taking behavior

Risk-taking behaviors involve increased motor activity and reduced anxiety in humans. Total sleep deprivation (SD) in animals produces a similar change in motor and fear behaviors. Investigators studied region-specific brain levels of glutamate in rats after TSD, an animal model of risk-taking behavior. We investigated the effects of sleep deprivation on these behaviors and associated levels of brain glutamate. Compared to the controls, the sleep-deprived rats spent a significantly greater percentage of time in the open arms of the elevated plus maze (EPM), demonstrating reduced fear-like and increased risk-taking behaviors. Additionally, sleep deprivation was associated with a significant increase in glutamate levels in the hippocampus and thalamus. An inverse relationship between glutamate in the medial prefrontal cortex and risk taking in the EPM and a positive association between the ratio of glutamate in the hippocampus to medial prefrontal cortex and risk taking was revealed. The role of sleep deprivation-induced changes in brain glutamate and its relationship to anxiety, fear, and posttraumatic stress disorder (PTSD) is discussed.

Excitatory amino acids in the forebrain of the Naples high-excitability rats: neurochemical and behavioural effects of subchronic D-aspartate and its diethyl ester prodrug

The excitatory amino acids (EAA) L-glutamate (L-Glu), L-aspartate (L-Asp) and D-aspartate (D-Asp) are thought to play a neurotransmitter/neuromodulator role in neuronal communications. Recently, a high level of EAA L-Glu, D- and L-Asp isomers has been found in the forebrain of Naples high-excitability (NHE) rat line that models the mesocortical variant of Attention-Deficit Hyperactivity Disorder (ADHD). The aim of this study was to assess the functions of D-Asp using two forms, i.e. free D-Asp or D-Asp diethyl ester (DEE) as prodrug, on brain and behaviour. Thus, prepuberal rats were given, for two weeks daily, an i.p. injection of D-Asp or DEE or vehicle. Then rats were exposed to two spatial novelties i.e. Làt and radial Olton maze. Behaviour was monitored for indices of activity, non-selective attention (NSA), selective spatial attention (SSA) and emotional reactivity. L-Glu and D- and L-Asp were detected by HPLC in cognitive and non-cognitive brain areas such as prefrontal cortex, striatum, hippocampus and hypothalamus. Results indicate that subchronic D-Asp or DEE (i) reduced EAA levels in the NHE and increased it in the random-bred controls (NRB) rats, (ii) in the Làt-maze D-Asp increased horizontal activity in NHE but DEE decreased it in NRB rats, (iii) in the Olton maze D-Asp and DEE decreased vertical activity in NHE and NRB rats respectively, (iv) D-Asp impaired attention only in NRB decreasing number of arms visited before first repetition. Therefore, data demonstrate differential effects of prepuberal subchronic D-Asp and DEE that may be related to different basal EAA levels in NHE and NRB rats.

MicroRNA-219 modulates NMDA receptor-mediated neurobehavioral dysfunction

N-methyl-D-aspartate (NMDA) glutamate receptors are regulators of fast neurotransmission and synaptic plasticity in the brain. Disruption of NMDA-mediated glutamate signaling has been linked to behavioral deficits displayed in psychiatric disorders such as schizophrenia. Recently, noncoding RNA molecules such as microRNAs (miRNAs) have emerged as critical regulators of neuronal functions. Here we show that pharmacological (dizocilpine) or genetic (NR1 hypomorphism) disruption of NMDA receptor signaling reduces levels of a brain-specific miRNA, miR-219, in the prefrontal cortex (PFC) of mice. Consistent with a role for miR-219 in NMDA receptor signaling, we identify calcium/calmodulin-dependent protein kinase II gamma subunit (CaMKIIgamma), a component of the NMDA receptor signaling cascade, as a target of miR-219. In vivo inhibition of miR-219 by specific antimiR in the murine brain significantly modulated behavioral responses associated with disrupted NMDA receptor transmission. Furthermore, pretreatment with the antipsychotic drugs haloperidol and clozapine prevented dizocilpine-induced effects on miR-219. Taken together, these data support an integral role for miR-219 in the expression of behavioral aberrations associated with NMDA receptor hypofunction.

Effects of methylphenidate and bupropion on DHEA-S and cortisol plasma levels in attention-deficit hyperactivity disorder

We evaluated plasma levels of DHEA-S and cortisol before and after treating ADHD patients with one of two medications: methylphenidate (n = 12) or bupropion (n = 10). Boys with ADHD (combined type) were evaluated with the Korean ADHD rating scale (K-ARS) and the computerized ADHD diagnostic system (ADS). All assessments were measured at baseline and repeated after 12 weeks. There were significant clinical improvements in both treatment groups as measured by K-ARS and ADS. DHEA-S levels increased from baseline to endpoint, but cortisol levels did not change significantly. This study suggests that both methylphenidate and bupropion increase plasma levels of DHEA-S in boys with ADHD.

N-methyl-D-aspartate receptor subunit dysfunction at hippocampal glutamatergic synapses in an animal model of attention-deficit/hyperactivity disorder

Attention-deficit/hyperactivity disorder (ADHD) is the most common neurobehavioural disorder among children. ADHD children are hyperactive, impulsive and have problems with sustained attention. These cardinal features are also present in the best validated animal model of ADHD, the spontaneously hypertensive rat (SHR), which is derived from the Wistar Kyoto rat (WKY). Current theories of ADHD relate symptom development to factors that alter learning. N-methyl-D-aspartate receptor (NMDAR) dependent long term changes in synaptic efficacy in the mammalian CNS are thought to represent underlying cellular mechanisms for some forms of learning. We therefore hypothesized that synaptic abnormality in excitatory, glutamatergic synaptic transmission might contribute to the altered behavior in SHRs. We studied physiological and anatomical aspects of hippocampal CA3-to-CA1 synapses in age-matched SHR and WKY (controls). Electrophysiological analysis of these synapses showed reduced synaptic transmission (reduced field excitatory postsynaptic potential for a defined fiber volley size) in SHR, whereas short-term forms of synaptic plasticity, like paired-pulse facilitation, frequency facilitation, and delayed response enhancement were comparable in the two genotypes, and long-term potentiation (LTP) of synaptic transmission was of similar magnitude. However, LTP in SHR was significantly reduced (by 50%) by the NR2B specific blocker CP-101,606 (10 microM), whereas the blocker had no effect on LTP magnitude in the control rats. This indicates that the SHR has a functional predominance of NR2B, a feature characteristic of early developmental stages in these synapses. Quantitative immunofluorescence and electron microscopic postembedding immunogold cytochemistry of the three major NMDAR subunits (NR1, NR2A; and NR2B) in stratum radiatum spine synapses revealed no differences between SHR and WKY. The results indicate that functional impairments in glutamatergic synaptic transmission may be one of the underlying mechanisms leading to the abnormal behavior in SHR, and possibly in human ADHD.

Reduced cingulate glutamate/glutamine-to-creatine ratios in adult patients with attention deficit/hyperactivity disorder -- a magnet resonance spectroscopy study

BACKGROUND

The dopaminergic system is thought to be essentially involved in the pathogenesis of attention deficit/hyperactivity disorder (ADHD). However, there is also evidence for abnormalities in the glutamatergic system and recent theories focus on a disturbed interaction between the two systems as the essential pathogenetic mechanism of ADHD. In the present study, we wanted to test the hypothesis that prefrontal glutamate signals indirectly indicate dopaminergic dysfunction in adult patients with ADHD.

METHODS

Twenty-eight adult patients with ADHD and 28 group-matched healthy volunteers were studied clinically and using chemical-shift MR spectroscopy (MRS) of the prefrontal cortex covering the anterior cingulate gyrus.

RESULTS

A significant reduction of the combined glutamate/glutamine to creatine ratio in the right anterior cingulate cortex in patients with ADHD was found.

DISCUSSION

Glutamatergic alterations as measured with MRS might play a role in the pathogenesis of adult patients with ADHD.

Sub-neurotoxic neonatal anoxia induces subtle behavioural changes and specific abnormalities in brain group-I metabotropic glutamate receptors in rats

Anoxia in the first week of life can induce neuronal death in vulnerable brain regions usually associated with an impairment of cognitive function that can be detected later in life. We set-up a model of subneurotoxic anoxia based on repeated exposures to 100% nitrogen during the first 7 days of post-natal life. This mild post-natal exposure to anoxia specifically modified the behaviour of the male adult rats, which showed an attention deficit and an increase in anxiety, without any impairment in spatial learning and any detectable brain damage (magnetic resonance imaging and histological analysis). Post-anoxic rats showed a reduction in the expression of group-I metabotropic glutamate receptors (i.e. mGlu1 and mGlu5 receptors) in the hippocampus and cerebral cortex, whereas expression of the mGlu 2/3 receptors, the NR1 subunit of NMDA receptors, and the GluR1 subunit of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) receptors was unchanged. mGlu1 and mGlu5 receptor signalling was also impaired in postanoxic rats, as revealed by a reduced efficacy of the agonist (1S,3R)-1-Aminocyclopentane-1,3-dicarboxylic acid (1S,3R-ACPD) to stimulate polyphosphoinositide hydrolysis in hippocampal slices. We conclude that rats subjected to subneurotoxic doses of anoxia during the early post-natal life develop behavioural symptoms that are frequently encountered in the inattentive subtype of the attention deficit hyperactivity disorder, and that group-I mGlu receptors may be involved in the pathophysiology of these symptoms.

Animal models of attention-deficit hyperactivity disorder

Although animals cannot be used to study complex human behaviour such as language, they do have similar basic functions. In fact, human disorders that have animal models are better understood than disorders that do not. ADHD is a heterogeneous disorder. The relatively simple nervous systems of rodent models have enabled identification of neurobiological changes that underlie certain aspects of ADHD behaviour. Several animal models of ADHD suggest that the dopaminergic system is functionally impaired. Some animal models have decreased extracellular dopamine concentrations and upregulated postsynaptic dopamine D1 receptors (DRD1) while others have increased extracellular dopamine concentrations. In the latter case, dopamine pathways are suggested to be hyperactive. However, stimulus-evoked release of dopamine is often decreased in these models, which is consistent with impaired dopamine transmission. It is possible that the behavioural characteristics of ADHD result from impaired dopamine modulation of neurotransmission in cortico-striato-thalamo-cortical circuits. There is considerable evidence to suggest that the noradrenergic system is poorly controlled by hypofunctional α₂-autoreceptors in some models, giving rise to inappropriately increased release of norepinephrine. Aspects of ADHD behaviour may result from an imbalance between increased noradrenergic and decreased dopaminergic regulation of neural circuits that involve the prefrontal cortex. Animal models of ADHD also suggest that neural circuits may be altered in the brains of children with ADHD. It is therefore of particular importance to study animal models of the disorder and not normal animals. Evidence obtained from animal models suggests that psychostimulants may not be acting on the dopamine transporter to produce the expected increase in extracellular dopamine concentration in ADHD. There is evidence to suggest that psychostimulants may decrease motor activity by increasing serotonin levels. In addition to providing unique insights into the neurobiology of ADHD, animal models are also being used to test new drugs that can be used to alleviate the symptoms of ADHD.

A family based study implicates solute carrier family 1-member 3 (SLC1A3) gene in attention-deficit/hyperactivity disorder

BACKGROUND

The glutamatergic system, the major excitatory neurotransmitter system in the central nervous system (CNS) has been proposed as contributing a possible role in the etiology of attention deficit hyperactivity disorder (ADHD). This is based upon observations from animal, neuroimaging, neuroanatomical and neuropsychological studies. Genes related to glutamate function are therefore good functional candidates for this disorder. The SLC1A3 (Solute Carrier Family 1, member 3) gene encodes a glial glutamate transporter which maps to chromosome 5p12, a region of linkage that coincides in two published ADHD genome scans so far. SLC1A3 is thus both a functional and positional candidate gene for ADHD.

METHODS

We have undertaken detailed association analysis of SLC1A3 using a multi-stage approach for candidate gene analysis.

RESULTS

In a family-based sample (n = 299) we found a significant association between marker rs2269272 (p = .007) and ADHD. Two, two-marker haplotypes, rs2269272/rs3776581 (p = .016) and rs2269272/rs2032893 (p = .013) also yielded evidence of association.

CONCLUSIONS

The results of our study suggest that genetic variation in SLC1A3 may contribute to susceptibility to ADHD.

Rodent models of attention-deficit/hyperactivity disorder

An ideal animal model should be similar to the disorder it models in terms of etiology, biochemistry, symptomatology, and treatment. Animal models provide several advantages over clinical research: simpler nervous systems, easily interpreted behaviors, genetic homogeneity, easily controlled environment, and a greater variety of interventions. Attention-deficit/hyperactivity disorder (ADHD) is a neurobehavioral disorder of childhood onset that is characterized by inattentiveness, hyperactivity, and impulsiveness. Its diagnosis is behaviorally based; therefore, the validation of an ADHD model must be based in behavior. An ADHD model must mimic the fundamental behavioral characteristics of ADHD (face validity), conform to a theoretical rationale for ADHD (construct validity), and predict aspects of ADHD behavior, genetics, and neurobiology previously uncharted in clinical settings (predictive validity). Spontaneously hypertensive rats (SHR) fulfill many of the validation criteria and compare well with clinical cases of ADHD. Poor performers in the five-choice serial reaction time task and Naples high-excitability rats (NHE) are useful models for attention-deficit disorder. Other animal models either focus on the less important symptom of hyperactivity and might be of limited value in ADHD research or are produced in ways that would not lead to a clinical diagnosis of ADHD in humans, even if ADHD-like behavior is displayed.