Glutamate-stimulated release of norepinephrine in hippocampal slices of animal models of attention-deficit/hyperactivity disorder (spontaneously hypertensive rat) and depression/anxiety-like behaviours (Wistar–Kyoto rat)

Safety, Tolerability and Pharmacokinetic Profile of the Low-Impact Ampakine CX717 in Young Healthy Male Subjects and Elderly Healthy Male and Female Subjects

Ampakines, AMPA-type glutamate receptors (AMPAR) positive allosteric modulators, possess the capacity to treat neurological and neuropsychiatric disorders underpinned by deficient excitatory synaptic communication. Low-impact ampakines partially offset AMPAR desensitization which may explain their lack of epileptogenic effects and acceptable safety margins in preclinical studies. The low-impact ampakine CX717 has shown efficacy in prior preclinical studies and the ability to prevent opiate-induced respiratory depression in humans. The current clinical study examines the tolerability and pharmacokinetics of CX717 in healthy male subjects and elderly male and female subjects in a four-part study. Part A was a single dose escalation study (25-1600 mg, 72 subjects). Part B was a two-period food effect crossover study (100 mg, 8 subjects). Part C was a multiple dose escalation study (100 mg QD - 800 mg BID, 10 days, 32 subjects), and Part D was a multiple dose study of CX717 (300 mg QD, 10 days, 7 males and 8 females) in elderly subjects. CX717 was well tolerated up to 1600 mg and 800 mg BID. CX717 was also well tolerated when fed or fasted and was well tolerated in the elderly with prominent side effects being headache, dizziness and nausea. The half-life of CX717 was 8-12 h, and Tmax was 3-5 h. Cmax and AUC were dose-proportional. These findings provide key dosing and safety pharmacology data that can be used to inform further investigations of CX717 in subsequent clinical studies such as ADHD, opiate-induced respiratory depression and spinal cord injury.

Hydrogen sulfide mitigates memory impairments via the restoration of glutamatergic neurons in a mouse model of hemorrhage shock and resuscitation

Impaired long-term memory, a complication of traumatic stress including hemorrhage shock and resuscitation (HSR), has been reported to be associated with multiple neurodegenerations. The ventral tegmental area (VTA) participates in both learned appetitive and aversive behaviors. In addition to being prospective targets for the therapy of addiction, depression, and other stress-related diseases, VTA glutamatergic neurons are becoming more widely acknowledged as powerful regulators of reward and aversion. This study revealed that HSR exposure induces memory impairments and decreases the activation in glutamatergic neurons, and decreased β power in the VTA. We also found that optogenetic activation of glutamatergic neurons in the VTA mitigated HSR-induced memory impairments, and restored β power. Moreover, hydrogen sulfide (H2S), a gasotransmitter with pleiotropic roles, has neuroprotective functions at physiological concentrations. In vivo, H2S administration improved HSR-induced memory deficits, elevated c-fos-positive vesicular glutamate transporters (Vglut2) neurons, increased β power, and restored the balance of γ-aminobutyric acid (GABA) and glutamate in the VTA. This work suggests that glutamatergic neuron stimulation via optogenetic assay and exogenous H2S may be useful therapeutic approaches for improving memory deficits following HSR.

Restoration of norepinephrine release, cognitive performance, and dendritic spines by amphetamine in aged rat brain

Age-related dysfunctions in specific neurotransmitter systems likely play an important role in cognitive decline even in its most subtle forms. Therefore, preservation or improvement of cognition via augmentation of neurotransmission is a potential therapeutic strategy to prevent further cognitive deficits. Here we identified a particular neuronal vulnerability in the aged Fischer 344 rat brain, an animal model of neurocognitive aging. Specifically, we demonstrated a marked impairment in glutamate-stimulated release of norepinephrine (NE) in the hippocampus and cerebral cortex of aged rats, and established that this release was mediated by N-methyl-D-aspartate (NMDA) receptors. Further, we also demonstrated that this decrease in NE release is fully rescued by the psychostimulant drug amphetamine (AMPH). Moreover, we showed that AMPH increases dendritic spine maturation, and importantly shows preclinical efficacy in restoring memory deficits in the aged rat through its actions to potentiate NE neurotransmission at β-adrenergic receptors. Taken together, our results suggest that deficits in glutamate-stimulated release of NE may contribute to and possibly be a determinant of neuronal vulnerability underlying cognitive decline during aging, and that these deficits can be corrected with currently available drugs. Overall these studies suggest that repurposing of psychostimulants for age-associated cognitive deficits is a potential avenue to delay or prevent cognitive decline and/or frank dementia later in life.

Integrating transcriptomics and metabolomics to analyze the mechanism of hypertension-induced hippocampal injury

Objective

Hypertension is a public health challenge worldwide due to its high prevalence and multiple complications. Hypertension-induced damage to the hippocampus leads to behavioral changes and various brain diseases. Despite the multifaceted effects of hypertension on the hippocampus, the mechanisms underlying hippocampal lesions are still unclear.

Methods

The 32-week-old spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats were selected as the study subjects. Behavioral experiments such as an open field test (OFT), an elevated plus maze (EPM) test, and the Morris water maze (MWM) test were performed to show the behavioral characteristics of the rats. A comprehensive transcriptomic and metabolomic analysis was performed to understand the changes in the hippocampus at the metabolic and genetic levels.

Results

Behavioral tests showed that, compared to WKY rats, SHR showed not only reduced memory capacity but more hyperactive and impulsive behavior. In addition, transcriptomic analysis screened for 103 differentially expressed genes. Metabolomic analysis screened 56 metabolites with significant differences, including various amino acids and their related metabolites.

Conclusion

Comprehensive analysis showed that hypertension-induced hippocampal lesions are closely associated with differential metabolites and differential genes detected in this study. The results provide a basis for analyzing the mechanisms of hypertension-induced hippocampal damage.

Neuroplasticity to autophagy cross-talk in a therapeutic effect of physical exercises and irisin in ADHD

Adaptive neuroplasticity is a pivotal mechanism for healthy brain development and maintenance, as well as its restoration in disease- and age-associated decline. Management of mental disorders such as attention deficit hyperactivity disorder (ADHD) needs interventions stimulating adaptive neuroplasticity, beyond conventional psychopharmacological treatments. Physical exercises are proposed for the management of ADHD, and also depression and aging because of evoked brain neuroplasticity. Recent progress in understanding the mechanisms of muscle-brain cross-talk pinpoints the role of the myokine irisin in the mediation of pro-cognitive and antidepressant activity of physical exercises. In this review, we discuss how irisin, which is released in the periphery as well as derived from brain cells, may interact with the mechanisms of cellular autophagy to provide protein recycling and regulation of brain-derived neurotrophic factor (BDNF) signaling via glia-mediated control of BDNF maturation, and, therefore, support neuroplasticity. We propose that the neuroplasticity associated with physical exercises is mediated in part by irisin-triggered autophagy. Since the recent findings give objectives to consider autophagy-stimulating intervention as a prerequisite for successful therapy of psychiatric disorders, irisin appears as a prototypic molecule that can activate autophagy with therapeutic goals.

Behavioral and neuroreceptor effects of the racetam derivative GIZh-290 in mouse experimental attention deficit model

Behavioral and neurochemical effects of the new racetam derivative GIZh-290 were studied in a mouse attention deficit model (the ED-Low animals subpopulation selected during preliminary behavioral typing in the “closed enriched cross maze” test). Subchronic administration of GIZh-290 (1 mg/kg, 3 mg/kg and 5 mg/kg, intraperitoneally, for 6 days), increased the initially low level of attention in ED-Low animals; the highest selectivity was observed at a dose of 3 mg/kg. Radioligand analysis showed that at this dose, the drug changed density (Bmax) of D2 and GABAB receptors as markers in the pre-frontal cortex of the ED-Low subpopulation to Bmax values observed in the ED-High subpopulation. In the prefrontal cortex of the ED-Low rodents treated with GIZh-290 in dose of 3 mg/kg, there was a normalization of tissue concentrations of both dopamine itself (DA) and its intra- and extracellular metabolites (DOPA/DA and HVA/DA). The obtained results indicate the effectiveness of the studied drug for pharmacotherapy of attention deficit in experimental modeling and impact on potential molecular targets identified in the study.

Curcumin for attention-deficit-hyperactivity disorder: a systematic review and preliminary behavioral investigation

Curcumin has protective actions in neuropsychiatric disorders, acting as a neuroprotective agent. As a first approach, the study aimed at a systematic review of the potential effects of curcumin on cognitive performance for attention-deficit-hyperactivity disorder (ADHD). This research was carried out in the databases of PubMed, Embase, SciELO, the Cochrane Central Register of Controlled Trials (CENTRAL), the Web of Science, and the Grey literature. Upon discovering the scarcity of relevant studies, and knowing that curcumin might have an ADHD hyperactive and anxious behavior, the study proposed to evaluate the effects of curcumin in an ADHD phenotype of spontaneously hypertensive Wistar rats (SHR). No studies were found that related to curcumin and ADHD. Fifteen SHRs were then divided into separate groups that received water (1 mg/kg/day), curcumin (50 mg/kg/day), or methylphenidate (1 mg/kg/day) for 42 days. Behavioral tests to assess activity (Open Field Test), anxiety and impulsivity (Elevated Plus-Maze, and Social Interaction), and memory (Y-Maze, and the Object Recognition Test) were all performed. The animals that were treated with curcumin showed less anxious and hyperactive behavior, as seen in the Open Field Test and the Social Interaction Test. Anxious behavior was measured by the EPM and was not modulated by any treatment. The results of the Y-Maze Test demonstrated that curcumin improved spatial memory. In the Object Recognition Test, neither the short nor the long-term memory was improved. The treatments that were used in this study beneficially modulated the anxious and hyperactive behavior of the SHR.

Astrocytes Render Memory Flexible by Releasing D-Serine and Regulating NMDA Receptor Tone in the Hippocampus

BACKGROUND

NMDA receptor (NMDAR) hypofunction has been implicated in several psychiatric disorders with impairment of cognitive flexibility. However, the molecular mechanism of how NMDAR hypofunction with decreased NMDAR tone causes the impairment of cognitive flexibility has been minimally understood. Furthermore, it has been unclear whether hippocampal astrocytes regulate NMDAR tone and cognitive flexibility.

METHODS

We employed cell type-specific genetic manipulations, ex vivo electrophysiological recordings, sniffer patch recordings, cutting-edge biosensor for norepinephrine, and behavioral assays to investigate whether astrocytes can regulate NMDAR tone by releasing D-serine and glutamate. Subsequently, we further investigated the role of NMDAR tone in heterosynaptic long-term depression, metaplasticity, and cognitive flexibility.

RESULTS

We found that hippocampal astrocytes regulate NMDAR tone via BEST1-mediated corelease of D-serine and glutamate. Best1 knockout mice exhibited reduced NMDAR tone and impairments of homosynaptic and α₁ adrenergic receptor-dependent heterosynaptic long-term depression, which leads to defects in metaplasticity and cognitive flexibility. These impairments in Best1 knockout mice can be rescued by hippocampal astrocyte-specific BEST1 expression or enhanced NMDAR tone through D-serine supplement. D-serine injection in Best1 knockout mice during initial learning rescues subsequent reversal learning.

CONCLUSIONS

These findings indicate that NMDAR tone during initial learning is important for subsequent learning, and hippocampal NMDAR tone regulated by astrocytic BEST1 is critical for heterosynaptic long-term depression, metaplasticity, and cognitive flexibility.

A Comparison of Methylphenidate (MPH) and Combined Methylphenidate with Crocus sativus (Saffron) in the Treatment of Children and Adolescents with ADHD: A Randomized, Double-blind, Parallel-Group, Clinical Trial

Background: Attention-deficit/hyperactivity disorder (ADHD) is characterized by behavioral and neurodevelopmental problems. It is estimated that 3 - 7% of children and adolescents suffer from this problem. Apart from synthetic drugs, other effective types of medication like herbal medicines are of great importance. Objectives: This study aimed to evaluate the effectiveness of methylphenidate (MPH) and its combination with Crocus sativus (saffron) in the treatment of children suffering from ADHD. Methods: The sample included 70 children aged between 6 and 16 years who had been diagnosed with ADHD. The patients were randomly assigned into two equal groups (n = 35 in each group). While both groups received 20 or 30 mg/d of MPH (20 and 30 mg/d for < 30 and > 30, respectively), one of them also received 20 or 30 mg/d of saffron in a capsule based on BMI (20 and 30 mg/d for < 30 and > 30, respectively). To collect data, parents and teachers completed Attention-Deficit/Hyperactivity Disorder Rating Scale-IV (ADHD-RS-IV). Also, for analyzing the data, the repeated measures analysis of variance (RMANOVA) was used. Results: The results of general linear model (GLM) repeated measures indicated that in both groups, the patients had less symptoms after eight weeks of treatment. However, after four weeks, the average score assigned by the parents and teachers in the MPH with saffron group was lower than the average total score in the MPH group (P < 0.05). Conclusions: Using MPH combined with saffron proved to be more effective in the treatment of patients suffering from ADHD compared to separate treatments. It seems that the duration of therapy can be reduced and the effectiveness be improved by prescribing proposed combined treatment.

Changes in the mesocorticolimbic pathway after low dose reserpine-treatment in Wistar and Spontaneously Hypertensive Rats (SHR): Implications for cognitive deficits in a progressive animal model for Parkinson's disease

Reserpine (RES) is an irreversible inhibitor of VMAT2 used to study Parkinson's disease (PD) and screening for antiparkinsonian treatments in rodents. Recently, the repeated treatment with a low dose of reserpine was proposed as a model capable of emulating progressive neurochemical, motor and non-motor impairments in PD. Conversely, compared to Wistar rats, Spontaneously Hypertensive Rats (SHR) are resistant to motor changes induced by repeated treatment with a low dose of RES. However, such resistance has not yet been investigated for RES-induced non-motor impairments. We aimed to assess whether SHR would have differential susceptibility to the object recognition deficit induced by repeated low-dose reserpine treatment. We submitted male Wistar and SHR rats to repeated RES treatment (15 s.c. injections of 0.1 mg/kg, every other day) and assessed object memory acquisition and retrieval 48 h after the 6^th RES injection (immediately before the appearance of motor impairments). Only RES Wistar rats displayed memory impairment after reserpine treatment. On the other hand, untreated SHR rats displayed object recognition memory deficit, but RES treatment restored such deficits. We also performed immunohistochemistry for tyrosine hydroxylase (TH) and α-synuclein (α-syn) 48 h after the last RES injection. In a different set of animals submitted to the same treatment, we quantified DA, 5-HT and products of lipid peroxidation in the prefrontal cortex (PFC) and hippocampus (HPC). SHR presented increased constitutive levels of DA in the PFC and reduced immunoreactivity to TH in the medial PFC and dorsal HPC. Corroborating the behavioral findings, RES treatment restored those constitutive alterations in SHR. These findings indicate that the neurochemical, molecular and genetic differences in the SHR strain are potentially relevant targets to the study of susceptibility to diseases related to dopaminergic alterations.

Negative relationship between brain α1A-AR neurotransmission and βArr2 levels in anxious adolescent rats subjected to early life stress

Early-life stress is correlated with the development of anxiety-related behavior in adolescence, but underlying mechanisms remain poorly known. The α_1A-adrenergic receptor (AR) is linked to mood regulation and its function is assumed to be regulated by β-arrestins (βArrs) via desensitization and downregulation. Here, we investigated correlation between changes in α_1A-AR and βArr2 levels in the prefrontal cortex (PFC) and hippocampus of adolescent and adult male rats subjected to maternal separation (MS) and their relationship with anxiety-like behavior in adolescence. MS was performed 3 h per day from postnatal days 2-11 and anxiety-like behavior was evaluated in the elevated plus-maze and open field tests. The protein levels were examined using western blot assay. MS decreased α_1A-AR expression and increased βArr2 expression in both brain regions of adolescent rats, while induced reverse changes in adulthood. MS adolescent rats demonstrated higher anxiety-type behavior and lower activity in behavioral tests than controls. Decreased α_1A-AR levels in MS adolescence strongly correlated with reduced time spent in the open field central area, consistent with increased anxiety-like behavior. An anxiety-like phenotype was mimicked by acute and chronic treatment of developing rats with prazosin, an α_1A-AR antagonist, suggesting α_1A-AR downregulation may facilitate anxiety behavior in MS adolescent rats. Together, our results indicate a negative correlation between α_1A-AR neurotransmission and βArr2 levels in both adults and anxious-adolescent rats and suggest that increased βArr2 levels may contribute to posttranslational regulation of α_1A-AR and modulation of anxiety-like behavior in adolescent rats. This may provide a path to develop more effective anxiolytic treatments.

Neuroprotective Potency of Saffron Against Neuropsychiatric Diseases, Neurodegenerative Diseases, and Other Brain Disorders: From Bench to Bedside

The increasing morbidity rates of brain disorders and conditions such as anxiety, depression, Alzheimer’s disease, and Parkinson’s disease have become a severe problem in recent years. Although researchers have spent considerable time studying these diseases and reported many positive outcomes, there still are limited drugs available for their treatment. As a common traditional Chinese medicine (TCM), saffron was employed to treat depression and some other inflammatory diseases in ancient China due to its antioxidant, anti-inflammatory, and antidepressant properties. In modern times, saffron and its constituents have been utilized, alone and in TCM formulas, to treat neuropsychiatric and neurodegenerative diseases. In this review, we mainly focus on recent clinical and preclinical trials of brain disorders in which saffron was applied, and summarize the neuroprotective properties of saffron and its constituents from chemical, pharmacokinetic, and pharmacological perspectives. We discuss the properties of saffron and its constituents, as well as their applications for treating brain disorders; we hope that this review will serve as a comprehensive reference for studies aimed at developing therapeutic drugs based on saffron.

The anxiolytic effect of perampanel and possible mechanisms mediating its anxiolytic effect in mice

AIMS

The aim of this study is to investigate the anxiolytic activity of perampanel, a non-competitive antagonist of alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA)-type glutamate receptors, which is approved for partial-onset seizures in patients with epilepsy, and its mechanism of action.

MAIN METHODS

The anxiolytic activity of perampanel at the doses of 0.25, 0.5, 1, 2, and 4 mg/kg intraperitoneally (i.p.) was investigated in mice using elevated plus-maze, hole-board, and open-field tests. The findings were compared to the anxiolytic activity of gamma-aminobutyric acid type A benzodiazepine (GABA_A/BZ) receptor allosteric modulator diazepam (1 mg/kg, i.p.) and AMPA antagonist GYKI-53655 (5 mg/kg, i.p.). The mechanisms of action of perampanel were evaluated by pre-treatment with GABA_A/BZ receptor antagonist flumazenil (3 mg/kg, i.p.), serotonin 5-hydroxytryptamine 1A (5-HT_1A) antagonist WAY-100635 (1 mg/kg, i.p.), and α₂-adrenoreceptor antagonist yohimbine (5 mg/kg, i.p.).

KEY FINDINGS

In the elevated plus-maze and open-field tests, perampanel at the dose of 0.5 mg/kg, and in the hole-board test, at the doses of 0.25, 0.5, and 1 mg/kg demonstrated an anxiolytic effect without altering the locomotor activity. The effect of perampanel was comparable to the effect of diazepam. Stimulation of GABA_A/BZ and α₂-adrenergic receptors contributed to the anxiolytic effect of perampanel, since significant antagonisms were determined in various behavioral parameters by the antagonist pre-treatments.

SIGNIFICANCE

AMPA antagonism is believed to provide the determined anxiolytic activity of perampanel. Increased GABAergic tonus induced by AMPA receptor antagonism along with other systems, especially the noradrenergic system, might be involved in the anxiolytic activity.

Differential effects of social isolation rearing on glutamate- and GABA-stimulated noradrenaline release in the rat prefrontal cortex and hippocampus

Social isolation rearing (SIR) provides an excellent model of early life adversity to investigate alterations in brain function. Few studies have investigated the effects of SIR on noradrenaline (NE) projections which arise from the locus coeruleus (LC), a system which regulates arousal and attentional processes, including the processing of novelty. In addition, there is a paucity of information on the effects of SIR in females. In this study we investigated the behavioural response to attentional processing of novelty and glutamate- and GABA-stimulated release of noradrenaline in the prefrontal cortex (PFC) and hippocampus (HC) of male and female rats. Sprague Dawley pups were reared in isolated or socialised housing conditions from weaning on postnatal day 21 (P21). At P78-83 animal behaviour was recorded from the three phases of the novel object recognition (NOR) task. Then at P90-94, NE release was measured in the PFC and HC after stimulating the tissue in vitro with either glutamate or GABA. Behaviourally SIR decreased novelty-related behaviour, male isolates showed effects of SIR during the NOR Test phase while female isolates showed effects of SIR during the Habituation phase. SIR PFC NE release was decreased when glutamate stimulation followed GABA stimulation and tended to increase when GABA stimulation followed glutamate stimulation, differences were predominantly due to male isolates. No SIR differences were found for HC. Early life adversity differentially affects the function of the LCNE system in males and females, evidenced by changes in attentional processing of novelty and stimulated noradrenaline release in the PFC.

Cerebral Ischemic Postconditioning Plays a Neuroprotective Role through Regulation of Central and Peripheral Glutamate

Following cerebral ischemia/reperfusion (I/R) injury, a series of pathophysiological processes are stimulated in both the central nervous system (CNS) and the periphery, including, but not limited to, the peripheral immune and endocrine systems and underregulation of the neuroendocrine-immune network. Glutamate (Glu) is an important excitatory neurotransmitter in the CNS; its excitotoxicity following cerebral ischemia has been a focus of study for several decades. In addition, as a novel immunoregulator, Glu also regulates immune activity in both the CNS and periphery and may connect the CNS and periphery through regulation of the neuroendocrine-immune network. Ischemic postconditioning (IPostC) is powerful and activates various endogenous neuroprotective mechanisms following cerebral I/R, but only a few studies have focused on the mechanisms associated with Glu to date. Given that Glu plays an important and complex pathophysiological role, the understanding of Glu-related mechanisms of IPostC is an interesting area of research, which we review here.

The Challenge of Pharmacotherapy in Children and Adolescents with Epilepsy-ADHD Comorbidity

Epilepsy is common in children and adolescents where its prevalence is 3.2-5.5/1000. About one-third of patients also have attention deficit hyperactivity/impulsivity disorder (ADHD). The possible relationship between epilepsy and ADHD is still unclear, and ADHD symptoms (such as inattention, hyperactivity, behavioral disturbances) are frequently considered as adverse effects of antiepileptic drugs (AEDs). The literature was searched for data on the behavioral effects of AEDs. Phenobarbital is the most frequently reported medication to induce symptoms of ADHD, followed by topiramate and valproic acid. Phenytoin seems to exert modest effects, while for levetiracetam there are contrasting data. Lacosamide induces some beneficial effects on behavior; carbamazepine and lamotrigine exert favorable effects on attention and behavior. Gabapentin and vigabatrin have limited adverse effects on cognition. Oxcarbazepine, rufinamide, and eslicarbazepine do not seem to aggravate or induce ADHD symptoms, whereas perampanel can lead to a high incidence of hostile/aggressive behavior, which increases with higher dosages. Information about the behavioral effects of ethosuximide, zonisamide, tiagabine, pregabalin, stiripentol, and retigabine is still limited. Because ADHD significantly affects the quality of life of epilepsy patients, the clinical management of this neuropsychiatric disorder should be a priority. Methylphenidate is effective most children and adolescents with ADHD symptoms and comorbid epilepsy, without a significant increase of seizure risk, although data are still limited with few controlled trials.

Sex Differences in Psychiatric Disease: A Focus on the Glutamate System

Alterations in glutamate, the primary excitatory neurotransmitter in the brain, are implicated in several psychiatric diseases. Many of these psychiatric diseases display epidemiological sex differences, with either males or females exhibiting different symptoms or disease prevalence. However, little work has considered the interaction of disrupted glutamatergic transmission and sex on disease states. This review describes the clinical and preclinical evidence for these sex differences with a focus on two conditions that are more prevalent in women: Alzheimer's disease and major depressive disorder, and three conditions that are more prevalent in men: schizophrenia, autism spectrum disorder, and attention deficit hyperactivity disorder. These studies reveal sex differences at multiple levels in the glutamate system including metabolic markers, receptor levels, genetic interactions, and therapeutic responses to glutamatergic drugs. Our survey of the current literature revealed a considerable need for more evaluations of sex differences in future studies examining the role of the glutamate system in psychiatric disease. Gaining a more thorough understanding of how sex differences in the glutamate system contribute to psychiatric disease could provide novel avenues for the development of sex-specific pharmacotherapies.

Attention-deficit/hyperactivity disorder associated with KChIP1 rs1541665 in Kv channels accessory proteins

Attention-deficit/hyperactivity disorder (ADHD) is an early onset childhood neurodevelopmental disorder with high heritability. A number of genetic risk factors and environment factors have been implicated in the pathogenesis of ADHD. Genes encoding for subtypes of voltage-dependent K channels (Kv) and accessory proteins to these channels have been identified in genome-wide association studies (GWAS) of ADHD. We conducted a two-stage case–control study to investigate the associations between five key genes (KChIP4, KChIP1, DPP10, FHIT, and KCNC1) and the risk of developing ADHD. In the discovery stage comprising 256 cases and 372 controls, KChIP1 rs1541665 and FHIT rs3772475 were identified; they were further genotyped in the validation stage containing 328cases and 431 controls.KChIP1 rs1541665 showed significant association with a risk of ADHD at both stages, with CC vs TT odds ratio (OR) = 1.961, 95% confidence interval (CI) = 1.366–2.497, in combined analyses (P-FDR = 0.007). Moreover, we also found rs1541665 involvement in ADHD-I subtype (OR (95% CI) = 2.341(1.713, 3.282), and Hyperactive index score (P = 0.005) in combined samples.Intriguingly, gene-environmental interactions analysis consistently revealed the potential interactionsof rs1541665 collaboratingwith maternal stress pregnancy (P_mul = 0.021) and blood lead (P_add = 0.017) to modify ADHD risk. In conclusion, the current study provides evidence that genetic variants of Kv accessory proteins may contribute to the susceptibility of ADHD.Further studies with different ethnicitiesare warranted to produce definitive conclusions.

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.

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.

Rearing in an enriched environment attenuated hyperactivity and inattention in the Spontaneously Hypertensive Rats, an animal model of Attention-Deficit Hyperactivity Disorder

Attention-deficit hyperactivity disorder (ADHD) is a prevalent neurodevelopmental disorder, characterized by symptoms of hyperactivity, inattention, and impulsivity. It is commonly treated with psychostimulants that typically begins during childhood and lasts for an extended period of time. However, there are concerns regarding the consequences of chronic psychostimulant treatment; thus, there is a growing search for an alternative management for ADHD. One non-pharmacological management that is gaining much interest is environmental enrichment. Here, we investigated the effects of rearing in an enriched environment (EE) on the expression of ADHD-like symptoms in the Spontaneously Hypertensive Rats (SHRs), an animal model of ADHD. SHRs were reared in EE or standard environment (SE) from post-natal day (PND) 21 until PND 49. Thereafter, behavioral tests that measure hyperactivity (open field test [OFT]), inattention (Y-maze task), and impulsivity (delay discounting task) were conducted. Additionally, electroencephalography (EEG) was employed to assess the effects of EE on rat's brain activity. Wistar-Kyoto (WKY) rats, the normotensive counterpart of the SHRs, were used to determine whether the effects of EE were specific to a particular genetic background. EE improved the performance of the SHRs and WKY rats in the OFT and Y-maze task, but not the delay discounting task. Interestingly, EE induced significant EEG changes in WKY rats, but not in the SHRs. These findings show that rearing environment may play a role in the expression of ADHD-like symptoms in the SHRs and that EE may be considered as a putative complementary approach in managing ADHD symptoms.

Effect of methylphenidate treatment during adolescence on norepinephrine transporter function in orbitofrontal cortex in a rat model of attention deficit hyperactivity disorder

Attention deficit hyperactivity disorder (ADHD) is associated with hypofunctional medial prefrontal cortex (mPFC) and orbitofrontal cortex (OFC). Methylphenidate (MPH) remediates ADHD, in part, by inhibiting the norepinephrine transporter (NET). MPH also reduces ADHD-like symptoms in spontaneously hypertensive rats (SHRs), a model of ADHD. However, effects of chronic MPH treatment on NET function in mPFC and OFC in SHR have not been reported. In the current study, long-term effects of repeated treatment with a therapeutically relevant oral dose of MPH during adolescence on NET function in subregions of mPFC (cingulate gyrus, prelimbic cortex and infralimbic cortex) and in the OFC of adult SHR, Wistar-Kyoto (WKY, inbred control) and Wistar (WIS, outbred control) rats were determined using in vivo voltammetry. Following local ejection of norepinephrine (NE), uptake rate was determined as peak amplitude (Amax)× first-order rate constant (k-1). In mPFC subregions, no strain or treatment effects were found in NE uptake rate. In OFC, NE uptake rate in vehicle-treated adult SHR was greater than in adult WKY and WIS administered vehicle. MPH treatment during adolescence normalized NE uptake rate in OFC in SHR. Thus, the current study implicates increased NET function in OFC as an underlying mechanism for reduced noradrenergic transmission in OFC, and consequently, the behavioral deficits associated with ADHD. MPH treatment during adolescence normalized NET function in OFC in adulthood, suggesting that the therapeutic action of MPH persists long after treatment cessation and may contribute to lasting reductions in deficits associated with ADHD.

MicroRNA-19b associates with Ago2 in the amygdala following chronic stress and regulates the adrenergic receptor beta 1

Activation of the stress response in the presence of diverse challenges requires numerous adaptive molecular and cellular changes. To identify specific microRNA molecules that are altered following chronic stress, mice were subjected to the chronic social defeat procedure. The amygdala from these mice was collected and a screen for microRNAs that were recruited to the RNA-induced silencing complex and differentially expressed between the stressed and unstressed mice was conducted. One of the microRNAs that were significantly altered was microRNA-19b (miR-19b). Bioinformatics analysis revealed the adrenergic receptor β-1 (Adrb1) as a potential target for this microRNA with multiple conserved seed sites. Consistent with its putative regulation by miR-19b, Adrb1 levels were reduced in the basolateral amygdala (BLA) following chronic stress. In vitro studies using luciferase assays showed a direct effect of miR-19b on Adrb1 levels, which were not evident when miR-19b seed sequences at the Adrb1 transcript were mutated. To assess the role of miR-19b in memory stabilization, previously attributed to BLA-Adrb1, we constructed lentiviruses designed to overexpress or knockdown miR-19b. Interestingly, adult mice injected bilaterally with miR-19b into the BLA showed lower freezing time relative to control in the cue fear conditioning test, and deregulation of noradrenergic circuits, consistent with downregulation of Adrb1 levels. Knockdown of endogenous BLA-miR-19b levels resulted in opposite behavioral and noradrenergic profile with higher freezing time and increase 3-methoxy-4-hydroxyphenylglycol/noradrenaline ratio. These findings suggest a key role for miR-19b in modulating behavioral responses to chronic stress and Adrb1 as an important target of miR-19b in stress-linked brain regions.

Attention-deficit/hyperactivity disorder and attention impairment in children with benign childhood epilepsy with centrotemporal spikes

Attention-deficit/hyperactivity disorder (ADHD) is a common comorbidity in children with epilepsy and has a negative impact on behavior and learning. The purposes of this study were to quantify the prevalence of ADHD in benign childhood epilepsy with centrotemporal spikes (BCECTS) and to identify clinical factors that affect ADHD or attention impairment in patients with BCECTS. The medical records of 74 children (44 males) with neuropsychological examination from a total of 198 children diagnosed with BCECTS at Asan Medical Center were retrospectively reviewed. Electroclinical factors were compared across patients with ADHD and those without ADHD. Mean T-scores of the continuous performance test were compared across patients grouped according to various epilepsy characteristics. Forty-eight (64.9%) patients had ADHD. A history of febrile convulsion was more common in patients with ADHD than in patients without ADHD (p=0.049). Bilateral centrotemporal spikes on electroencephalogram were more common in patients receiving ADHD medication than in patients with untreated ADHD (p=0.004). Male patients, patients with frequent seizures prior to diagnosis, and patients with a high spike index (≥40/min) on sleep EEG at diagnosis had significantly lower visual selective attention (p<0.05). Children with BCECTS had a high prevalence of ADHD, and frequent seizures or interictal epileptiform abnormalities were closely related to impairment of visual selective attention in children with BCECTS, indicating the need for ADHD or attention impairment screening in children with BCECTS.

Evidence for reduced tonic levels of GABA in the hippocampus of an animal model of ADHD, the spontaneously hypertensive rat

Recent studies have investigated the role of γ-aminobutyric acid (GABA) in the behavioural symptoms of attention-deficit/hyperactivity disorder (ADHD), specifically in behavioural disinhibition. Spontaneously hypertensive rats (SHR) are widely accepted as an animal model of ADHD, displaying core symptoms of the disorder. Using an in vitro superfusion technique, we have shown that glutamate-stimulated release of radio-actively labelled norepinephrine ([(3)H]NE) from prefrontal cortex and hippocampal slices is greater in SHR than in their normotensive control strain, Wistar-Kyoto rats (WKY), and/or a standard control strain, Sprague-Dawley rats (SD). In the present study, we investigated how the level of extracellular (tonic) GABA affects release of [(3)H]NE in hippocampal slices of male and female SHR, WKY and SD rats, in response to 3 glutamate stimulations (S1, S2, and S3). The hippocampal slices were prelabelled with [(3)H]NE and superfused with buffer containing 0μM, 1μM, 10μM, or 100μM GABA. Three consecutive glutamate stimulations were achieved by exposing slices to 3 pulses of glutamate (1mM), each separated by 10min. Increasing tonic levels of GABA increased basal and stimulated release of [(3)H]NE in all strains. When GABA was omitted from the superfusion buffer used to perfuse SHR hippocampal slices, but present at 100µM in the buffer used to perfuse WKY and SD hippocampal slices, glutamate-stimulated release of [(3)H]NE was similar in all three strains. In these conditions, the decrease in [(3)H]NE release from S1 to S2 and S3 was also similar in all three strains. These findings suggest that extracellular concentrations of GABA may be reduced in SHR hippocampus, in vivo, compared to WKY and SD. An underlying defect in GABA function may be at the root of the dysfunction in catecholamine transmission noted in SHR, and may underlie their ADHD-like behaviours.

A behavioral neuroenergetics theory of ADHD

Energetic insufficiency in neurons due to inadequate lactate supply is implicated in several neuropathologies, including attention-deficit/hyperactivity disorder (ADHD). By formalizing the mechanism and implications of such constraints on function, the behavioral Neuroenergetics Theory (NeT) predicts the results of many neuropsychological tasks involving individuals with ADHD and kindred dysfunctions, and entails many novel predictions. The associated diffusion model predicts that response times will follow a mixture of Wald distributions from the attentive state, and ex-Wald distributions after attentional lapses. It is inferred from the model that ADHD participants can bring only 75-85% of the neurocognitive energy to bear on tasks, and allocate only about 85% of the cognitive resources of comparison groups. Parameters derived from the model in specific tasks predict performance in other tasks, and in clinical conditions often associated with ADHD. The primary action of therapeutic stimulants is to increase norepinephrine in active regions of the brain. This activates glial adrenoceptors, increasing the release of lactate from astrocytes to fuel depleted neurons. The theory is aligned with other approaches and integrated with more general theories of ADHD. Therapeutic implications are explored.

Maternal separation increases GABA(A) receptor-mediated modulation of norepinephrine release in the hippocampus of a rat model of ADHD, the spontaneously hypertensive rat

Experiencing early life stress increases the risk of developing a psychiatric disorder later in life, possibly by altering neural networks, such as the locus-coeruleus norepinephrine (LC-NE) system. Whether early life stress affects the LC-NE system directly, or whether the effects are via changes in glutamate and GABA modulation of the LC-NE system, is unclear. Early life stress has been shown to alter glutamate and GABA transmission, and in particular, to alter GABA(A) receptor expression. The LC-NE system has been implicated in attention-deficit/hyperactivity disorder (ADHD), amongst other disorders, and is over-responsive to glutamate stimulation in a validated rat model of ADHD, the spontaneously hypertensive rat (SHR). It is plausible that the LC-NE system, or glutamate and GABA modulation thereof, in an individual already genetically predisposed to develop ADHD, or in SHR, may respond in a unique way to early life stress. To investigate this we applied a mild developmental stressor, maternal separation, onto SHR, and onto their control strain, Wistar-Kyoto rats (WKY), from post-natal day (P)2-14. On P50-52, in early adulthood, we assayed glutamate and potassium stimulated release of radio-actively labelled NE ((3)[H]NE) from hippocampal slices using an in vitro superfusion technique, in the presence or absence of a GABA(A) receptor antagonist, bicuculline. Our results show that maternal separation altered GABA(A) receptor-mediated modulation of NE release in the hippocampus of the two strains in opposite directions, increasing it in SHR and decreasing it in WKY. Our findings indicate that effects of early life stress are highly dependent on genetic predisposition, since opposite changes in GABA(A) receptor-mediated modulation of NE release were observed in the rat model of ADHD, SHR, and their control strain, WKY.

Synergistic tonic and phasic activity of the locus coeruleus norepinephrine (LC-NE) arousal system is required for optimal attentional performance

A certain level of arousal is required for an individual to perform optimally, and the locus coeruleus norepinephrine (LC-NE) system plays a central role in optimizing arousal. Tonic firing of LC-NE neurons needs to be held within a narrow range of 1-3 Hz to facilitate phasic firing of the LC-NE neurons; these two modes of activity act synergistically, to allow the individual to perform attentional tasks optimally. How this information can be applied to further our understanding of psychiatric disorders has not been fully elucidated. Here we propose two models of altered LC-NE activity that result in attentional deficits characteristic of psychiatric disorders: 1) 'hypoaroused' individuals with e.g. attention-deficit/hyperactivity disorder (ADHD) have decreased tonic firing of the LC-NE system, resulting in decreased cortical arousal and poor attentional performance and 2) 'hyperaroused' individuals with e.g. anxiety disorders have increased tonic firing of the LC-NE system, resulting in increased cortical arousal and impaired attentional performance. We argue that hypoarousal (decreased tonic firing of LC-NE neurons) and hyperarousal (increased tonic firing of LC-NE neurons) are suboptimal states in which phasic activity of LC-NE neurons is impeded. To further understand the neurobiology of attentional dysfunction in psychiatric disorders a translational approach that integrates findings on the LC-NE arousal system from animal models and human imaging studies may be useful.

Effects of early life trauma are dependent on genetic predisposition: a rat study

BACKGROUND

Trauma experienced early in life increases the risk of developing a number of psychological and/or behavioural disorders. It is unclear, however, how genetic predisposition to a behavioural disorder, such as attention-deficit/hyperactivity disorder (ADHD), modifies the long-term effects of early life trauma. There is substantial evidence from family and twin studies for susceptibility to ADHD being inherited, implying a strong genetic component to the disorder. In the present study we used an inbred animal model of ADHD, the spontaneously hypertensive rat (SHR), to investigate the long-term consequences of early life trauma on emotional behaviour in individuals predisposed to developing ADHD-like behaviour.

METHODS

We applied a rodent model of early life trauma, maternal separation, to SHR and Wistar-Kyoto rats (WKY), the normotensive control strain from which SHR were originally derived. The effects of maternal separation (removal of pups from dam for 3 h/day during the first 2 weeks of life) on anxiety-like behaviour (elevated-plus maze) and depressive-like behaviour (forced swim test) were assessed in prepubescent rats (postnatal day 28 and 31). Basal levels of plasma corticosterone were measured using radioimmunoassay.

RESULTS

The effect of maternal separation on SHR and WKY differed in a number of behavioural measures. Similar to its reported effect in other rat strains, maternal separation increased the anxiety-like behaviour of WKY (decreased open arm entries) but not SHR. Maternal separation increased the activity of SHR in the novel environment of the elevated plus-maze, while it decreased that of WKY. Overall, SHR showed a more active response in the elevated plus-maze and forced swim test than WKY, regardless of treatment, and were also found to have higher basal plasma corticosterone compared to WKY. Maternal separation increased basal levels of plasma corticosterone in SHR females only, possibly through adaptive mechanisms involved in maintaining their active response in behavioural tests. Basal plasma corticosterone was found to correlate positively with an active response to a novel environment and inescapable stress across all rats.

CONCLUSION

SHR are resilient to the anxiogenic effects of maternal separation, and develop a non-anxious, active response to a novel environment following chronic mild stress during the early stages of development. Our findings highlight the importance of genetic predisposition in determining the outcome of early life adversity. SHR may provide a model of early life trauma leading to the development of hyperactivity rather than anxiety and depression. Basal levels of corticosterone correlate with the behavioural response to early life trauma, and may therefore provide a useful marker for susceptibility to a certain behavioural temperament.

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.

Medial temporal lobe functioning and structure in the spontaneously hypertensive rat: comparison with Wistar-Kyoto normotensive and Wistar-Kyoto hypertensive strains

The spontaneously hypertensive rat (SHR) is used as an animal model of attention deficit hyperactivity disorder (ADHD). It displays deficits in frontostriatal functioning, but it is unclear if medial temporal lobe functioning and structure are affected. We used behavioral tasks that evaluate functioning of the amygdala and hippocampus to compare male SHR to male rats from two inbred comparator strains, the normotensive Wistar-Kyoto (WKY) and the hypertensive Wistar-Kyoto (WKHT) rat (n = 8/strain). The three strains showed similar levels of amygdala-related stimulus-reward learning during conditioned cue preference testing. In the ambiguous T-maze task, which dissociates between spatial and habit learning, significantly more WKHT than SHR or WKY used a response (indicative of habit learning) versus a place (indicative of spatial learning) strategy during an early probe test on day 8. During a later probe test on day 24, WKY progressed significantly from using a place strategy to a response strategy. Throughout all probe tests, a place strategy was used predominately by SHR and a response strategy by WKHT. Thus, SHR exhibited deficits in dorsal striatum-related habit learning, whereas WKHT exhibited deficits in hippocampus-related spatial learning. Following behavioral testing, fluid attenuated inversion recovery (FLAIR) magnetic resonance imaging scans were conducted in subgroups of rats from each strain (n = 4/strain). FLAIR imaging detected bilateral hippocampal hyperintensities in three of four WKHT and unilateral hippocampal atrophy in one of four SHR. The association between response strategy use during the initial probe test to forage for food in the ambiguous T-maze task and bilateral hippocampal abnormalities was significant. Collectively, while medial temporal lobe functioning appears to be normal in SHR exhibiting an ADHD-like phenotype, WKHT rats display both hippocampal functioning deficits and signs of bilateral hippocampal cell loss. The latter characteristics might be used to develop a new animal model of age- or disease-related decline in hippocampal functioning.

Rare structural variants found in attention-deficit hyperactivity disorder are preferentially associated with neurodevelopmental genes

Attention-deficit/hyperactivity disorder (ADHD) is a common and highly heritable disorder, but specific genetic factors underlying risk remain elusive. To assess the role of structural variation in ADHD, we identified 222 inherited copy number variations (CNVs) within 335 ADHD patients and their parents that were not detected in 2026 unrelated healthy individuals. Although no excess CNVs, either deletions or duplications, were found in the ADHD cohort relative to controls, the inherited rare CNV-associated gene set was significantly enriched for genes reported as candidates in studies of autism, schizophrenia and Tourette syndrome, including A2BP1, AUTS2, CNTNAP2 and IMMP2L. The ADHD CNV gene set was also significantly enriched for genes known to be important for psychological and neurological functions, including learning, behavior, synaptic transmission and central nervous system development. Four independent deletions were located within the protein tyrosine phosphatase gene, PTPRD, recently implicated as a candidate gene for restless legs syndrome, which frequently presents with ADHD. A deletion within the glutamate receptor gene, GRM5, was found in an affected parent and all three affected offspring whose ADHD phenotypes closely resembled those of the GRM5 null mouse. Together, these results suggest that rare inherited structural variations play an important role in ADHD development and indicate a set of putative candidate genes for further study in the etiology of ADHD.

Attention deficit hyperactivity disorder in children with epilepsy

Attention deficit hyperactivity disorder (ADHD) is more frequent in children with epilepsy than in general pediatric population. Several factors may contribute to this comorbidity, including the underlying brain pathology, the chronic effects of seizures and of the epileptiform EEG discharges, and the effects of antiepileptic drugs. Symptoms of ADHD are more common in some specific types of epilepsies, such as frontal lobe epilepsy, childhood absence epilepsy and Rolandic epilepsy, and may antedate seizure onset in a significant proportion of cases. In epileptic children with symptoms of ADHD, treatment might become a challenge for child neurologists, who are forced to prescribe drugs combinations, to improve the long-term cognitive and behavioral prognosis. Treatment with psychotropic drugs can be initiated safely in most children with epilepsy and ADHD symptoms.

The spontaneously hypertensive rat model of ADHD--the importance of selecting the appropriate reference strain

Although several molecular and genetic manipulations may produce hyperactive animals, hyperactivity alone is insufficient for the animal to qualify as a model of ADHD. Based on a wider range of criteria - behavioral, genetic and neurobiological - the spontaneously hypertensive rat (SHR) obtained from Charles River, Germany (SHR/NCrl) at present constitutes the best validated animal model of ADHD combined subtype (ADHD-C), and the Wistar Kyoto substrain obtained from Harlan, UK (WKY/NHsd) is its most appropriate control. Although other rat strains may behave like WKY/NHsd rats, genetic results indicate significant differences when compared to the WKY/NHsd substrain, making them less suitable controls for the SHR/NCrl. The use of WKY/NCrl, outbred Wistar, Sprague Dawley or other rat strains as controls for SHRs may produce spurious neurobiological differences. Consequently, data may be misinterpreted if insufficient care is taken in the selection of the control group. It appears likely that the use of different control strains may underlie some of the discrepancies in results and interpretations in studies involving the SHR and WKY. Finally, we argue that WKY rats obtained from Charles River, Germany (WKY/NCrl) provide a promising model for the predominantly inattentive subtype of ADHD (ADHD-PI); in this case also the WKY/NHsd substrain should be used as control.

Cross-fostering does not alter the neurochemistry or behavior of spontaneously hypertensive rats

Background

Attention-deficit/hyperactivity disorder (ADHD) is a highly heritable developmental disorder resulting from complex gene-gene and gene-environment interactions. The most widely used animal model, the spontaneously hypertensive rat (SHR), displays the major symptoms of ADHD (deficits in attention, impulsivity and hyperactivity) and has a disturbance in the noradrenergic system when compared to control Wistar-Kyoto rats (WKY). The aim of the present study was to determine whether the ADHD-like characteristics of SHR were purely genetically determined or dependent on the gene-environment interaction provided by the SHR dam.

Methods

SHR/NCrl (Charles River, USA), WKY/NCrl (Charles River, USA) and Sprague Dawley rats (SD/Hsd, Harlan, UK) were bred at the University of Cape Town. Rat pups were cross-fostered on postnatal day 2 (PND 2). Control rats remained with their birth mothers to serve as a reference for their particular strain phenotype. Behavior in the open-field and the elevated-plus maze was assessed between PND 29 and 33. Two days later, rats were decapitated and glutamate-stimulated release of [³H]norepinephrine was determined in prefrontal cortex and hippocampal slices.

Results

There was no significant effect of "strain of dam" but there was a significant effect of "pup strain" on all parameters investigated. SHR pups travelled a greater distance in the open field, spent a longer period of time in the inner zone and entered the inner zone of the open-field more frequently than SD or WKY. SD were more active than WKY in the open-field. WKY took longer to enter the inner zone than SHR or SD. In the elevated-plus maze, SHR spent less time in the closed arms, more time in the open arms and entered the open arms more frequently than SD or WKY. There was no difference between WKY and SD behavior in the elevated-plus maze. SHR released significantly more [³H]norepinephrine in response to glutamate than SD or WKY in both hippocampus and prefrontal cortex while SD prefrontal cortex released more [³H]norepinephrine than WKY. SHR were resilient, cross-fostering did not reduce their ADHD-like behavior or change their neurochemistry. Cross-fostering of SD pups onto SHR or WKY dams increased their exploratory behavior without altering their anxiety-like behavior.

Conclusion

The ADHD-like behavior of SHR and their neurochemistry is genetically determined and not dependent on nurturing by SHR dams. The similarity between WKY and SD supports the continued use of WKY as a control for SHR and suggests that SD may be a useful additional reference strain for SHR. The fact that SD behaved similarly to WKY in the elevated-plus maze argues against the use of WKY as a model for anxiety-like disorders.