Non-selective attention and nitric oxide in putative animal models of Attention-Deficit Hyperactivity Disorder

5-HT1A and 5-HT2A receptor effects on recognition memory, motor/exploratory behaviors, emotionality and regional dopamine transporter binding in the rat

Both dopamine (DA) and serotonin (5-HT) play key roles in numerous functions including motor control, stress response and learning. So far, there is scarce or conflicting evidence about the effects of 5-HT1A and 5-HT2A receptor (R) agonists and antagonists on recognition memory in the rat. This also holds for their effect on cerebral DA as well as 5-HT release. In the present study, we assessed the effects of the 5-HT1AR agonist 8-OH-DPAT and antagonist WAY100,635 and the 5-HT2AR agonist DOI and antagonist altanserin (ALT) on rat behaviors. Moreover, we investigated their impact on monoamine efflux by measuring monoamine transporter binding in various regions of the rat brain. After injection of either 8-OH-DPAT (3 mg/kg), WAY100,635 (0.4 mg/kg), DOI (0.1 mg/kg), ALT (1 mg/kg) or the respective vehicle (saline, DMSO), rats underwent an object and place recognition memory test in the open field. Upon the assessment of object exploration, motor/exploratory parameters and feces excretion, rats were administered the monoamine transporter radioligand N-o-fluoropropyl-2b-carbomethoxy-3b-(4-[123I]iodophenyl)-nortropane ([123I]-FP-CIT; 8.9 ± 2.6 MBq) into the tail vein. Regional radioactivity accumulations in the rat brain were determined post mortem. Compared vehicle, administration of 8-OH-DPAT impaired memory for place, decreased rearing behavior, and increased ambulation as well as head-shoulder movements. DOI administration led to a reduction in rearing behavior but an increase in head-shoulder motility relative to vehicle. Feces excretion was diminished after ALT relative to vehicle. Dopamine transporter (DAT) binding was increased in the caudateputamen (CP), but decreased in the nucleus accumbens (NAC) after 8-OH-DPAT relative to vehicle. Moreover, DAT binding was decreased in the NAC after ALT relative to vehicle. Findings indicate that 5-HT1AR inhibition and 5-HT2AR activation may impair memory for place. Furthermore, results imply associations not only between recognition memory, motor/exploratory behavior and emotionality but also between the respective parameters and the levels of available DA in CP and NAC.

BH4 as a Therapeutic Target for ADHD: Relevance to Neurotransmitters and Stress-Driven Symptoms

Tetrahydrobiopterin (BH4) is a critical cofactor in a variety of metabolic pathways that have been linked to ADHD. There have been no previous studies utilizing BH4 as a supplement for ADHD. BH4 has been approved as a treatment for phenylketonuria (PKU). Individuals with PKU and ADHD appear to have low DA levels in common, suggesting that the hypodopaminergic state seen in both illnesses could be a relationship between the two. Clinical research involving supplementation of BH4 has shown low occurrence of adverse. In experiments, BH4 has also been found to have good blood-brain barrier permeability. BH4 also has the ability in scavenging ROS activity, which is an implication of stress and is seen in ADHD. BH4's significance in ADHD is reviewed in this paper because of its involvement in numerous neurodevelopmental metabolic pathways, and we anticipate that exogenous BH4 can be used to treat ADHD.

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

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

Modafinil Administration to Preadolescent Rat Impairs Non-Selective Attention, Frontal Cortex D2 Expression and Mesolimbic GABA Levels

The misuse of psychostimulants is an increasing behavior among young people, highlighting in some countries the abuse of modafinil (MOD) as a neuropotentiator. However, several clinical trials are investigating MOD as an alternative pharmacological treatment for attentional deficit and hyperactivity disorder (ADHD) in children and adolescents. On the other hand, the early use of psychostimulants and the misdiagnosis rates in ADHD make it crucial to investigate the brain effects of this type of drug in young healthy individuals. The aim of this work was to evaluate the effects of chronic MOD treatment on neurochemicals (γ-aminobutyric acid and glutamate), dopamine receptor 2 (D₂) expression and behavior (non-selective attention "NSA") in the mesocorticolimbic system of young healthy Sprague-Dawley rats. Preadolescent male rats were injected with MOD (75 mg/kg, i.p.) or a vehicle for 14 days (from postnatal day 22 to 35). At postnatal day 36, we measured the GLU and GABA contents and their extracellular levels in the nucleus accumbens (NAc). In addition, the GLU and GABA contents were measured in the ventral tegmental area (VTA) and D₂ protein levels in the prefrontal cortex (PFC). Chronic use of MOD during adolescence induces behavioral and neurochemical changes associated with the mesocorticolimbic system, such as a reduction in PFC D₂ expression, VTA GABA levels and NSA. These results contribute to the understanding of the neurological effects of chronic MOD use on a young healthy brain.

Functional Convergence of Motor and Social Processes in Lobule IV/V of the Mouse Cerebellum

Topographic organization of the cerebellum is largely segregated into the anterior and posterior lobes that represent its "motor" and "non-motor" functions, respectively. Although patients with damage to the anterior cerebellum often exhibit motor deficits, it remains unclear whether and how such an injury affects cognitive and social behaviors. To address this, we perturbed the activity of major anterior lobule IV/V in mice by either neurotoxic lesion or chemogenetic excitation of Purkinje cells in the cerebellar cortex. We found that both of the manipulations impaired motor coordination, but not general locomotion or anxiety-related behavior. The lesioned animals showed memory deficits in object recognition and social-associative recognition tests, which were confounded by a lack of exploration. Chemogenetic excitation of Purkinje cells disrupted the animals' social approach in a less-preferred context and social memory, without affecting their overall exploration and object-based memory. In a free social interaction test, the two groups exhibited less interaction with a stranger conspecific. Subsequent c-Fos imaging indicated that decreased neuronal activities in the medial prefrontal cortex, hippocampal dentate gyrus, parahippocampal cortices, and basolateral amygdala, as well as disorganized modular structures of the brain networks might underlie the reduced social interaction. These findings suggest that the anterior cerebellum plays an intricate role in processing motor, cognitive, and social functions.

Elevated Melatonin Levels in Children With Attention Deficit Hyperactivity Disorder: Relationship to Oxidative and Nitrosative Stress

Objective: The aim of this article is to measure serum antioxidant melatonin, the oxidants of nitric oxide, and malondialdehyde levels to calculate the serum oxidant-antioxidant balance based on the nitric oxide/melatonin and malondialdehyde/melatonin ratios in children with ADHD. Method: The serum melatonin, nitric oxide, malondialdehyde, and the nitric oxide/melatonin and malondialdehyde/melatonin ratios were calculated and compared between the children with ADHD (n = 103) and healthy control participants (n = 73). Results: Serum melatonin and nitric oxide levels were higher, and the nitric oxide/melatonin and malondialdehyde/melatonin ratios were lower in ADHD children than the control group. Melatonin was found to be significantly high, and the malondialdehyde/melatonin ratio was found to be significantly low in children with a positive ADHD family history. Conclusion: The serum oxidant-antioxidant balance was impaired in children with ADHD. Within the ADHD group, higher melatonin levels were determined in the children with a positive family history.

Motor Function Deficits in the Estrogen Receptor Beta Knockout Mouse: Role on Excitatory Neurotransmission and Myelination in the Motor Cortex

BACKGROUND

Male estrogen receptor beta (ERβ) knockout (BERKO) mice display anxiety and aggression linked to, among others, altered serotonergic signaling in the basolateral amygdala and dorsal raphe, impaired cortical radial glia migration, and reduced GABAergic signaling. The effects on primary motor cortex (M1 cortex) and locomotor activity as a consequence of ERβ loss have not been investigated.

OBJECTIVE

The aim of this study was to determine whether locomotor activity is altered as a consequence of the changes in the M1 cortex.

METHODS

The locomotor activity of male wild-type (WT) and BERKO mice was evaluated using the open-field and rotarod tests. Molecular changes in the M1 cortex were analyzed by RNA sequencing, electron microscopy, electrophysiology, and immunohistological techniques. In addition, we established oligodendrocyte (OL) cultures from WT and BERKO mouse embryonic stem cells to evaluate OL function.

RESULTS

Locomotor profiling revealed that BERKO mice were more active than WT mice but had impaired motor coordination. Analysis of the M1 cortex pointed out differences in synapse function and myelination. There was a reduction in GABAergic signaling resulting in imbalanced excitatory and inhibitory neurotransmission as well as a defective OL differentiation accompanied by myelin defects. The effects of ERβ loss on OL differentiation were confirmed in vitro.

CONCLUSION

ERβ is an important regulator of GABAergic interneurons and OL differentiation, which impacts on adult M1 cortex function and may be linked to increased locomotor activity and decreased motor coordination in BERKO mice.

Role of Oxidative Stress and Neuroinflammation in Attention-Deficit/Hyperactivity Disorder

Attention-deficit/hyperactivity disorder (ADHD) is a neurodevelopmental disorder of childhood. Although abnormalities in several brain regions and disturbances of the catecholaminergic pathway have been demonstrated, the pathophysiology of ADHD is not completely understood, but as a multifactorial disorder, has been associated with an increase in oxidative stress and neuroinflammation. This review presents an overview of factors that increase oxidative stress and neuroinflammation. The imbalance between oxidants and antioxidants and also the treatment with medications are two factors that can increase oxidative damage, whereas the comorbidity between ADHD and inflammatory disorders, altered immune response, genetic and environmental associations, and polymorphisms in inflammatory-related genes can increase neuroinflammation. Evidence of an association with these factors has become valuable for research on ADHD. Such evidence opens up new intervention routes for the use of natural products as antioxidants that could have potential as a treatment against oxidative stress and neuroinflammation in ADHD.

Altered dopaminergic pathways and therapeutic effects of intranasal dopamine in two distinct mouse models of autism

The dopamine (DA) system has a profound impact on reward-motivated behavior and is critically involved in neurodevelopmental disorders, such as autism spectrum disorder (ASD). Although DA defects are found in autistic patients, it is not well defined how the DA pathways are altered in ASD and whether DA can be utilized as a potential therapeutic agent for ASD. To this end, we employed a phenotypic and a genetic ASD model, i.e., Black and Tan BRachyury T+Itpr3tf/J (BTBR) mice and Fragile X Mental Retardation 1 knockout (Fmr1-KO) mice, respectively. Immunostaining of tyrosine hydroxylase (TH) to mark dopaminergic neurons revealed an overall reduction in the TH expression in the substantia nigra, ventral tegmental area and dorsal striatum of BTBR mice, as compared to C57BL/6 J wild-type ones. In contrast, Fmr1-KO animals did not show such an alteration but displayed abnormal morphology of TH-positive axons in the striatum with higher "complexity" and lower "texture". Both strains exhibited decreased expression of striatal dopamine transporter (DAT) and increased spatial coupling between vesicular glutamate transporter 1 (VGLUT1, a label for glutamatergic terminals) and TH signals, while GABAergic neurons quantified by glutamic acid decarboxylase 67 (GAD67) remained intact. Intranasal administration of DA rescued the deficits in non-selective attention, object-based attention and social approaching of BTBR mice, likely by enhancing the level of TH in the striatum. Application of intranasal DA to Fmr1-KO animals alleviated their impairment of social novelty, in association with reduced striatal TH protein. These results suggest that although the DA system is modified differently in the two ASD models, intranasal treatment with DA effectively rectifies their behavioral phenotypes, which may present a promising therapy for diverse types of ASD.

Oral Cannabidiol Prevents Allodynia and Neurological Dysfunctions in a Mouse Model of Mild Traumatic Brain Injury

Neurological dysfunctions are the most impactful and persistent consequences of traumatic brain injury (TBI). Indeed, previous reports suggest that an association between TBI and chronic pain syndromes, as well anxio-depressive behaviors, tends to be more common in patients with mild forms of TBI. At present, no effective treatment options are available for these symptoms. In the present study, we used a weight drop mild TBI mouse model to investigate the effect of a commercially available 10% Cannabidiol (CBD) oil on both the sensorial and neuropsychiatric dysfunctions associated with mild TBI through behavioral and biomolecular approaches. TBI mice developed chronic pain associated with anxious and aggressive behavior, followed by a late depressive-like behavior and impaired social interaction. Such behaviors were related with specific changes in neurotransmitters release at cortical levels. CBD oral treatment restored the behavioral alterations and partially normalized the cortical biochemical changes. In conclusion, our data show some of the brain modifications probably responsible for the behavioral phenotype associated with TBI and suggest the CBD as a pharmacological tool to improve neurological dysfunctions caused by the trauma.

Oral Cannabidiol Prevents Allodynia and Neurological Dysfunctions in a Mouse Model of Mild Traumatic Brain Injury

Neurological dysfunctions are the most impactful and persistent consequences of traumatic brain injury (TBI). Indeed, previous reports suggest that an association between TBI and chronic pain syndromes, as well anxio-depressive behaviors, tends to be more common in patients with mild forms of TBI. At present, no effective treatment options are available for these symptoms. In the present study, we used a weight drop mild TBI mouse model to investigate the effect of a commercially available 10% Cannabidiol (CBD) oil on both the sensorial and neuropsychiatric dysfunctions associated with mild TBI through behavioral and biomolecular approaches. TBI mice developed chronic pain associated with anxious and aggressive behavior, followed by a late depressive-like behavior and impaired social interaction. Such behaviors were related with specific changes in neurotransmitters release at cortical levels. CBD oral treatment restored the behavioral alterations and partially normalized the cortical biochemical changes. In conclusion, our data show some of the brain modifications probably responsible for the behavioral phenotype associated with TBI and suggest the CBD as a pharmacological tool to improve neurological dysfunctions caused by the trauma.

Sex-dependent alterations in motor and anxiety-like behavior of aged bacterial peptidoglycan sensing molecule 2 knockout mice

Peptidoglycan recognition proteins (PGRPs) are key sensing-molecules of the innate immune system that specifically detect bacterial peptidoglycan (PGN) and its derivates. PGRPs have recently emerged as potential key regulators of normal brain development and behavior. To test the hypothesis that PGRPs play a role in motor control and anxiety-like behavior in later life, we used 15-month old male and female peptidoglycan recognition protein 2 (Pglyrp2) knockout (KO) mice. Pglyrp2 is an N-acetylmuramyl-l-alanine amidase that hydrolyzes PGN between the sugar backbone and the peptide chain (which is unique among the mammalian PGRPs). Using a battery of behavioral tests, we demonstrate that Pglyrp2 KO male mice display decreased levels of anxiety-like behavior compared with wild type (WT) males. In contrast, Pglyrp2 KO female mice show reduced rearing activity and increased anxiety-like behavior compared to WT females. In the accelerated rotarod test, however, Pglyrp2 KO female mice performed better compared to WT females (i.e., they had longer latency to fall off the rotarod). Further, Pglyrp2 KO male mice exhibited decreased expression levels of synaptophysin, gephyrin, and brain-derived neurotrophic factor in the frontal cortex, but not in the amygdala. Pglyrp2 KO female mice exhibited increased expression levels of spinophilin and alpha-synuclein in the frontal cortex, while exhibiting decreased expression levels of synaptophysin, gephyrin and spinophilin in the amygdala. Our findings suggest a novel role for Pglyrp2asa key regulator of motor and anxiety-like behavior in late life.

Attentional deficits and altered neuronal activation in medial prefrontal and posterior parietal cortices in mice with reduced dopamine transporter levels

The executive control function of attention is regulated by the dopaminergic (DA) system. Dopamine transporter (DAT) likely plays a role in controlling the influence of DA on cognitive processes. We examined the effects of DAT depletion on cognitive processes related to attention. Mice with the DAT gene genetically deleted (DAT+/- heterozygotes) were compared to wild type (WT) mice on the Attentional Set-Shifting Task (ASST). Changes in neuronal activity during the ASST were shown with early growth response genes 1 and 2 (egr-1 and egr-2) immunohistochemistry in the medial prefrontal cortex (mPFC) and in the posterior parietal cortex (PPC). Heterozygotes were impaired in tasks that tax reversal learning, attentional-set formation and set-shifting. Densities of egr-2 labeled cells in the mPFC were lower in mutant mice when compared with wild-types in intradimensional shift of attention (IDS), extradimensional shift of attention and extradimensional shift of attention-reversal phases of the ASST task, and in PPC in the IDS phase of the task. The results demonstrate impairments of the areas associated with attentional functions in DAT+/- mice and show that an imbalance of the dopaminergic system has an impact on the complex attention-related executive functions.

GABAergic control of neostriatal dopamine D2 receptor binding and behaviors in the rat

PURPOSE

The present study assessed the influence of the GABA_A receptor agonist muscimol and the GABA_A receptor antagonist bicuculline on neostriatal dopamine D₂ receptor binding in relation to motor and exploratory behaviors in the rat.

METHODS

D₂ receptor binding was measured in baseline and after challenge with either 1mg/kg muscimol or 1mg/kg bicuculline. In additional rats, D₂ receptor binding was measured after injection of saline. After treatment with muscimol, bicuculline and saline, motor and exploratory behaviors were assessed for 30min in an open field prior to administration of [¹²³I]S-3-iodo-N-(1-ethyl-2-pyrrolidinyl)methyl-2-hydroxy-6-methoxybenzamide ([¹²³I]IBZM). For baseline and challenges, striatal equilibrium ratios (V₃″) were computed as estimation of the binding potential.

RESULTS

Muscimol but not bicuculline reduced D₂ receptor binding relative to baseline and to saline. Travelled distance, duration of rearing and frequency of rearing and of head-shoulder motility were lower after muscimol compared to saline. In contrast, duration of rearing and grooming and frequency of rearing, head-shoulder motility and grooming were elevated after bicuculline relative to saline. Moreover, bicuculline decreased duration of sitting and head-shoulder motility.

CONCLUSIONS

The muscimol-induced decrease of motor/exploratory behaviors can be related to an elevation of striatal dopamine levels. In contrast, bicuculline is likely to elicit a decline of synaptic dopamine, which, however, is compensated by the time of D₂ receptor imaging studies. The results indicate direct GABAergic control over D₂ receptor binding in the neostriatum in relation to behavioral action, and, thus, complement earlier pharmacological studies.

Chronic corticosterone treatment enhances extinction-induced depression in aged rats

Withdrawal and avoidance behavior are common symptoms of depression and can appear as a consequence of absence of reward, i.e. extinction-induced depression (EID). This is particularly relevant for the aged organism subjected to pronounced loss of former rewards. Avoidance of the former site of reward and increased withdrawal into a distant compartment accompany extinction of food-rewarded behavior in rodent models. During extinction, behavioral markers for re-learning dissociate from indicators of extinction-induced depression. Here we examined the effect of a chronic treatment with corticosterone (CORT), a well-known inducer of depression-related behavior, on EID in adult and aged rats. Adult (3-4months) and aged (18months) male rats were treated with CORT via drinking water for 3weeks prior to extinction of a cued food-reward task. CORT treatment increased the distance from the site of reward and decreased goal tracking behavior during extinction, especially in the aged rats. Plasma hormone levels measured before and after restraint stress showed a decline in basal ACTH- and CORT-levels after chronic CORT treatment in aged animals. The treatment significantly impaired the HPA-axis activation after acute stress in both, adult and aged animals, alike. Altogether, these findings show an enhancement of EID after chronic CORT treatment in the aged organism, which may be mediated by an impaired HPA-axis sensitivity. These findings may have special relevance for the investigation of human geriatric depression.

DAT versus D2 receptor binding in the rat striatum: l-DOPA-induced motor activity is better predicted by reuptake than release of dopamine

The reuptake and release of dopamine (DA) can be estimated using in vivo imaging methods by assessing the competition between endogenous DA and an administered exogenous DA transporter (DAT) and D2 receptor (D2 R) radioligand, respectively. The aim of this study was to investigate the comparative roles of DA release vs DA reuptake in the rat striatum with small animal SPECT in relation to l-DOPA-induced behaviors. DAT and D2 R binding, together with behavioral measures, were obtained in 99 rats in response to treatment with either 5 or 10 mg/kg l-DOPA or vehicle. The behavioral parameters included the distance travelled, and durations and frequencies of ambulation, sitting, rearing, head-shoulder motility, and grooming. Data were subjected to a cluster analysis and to a multivariate principal component analysis. The highest DAT binding (i.e., the lowest DA reuptake) was associated with the highest, and the lowest DAT binding (i.e., the highest DA reuptake) was associated with the lowest motor/exploratory activity. The highest and the lowest D2 R binding (i.e., the lowest and the highest DA release, respectively) were merely associated with the second highest and second lowest levels of motor/exploratory activity. These findings indicate that changes in DA reuptake in response to fluctuating DA levels offer a better prediction of motor activity than the release of DA into the synaptic cleft. This dissociation, as reflected by in vivo DAT and D2 R binding data, may be accounted for by the regulatory sensitization meachnisms that occur at D2 R binding sites in response to altered levels of DA. Synapse 70:369-377, 2016. © 2016 Wiley Periodicals, Inc.

Relationship Between L-DOPA-Induced Reduction in Motor and Exploratory Activity and Striatal Dopamine D2 Receptor Binding in the Rat

Purpose: The present study assessed the influence of L-DOPA administration on neostriatal dopamine (DA) D₂ receptor binding in relation to motor and exploratory behaviors in the rat.

Methods: D₂ receptor binding was measured in baseline, after challenge with the aromatic L-amino acid decarboxylase inhibitor benserazide, and after challenge with either 5 or 10 mg/kg L-DOPA plus benserazide. Additional rats received injections of saline. For baseline and challenges, striatal equilibrium ratios (V3″) were computed as estimation of the binding potential. Motor and exploratory behaviors were assessed for 30 min in an open field prior to administration of [¹²³I]IBZM. D₂ receptor binding was measured with small animal SPECT 2 h after radioligand administration for 60 min.

Results: Both L-DOPA doses significantly reduced D₂ receptor binding relative to baseline and led to significantly less ambulation, less head-shoulder motility, and more sitting relative to saline. Moreover, 10 mg/kg L-DOPA induced less head-shoulder motility, more sitting, and more grooming than 5 mg/kg L-DOPA. Analysis of time-behavior curves showed that L-DOPA-treated animals relative to saline exhibited a faster rate of decrease of ambulation frequency and a slower rate of decrease of both duration and frequency of head-shoulder motility from a lower maximum level.

Conclusions: The reductions of striatal D₂ receptor binding after L-DOPA may be conceived to reflect elevated concentrations of synaptic DA. L-DOPA-treated animals showed less ambulation and less head-shoulder motility than saline-treated animals, indicating an association between less behavioral activity and increased availability of striatal DA. The faster rate of decrease of ambulation frequency and the lower maximum levels of both head-shoulder motility duration and frequency may be interpreted in terms of influence of increased DA availability on behavioral habituation to a novel environment.

Oxidative Stress and ADHD: A Meta-Analysis

OBJECTIVE

To clarify the role of oxidative stress and antioxidant activity in ADHD.

METHOD

We examined the association of ADHD and oxidative stress by applying random effects meta-analysis to studies of oxidative stress and antioxidant status in medication naive patients with ADHD and controls.

RESULTS

Six studies of a total of 231 ADHD patients and 207 controls met our selection criteria. The association between ADHD and antioxidant status was not significant. We found a significant association between ADHD and oxidative stress that could not be accounted for by publication bias. The significant association lost significance after correcting for intrastudy clustering. No one observation accounted for the positive result.

CONCLUSION

These results are preliminary given the small number of studies. They suggest that patients with ADHD have normal levels of antioxidant production, but that their response to oxidative stress is insufficient, leading to oxidative damage.

Multi-level biomarker analysis of nitric oxide synthase isoforms in bipolar disorder and adult ADHD

INTRODUCTION

Several studies have shown altered levels of nitric oxide (NO) and its stable metabolites (NOx (-)) in blood and cerebrospinal fluid of psychiatric patients. The aim of our study was to replicate previous findings and investigate the influence of the nitrinergic system in bipolar disorder and adult attention-deficit/hyperactivity disorder (aADHD) in particular.

METHODS

The concentrations of NO2 (-) and NO3 (-) in peripheral blood in a sample of aADHD, bipolar disorder (BPD) and controls were analysed. The sample was genotyped for a three marker haplotype in the NOS3 gene (rs2070744, rs1799983 and Intron 4 VNTR) and for genetic variants of the NOS1 gene (NOS1 ex 1c, NOS1 ex 1f). Finally, qRT PCR was performed.

RESULTS

We found significantly lower NOx (-) levels in BPD (p<0.001). rs2070744 T/T-carriers of the whole sample showed increased mRNA expression of NOS3 (p=0.05). Only in BPD an influence of rs2070744 was seen regarding NO metabolite levels; C/C carriers displayed lower NOx (-) levels (p=0.05).

CONCLUSION

We could replicate and extend previous findings showing altered NOx (-) levels in BPD and an influence of NOS3 rs2070744 on NOS3 expression and NOx (-) concentration. Together, these data point to a role of the nitrinergic pathway in BPD.

Relationship between L-DOPA-induced reduction in motor and exploratory activity and degree of DAT binding in the rat

Purpose: The present study assessed the influence of L-DOPA administration on neostriatal dopamine (DA) transporter (DAT) binding in relation to motor and exploratory behaviors in the rat.

Methods: Rats received injections of 5 mg/kg L-DOPA, 10 mg/kg L-DOPA or vehicle. Motor and exploratory behaviors were assessed for 30 min in an open field prior to administration of [¹²³I]FP-CIT. Dopamine transporter binding was measured with small animal single-photon emission computed tomography (SPECT) 2 h after radioligand administration for 60 min.

Results: Both L-DOPA doses significantly reduced DAT binding and led to significantly less head-shoulder motility and more sitting relative to vehicle. Moreover, 10 mg/kg L-DOPA induced less distance traveled and ambulation than 5 mg/kg L-DOPA. Analysis of time-behavior (t-b) curves showed that L-DOPA-treated animals relative to vehicle exhibited (1) a faster rate of increase in duration of sitting; (2) a slower rate of increase in duration of head-shoulder motility; and (3) a slower rate of decrease in frequency of head-shoulder motility.

Conclusions: The reductions of striatal DAT binding after L-DOPA challenges reflected elevated concentrations of synaptic DA. L-DOPA-treated animals showed less head-shoulder motility and more sitting than vehicle-treated animals, indicating an association between less behavioral activity and increased availability of striatal DA. The faster increase of sitting duration to a higher final level and the slower increase of head-shoulder motility to a lower final level relative to controls may be interpreted in terms on behavioral habituation to a novel environment.

Regulation of motor function and behavior by atypical chemokine receptor 1

Atypical Chemokine Receptor 1 (ACKR1), previously known as Duffy Antigen Receptor for Chemokines, stands out among chemokine receptors for high selective expression on cerebellar Purkinje neurons. Although ACKR1 ligands activate Purkinje cells in vitro, evidence for ACKR1 regulation of brain function in vivo is lacking. Here we demonstrate that Ackr1 (-/-) mice have markedly impaired balance and ataxia on a rotating rod and increased tremor when injected with harmaline, which induces whole-body tremor by activating Purkinje cells. Ackr1 (-/-) mice also exhibited impaired exploratory behavior, increased anxiety-like behavior and frequent episodes of marked hypoactivity under low-stress conditions. Surprisingly, Ackr1 (+/-) had similar behavioral abnormalities, indicating pronounced haploinsufficiency. The behavioral phenotype of Ackr1 (-/-) mice was the opposite of mouse models of cerebellar degeneration, and the defects persisted when Ackr1 was deficient only on non-hematopoietic cells. Together, the results suggest that normal motor function and behavior may partly depend on negative regulation of Purkinje cell activity by Ackr1.

Predictability and heritability of individual differences in fear learning

Our objective was to characterize individual differences in fear conditioning and extinction in an outbred rat strain, to test behavioral predictors of these individual differences, and to assess their heritability. We fear-conditioned 100 Long-Evans rats, attempted to extinguish fear the next day, and tested extinction recall on the third day. The distribution of freezing scores after fear conditioning was skewed, with most rats showing substantial freezing; after fear extinction, the distribution was bimodal with most rats showing minimal freezing, but a substantial portion showing maximal freezing. Longer rearing episodes measured prior to conditioning predicted less freezing at the beginning of extinction, but differences in extinction learning were not predicted by any baseline exploratory behaviors. We tested the heritability of extinction differences by breeding rats from the top and bottom 20 % of freezing scores during extinction recall. We then ran the offspring through the same conditioning/extinction procedure, with the addition of recording ultrasonic vocalizations throughout training and testing. Only a minority of rats emitted distress vocalizations during fear acquisition, but the incidence was less frequent in the offspring of good extinguishers than in poor extinguishers or randomly bred controls. The occurrence of distress vocalizations during acquisition predicted higher levels of freezing during fear recall regardless of breeding line, but the relationship between vocalization and freezing was no longer evident following extinction training, at which point freezing levels were influenced only by breeding and not by vocalization. The heritability (h²) of extinction recall was estimated at 0.36, consistent with human estimates.

Increased locomotor activity and non-selective attention and impaired learning ability in SD rats after lentiviral vector-mediated RNA interference of Homer 1a in the brain

Our previous studies found that Homer 1a, a scaffolding protein localized at the post-synaptic density (PSD) of glutamatergic excitatory synapses, is significantly down-regulated in the brain of spontaneous hypertensive rats (SHR), an animal model of attention deficit hyperactivity disorder (ADHD). Furthermore, a first-line treatment drug for ADHD, methylphenidate, can up-regulate the expression of Homer 1a. To investigate the possible role of Homer 1a in the etiology and pathogenesis of ADHD, a lentiviral vector containing miRNA specific for Homer 1a was constructed in this study. Intracerebroventricular injection of this vector into the brain of Sprague Dawley (SD) rats significantly decreased Homer 1a mRNA and protein expression levels. Compared to their negative controls, these rats displayed a range of abnormal behaviors, including increased locomotor activity and non-selective attention and impaired learning ability. Our results indicated that Homer 1a down-regulation results in deficits in control over behavioral output and learning similar to ADHD.

Animal models of ADHD

Studies employing animal models of attention-deficit/hyperactivity disorder (ADHD) present clear inherent advantages over human studies. Animal models are invaluable tools for the study of underlying neurochemical, neuropathological and genetic alterations that cause ADHD, because they allow relatively fast, rigorous hypothesis testing and invasive manipulations as well as selective breeding. Moreover, especially for ADHD, animal models with good predictive validity would allow the assessment of potential new therapeutics. In this chapter, we describe and comment on the most frequently used animal models of ADHD that have been created by genetic, neurochemical and physical alterations in rodents. We then discuss that an emerging and promising direction of the field is the analysis of individual behavioural differences among a normal population of animals. Subjects presenting extreme characteristics related to ADHD can be studied, thereby avoiding some of the problems that are found in other models, such as functional recovery and unnecessary assumptions about aetiology. This approach is justified by the theoretical need to consider human ADHD as the extreme part of a spectrum of characteristics that are distributed normally in the general population, as opposed to the predominant view of ADHD as a separate pathological category.

Deficits in fine motor skills in a genetic animal model of ADHD

Background

In an attempt to model some behavioral aspects of Attention Deficit/Hyperactivity Disorder (ADHD), we examined whether an existing genetic animal model of ADHD is valid for investigating not only locomotor hyperactivity, but also more complex motor coordination problems displayed by the majority of children with ADHD.

Methods

We subjected young adolescent Spontaneously Hypertensive Rats (SHRs), the most commonly used genetic animal model of ADHD, to a battery of tests for motor activity, gross motor coordination, and skilled reaching. Wistar (WIS) rats were used as controls.

Results

Similar to children with ADHD, young adolescent SHRs displayed locomotor hyperactivity in a familiar, but not in a novel environment. They also had lower performance scores in a complex skilled reaching task when compared to WIS rats, especially in the most sensitive measure of skilled performance (i.e., single attempt success). In contrast, their gross motor performance on a Rota-Rod test was similar to that of WIS rats.

Conclusion

The results support the notion that the SHR strain is a useful animal model system to investigate potential molecular mechanisms underlying fine motor skill problems in children with ADHD.

Adolescent female rats are more resistant than males to the effects of early stress on prefrontal cortex and impulsive behavior

We tested the hypothesis that adolescent Sprague-Dawley females may be more resistant than males to display impulsive behavior and lower prefrontal cortex thickness after mother-infant separation (MS). Starting at postnatal day 2 (P2), the MS group was separated 6 hr/day and the early handled (EH) group 15 min/day for 10 days, and another group was standard facility reared (SFR). Subjects were examined for novel open-field activity (P28), light-dark apparatus (P29), familiar open-field (P30) and frontal cortical thickness. This protocol resulted in impulsive behavior in MS rats relative to EH and SFR, but this effect was less pronounced in females than males. MS affected the two sexes differently in terms of decreased prefrontal cortex dorsoventral thickness, with this effect being significant in males but not females. Neuroanatomical and behavioral documentation that adolescent females are more resistant than males to ADHD-like effects of maternal separation have not been previously reported.

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

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

A trouble shared is a trouble halved: social context and status affect pain in mouse dyads

In mice behavioral response to pain is modulated by social status. Recently, social context also has been shown to affect pain sensitivity. In our study, we aimed to investigate the effects of interaction between status and social context in dyads of outbred CD-1 male mice in which the dominance/submission relationship was stable. Mice were assessed for pain response in a formalin (1% concentration) test either alone (individually tested-IT), or in pairs of dominant and subordinate mice. In the latter condition, they could be either both injected (BI) or only one injected (OI) with formalin. We observed a remarkable influence of social context on behavioral response to painful stimuli regardless of the social status of the mice. In the absence of differences between OI and IT conditions, BI mice exhibited half as much Paw-licking behavior than OI group. As expected, subordinates were hypoalgesic in response to the early phase of the formalin effects compared to dominants. Clear cut-differences in coping strategies of dominants and subordinates appeared. The former were more active, whereas the latter were more passive. Finally, analysis of behavior of the non-injected subjects (the observers) in the OI dyads revealed that dominant observers were more often involved in Self-grooming behavior upon observation of their subordinate partner in pain. This was not the case for subordinate mice observing the pain response of their dominant partner. In contrast, subordinate observers Stared at the dominant significantly more frequently compared to observer dominants in other dyads. The observation of a cagemate in pain significantly affected the observer's behavior. Additionally, the quality of observer's response was also modulated by the dominance/submission relationship.

Galactosylated dopamine enters into the brain, blocks the mesocorticolimbic system and modulates activity and scanning time in Naples high excitability rats

Pathological conditions, such as Parkinson's disease and attention deficit hyperactivity disorder, have been linked to alterations of specific dopamine (DA) pathways. However, since exogenous DA does not cross the blood-brain barrier, DA levels can be modulated e.g. by DA precursors or DA reuptake blockers. Hereby histochemical, analytical and behavioral evidence shows that a galactosylated form of DA (GAL-DA) carries DA into the brain, thus modulating activity and nonselective attention in rats. To this aim adult male rats of the Naples high-excitability (NHE) and random bred controls (NRB) lines were given a single i.p. injection of GAL-DA (10 or 100 mg/kg). Three hours later the behavior was videotaped and analyzed for horizontal activity, orienting frequency and scanning duration. The dose of 100 mglkg of GAL-DA reduced by 25% the horizontal activity in NHE rats, mainly in the first part of the testing period. No effect was observed on orienting frequency or on scanning duration. However, GAL-DA 100 mg/kg was associated with longer rearing episodes in the second part of the testing period in NHE rats. In parallel experiments histochemistry with a galactose-specific lectin showed 10% increase in galactose residues into the striatum between 0.5 and 3.0 h. To quantify the level of GAL-DA, its metabolite DA-succinate and DA in the prefrontal cortex, neostriatum, and cerebellum, rats were killed 2.0 h after the injection of prodrug. Mass high performance liquid chromatography (HPLC) was used for analysis of GAL-DA and DA succinate whereas electrochemical HPLC for DA. Both HPLC techniques demonstrate that GAL-DA carries and releases DA into the brain. Specifically 100 mg/kg of GAL-DA increased DA level in the striatum in the NHE rats only. Moreover, DA in the mesencephalon (MES) was correlated positively with striatal and prefrontal cortex DA in NHE rats. In contrast DA in the MES was negatively correlated with striatal DA in NRB. GAL-DA disrupted these correlations in both rat lines. Thus, this new DA prodrug may modify DA neurotransmission and might have a potential clinical application.

Oxidative imbalance in adult attention deficit/hyperactivity disorder

OBJECTIVE

There are few studies evaluating the biochemical basis of adult attention deficit/hyperactivity disorder (A-ADHD). In the present study, we evaluated whether nitric oxide (NO), an oxidant, level and superoxide dismutase (SOD), an antioxidant, activity are associated with A-ADHD or not.

METHODS

Twenty A-ADHD patients from Gaziantep University Sahinbey Research Hospital, Psychiatry Clinic, diagnosed according to The Turkish version of Adult ADD/ADHD DSM IV-Based Diagnostic Screening and Rating Scale by two psychiatrists (H.A.S. and S.S.), and twenty-one healthy volunteer controls were included. Blood samples were collected; NO levels and SOD activities were measured.

RESULTS

The mean NO levels in patients were significantly higher than those of controls and SOD activity of patients was significantly lower than controls.

CONCLUSIONS

Remarkable high levels of oxidant NO, and low SOD activities suggest an oxidative imbalance in A-ADHD. This is the first study evaluating the oxidative metabolism in A-ADHD.

Mother-infant separation leads to hypoactive behavior in adolescent Holtzman rats

This is the first study of the effects of mother-infant separation (MS) on adolescent behavior of Holtzman (HO) rats. Different rat strains, such as Harlan Sprague-Dawley and HO, share a common origin. However, MS may lead to hypoactive behavioral effects in HO rats because of their greater susceptibility to show depressive-like responses to stress. Sixty HO pups were divided into three groups at postnatal day 2 (P2). For 10 days, the MS group was separated 6h daily and the early handled (EH) group 15 min daily. A standard facility reared (SFR) group was not separated. Animals were tested for novel open-field activity (P28), defensive withdrawal in a light-dark (LD) apparatus (P29) and familiar open-field (P30). Behavioral measures were classified into general activity (ambulatory and short movement time), orienting (rearing time) and risk-taking (velocity and exposed zone time). MS rats displayed reductions in general activity and risk-taking, and increases in orienting time. In contrast, EH favored risk-taking behavior, which may be consistent with previous findings implicating early handling as beneficial in coping with stress. Sex differences in these behaviors were limited. This study suggests a genetic predisposition in HO rats for predominantly hypoactive/anxiety-like behaviors when exposed to an early life stressor.

Gabrb3 gene deficient mice exhibit impaired social and exploratory behaviors, deficits in non-selective attention and hypoplasia of cerebellar vermal lobules: a potential model of autism spectrum disorder

OBJECTIVE

GABA(A) receptors play an important regulatory role in the developmental events leading to the formation of complex neuronal networks and to the behaviors they govern. The primary aim of this study was to assess whether gabrb3 gene deficient (gabrb3(-/-)) mice exhibit abnormal social behavior, a core deficit associated with autism spectrum disorder.

METHODS

Social and exploratory behaviors along with non-selective attention were assessed in gabrb3(-/-), littermates (gabrb3(+/+)) and progenitor strains, C57BL/6J and 129/SvJ. In addition, semi-quantitative assessments of the size of cerebellar vermal lobules were performed on gabrb3(+/+) and gabrb3(-/-) mice.

RESULTS

Relative to controls, gabrb3(-/-) mice exhibited significant deficits in activities related to social behavior including sociability, social novelty and nesting. In addition, gabrb3(-/-) mice also exhibited differences in exploratory behavior compared to controls, as well as reductions in the frequency and duration of rearing episodes, suggested as being an index of non-selective attention. Gabrb3(-/-) mice also displayed significant hypoplasia of the cerebellar vermis compared to gabrb3(+/+) mice.

CONCLUSIONS

The observed behavioral deficits, especially regarding social behaviors, strengthens the face validity of the gabrb3 gene deficient mouse as being a model of autism spectrum disorder.

Connexin31.1 deficiency in the mouse impairs object memory and modulates open-field exploration, acetylcholine esterase levels in the striatum, and cAMP response element-binding protein levels in the striatum and piriform cortex

Neuronal gap junctions in the brain, providing intercellular electrotonic signal transfer, have been implicated in physiological and behavioral correlates of learning and memory. In connexin31.1 (Cx31.1) knockout (KO) mice the coding region of the Cx31.1 gene was replaced by a LacZ reporter gene. We investigated the impact of Cx31.1 deficiency on open-field exploration, the behavioral response to an odor, non-selective attention, learning and memory performance, and the levels of memory-related proteins in the hippocampus, striatum and the piriform cortex. In terms of behavior, the deletion of the Cx31.1 coding DNA in the mouse led to increased exploratory behaviors in a novel environment, and impaired one-trial object recognition at all delays tested. Despite strong Cx31.1 expression in the peripheral and central olfactory system, Cx31.1 KO mice exhibited normal behavioral responses to an odor. We found increased levels of acetylcholine esterase (AChE) and cAMP response element-binding protein (CREB) in the striatum of Cx31.1 KO mice. In the piriform cortex the Cx31.1 KO mice had an increased heterogeneity of CREB expression among neurons. In conclusion, gap-junctions featuring the Cx31.1 protein might be involved in open-field exploration as well as object memory and modulate levels of AChE and CREB in the striatum and piriform cortex.

Amphetamine and mCPP effects on dopamine and serotonin striatal in vivo microdialysates in an animal model of hyperactivity

In the neonatally 6-hydroxydopamine (6-OHDA)-lesioned rat hyperlocomotor activity, first described in the 1970s, was subsequently found to be increased by an additional lesion with 5,7-dihydroxytryptamine (5,7-DHT) (i.c.v.) in adulthood. The latter animal model (i.e., 134 microg 6-OHDA at 3 d postbirth plus 71 microg 5,7-DHT at 10 weeks; desipramine pretreatments) was used in this study, in an attempt to attribute hyperlocomotor attenuation by D,L-amphetamine sulfate (AMPH) and m-chlorophenylpiperazine di HCl (mCPP), to specific changes in extraneuronal (i.e., in vivo microdialysate) levels of dopamine (DA) and/or serotonin (5-HT). Despite the 98-99% reduction in striatal tissue content of DA, the baseline striatal microdialysate level of DA was reduced by 50% or less at 14 weeks, versus the intact control group. When challenged with AMPH (0.5 mg/kg), the microdialysate level of DA went either unchanged or was slightly reduced over the next 180 min (i.e., 20 min sampling), while in the vehicle group and 5,7-DHT (alone) lesioned group, the microdialysate level was maximally elevated by approximately 225% and approximately 450%, respectively--and over a span of nearly 2 h. Acute challenge with mCPP (1 mg/kg salt form) had little effect on microdialysate levels of DA, DOPAC and 5-HT. Moreover, there was no consistent change in the microdialysate levels of DA, DOPAC, and 5-HT between intact, 5-HT-lesioned rats, and DA-lesioned rats which might reasonably account for an attenuation of hyperlocomotor activity. These findings indicate that there are other important neurochemical changes produced by AMPH- and mCPP-attenuated hyperlocomotor activity, or perhaps a different brain region or multiple brain regional effects are involved in AMPH and mCPP behavioral actions.