Attention deficit/hyperactivity disorder: characteristics, interventions and models

Effects of Methylphenidate on the Dopamine Transporter and Beyond

The dopamine transporter (DAT) is the main target of methylphenidate (MPH), which remains the number one drug prescribed worldwide for the treatment of Attention-Deficit Hyperactivity Disorder (ADHD). In addition, abnormalities of the DAT have been widely associated with ADHD. Based on clinical and preclinical studies, the direction of DAT abnormalities in ADHD are, however, still unclear. Moreover, chronic treatment of MPH has been shown to increase brain DAT expression in both animals and ADHD patients, suggesting that findings of overexpressed levels of DAT in ADHD patients are possibly attributable to the effects of long-term MPH treatment rather than the pathology of the condition itself. In this chapter, we will discuss some of the effects exerted by MPH, which are related to its actions on catecholamine protein targets and brain metabolites, together with genes and proteins mediating neuronal plasticity. For this purpose, we present data from biochemical, proton nuclear magnetic resonance spectroscopy (¹H-NMR) and gene/protein expression studies. Overall, results of the studies discussed in this chapter show that MPH has a complex biological/pharmacological action well beyond the DAT.

Review of rodent models of attention deficit hyperactivity disorder

Attention deficit hyperactivity disorder (ADHD) is a polygenic neurodevelopmental disorder that affects 8-12 % of children and >4 % of adults. Environmental factors are believed to interact with genetic predispositions to increase susceptibility to ADHD. No existing rodent model captures all aspects of ADHD, but several show promise. The main genetic models are the spontaneous hypertensive rat, dopamine transporter knock-out (KO) mice, dopamine receptor subtype KO mice, Snap-25 KO mice, guanylyl cyclase-c KO mice, and latrophilin-3 KO mice and rats. Environmental factors thought to contribute to ADHD include ethanol, nicotine, PCBs, lead (Pb), ionizing irradiation, 6-hydroxydopamine, neonatal hypoxia, some pesticides, and organic pollutants. Model validation criteria are outlined, and current genetic models evaluated against these criteria. Future research should explore induced multiple gene KOs given that ADHD is polygenic and epigenetic contributions. Furthermore, genetic models should be combined with environmental agents to test for interactions.

Spontaneously hypertensive (SHR) rats choose more impulsively than Wistar-Kyoto (WKY) rats on a delay discounting task

Indications of Attention Deficit Hyperactivity Disorder (ADHD) in the spontaneously hypertensive rat (SHR) are not consistent across different tests of impulsivity, questioning the SHR's validity as a rodent model of ADHD. This study used a concurrent-chains procedure to examine possible differences in impulsive choice between SHRs and control-normotensive Wistar Kyoto (WKY) rats. The aim was to extend the generality of findings showing regularities between the hyperbolic-decay model and the generalized matching law fitting delay discounting data from nonhuman animals. The objectives were to: (1) examine differences in impulsive choice between SHRs and WKYs; (2) add evidence suggesting that the SHR is a suitable model of ADHD; (3) demonstrate that concurrent-chains procedures requiring locomotion detect differences in impulsive choice between SHRs and WKYs; (4) support the idea that impulsivity in nonhuman animals increases with training. The initial link used two non-independent random interval schedules arranging entries to the terminal links, where one fixed-time (FT) schedule delayed 1-food pellet and the other FT 4-food pellets. The FT delaying the former was kept constant at 0.1s and that delaying the latter changed after every 10 food deliveries, defining six delay components (0.1, 5, 10, 20, 40, and 80s) presented in random order each session. Results showed that the SHRs choose more impulsively than the WKYs, adding to the body of evidence suggesting that the SHR may be a suitable model of ADHD. Both models of choice fitted the impulsive choices of the SHRs and WKYs well; positive correlations between estimates of parameters k and s suggested compatibility between models of choice showing that impulsivity increases with training.

The Role of Nutritional Supplements in the Treatment of ADHD: What the Evidence Says

Attention-deficit hyperactivity disorder (ADHD) is a common behavioral disorder in children and adolescents and may persist into adulthood. Insufficient nutritional supply of long-chain polyunsaturated fatty acids (LC-PUFAs) and other components including various minerals has been suggested to play a role in the development of ADHD symptoms. This review presents the evidence regarding the role of nutritional PUFA, zinc, iron, and magnesium supplements in the treatment of ADHD with a focus on the critical evaluation of the relevant literature published from 2014 to April 2016. The evaluation of therapeutic nutritional LC-PUFA supplementation in ADHD has shown mixed and inconclusive results and at best marginal beneficial effects. The benefits of PUFAs are much smaller than the effect sizes observed for traditional pharmacological treatments of ADHD. The effectiveness of PUFA supplements in reducing medication dosage has been suggested but needs to be confirmed. Zinc, iron, and magnesium supplementation may reduce ADHD symptoms in children with or at high risk of deficiencies in these minerals. However, convincing evidence in this regard is lacking.

Comparing Auditory Noise Treatment with Stimulant Medication on Cognitive Task Performance in Children with Attention Deficit Hyperactivity Disorder: Results from a Pilot Study

Background: Recent research has shown that acoustic white noise (80 dB) can improve task performance in people with attention deficits and/or Attention Deficit Hyperactivity Disorder (ADHD). This is attributed to the phenomenon of stochastic resonance in which a certain amount of noise can improve performance in a brain that is not working at its optimum. We compare here the effect of noise exposure with the effect of stimulant medication on cognitive task performance in ADHD. The aim of the present study was to compare the effects of auditory noise exposure with stimulant medication for ADHD children on a cognitive test battery. A group of typically developed children (TDC) took the same tests as a comparison.

Methods: Twenty children with ADHD of combined or inattentive subtypes and twenty TDC matched for age and gender performed three different tests (word recall, spanboard and n-back task) during exposure to white noise (80 dB) and in a silent condition. The ADHD children were tested with and without central stimulant medication.

Results: In the spanboard- and the word recall tasks, but not in the 2-back task, white noise exposure led to significant improvements for both non-medicated and medicated ADHD children. No significant effects of medication were found on any of the three tasks.

Conclusion: This pilot study shows that exposure to white noise resulted in a task improvement that was larger than the one with stimulant medication thus opening up the possibility of using auditory noise as an alternative, non-pharmacological treatment of cognitive ADHD symptoms.

Single-dose effects on the P3no-go ERP component predict clinical response to stimulants in pediatric ADHD

OBJECTIVE

Approximately 30% of children and adolescents diagnosed with attention-deficit/hyperactivity disorder (ADHD) and treated with stimulants are considered non-responders (non-REs). Reliable predictors of response are missing. We examined changes in Event-Related Potentials (ERPs) induced by a single dose of stimulant medication in order to predict later clinical response.

METHODS

ERPs were registered twice during performance of a visual cued go/no-go task in 87 ADHD patients (27 girls) aged 8-18years; the second recording on a single dose of stimulant medication, followed by a systematic medication trial lasting 4weeks. Based on the four-week trial, participants were categorized as responders (REs, N=62) or non-REs (N=25). Changes among REs and non-REs in ERP components (cueP3, CNV, P3go, N2no-go, P3no-go) and behavioral-test variables were then compared.

RESULTS

REs and non-REs differed significantly in medication-induced changes in P3no-go, cue-P3, CNV, omission errors, reaction time, and reaction-time variability. The largest effect size was found for P3no-go amplitude (p<.001; d=1.76). Changes in P3no-go and omission errors correctly classified 90% of the REs and 76% of the non-REs, when controlling for the age of the participants.

CONCLUSION

Clinical response to stimulants can be predicted by assessing single-dose changes in the P3no-go ERP component amplitude.

SIGNIFICANCE

Changes in P3no-go may be a clinically useful marker of response to stimulants.

Reaction Time and Attention: Toward a New Standard in the Assessment of ADHD? A Pilot Study

This pilot study shows results of an experiment comparing reaction times (RTs) and attentional performance between an ADHD group of 30 children and 30 controls, both Spanish speaking. The experiment was carried out using the Seville computerized neuropsychological battery (SNB).

OBJECTIVE

This study had two goals: One was to test sensitivity of SNB for attention deficits in ADHD and the second was to detect differences in RTs between ADHD and controls. Possible explanations and implications of such differences are also discussed.

METHOD

SNB computerized system was used to assess RTs and accuracy, and alternate forms of continuous performance task were used.

RESULTS

Results showed high sensitivity of some of the SNB tests, especially cancellation tests. RTs were significantly different between groups.

CONCLUSION

SNB represents a helpful tool for detection of attention deficits, and RT indices represent the most significant variable in differentiation of both groups studied.

Relationship between ADHD and depression among university students in macedonia

INTRODUCTION

Attention deficit hyperactivity disorder (ADHD) is a neurobehavioral developmental disorder usually diagnosed in children, with appearance of the first symptoms before the age of seven years. The disorder is characterized by inattention and/or impulsivity and hyperactivity that can seriously affect many aspects of behavior and performance at school. ADHD can be associated with comorbidities, such as oppositional defiant disorder, conduct disorder, anxiety or depression.

MATERIAL AND METHODS

The study was done on a sample of 500 university students. For the measurement of ADHD symptoms, the ADHD Adult Self-report Scale was used and for depression measurement DASS.

RESULTS

The results of this screening study showed that ADHD is highly significant associated with gender (p = 0.0004). Men more often than women have this kind of disorder. Female students have attention subtype deficit, while man student have often hyperactivity/impulsivity disorder and combined subtype due to psychological, temperament and character gender differences among boys and girls. Female examinees are significantly (p=0.028) more often depressed compared to male examinees.

CONCLUSION

The examined correlations are positive ones or direct, meaning that by increasing the values of the scores from both subscales from the Evaluation ADHD Scale one also increases the scores from the Depression Scale, and vice versa. For a value of p=0.001 and p=0.004 these correlations are statistically highly significant, in other words highly important.

Prevalence and contributing factors to attention deficit hyperactivity disorder: a study of five- to fifteen-year-old children in Zhabei District, Shanghai

INTRODUCTION

This work aims to understand the features among 5- to 15-year-old children with attention deficit hyperactivity disorder (ADHD) in Zhabei District in Shanghai.

METHODS

Children with ADHD were studied using general background questionnaire, ADHD symptom rating questionnaire, and cluster-stratified sampling. A total of 9,900 valid questionnaires were utilized in this study. We conducted diagnostic interviews with suspected ADHD children and their parents using the criteria of the Diagnostic and Statistical Manual of Mental Disorders (4th Edition) for ADHD.

RESULTS

The prevalence rate of ADHD among the children was 4.6%, of which 2.4%, 0.4%, and 1.8% had ADHD-I ADHD-HI, and ADHD-C types, respectively. The prevalence rates in boys and girls were 6.6% and 2.7% (ratio, 2.41 : 1), respectively. Significant differences in prevalence rate were found among children with different age groups and ADHD types. Children aged 7-10 years had the highest prevalence rate (6.3%). Externally, residence children had higher prevalence than local residents. Significant differences in prevalence rate were also found among children with parents having different educational and socioeconomic level.

DISCUSSION

The prevalence of ADHD-HI was higher than the other two types. The highest prevalence was observed in 7- to 10-year-old children. The influential factors of ADHD prevalence were age, gender, and educational level.

Prevalence, gender distribution and presence of attention deficit hyperactivity disorder by certain sociodemographic characteristics among university students

INTRODUCTION

Attention deficit hyperactivity disorder (ADHD) is a neurobehavioral developmental disorder usually diagnosed in children, with appearance of the first symptoms before the age of seven years. The disorder is characterized by inattention and/or impulsivity and hyperactivity that can seriously affect many aspects of behavior and performance at school. Specific sociodemographic characteristics seem to contribute to the appearance of ADHD.

MATERIAL AND METHODS

The study was done on a sample of 500 university students. For the measurement of ADHD symptoms, the ADHD Adult Self-report Scale was used and a specifically designed questionnaire for collecting sociodemographic data.

RESULTS

The results of this screening study showed that in 184 (48.7%) respondents the symptoms of the disorder in the activity and attention were registered. ADHD is highly significant associated with gender (p = 0.0004). Men more often than women have this kind of disorder. Our results also showed that living and material conditions were not associated with a higher prevalence of ADHD.

Subclinical immune reactions to viral infections may correlate with child and adolescent diagnosis of attention-deficit/hyperactivity disorder: a preliminary study from Turkey

BACKGROUND

Attention-Deficit/Hyperactivity Disorder (ADHD) is one of the most common neuro-developmental disorders of childhood and adolescence. Studies focusing on the relationship of infectious agents and ADHD are scarce. It is also known that cerebellar injury may lead to hyperactive behavior. This study aimed to evaluate the relationship between viral agents of cerebellitis and the diagnosis of ADHD.

METHODS

The study group was formed of 60 consecutive ADHD patients and 30 healthy children. IgG levels for VZV; HSV-1, CMV, Measles, Mumps, Rubella and EBV were evaluated.

RESULTS

Males were significantly higher among patients with ADHD (65% vs. 40%, p=0.025). Patients with ADHD displayed significantly higher positivity for measles IgG (80% vs. 60%, p=0.044). When patients with ADHD were classified according to their pubertal status, adolescents with ADHD displayed higher positivity for mumps (100% vs. 74.4%, p=0.043). Most of the patients were diagnosed with ADHD-Combined or Hyperactive/Impulsive Subtypes (56.6%) while 43.3% were diagnosed with ADHD-predominantly inattentive type. When patients with subtypes of ADHD were compared in terms of seropositivity, it was found that patients with ADHD-Combined/ Hyperactive-Impulsive subtypes had significantly elevated reactions for Rubella (100% vs. 88.5%, p=0.044).

CONCLUSION

Although limited to a single center and may be prone to sampling biases, our results may support the notion that immune reactions may be related with ADHD among children and adolescents. Further, prospective studies from multiple centers are needed to support our findings and establish causality.

Sex-dependent changes in ADHD-like behaviors in juvenile rats following cortical dopamine depletion

Reduced cortical dopamine levels have been observed in individuals with attention deficit hyperactivity disorder (ADHD). Global dopamine depletions by 6-hydroxydopamine (6-OHDA; with noradrenergic protection) in neonatal rats produces locomotor hyperactivity, with less known about how cortical depletion modulates risky behaviors. Here, we determined the effect of a medial prefrontal cortex (PFC) 6-OHDA depletions (30-60%) or sham microinjection at postnatal day 11 on behavior in male and female juvenile rats. Separate groups were studied for delay discounting (impulsive choice), novelty-preference, and preferences for cues and environments associated with cocaine (10, 20, and 40 mg/kg), their extinction, and reinstatement with place conditioning. Because PFC D1 receptors play a role in these behaviors, confocal microscopy was used to measure D1-immunoreactive projections to the nucleus accumbens core. Both 6-OHDA males and females increased delay discounting relative to sham controls, although only 6-OHDA females increased novelty preferences. Preferences for cocaine-associated environments, their extinction, and reinstatement with a priming dose of cocaine were reduced in 6-OHDA subjects overall. However, impulsive choice at 5s positively correlated with preferences for cocaine-associated environments in 6-OHDA subjects, but not sham controls. As possible compensation for low dopamine levels, D1-immunoreactivity on traced neurons increased in 6-OHDA females; dopamine levels did not remain low in adolescent 6-OHDA males and D1 did not change. We believe that these modest depletions restricted to the PFC demonstrate the role of dopamine, and not norepinephrine, in understanding these behaviors in other animal models where cortical dopamine is reduced during development.

The effects of nutritional polyunsaturated fatty acids on locomotor activity in spontaneously hypertensive rats

The present study investigated the effects of nutritional omega-3 polyunsaturated fatty acids on locomotor activity in spontaneously hypertensive rats (SHRs), which are used as an animal model of attention-deficit/hyperactivity disorder (ADHD). For 6 weeks, two groups of randomly assigned SHRs received food either enriched with or deficient in omega-3 fatty acids (based on the American Institute of Nutrition-93 G/AIN93G). Using an open field, locomotor activity was subsequently assessed for 6 days. A marked difference in locomotor activity as assessed by the distance travelled in the open field was found between the two groups of rats. In comparison with rats fed with omega-3 fatty acid-enriched food, the animals on the omega-3 fatty acid-deficient diet showed a significantly higher locomotor activity. The present findings demonstrated that nutritional enrichment with omega-3 fatty acids was associated with reduced motor activity in an established animal model of ADHD and support the notion that omega-3 polyunsaturated fatty acids may play a role in the pathophysiology of ADHD.

Mice lacking collapsin response mediator protein 1 manifest hyperactivity, impaired learning and memory, and impaired prepulse inhibition

Collapsin response mediator protein 1 (CRMP1) is one of the CRMP family members that are involved in various aspects of neuronal development such as axonal guidance and neuronal migration. Here we provide evidence that crmp1 (-/-) mice exhibited behavioral abnormalities related to schizophrenia. The crmp1 (-/-) mice exhibited hyperactivity and/or impaired emotional behavioral phenotype. These mice also exhibited impaired context-dependent memory and long-term memory retention. Furthermore, crmp1 (-/-) mice exhibited decreased prepulse inhibition, and this phenotype was rescued by administration of chlorpromazine, a typical antipsychotic drug. In addition, in vivo microdialysis revealed that the methamphetamine-induced release of dopamine in prefrontal cortex was exaggerated in crmp1 (-/-) mice, suggesting that enhanced mesocortical dopaminergic transmission contributes to their hyperactivity phenotype. These observations suggest that impairment of CRMP1 function may be involved in the pathogenesis of schizophrenia. We propose that crmp1 (-/-) mouse may model endophenotypes present in this neuropsychiatric disorder.

Acupuncture for Attention Deficit Hyperactivity Disorder (ADHD) in children and adolescents

BACKGROUND

Attention Deficit Hyperactivity Disorder (ADHD) is a common childhood psychiatric disorder with features of inattention, hyperactivity and impulsivity. There is increasing interest in complementary and alternative therapies such as acupuncture; however, it remains unclear whether the use of acupuncture in children and adolescents with ADHD is supported by the existing evidence.

OBJECTIVES

To assess the efficacy and safety of acupuncture as a treatment for ADHD in children and adolescents.

SEARCH STRATEGY

We searched CENTRAL (The Cochrane Library 2010, Issue 2); MEDLINE (21 May 2010); CINAHL (21 May 2010); EMBASE (21 May 2010); ERIC (21 May 2010); PsycINFO (21 May 2010), Chinese Biological Medicine Database (10 May 2010); Chinese Scientific Periodical Database of VIP INFORMATION (10 May 2010); China Periodical in China National Knowledge Infrastructure (10 May 2010); and Chinese Evidence-Based Medicine Database (10 May 2010). We handsearched Chinese language journals and conference proceedings.

SELECTION CRITERIA

Randomised controlled trials and quasi-randomised controlled trials comparing acupuncture with placebo or sham acupuncture, or conventional treatment. Participants under the age of 18 years with any type of ADHD were included. Papers in any language were included.

DATA COLLECTION AND ANALYSIS

Two review authors (S Li, B Yu) independently determined the studies to be included in the review based on inclusion and exclusion criteria and extracted the data using pre-developed extraction forms. The risk of bias within the trials was assessed by the same review authors in relation to allocation concealment, blinding and withdrawals. The measures of ADHD outcomes were extracted from core symptoms rating scales and additional secondary outcomes were considered.

MAIN RESULTS

No studies met the inclusion criteria for this review.

AUTHORS' CONCLUSIONS

A comprehensive search showed that there is no evidence base of randomised or quasi-randomised controlled trials to support the use of acupuncture as a treatment for ADHD in children and adolescents. Due to the lack of trials, we cannot reach any conclusions about the efficacy and safety of acupuncture for ADHD in children and adolescents. This review highlights the need for further research in this area in the form of high quality, large scale, randomised controlled trials. 

Attention-modulating effects of cognitive enhancers

Attention can be readily measured in experimental animal models. Animal models of attention have been used to better understand the neural systems involved in attention, how attention is impaired, and how therapeutic treatments can ameliorate attentional deficits. This review focuses on the ways in which animal models are used to better understand the neuronal mechanism of attention and how to develop new therapeutic treatments for attentional impairment. Several behavioral test methods have been developed for experimental animal studies of attention, including a 5-choice serial reaction time task (5-CSRTT), a signal detection task (SDT), and a novel object recognition (NOR) test. These tasks can be used together with genetic, lesion, pharmacological and behavioral models of attentional impairment to test the efficacy of novel therapeutic treatments. The most prominent genetic model is the spontaneously hypertensive rat (SHR). Well-characterized lesion models include frontal cortical or hippocampal lesions. Pharmacological models include challenge with the NMDA glutamate antagonist dizocilpine (MK-801), the nicotinic cholinergic antagonist mecamylamine and the muscarinic cholinergic antagonist scopolamine. Behavioral models include distracting stimuli and attenuated target stimuli. Important validation of these behavioral tests and models of attentional impairments for developing effective treatments for attentional dysfunction is the fact that stimulant treatments effective for attention deficit hyperactivity disorder (ADHD), such as methylphenidate (Ritalin®), are effective in the experimental animal models. Newer lines of treatment including nicotinic agonists, α4β2 nicotinic receptor desensitizers, and histamine H₃ antagonists, have also been found to be effective in improving attention in these animal models. Good carryover has also been seen for the attentional improvement caused by nicotine in experimental animal models and in human populations. Animal models of attention can be effectively used for the development of new treatments of attentional impairment in ADHD and other syndromes in which have attentional impairments occur, such as Alzheimer's disease and schizophrenia.

Inhibitory control and psychopathology: a meta-analysis of studies using the stop signal task

The Stop Signal Task (SST) is a measure that has been used widely to assess response inhibition. We conducted a meta-analysis of studies that examined SST performance in patients with various psychiatric disorders to determine the magnitude and generality of deficient inhibition. A five-item instrument was used to assess the methodological quality of studies. We found medium deficits in stop signal reaction time (SSRT), reflecting the speed of the inhibitory process, for attention-deficit hyperactivity disorder (ADHD) (g = 0.62), obsessive compulsive disorder (OCD) (g = 0.77) and schizophrenia (SCZ) (g = 0.69). SSRT was less impaired or normal for anxiety disorder (ANX), autism, major depressive disorder (MDD), oppositional defiant disorder/conduct disorder (ODD/CD), pathological gambling, reading disability (RD), substance dependence, and Tourette syndrome. We observed a large SSRT deficit for comorbid ADHD + RD (g = 0.82). SSRT was less than moderately impaired for ADHD + ANX and ADHD + ODD/CD. Study quality did not significantly affect SSRT across ADHD studies. This confirms an inhibition deficit in ADHD, and suggests that comorbid ADHD has different effects on inhibition in patients with ANX, ODD/CD, and RD. Further studies are needed to firmly establish an inhibition deficit in OCD and SCZ.

Effects of d-amphetamine on short- and long-term memory in spontaneously hypertensive, Wistar-Kyoto and Sprague-Dawley rats

Diverse studies indicate that the attention deficit hyperactivity disorder (ADHD) is associated with alterations in encoding processes, including working or short-term memory. Some ADHD dysfunctional domains are reflected in the spontaneously hypertensive rat (SHR). Here SHR-saline group showed significantly poor STM and LTM relative to SD and WKY saline rats. SD and WKY rats treated with d-amphetamine displayed better STM and LTM, compared to SD-vehicle, WKY-vehicle or SHR-d-amphetamine groups.

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.

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

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

Case-control study of six genes asymmetrically expressed in the two cerebral hemispheres: association of BAIAP2 with attention-deficit/hyperactivity disorder

BACKGROUND

Attention-deficit/hyperactivity disorder (ADHD) is a childhood-onset neuropsychiatric disease that persists into adulthood in at least 30% of patients. There is evidence suggesting that abnormal left-right brain asymmetries in ADHD patients may be involved in a variety of ADHD-related cognitive processes, including sustained attention, working memory, response inhibition and planning. Although mechanisms underlying cerebral lateralization are unknown, left-right cortical asymmetry has been associated with transcriptional asymmetry at embryonic stages and several genes differentially expressed between hemispheres have been identified.

METHODS

We selected six functional candidate genes showing at least 1.9-fold differential expression between hemispheres (BAIAP2, DAPPER1, LMO4, NEUROD6, ATP2B3, and ID2) and performed a case-control association study in an initial Spanish sample of 587 ADHD patients (270 adults and 317 children) and 587 control subjects.

RESULTS

The single- and multiple-marker analysis provided evidence for a contribution of BAIAP2 to adulthood ADHD (p = .0026 and p = .0016, respectively). We thus tested BAIAP2 for replication in two independent adult samples from Germany (639 ADHD patients and 612 control subjects) and Norway (417 ADHD cases and 469 control subjects). While no significant results were observed in the Norwegian sample, we replicated the initial association between BAIAP2 and adulthood ADHD in the German population (p = .0062).

CONCLUSIONS

Our results support the participation of BAIAP2 in the continuity of ADHD across life span, at least in some of the populations analyzed, and suggest that genetic factors potentially influencing abnormal cerebral lateralization may be involved in this disorder.

Maternal social separation of adolescent rats induces hyperactivity and anxiolytic behavior

Exposure to early stressful adverse life events such as maternal and social separation plays an essential role in the development of the nervous system. Adolescent Sprague-Dawley rats that were separated on postnatal day 14 from their dam and litters (maternal social separation, MSS) showed hyperactivity and anxiolytic behavior in the open field test, elevated plus-maze test, and forced-swim test. Biologically, the number of astrocytes was significantly increased in the prefrontal cortex of MSS adolescent rats. The hyperactive and anxiolytic phenotype and biological alteration produced by this MSS protocol may provide a useful animal model for investigating the neurobiology of psychiatric disorders of childhood-onset diseases, such as attention deficient hyperactive disorder.

Mice lacking the schizophrenia-associated protein FEZ1 manifest hyperactivity and enhanced responsiveness to psychostimulants

FEZ1 (fasciculation and elongation protein zeta 1), a mammalian ortholog of Caenorhabditis elegans UNC-76, interacts with DISC1 (disrupted in schizophrenia 1), a schizophrenia susceptibility gene product, and polymorphisms of human FEZ1 have been associated with schizophrenia. We have now investigated the role of FEZ1 in brain development and the pathogenesis of schizophrenia by generating mice that lack Fez1. Immunofluorescence staining revealed FEZ1 to be located predominantly in gamma-aminobutyric acid-containing interneurons. The Fez1(-/-) mice showed marked hyperactivity in a variety of behavioral tests as well as enhanced behavioral responses to the psychostimulants MK-801 and methamphetamine. In vivo microdialysis revealed that the methamphetamine-induced release of dopamine in the nucleus accumbens was exaggerated in the mutant mice, suggesting that enhanced mesolimbic dopaminergic transmission contributes to their hyperactivity phenotype. These observations implicate impairment of FEZ1 function in the pathogenesis of schizophrenia.

The neuropsychopharmacology of action inhibition: cross-species translation of the stop-signal and go/no-go tasks

BACKGROUND AND RATIONALE

The term 'action inhibition' encapsulates the ability to prevent any form of planned physical response. Growing evidence suggests that different 'stages' or even subtypes of action inhibition activate subtly different neuropharmacological and neuroanatomical processes.

OBJECTIVES

In this review, we present evidence from two commonly used and apparently similar behavioural tests, the stop-signal task and the go/no-go task, to determine if these have similar neuroanatomical and neurochemical modulation.

RESULTS

Whilst performance of the stop-signal and go/no-go tasks is modulated across only subtly different anatomical networks, serotonin (5-HT) is strongly implicated in inhibitory control on the go/no-go but not the stop-signal task, whereas the stop-signal reaction time appears more sensitive to the action of noradrenaline.

CONCLUSIONS

There is clear neuropharmacological and neuroanatomical evidence that stop-signal and go/no-go tasks represent different forms of action inhibition. This evidence translates with remarkable consistency across species. We discuss the possible implications of this evidence with respect to the development of novel therapeutic treatments for disorders in which inhibitory deficits are prominent and debilitating.

Pharmacological models of ADHD

For more than 50 years, heavy metal exposure during pre- or post-natal ontogeny has been known to produce long-lived hyperactivity in rodents. Global brain injury produced by neonatal hypoxia also produced hyperactivity, as did (mainly) hippocampal injury produced by ontogenetic exposure to X-rays, and (mainly) cerebellar injury produced by the ontogenetic treatments with the antimitotic agent methylazoxymethanol or with polychlorinated biphenyls (PCBs). More recently, ontogenetic exposure to nicotine has been implicated in childhood hyperactivity. Because attention deficits most often accompany the hyperactivity, all of the above treatments have been used as models of attention deficit hyperactivity disorder (ADHD). However, the causation of childhood hyperactivity remains unknown. Neonatal 6-OHDA-induced dopaminergic denervation of rodent forebrain also produces hyperactivity - and this model, or variations of it, remain the most widely-used animal model of ADHD. In all models, amphetamine (AMPH) and methylphenidate (MPH), standard treatments of childhood ADHD, typically attenuate the hyperactivity and/or attention deficit. On the basis of genetic models and the noted animal models, monoaminergic phenotypes appear to most-closely attend the behavioral dysfunctions, notably dopaminergic, noradrenergic and serotoninergic systems in forebrain (basal ganglia, nucleus accumbens, prefrontal cortex). This paper describes the various pharmacological models of ADHD and attempts to ascribe a neuronal phenotype with specific brain regions that may be associated with ADHD.

Muscarinic acetylcholine receptors: mutant mice provide new insights for drug development

Muscarinic acetylcholine receptors (mAChRs), M(1)-M(5), regulate the activity of numerous fundamental central and peripheral functions. The lack of small-molecule ligands that can block or activate specific mAChR subtypes with high selectivity has remained a major obstacle in defining the roles of the individual receptor subtypes and in the development of novel muscarinic drugs. Recently, phenotypic analysis of mutant mouse strains deficient in each of the five mAChR subtypes has led to a wealth of new information regarding the physiological roles of the individual receptor subtypes. Importantly, these studies have identified specific mAChR-regulated pathways as potentially novel targets for the treatment of various important disorders including Alzheimer's disease, schizophrenia, pain, obesity and diabetes.

Comparison of a standard psychiatric evaluation to rating scales and EEG in the differential diagnosis of attention-deficit/hyperactivity disorder

The objective was to investigate the effectiveness of rating scales and electroencephalography (EEG) in detecting the presence of attention-deficit/hyperactivity disorder (ADHD) within a diverse clinical sample. A standard psychiatric evaluation was used to assess 26 children/adolescents who presented to a clinic because a parent suspected the presence of ADHD. EEG data was collected in a blinded protocol, and rating scales were collected as well. Although all subjects had presented with ADHD-like symptoms, only 62% were diagnosed with ADHD, while the remaining 38% had other disorders or no diagnosis. Rating scales readily classified inattentive, impulsive, and/or hyperactive symptoms as being due to ADHD, regardless of the actual underlying disorder, leading to a sensitivity of 81% and a specificity of 22%. Previous studies have observed that there is an EEG marker that identifies ADHD vs. controls, and this marker was present in 15 out of 16 of the ADHD subjects (sensitivity=94%) and in none of the subjects with ADHD-like symptoms due to other disorders (specificity=100%). In the detection of ADHD in a diverse clinical sample, rating scales and EEG were both sensitive markers, whereas only EEG was specific. These results may have important implications to ADHD differential diagnosis.

Maternal smoking habits and cognitive development of children at age 4 years in a population-based birth cohort

BACKGROUND

Active maternal smoking during pregnancy has been associated with a higher risk of behavioural disorders in children, but a few cohort studies measuring smoking data prospectively have studied its specific effects on the cognitive abilities of pre-schoolers.

METHOD

A birth cohort was set up in Menorca Island in 1997 within the Asthma Multicenter Infants Cohort Study. A total of 420 (87% of those eligible) children had complete data for final analyses at age 4 years. Interviewer-administered questionnaires were completed by mothers during the third trimester of pregnancy and then every year up to age 4 years of their child. A standardized version of the McCarthy Scales of Children's Abilities (MCSA) was used to evaluate the child's motor and cognitive capabilities. Multivariable regressions were used with MCSA's assessed outcomes adjusting for: home location, maternal alcohol consumption, mother's social class and level of education during pregnancy, parity, marital status, father's education level, child's gender, birth weight and height, breastfeeding duration, passive smoking, school season, age during test administration and evaluator (psychologist).

RESULTS

A high global consistency in maternal smoking habits was found (total agreement = 88.7%). Maternal social class and education level were inversely associated with maternal smoking behaviour. Maternal smoking during pregnancy (in cig./day) was associated with a decrease (in points) of children's global cognitive score [beta = -0.60, (95% CI: -1.10; -0.09)]; as well as global cognitive sub-areas like verbal score [beta = -0.59, (95% CI: -1.11; -0.07)]; quantitative score [beta = -0.57, (95% CI: -1.08; -0.06)]; executive function score [beta = -0.71, (95% CI: -1.23; -0.20)]; and working memory score [beta = -0.46, (95% CI: -0.92; -0.01)].

CONCLUSION

Our findings suggest an association with maternal smoking during pregnancy and lowered cognitive development in children at age 4 years.

Animal models concerning the role of dopamine in attention-deficit hyperactivity disorder

Several models of attention-deficit hyperactivity disorder (ADHD) have been proposed, ranging from administration of neurotoxins to genetically manipulated models. These models are used to gain insight into ADHD as a disorder and assist in the discovery of new therapeutic strategies. However, the information gained from these models differs, depending to a large extent on the validity (or otherwise) of the model. Thus the insights gained from these models with respect to the pathophysiology and aetiology of ADHD remains inconclusive. No animal model resembles the clinical situation of ADHD perfectly but good animal models of ADHD should mimic its characteristics, confirm to an underlying theory of ADHD and ultimately make predictions of future therapies. While the involvement of dopamine (DA) in ADHD has been established, the evaluation of rodent models of ADHD particularly with respect to dopaminergic systems is attempted here. It is concluded that the neonatal 6-hydroxy-dopamine lesioned rat and DA transporter knockout/knockdown mice have the highest degree of validity for ADHD.

Attention problems among children with a positive family history of alcohol abuse or dependence and controls. Prevalence and course for the period from preteen to early teen years

This longitudinal study investigated the scope and course of attention problems over a period of time from preteen (ages 7-12 years) to early teen years (ages 13-17 years). We compared symptoms in subjects with and without a family history (FH) of alcohol abuse or dependence from among families without evidence of antisocial personality disorder. Evaluations of attention problems for the offspring were based on the Child Behavior Checklist and a validated semistructured interview carried out with the mother. The findings indicate no higher risk for attention problems and attention-deficit hyperactivity disorder (ADHD)-like symptoms in the children of families with an alcohol use disorder. Regarding the course of problems, the ADHD symptom count tended to decrease over time, especially for children without a FH of alcohol abuse or dependence. Further research will be needed to determine whether results can be replicated with families from different social strata and including subjects with the antisocial personality disorder.

Mechanisms of working memory dysfunction after mild and moderate TBI: evidence from functional MRI and neurogenetics

Cognitive complaints are a frequent source of distress and disability after mild and moderate traumatic brain injury (TBI). While there are deficits in several cognitive domains, many aspects of these complaints and deficits suggest that problems in working memory (WM) play an important role. Functional imaging studies in healthy individuals have outlined the neural substrate of WM and have shown that regions important in WM circuitry overlap with regions commonly vulnerable to damage in TBI. Use of functional MRI (fMRI) in individuals with mild and moderate TBI suggests that they can have problems in the activation and allocation of WM, and several lines of evidence suggest that subtle alterations in central catecholaminergic sensitivity may underlie these problems. We review the evidence from fMRI and neurogenetic studies that support the role of catecholaminergic dysregulation in the etiology of WM complaints and deficits after mild and moderate TBI.

Integrative neuroscience approach to predict ADHD stimulant response

Despite high rates of prescription, little is known about the long-term consequences of stimulant medication therapy for attention-deficit hyperactivity disorder (ADHD) sufferers. Historically, the clinical use of stimulants for ADHD has been based on trial and error before optimal therapy is reached. Concurrently, scientific research on the mechanism of action of stimulants has influenced neurobiological models of ADHD, but has not always informed their prescription. Whilst the two main stimulant types (methylphenidate and dexamphetamine) have numerous similarities, they also differ (slightly) in mechanism and possibly individual response. A further issue relates to differences in cost and availability compounded by the expectation for stimulants to be effective in ameliorating a broad spectrum of ADHD-related symptoms. Thus, there is an increasing need for treating clinicians to prescribe not only the most effective drug, but also the most appropriate dose with the associated release mechanism and schedule for each ADHD patient presented. In this regard, the field is witnessing an emergence of the personalized medicine approach to ADHD, in which treatment decisions are tailored to each individual. This shift requires a new approach to research into treatment response prediction. Given the heterogeneity of ADHD, a profile of information may be required to capture the most sensitive predictors of treatment response in individuals. These profiles will also benefit from the integration of data from clinical rating scales with more direct measures of cognition and brain function. In conclusion, there is a need to establish a more robust normative framework as the baseline for treatment, as well as diagnostic decisions, and as discussed, the growth of integrated neuroscience databases will be important in this regard.

The association between early minor motor difficulties in extreme low birth weight infants and school age attentional difficulties

INTRODUCTION

Extremely premature infants of normal intellectual ability have an increased prevalence of motor and attentional difficulties. Knowledge of the relationship between early motor difficulties and measures of attention at school age would enhance understanding of these developmental pathways, their interrelationship and opportunities for intervention.

OBJECTIVE

This study examines whether an association exists between early findings of minor motor difficulties and school age clinical and psychometric measures of attention.

METHODOLOGY

45/60 eligible ELBW(1000 g) or preterm (< 27/40 gestation) infants born at the Mater Mother's Hospital were assessed at 12 and 24 months for minor motor deficits (using NSMDA) and at 7-9 years for attention, using clinical (Conners and Du Paul Rating Scales) and psychometric (assessing attention span, selective and divided attention) measures.

RESULTS

NSMDA at 12 months was only associated with the psychometric measures of verbal attention span. It was not associated with later clinical measures of attention. NSMDA at 24 months was strongly associated with specific clinical measures of attention at school age, independent of biological and social factors. It was not associated with psychometric measures of attention.

CONCLUSION

The major finding of this study is that motor difficulties in ELBW infants at 2 years are associated with later clinical measures of attention. Possible mechanisms underlying this relationship are considered.

Algorithmically designed peptides ameliorate behavioral defects in animal model of ADHD by an allosteric mechanism

This study exemplifies the use of three ADHD-relevant methodological innovations. (1) The use of novel, patented, computational peptide design techniques to generate peptides targeting the extra-cellular and para-transmembrane amino acid loops of the putatively ADHD-involved, D(2) dopamine receptor, D(2)DAR; (2) experimental evidence that these peptides in L-amino acid/ortho ordered or D-amino acid/reverse ordered (retro-inverso), D(2)DAR, hydrophobic eigenmode matched forms, evoked positive allosteric and indirect agonist influences on in vitro stably receptor transfected CHO and LtK cells and on in vivo, brain mediated activity; (3) a representative 15 residue all-D-amino acid, D(2) mode matched peptide, given parenterally, was found to "repair" a key aberrant ADHD behavioral characteristic in a standard animal model of ADHD, the Spontaneously Hypertensive Rat, SHR, relative to its progenitor species control, the Wistar-Kyoto rat, WKY. The representative, retro-inverso peptide, all-D-LLYKNKPRYPKRNRE, reversed SHR's relative deficiency in sensory motor gating (pre-pulse inhibition, PPI) while leaving SHR's nonselective attention (rearings), impulsive behavior (time in center), and activity level (timed total motor behavior) unchanged. Amphetamine also reversed SHRs sensory gating defect, but with significant increases in nonselective attention, impulsivity and hyperactivity. These preliminary results suggest the possibility of a new, "softer" pharmacological approach to ADHD: hydrophobic mode matched peptide allosteric augmentation of the activity of indigenous dopamine with respect to D(2)DAR mediated function, in place of stimulant drug-induced presynaptic dopamine release or impairment of dopamine uptake.

ADHD and the dopamine transporter: are there reasons to pay attention?

The catecholamine dopamine (DA) plays an important role as a neurotransmitter in the brain in circuits linked to motor function, reward, and cognition. The presynaptic DA transporter (DAT) inactivates DA following release and provides a route for non-exocytotic DA release (efflux) triggered by amphetamines. The synaptic role of DATs first established through antagonist studies and more recently validated through mouse gene-knockout experiments, raises questions as to whether altered DAT structure or regulation support clinical disorders linked to compromised DA signaling, including drug abuse, schizophrenia, and attention deficit hyperactivity disorder (ADHD). As ADHD appears to have highly heritable components and the most commonly prescribed therapeutics for ADHD target DAT, studies ranging from brain imaging to genomic and genetic analyses have begun to probe the DAT gene and its protein for possible contributions to the disorder and/or its treatment. In this review, after a brief overview of ADHD prevalence and diagnostic criteria, we examine the rationale and experimental findings surrounding a role for human DAT in ADHD. Based on the available evidence from our lab and labs of workers in the field, we suggest that although a common variant within the human DAT (hDAT) gene (SLC6A3) is unlikely to play a major role in the ADHD, contributions of hDAT to risk maybe most evident in phenotypic subgroups. The in vitro and in vivo validation of functional variants, pursued for contributions to endophenotypes in a within family approach, may help elucidate DAT and DA contributions to ADHD and its treatment.

Predictors of attention problems for the period from pre-teen to early teen years

OBJECTIVE

This longitudinal study investigated the scope, persistence, and predictors of attention problems (AP) over a period of time from pre-teen (7-12 years) to early teen years (13-17 years).

METHOD

AP evaluations used the Child Behavior Checklist (CBCL) and a semi-structured interview (C-SSAGA-P) with the parents. In addition, data relating to birth complications, family histories of affective disorders and alcohol-use disorders, home supervision, emotional, social and behavioral problems, school performance and school activities at two different measurement points were also collected.

RESULTS

The findings indicate a high degree of comorbidity between AP and emotional and behavioral problems, difficulties in school, social problems and peer rejection. Furthermore, a cross-sectional association between childhood AP and parental affective disorders was also evident. Longitudinally, there was no increase in AP over the age span covered by the study, and symptoms often did not persist over time. Multiple regression analyses confirmed poorer school performance, problems with peers and AP at time point 15 as predictors for subsequent AP.

CONCLUSION

The findings indicate that AP symptoms do not occur more frequently in early teen than in pre-teen years, and tend to be temporary phenomena. Difficulties in school and with peers were noted as particularly strong predictors of subsequent AP.

Online measurement of motivational processes: introducing the Continuous Delay Aversion Test (ConDAT)

The Continuous Delay Aversion Test (ConDAT), a new computer task for online monitoring and continuously measuring delay aversion (DA), is introduced. DA is a motivational style related to a shortened delay gradient which is proposed as a major endophenotype of attention deficit hyperactivity disorder (ADHD). It is characterised by avoiding or escaping from delay-rich situations despite the prospects of a reward. In each ConDAT trial the rapidly diminishing reward/delay ratio, which tends asymptotically towards zero, is visually presented on the computer screen. The test subject is permanently confronted with the question whether to quit or to continue the trial in the face of the deteriorating reward/time ratio. An elaborated control of stimuli and responses, including the sending of trigger codes to external recording devices, makes the task useful for neurophysiological or brain imaging experiments. Compared to existing tasks, the ConDAT is more flexible and sensitive due to its asymptotic open-ended trials and the interval-scaled output measure. Pilot data give evidence for satisfactory reliability and external validity of the task.

Stimulus processing and associative learning in Wistar and WKHA rats

This study assessed basic learning and attention abilities in Wistar-Kyoto hyperactive (WKHA) rats using appetitive conditioning preparations. Two measures of conditioned responding to a visual stimulus, orienting behavior (rearing on the hind legs), and food cup behavior (placing the head inside the recessed food cup) were measured. In Experiment 1, simple conditioning, but not extinction, was impaired in WKHA rats compared with Wistar rats. In Experiment 2, nonreinforced presentations of the visual cue preceded the conditioning sessions. WKHA rats displayed less orienting behavior than Wistar rats but comparable levels of food cup behavior. These data suggest that WKHA rats exhibit specific abnormalities in attentional processing as well as in learning stimulus-reward relationships.

Attention-deficit/hyperactivity disorder: an overview of the etiology and a review of the literature relating to the correlates and lifecourse outcomes for men and women

This paper provides a summary of the current conceptualization of what AD/HD is, and its etiology, and then reviews some of the recent literature on the correlates and lifecourse outcomes for individuals diagnosed with Attention-Deficit/Hyperactivity Disorder (AD/HD). The intention is to synthesize that which is known, and to identify important gaps in the literature and knowledge base, which secondary analysis of prospective large-scale longitudinal cohorts, tracking individuals from birth to adulthood, could help to fill. This review highlights the fact that such datasets are rare and that their analysis offers important opportunities for advancing knowledge, particularly of the adult outcomes of childhood AD/HD.

Behavioral effects of intra-cranial self-stimulation in an animal model of attention-deficit/hyperactivity disorder (ADHD)

Attention deficit/hyperactivity disorder (ADHD), characterized by inappropriate levels of activity, attention, and impulsivity, has been suggested to be caused by changes in reinforcement and extinction processes possibly linked to dysfunctioning dopamine systems. The present study investigated reinforcement processes in spontaneously hypertensive rats (SHR), an animal model of ADHD. Using intra-cranial self-stimulation (ICSS), behavioral effects of varying current intensity, reinforcer density, and reinforcer delay were tested. Current was varied in order to find the weakest current producing the maximal response rate (optimal current) in the SHR and the controls during high (120 reinforcers/min) and low reinforcer densities (1 reinforcer/min). The results showed that optimal current was significantly lower in the SHR than in the controls during high reinforcer density while maximal response rates were not significantly different. During low reinforcer density, optimal current was not significantly different in the two strains, but maximal response rate was significantly higher in the SHR than in the controls. The SHR produced more responses during the testing of reinforcer density, but changes in reinforcer density affected response rates similarly in the two strains. The decrease in response rate as a function of reinforcer delay was more pronounced in the SHR than in the controls. Overall, more responses with short inter-response times (IRT) were found in the SHR compared to the controls during intermittent reinforcement. The results are consistent with a steepened delay-of-reinforcement gradient in SHR.

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.