Altered parvalbumin-positive neuron distribution in basal ganglia of individuals with Tourette syndrome

Rats overexpressing the dopamine transporter display behavioral and neurobiological abnormalities with relevance to repetitive disorders

The dopamine transporter (DAT) plays a pivotal role in maintaining optimal dopamine signaling. DAT-overactivity has been linked to various neuropsychiatric disorders yet so far the direct pathological consequences of it has not been fully assessed. We here generated a transgenic rat model that via pronuclear microinjection overexpresses the DAT gene. Our results demonstrate that DAT-overexpression induces multiple neurobiological effects that exceeded the expected alterations in the corticostriatal dopamine system. Furthermore, transgenic rats specifically exhibited behavioral and pharmaco-therapeutic profiles phenotypic of repetitive disorders. Together our findings suggest that the DAT rat model will constitute a valuable tool for further investigations into the pathological influence of DAT overexpression on neural systems relevant to neuropsychiatric disorders.

Microglial Dysregulation in OCD, Tourette Syndrome, and PANDAS

There is accumulating evidence that immune dysregulation contributes to the pathophysiology of obsessive-compulsive disorder (OCD), Tourette syndrome, and Pediatric Autoimmune Neuropsychiatric Disorders Associated with Streptococcal Infections (PANDAS). The mechanistic details of this pathophysiology, however, remain unclear. Here we focus on one particular component of the immune system: microglia, the brain's resident immune cells. The role of microglia in neurodegenerative diseases has been understood in terms of classic, inflammatory activation, which may be both a consequence and a cause of neuronal damage. In OCD and Tourette syndrome, which are not characterized by frank neural degeneration, the potential role of microglial dysregulation is much less clear. Here we review the evidence for a neuroinflammatory etiology and microglial dysregulation in OCD, Tourette syndrome, and PANDAS. We also explore new hypotheses as to the potential contributions of microglial abnormalities to pathophysiology, beyond neuroinflammation, including failures in neuroprotection, lack of support for neuronal survival, and abnormalities in synaptic pruning. Recent advances in neuroimaging and animal model work are creating new opportunities to elucidate these issues.

A Low-Correlation Resting State of the Striatum during Cortical Avalanches and Its Role in Movement Suppression

During quiet resting behavior, involuntary movements are suppressed. Such movement control is attributed to cortico-basal ganglia loops, yet population dynamics within these loops during resting and their relation to involuntary movements are not well characterized. Here, we show by recording cortical and striatal ongoing population activity in awake rats during quiet resting that intrastriatal inhibition maintains a low-correlation striatal resting state in the presence of cortical neuronal avalanches. Involuntary movements arise from disturbed striatal resting activity through two different population dynamics. Nonselectively reducing intrastriatal γ-aminobutyric acid (GABA) receptor-A inhibition synchronizes striatal dynamics, leading to involuntary movements at low rate. In contrast, reducing striatal interneuron (IN)-mediated inhibition maintains decorrelation and induces intermittent involuntary movements at high rate. This latter scenario was highly effective in modulating cortical dynamics at a subsecond timescale. To distinguish intrastriatal processing from loop dynamics, cortex-striatum-midbrain cultures, which lack feedback to cortex, were used. Cortical avalanches in vitro were accompanied by low-correlated resting activity in the striatum and nonselective reduction in striatal inhibition synchronized striatal neurons similar to in vivo. Importantly, reduction of inhibition from striatal INs maintained low correlations in the striatum while reorganizing functional connectivities among striatal neurons. Our results demonstrate the importance of two major striatal microcircuits in distinctly regulating striatal and cortical resting state dynamics. These findings suggest that specific functional connectivities of the striatum that are maintained by local inhibition are important in movement control.

Why don’t neuronal “avalanches” in resting-state cortex cause involuntary movements? This study shows that a low-correlation striatal resting state suppresses such movements and explores mechanisms that disrupt this inhibition.

Even in the absence of apparent motor output, the brain produces a rich repertoire of neuronal activity patterns known as “resting state” activity. In the outer layer of the cortex, resting state patterns emerge as neuronal avalanches, precisely scale-invariant spatiotemporal bursts that often engage large populations of neurons. Little is known about how the brain suppresses involuntary movements during such activity. Here, we show that the striatum, which is part of the cortex-basal ganglia loop, maintains a low-correlation state during resting activity. By using a combination of in vivo and in vitro approaches with pharmacological manipulations, we demonstrate that the precise configuration of this low-correlation state effectively contributes to involuntary movements. Nonselective blockade of intra-striatal inhibition abolished the low-correlation striatal resting state, barely affected cortical avalanches, and led to involuntary movements at low rate. In contrast, selectively reducing striatal interneuron inhibition strongly affected cortical avalanches and triggered involuntary movements at high rate while maintaining a relatively decorrelated striatal resting state. Our results demonstrate the importance of different inhibitory striatal circuits in the suppression of involuntary movements and suggest that the precise spatiotemporal configuration of striatal activity plays an active role in the regulation of cortical resting state activity and motor control.

Decreased Anterior Cingulate Cortex γ-Aminobutyric Acid in Youth With Tourette's Disorder

BACKGROUND

γ-Aminobutyric acid has been implicated in the pathophysiology of Tourette's disorder. The present study primarily sought to examine in vivo γ-aminobutyric acid levels in the anterior cingulate cortex in psychotropic medication-free adolescents and young adults. Secondarily, we sought to determine associations between γ-aminobutyric acid in the anterior cingulate cortex and measures of tic severity, tic-related impairment, and anxiety and depression symptoms.

METHODS

γ-Aminobutyric acid levels were measured using proton magnetic resonance spectroscopy. Analysis of covariance compared γ-aminobutyric acid levels in 15 youth with Tourette's disorder (mean age = 15.0, S.D. = 2.7) and 36 healthy comparison subjects (mean age = 15.9, S.D. = 2.1). Within the Tourette disorder group, we examined correlations between γ-aminobutyric acid levels and tic severity and tic-related impairment, as well as anxiety and depression severity.

RESULTS

Anterior cingulate cortex γ-aminobutyric acid levels were lower in participants with Tourette's disorder compared with control subjects. Within the Tourette disorder group, γ-aminobutyric acid levels did not correlate with any clinical measures.

CONCLUSIONS

Our findings support a role for γ-aminobutyric acid in Tourette's disorder. Larger prospective studies will further elucidate this role.

Representation of the body in the lateral striatum of the freely moving rat: Fast Spiking Interneurons respond to stimulation of individual body parts

Numerous studies have shown that certain types of striatal interneurons play a crucial role in selection and regulation of striatal output. Striatal Fast-Spiking Interneurons (FSIs) are parvalbumin positive, GABAergic interneurons that constitute less than 1% of the total striatal population. It is becoming increasingly evident that these sparsely distributed neurons exert a strong inhibitory effect on Medium Spiny projection Neurons (MSNs). MSNs in lateral striatum receive direct synaptic input from regions of cortex representing discrete body parts, and show phasic increases in activity during touch or movement of specific body parts. In the present study, we sought to determine whether lateral striatal FSIs identified by their electrophysiological properties, i.e., short-duration spike and fast firing rate (FR), display body part sensitivity similar to that exhibited by MSNs. During video recorded somatosensorimotor exams, each individual body part was stimulated and responses of single neurons were observed and quantified. Individual FSIs displayed patterns of activity related selectively to stimulation of a discrete body part. Most patterns of activity were similar to those exhibited by typical MSNs, but some phasic decreases were observed. These results serve as evidence that some striatal FSIs process information related to discrete body parts and participate in sensorimotor processing by striatal networks that contribute to motor output.

STATEMENT OF SIGNIFICANCE

Parvalbumin positive, striatal FSIs are hypothesized to play an important role in behavior by inhibiting MSNs. We asked a fundamental question regarding information processed during behavior by FSIs: whether FSIs, which preferentially occupy the sensorimotor portion of the striatum, process activity of discrete body parts. Our finding that they do, in a selective manner similar to MSNs, begins to reveal the types of phasic signals that FSI feed forward to projection neurons during striatal processing of cortical input regarding a specific sensorimotor event. These findings suggest new avenues for testing feed-forward inhibition theory as applied to striatum in naturalistic conditions, such as whether FSI decreases facilitate excitation of MSNs related to the current movement while FSI increases silence MSNs unrelated to the current movement.

Deep Brain Stimulation for Tourette's Syndrome: The Case for Targeting the Thalamic Centromedian-Parafascicular Complex

Tourette’s syndrome (TS) is a neurologic condition characterized by both motor and phonic tics and is typically associated with psychiatric comorbidities, including obsessive-compulsive disorder/behavior and attention-deficit hyperactivity disorder, and can be psychologically and socially debilitating. It is considered a disorder of the cortico–striato–thalamo–cortical circuitry, as suggested by pathophysiology studies and therapeutic options. Among these, deep brain stimulation (DBS) of the centromedian–parafascicular nucleus (CM-Pf) of the thalamus is emerging as a valuable treatment modality for patients affected by severe, treatment-resistant TS. Here, we review the most recent experimental evidence for the pivotal role of CM-Pf in the pathophysiology of TS, discuss potential mechanisms of action that may mediate the effects of CM-Pf DBS in TS, and summarize its clinical efficacy.

Changes in activity of fast-spiking interneurons of the monkey striatum during reaching at a visual target

Recent works highlight the importance of local inhibitory interneurons in regulating the function of the striatum. In particular, fast-spiking interneurons (FSIs), which likely correspond to a subgroup of GABAergic interneurons, have been involved in the control of movement by exerting strong inhibition on striatal output pathways. However, little is known about the exact contribution of these presumed interneurons in movement preparation, initiation, and execution. We recorded the activity of FSIs in the striatum of monkeys as they performed reaching movements to a visual target under two task conditions: one in which the movement target was presented at unsignaled left or right locations, and another in which advance information about target location was available, thus allowing monkeys to react faster. Modulations of FSI activity around the initiation of movement (53% of 55 neurons) consisted mostly of increases reaching maximal firing immediately before or, less frequently, after movement onset. Another subset of FSIs showed decreases in activity during movement execution. Rarely did movement-related changes in FSI firing depend on response direction and movement speed. Modulations of FSI activity occurring relatively early in relation to movement initiation were more influenced by the preparation for movement, compared with those occurring later. Conversely, FSI activity remained unaffected, as monkeys were preparing a movement toward a specific location and instead moved to the opposite direction when the trigger occurred. These results provide evidence that changes in activity of presumed GABAergic interneurons of the primate striatum could make distinct contributions to processes involved in movement generation.

NEW & NOTEWORTHY

We explored the functional contributions of striatal fast-spiking interneurons (FSIs), presumed GABAergic interneurons, to distinct steps of movement generation in monkeys performing a reaching task. The activity of individual FSIs was modulated before and during the movement, consisting mostly of increased in firing rates. Changes in activity also occurred during movement preparation. We interpret this variety of modulation types at different moments of task performance as reflecting differential FSI control over distinct phases of movement.

Targeted Re-Sequencing Approach of Candidate Genes Implicates Rare Potentially Functional Variants in Tourette Syndrome Etiology

Although the genetic basis of Tourette Syndrome (TS) remains unclear, several candidate genes have been implicated. Using a set of 382 TS individuals of European ancestry we investigated four candidate genes for TS (HDC, SLITRK1, BTBD9, and SLC6A4) in an effort to identify possibly causal variants using a targeted re-sequencing approach by next generation sequencing technology. Identification of possible disease causing variants under different modes of inheritance was performed using the algorithms implemented in VAAST. We prioritized variants using Variant ranker and validated five rare variants via Sanger sequencing in HDC and SLITRK1, all of which are predicted to be deleterious. Intriguingly, one of the identified variants is in linkage disequilibrium with a variant that is included among the top hits of a genome-wide association study for response to citalopram treatment, an antidepressant drug with off-label use also in obsessive compulsive disorder. Our findings provide additional evidence for the implication of these two genes in TS susceptibility and the possible role of these proteins in the pathobiology of TS should be revisited.

A verbal strength in children with Tourette syndrome? Evidence from a non-word repetition task

Tourette syndrome (TS) is characterized by motor and vocal tics, and frontal/basal-ganglia abnormalities. Whereas cognitive strengths have been found in other neurodevelopmental disorders, less attention has been paid to strengths in TS, or to verbal strengths in any neurodevelopmental disorder. We examined whether the finding of speeded TS production of rule-governed morphological forms (e.g., "slipped") that involve composition (Walenski, Mostofsky, & Ullman, 2007) might extend to another language domain, phonology. Thirteen children with TS and 14 typically-developing (TD) children performed a non-word repetition task: they repeated legal phonological strings (e.g.,"naichovabe"), a task that taps rule-governed (de)composition. Parallel to the morphology findings, the children with TS showed speeded production, while the two groups had similar accuracy. The results were not explained by potentially confounding factors, including IQ. Overall, the findings suggest that rule-governed grammatical composition may be speeded in TS, perhaps due to frontal/basal-ganglia abnormalities.

The Genetic Etiology of Tourette Syndrome: Large-Scale Collaborative Efforts on the Precipice of Discovery

Gilles de la Tourette Syndrome (TS) is a childhood-onset neurodevelopmental disorder that is characterized by multiple motor and phonic tics. It has a complex etiology with multiple genes likely interacting with environmental factors to lead to the onset of symptoms. The genetic basis of the disorder remains elusive. However, multiple resources and large-scale projects are coming together, launching a new era in the field and bringing us on the verge of discovery. The large-scale efforts outlined in this report are complementary and represent a range of different approaches to the study of disorders with complex inheritance. The Tourette Syndrome Association International Consortium for Genetics (TSAICG) has focused on large families, parent-proband trios and cases for large case-control designs such as genomewide association studies (GWAS), copy number variation (CNV) scans, and exome/genome sequencing. TIC Genetics targets rare, large effect size mutations in simplex trios, and multigenerational families. The European Multicentre Tics in Children Study (EMTICS) seeks to elucidate gene-environment interactions including the involvement of infection and immune mechanisms in TS etiology. Finally, TS-EUROTRAIN, a Marie Curie Initial Training Network, aims to act as a platform to unify large-scale projects in the field and to educate the next generation of experts. Importantly, these complementary large-scale efforts are joining forces to uncover the full range of genetic variation and environmental risk factors for TS, holding great promise for identifying definitive TS susceptibility genes and shedding light into the complex pathophysiology of this disorder.

Histamine and the striatum

The neuromodulator histamine is released throughout the brain during periods of wakefulness. Combined with an abundant expression of histamine receptors, this suggests potential widespread histaminergic control of neural circuit activity. However, the effect of histamine on many of these circuits is unknown. In this review we will discuss recent evidence for histaminergic modulation of the basal ganglia circuitry, and specifically its main input nucleus; the striatum. Furthermore, we will discuss recent findings of histaminergic dysfunction in several basal ganglia disorders, including in Parkinson's disease and most prominently, in Tourette's syndrome, which has led to a resurgence of interest in this neuromodulator. Combined, these recent observations not only suggest a central role for histamine in modulating basal ganglia activity and behaviour, but also as a possible target in treating basal ganglia disorders. This article is part of the Special Issue entitled 'Histamine Receptors'.

A Primary Role for Nucleus Accumbens and Related Limbic Network in Vocal Tics

Inappropriate vocal expressions, e.g., vocal tics in Tourette syndrome, severely impact quality of life. Neural mechanisms underlying vocal tics remain unexplored because no established animal model representing the condition exists. We report that unilateral disinhibition of the nucleus accumbens (NAc) generates vocal tics in monkeys. Whole-brain PET imaging identified prominent, bilateral limbic cortico-subcortical activation. Local field potentials (LFPs) developed abnormal spikes in the NAc and the anterior cingulate cortex (ACC). Vocalization could occur without obvious LFP spikes, however, when phase-phase coupling of alpha oscillations were accentuated between the NAc, ACC, and the primary motor cortex. These findings contrasted with myoclonic motor tics induced by disinhibition of the dorsolateral putamen, where PET activity was confined to the ipsilateral sensorimotor system and LFP spikes always preceded motor tics. We propose that vocal tics emerge as a consequence of dysrhythmic alpha coupling between critical nodes in the limbic and motor networks. VIDEO ABSTRACT.

Neuroimaging of tic genesis: Present status and future perspectives

Tics are hyperkinetic movements that are distinctive by their variety in semiology and duration and by their ability to be modulated by cognitive control. They are the hallmark of Gilles de la Tourette syndrome. Despite the variety of clinical presentations in this syndrome, dysfunction of cortico-striato-pallido-thalamo-cortical networks is suggested as a core pathophysiological mechanism. We review recent structural and functional neuroimaging studies that focused on the anatomical substrate of tics and their possible genesis. These studies showed a consistent relationship between structural and functional abnormalities within motor cortico-basal ganglia circuits and occurrence of tics. The failure of top-down cortical control over motor pathways because of the atypical trajectory of brain development could be a possible mechanism of tic genesis. Occurrence of tics results in several adaptive mechanisms, including modification of cortico-striatal network activity (reduced functional activation of the primary motor cortex) and neurochemical (increased γ-aminobutyric acid concentrations in the supplementary motor area) and microstructural white matter pathways rearrangements.

Association of Tic Disorders and Enterovirus Infection: A Nationwide Population-Based Study

There has been growing interest in the association between infectious disease and mental disorders, but an association between enterovirus (EV) infection and tic disorders has not been sufficiently explored. Herein, we aim to investigate the association between EV infection and incidence of tic disorders in a nationwide population-based sample using Taiwan's National Health Insurance Research Database. We identified individuals aged ≤18 years prior to 2005 with an inpatient diagnosis of EV infection and/or history of EV infection. Tic disorder was operationalized using International Classification of Disease, Revision 9, Clinical Modification (ICD-9-CM) codes 307.20-307.23. A total of 47,998 individuals with history of EV infection were compared to 47,998 sex-, age-, and urbanization-matched controls on incidence of tic disorders. The mean ± standard deviation follow-up period for all subjects was 9.7 ± 3.6 years; the mean latency period between initial EV infection and incident diagnosis of tic disorder diagnosis was 5.4 ± 2.8 years. EV infection was significantly associated with greater incidence of tic disorders (hazard ratio [HR] = 1.24, 95% CI: 1.07-1.45). When subgrouped on the basis of central nervous system (CNS) involvement, EV infection with CNS involvement was not significantly associated with greater incidence of tic disorders when compared to controls (HR = 1.25, 95% CI: 0.64-2.43); EV infection without CNS involvement was significantly associated greater incidence of tic disorders when compared to controls (HR = 1.24, 95% CI: 1.07-1.45). In addition, hospitalization for an EV infection did not increase the hazard for greater incidence of tic disorders (HR = 1.32, 95% CI: 1.04-1.67 with hospitalization and 1.22, 95% CI: 1.04-1.44 without hospitalization). EV infection is temporally associated with incidence of tic disorders. Our observations add to the growing body of literature implicating immune-inflammatory system in the pathoetiology of brain disorders in a subpopulation of individuals and serve as a clarion call for surveillance of symptoms suggestive of tic disorders in individuals with history of EV infection.

Animal Models of Tourette Syndrome-From Proliferation to Standardization

Tourette syndrome (TS) is a childhood onset disorder characterized by motor and vocal tics and associated with multiple comorbid symptoms. Over the last decade, the accumulation of findings from TS patients and the emergence of new technologies have led to the development of novel animal models with high construct validity. In addition, animal models which were previously associated with other disorders were recently attributed to TS. The proliferation of TS animal models has accelerated TS research and provided a better understanding of the mechanism underlying the disorder. This newfound success generates novel challenges, since the conclusions that can be drawn from TS animal model studies are constrained by the considerable variation across models. Typically, each animal model examines a specific subset of deficits and centers on one field of research (physiology/genetics/pharmacology/etc.). Moreover, different studies do not use a standard lexicon to characterize different properties of the model. These factors hinder the evaluation of individual model validity as well as the comparison across models, leading to a formation of a fuzzy, segregated landscape of TS pathophysiology. Here, we call for a standardization process in the study of TS animal models as the next logical step. We believe that a generation of standard examination criteria will improve the utility of these models and enable their consolidation into a general framework. This should lead to a better understanding of these models and their relationship to TS, thereby improving the research of the mechanism underlying this disorder and aiding the development of new treatments.

Ablation of fast-spiking interneurons in the dorsal striatum, recapitulating abnormalities seen post-mortem in Tourette syndrome, produces anxiety and elevated grooming

Tic disorders, including Tourette syndrome (TS), are thought to involve pathology of cortico-basal ganglia loops, but their pathology is not well understood. Post-mortem studies have shown a reduced number of several populations of striatal interneurons, including the parvalbumin-expressing fast-spiking interneurons (FSIs), in individuals with severe, refractory TS. We tested the causal role of this interneuronal deficit by recapitulating it in an otherwise normal adult mouse using a combination transgenic-viral cell ablation approach. FSIs were reduced bilaterally by ∼40%, paralleling the deficit found post-mortem. This did not produce spontaneous stereotypies or tic-like movements, but there was increased stereotypic grooming after acute stress in two validated paradigms. Stereotypy after amphetamine, in contrast, was not elevated. FSI ablation also led to increased anxiety-like behavior in the elevated plus maze, but not to alterations in motor learning on the rotorod or to alterations in prepulse inhibition, a measure of sensorimotor gating. These findings indicate that a striatal FSI deficit can produce stress-triggered repetitive movements and anxiety. These repetitive movements may recapitulate aspects of the pathophysiology of tic disorders.

Transcriptome Analysis of the Human Striatum in Tourette Syndrome

BACKGROUND

Genome-wide association studies have not revealed any risk-conferring common genetic variants in Tourette syndrome (TS), requiring the adoption of alternative approaches to investigate the pathophysiology of this disorder.

METHODS

We obtained the basal ganglia transcriptome by RNA sequencing in the caudate and putamen of nine TS and nine matched normal control subjects.

RESULTS

We found 309 downregulated and 822 upregulated genes in the caudate and putamen (striatum) of TS individuals. Using data-driven gene network analysis, we identified 17 gene coexpression modules associated with TS. The top-scoring downregulated module in TS was enriched in striatal interneuron transcripts, which was confirmed by decreased numbers of cholinergic and gamma-aminobutyric acidergic interneurons by immunohistochemistry in the same regions. The top-scoring upregulated module was enriched in immune-related genes, consistent with activation of microglia in patients' striatum. Genes implicated by copy number variants in TS were enriched in the interneuron module, as well as in a protocadherin module. Module clustering revealed that the interneuron module was correlated with a neuronal metabolism module.

CONCLUSIONS

Convergence of differential expression, network analyses, and module clustering, together with copy number variants implicated in TS, strongly implicates disrupted interneuron signaling in the pathophysiology of severe TS and suggests that metabolic alterations may be linked to their death or dysfunction.

Multivariate pattern classification of pediatric Tourette syndrome using functional connectivity MRI

Tourette syndrome (TS) is a developmental neuropsychiatric disorder characterized by motor and vocal tics. Individuals with TS would benefit greatly from advances in prediction of symptom timecourse and treatment effectiveness. As a first step, we applied a multivariate method – support vector machine (SVM) classification – to test whether patterns in brain network activity, measured with resting state functional connectivity (RSFC) MRI, could predict diagnostic group membership for individuals. RSFC data from 42 children with TS (8–15 yrs) and 42 unaffected controls (age, IQ, in‐scanner movement matched) were included. While univariate tests identified no significant group differences, SVM classified group membership with ~70% accuracy (p < .001). We also report a novel adaptation of SVM binary classification that, in addition to an overall accuracy rate for the SVM, provides a confidence measure for the accurate classification of each individual. Our results support the contention that multivariate methods can better capture the complexity of some brain disorders, and hold promise for predicting prognosis and treatment outcome for individuals with TS.

Effect of Jian-Pi-Zhi-Dong Decoction on striatal glutamate and γ-aminobutyric acid levels detected using microdialysis in a rat model of Tourette syndrome

BACKGROUND

Jian-Pi-Zhi-Dong Decoction (JPZDD) is a dedicated treatment of Tourette syndrome (TS). The balance of neurotransmitters in the cortico-striato-pallido-thalamo-cortical network is crucial to the occurrence of TS and related to its severity. This study evaluated the effect of JPZDD on glutamate (Glu) and γ-aminobutyric acid (GABA) and their receptors in a TS rat model.

MATERIALS AND METHODS

Rats were divided into four groups (n=12 each). TS was induced in three of the groups by injecting them with 3,3'-iminodipropionitrile for 7 consecutive days. Two model groups were treated with tiapride (Tia) or JPZDD, while the control and the remaining model group were gavaged with saline. Behavior was assessed by stereotypic score and autonomic activity. Striatal Glu and GABA contents were detected using microdialysis. Expressions of N-methyl-D-aspartate receptor 1 and GABAA receptor (GABAAR) were observed using Western blot and real-time polymerase chain reaction.

RESULTS

Tia and JPZDD groups had decreased stereotypy compared with model rats; however, the JPZDD group showed a larger decrease in stereotypy than the Tia group at a 4-week time point. In a spontaneous activity test, the total distance of the JPZDD and Tia groups was significantly decreased compared with the model group. The Glu levels of the model group were higher than the control group and decreased with Tia or JPZDD treatment. The GABA level was higher in the model group than the control group. Expressions of GABAAR protein in the model group were higher than in the control group. Treatment with Tia or JPZDD reduced the expression of GABAAR protein. In the case of the mRNA expression, only Tia reduced the expression of N-methyl-D-aspartate receptor 1, compared with the model group.

CONCLUSION

JPZDD could alleviate impairments in behavior and dysfunctional signaling by downregulating GABAAR in the striatum. We suggest that this acts to maintain the balance of Glu and GABA.

Effect of Deep Brain Stimulation on Regional Cerebral Blood Flow in Patients with Medically Refractory Tourette Syndrome

In this study, alterations in brain perfusion have been investigated in patients with Tourette syndrome (TS) compared with control subjects. In addition, we investigated the effects of deep brain stimulation (DBS) in both globus pallidus internus (GPi) and centromedian-parafascicular/ventralis oralis internus nuclei of the thalamus (CM/Voi) and sham (SHAM) stimulation on cerebral blood flow. In a prospective controlled, randomized, double-blind setting, five severely affected adult patients with TS with predominant motor or vocal tics (mean total tic score on the Yale Global Tic Severity Scale: 39) underwent serial brain perfusion single photon emission computed tomography with (99m)Tc-ECD. Results were compared with data from six age-matched control subjects. All patients were investigated at four different time points: once before DBS implantation (preOP) and three times postoperatively. Postoperative scans were performed in a randomized order, each after 3 months of either GPi, CM/Voi, or SHAM stimulation. At each investigation, patients were injected at rest while awake, but scanned during anesthesia. This procedure ensured that neither anesthesia nor movement artifacts influenced our results. Control subjects were investigated only once at baseline (without DBS or anesthesia). At baseline, cerebral blood flow was significantly reduced in patients with TS (preOP) compared with controls in the central region, frontal, and parietal lobe, specifically in Brodmann areas 1, 4-9, 30, 31, and 40. Significantly increased perfusion was found in the cerebellum. When comparing SHAM stimulation to preOP condition, we found significantly decreased perfusion in basal ganglia and thalamus, but increased perfusion in different parts of the frontal cortex. Compared with SHAM condition both GPi and thalamic stimulation resulted in a significant decrease in cerebral blood flow in basal ganglia and cerebellum, while perfusion in the frontal cortex was significantly increased. Our results provide substantial evidence that, in TS, brain perfusion is altered in the frontal cortex and the cerebellum and that these changes can be reversed by both GPi and CM/Voi DBS.

Functional Evaluations of Genes Disrupted in Patients with Tourette's Disorder

Tourette's disorder (TD) is a highly heritable neurodevelopmental disorder with complex genetic architecture and unclear neuropathology. Disruptions of particular genes have been identified in subsets of TD patients. However, none of the findings have been replicated, probably due to the complex and heterogeneous genetic architecture of TD that involves both common and rare variants. To understand the etiology of TD, functional analyses are required to characterize the molecular and cellular consequences caused by mutations in candidate genes. Such molecular and cellular alterations may converge into common biological pathways underlying the heterogeneous genetic etiology of TD patients. Herein, we review specific genes implicated in TD etiology, discuss the functions of these genes in the mammalian central nervous system and the corresponding behavioral anomalies exhibited in animal models, and importantly, review functional analyses that can be performed to evaluate the role(s) that the genetic disruptions might play in TD. Specifically, the functional assays include novel cell culture systems, genome editing techniques, bioinformatics approaches, transcriptomic analyses, and genetically modified animal models applied or developed to study genes associated with TD or with other neurodevelopmental and neuropsychiatric disorders. By describing methods used to study diseases with genetic architecture similar to TD, we hope to develop a systematic framework for investigating the etiology of TD and related disorders.

Learning From Animal Models of Obsessive-Compulsive Disorder

Obsessive-compulsive disorder (OCD) affects 2%-3% of the population worldwide and can cause significant distress and disability. Substantial challenges remain in the field of OCD research and therapeutics. Approved interventions alleviate symptoms only partially, with 30%-40% of patients being resistant to treatment. Although the etiology of OCD is still unknown, research evidence points toward the involvement of cortico-striato-thalamocortical circuitry. This review focuses on the most recent behavioral, genetics, and neurophysiologic findings from animal models of OCD. Based on evidence from these models and parallels with human studies, we discuss the circuit hyperactivity hypothesis for OCD, a potential circuitry dysfunction of action termination, and the involvement of candidate genes. Adding a more biologically valid framework to OCD will help researchers define and test new hypotheses and facilitate the development of targeted therapies based on disease-specific mechanisms.

Striatal magnetic resonance spectroscopy abnormalities in young adult SAPAP3 knockout mice

BACKGROUND

Obsessive compulsive disorder (OCD) is a debilitating condition with lifetime prevalence of 1-3%. OCD typically arises in youth but delays in diagnosis impede optimal treatment and developmental studies of the disorder. Research using genetically modified rodents may provide models of etiology that enable earlier detection and intervention. The SAPAP3 knockout (KO) transgenic mouse was developed as an animal model of OCD and related disorders (OCRD). KO mice exhibit compulsive self-grooming behavior analogous to behaviors found in people with OCRD. Striatal hyperactivity has been reported in these mice and in humans with OCD.

METHODS

Striatal and medial frontal cortex 9.4 Tesla proton spectra were acquired from young adult SAPAP3 KO and wild-type control mice to determine whether KO mice have metabolic and neurochemical abnormalities.

RESULTS

Young adult KO mice had lower striatal lactate (P=0.006) and glutathione (P=0.039) levels. Among all mice, striatal lactate and glutathione levels were associated (R=0.73, P=0.007). We found no group differences in medial frontal cortex metabolites. At the age range studied, only 1 of 8 KO mice had skin lesions indicative of severe compulsive grooming.

CONCLUSION

Young adult SAPAP3 KO mice have striatal but not medial frontal cortex MRS abnormalities that may reflect striatal hypermetabolism accompanied by oxidative stress. These abnormalities typically preceded the onset of severe compulsive grooming. Our findings are consistent with striatal hypermetabolism in OCD. Together, these results suggest that striatal MRS measures of lactate or glutathione might be useful biomarkers for early detection of risk for developing compulsive behavior disorders.

Corticostriatal Divergent Function in Determining the Temporal and Spatial Properties of Motor Tics

Striatal disinhibition leads to the formation of motor tics resembling those expressed during Tourette syndrome and other tic disorders. The spatial properties of these tics are dependent on the location of the focal disinhibition within the striatum; however, the factors affecting the temporal properties of tic expression are still unknown. Here, we used microstimulation within the motor cortex of freely behaving rats before and after striatal disinhibition to explore the factors underlying the timing of individual tics. Cortical activation determined the timing of individual tics via an accumulation process of inputs that was dependent on the frequency and amplitude of the inputs. The resulting tics and their neuronal representation within the striatum were highly stereotypic and independent of the cortical activity properties. The generation of tics was limited by absolute and relative tic refractory periods that were derived from an internal striatal state. Thus, the precise time of the tic expression depends on the interaction between the summation of incoming excitatory inputs to the striatum and the timing of the previous tic. A data-driven computational model of corticostriatal function closely replicated the temporal properties of tic generation and enabled the prediction of tic timing based on incoming cortical activity and tic history. These converging experimental and computational findings suggest a clear functional dichotomy within the corticostriatal network, pointing to disparate temporal (cortical) versus spatial (striatal) encoding. Thus, the abnormal striatal inhibition typical of Tourette syndrome and other tic disorders results in tics due to cortical activation of the abnormal striatal network.

SIGNIFICANCE STATEMENT

The factors underlying the temporal properties of tics expressed in Tourette syndrome and other tic disorders have eluded clinicians and scientists for decades. In this study, we highlight the key role of corticostriatal activity in determining the timing of individual tics. We found that cortical activation determined the timing of tics but did not determine their form. A data-driven computational model of the corticostriatal network closely replicated the temporal properties of tic generation and enabled the prediction of tic timing based on incoming cortical activity and tic history. This study thus shows that, although tics originate in the striatum, their timing depends on the interplay between incoming excitatory corticostriatal inputs and the internal striatal state.

Optogenetic stimulation reveals distinct modulatory properties of thalamostriatal vs corticostriatal glutamatergic inputs to fast-spiking interneurons

Parvalbumin-containing fast-spiking interneurons (FSIs) exert a powerful feed-forward GABAergic inhibition on striatal medium spiny neurons (MSNs), playing a critical role in timing striatal output. However, how glutamatergic inputs modulate their firing activity is still unexplored. Here, by means of a combined optogenetic and electrophysiological approach, we provide evidence for a differential modulation of cortico- vs thalamo-striatal synaptic inputs to FSIs in transgenic mice carrying light-gated ion channels channelrhodopsin-2 (ChR2) in glutamatergic fibers. Corticostriatal synapses show a postsynaptic facilitation, whereas thalamostriatal synapses present a postsynaptic depression. Moreover, thalamostriatal synapses exhibit more prominent AMPA-mediated currents than corticostriatal synapses, and an increased release probability. Furthermore, during current-evoked firing activity, simultaneous corticostriatal stimulation increases bursting activity. Conversely, thalamostriatal fiber activation shifts the canonical burst-pause activity to a more prolonged, regular firing pattern. However, this change in firing pattern was accompanied by a significant rise in the frequency of membrane potential oscillations. Notably, the responses to thalamic stimulation were fully abolished by blocking metabotropic glutamate 1 (mGlu1) receptor subtype, whereas both acetylcholine and dopamine receptor antagonists were ineffective. Our findings demonstrate that cortical and thalamic glutamatergic input differently modulate FSIs firing activity through specific intrinsic and synaptic properties, exerting a powerful influence on striatal outputs.

Characteristics of fast-spiking neurons in the striatum of behaving monkeys

Inhibitory interneurons are the fundamental constituents of neural circuits that organize network outputs. The striatum as part of the basal ganglia is involved in reward-directed behaviors. However, the role of the inhibitory interneurons in this process remains unclear, especially in behaving monkeys. We recorded the striatal single neuron activity while monkeys performed reward-directed hand or eye movements. Presumed parvalbumin-containing GABAergic interneurons (fast-spiking neurons, FSNs) were identified based on narrow spike shapes in three independent experiments, though they were a small population (4.2%, 42/997). We found that FSNs are characterized by high-frequency and less-bursty discharges, which are distinct from the basic firing properties of the presumed projection neurons (phasically active neurons, PANs). Besides, the encoded information regarding actions and outcomes was similar between FSNs and PANs in terms of proportion of neurons, but the discharge selectivity was higher in PANs than that of FSNs. The coding of actions and outcomes in FSNs and PANs was consistently observed under various behavioral contexts in distinct parts of the striatum (caudate nucleus, putamen, and anterior striatum). Our results suggest that FSNs may enhance the discharge selectivity of postsynaptic output neurons (PANs) in encoding crucial variables for a reward-directed behavior.

Regulatory domain or CpG site variation in SLC12A5, encoding the chloride transporter KCC2, in human autism and schizophrenia

Many encoded gene products responsible for neurodevelopmental disorders (NDs) like autism spectrum disorders (ASD), schizophrenia (SCZ), intellectual disability (ID), and idiopathic generalized epilepsy (IGE) converge on networks controlling synaptic function. An increase in KCC2 (SLC12A5) Cl⁻ transporter activity drives the developmental GABA excitatory-inhibitory sequence, but the role of KCC2 in human NDs is essentially unknown. Here, we report two rare, non-synonymous (NS), functionally-impairing variants in the KCC2 C-terminal regulatory domain (CTRD) in human ASD (R952H and R1049C) and SCZ (R952H) previously linked with IGE and familial febrile seizures, and another novel NS KCC2 variant in ASD (R1048W) with highly-predicted pathogenicity. Exome data from 2517 simplex families in the ASD Simon Simplex Collection (SSC) revealed significantly more KCC2 CTRD variants in ASD cases than controls, and interestingly, these were more often synonymous and predicted to disrupt or introduce a CpG site. Furthermore, full gene analysis showed ASD cases are more likely to contain rare KCC2 variants affecting CpG sites than controls. These data suggest genetically-encoded dysregulation of KCC2-dependent GABA signaling may contribute to multiple human NDs.

"Hyperglutamatergic cortico-striato-thalamo-cortical circuit" breaker drugs alleviate tics in a transgenic circuit model of Tourette׳s syndrome

The brain circuits underlying tics in Tourette׳s syndrome (TS) are unknown but thought to involve cortico/amygdalo-striato-thalamo-cortical (CSTC) loop hyperactivity. We previously engineered a transgenic mouse "circuit model" of TS by expressing an artificial neuropotentiating transgene (encoding the cAMP-elevating, intracellular A1 subunit of cholera toxin) within a small population of dopamine D1 receptor-expressing somatosensory cortical and limbic neurons that hyperactivate cortico/amygdalostriatal glutamatergic output circuits thought to be hyperactive in TS and comorbid obsessive-compulsive (OC) disorders. As in TS, these D1CT-7 ("Ticcy") transgenic mice׳s tics were alleviated by the TS drugs clonidine and dopamine D2 receptor antagonists; and their chronic glutamate-excited striatal motor output was unbalanced toward hyperactivity of the motoric direct pathway and inactivity of the cataleptic indirect pathway. Here we have examined whether these mice׳s tics are countered by drugs that "break" sequential elements of their hyperactive cortical/amygdalar glutamatergic and efferent striatal circuit: anti-serotonoceptive and anti-noradrenoceptive corticostriatal glutamate output blockers (the serotonin 5-HT2a,c receptor antagonist ritanserin and the NE alpha-1 receptor antagonist prazosin); agmatinergic striatothalamic GABA output blockers (the presynaptic agmatine/imidazoline I1 receptor agonist moxonidine); and nigrostriatal dopamine output blockers (the presynaptic D2 receptor agonist bromocriptine). Each drug class alleviates tics in the Ticcy mice, suggesting a hyperglutamatergic CSTC "tic circuit" could exist in TS wherein cortical/amygdalar pyramidal projection neurons׳ glutamatergic overexcitation of both striatal output neurons and nigrostriatal dopaminergic modulatory neurons unbalances their circuit integration to excite striatothalamic output and create tics, and illuminating new TS drug strategies.

Common therapeutic mechanisms of pallidal deep brain stimulation for hypo- and hyperkinetic movement disorders

Abnormalities in cortico-basal ganglia (CBG) networks can cause a variety of movement disorders ranging from hypokinetic disorders, such as Parkinson's disease (PD), to hyperkinetic conditions, such as Tourette syndrome (TS). Each condition is characterized by distinct patterns of abnormal neural discharge (dysrhythmia) at both the local single-neuron level and the global network level. Despite divergent etiologies, behavioral phenotypes, and neurophysiological profiles, high-frequency deep brain stimulation (HF-DBS) in the basal ganglia has been shown to be effective for both hypo- and hyperkinetic disorders. The aim of this review is to compare and contrast the electrophysiological hallmarks of PD and TS phenotypes in nonhuman primates and discuss why the same treatment (HF-DBS targeted to the globus pallidus internus, GPi-DBS) is capable of ameliorating both symptom profiles. Recent studies have shown that therapeutic GPi-DBS entrains the spiking of neurons located in the vicinity of the stimulating electrode, resulting in strong stimulus-locked modulations in firing probability with minimal changes in the population-scale firing rate. This stimulus effect normalizes/suppresses the pathological firing patterns and dysrhythmia that underlie specific phenotypes in both the PD and TS models. We propose that the elimination of pathological states via stimulus-driven entrainment and suppression, while maintaining thalamocortical network excitability within a normal physiological range, provides a common therapeutic mechanism through which HF-DBS permits information transfer for purposive motor behavior through the CBG while ameliorating conditions with widely different symptom profiles.

Inhibition, Disinhibition, and the Control of Action in Tourette Syndrome

Tourette syndrome (TS) is a neurological disorder characterized by vocal and motor tics. TS is associated with impairments in behavioral inhibition, dysfunctional signaling of the inhibitory neurotransmitter GABA, and alterations in the balance of excitatory and inhibitory influences within brain networks implicated in motor learning and the selection of actions. We review evidence that increased control over motor outputs, including the suppression of tics, may develop during adolescence in TS and be accompanied by compensatory, neuromodulatory, alterations in brain structure and function. In particular, we argue that increased control over motor outputs in TS is brought about by local increases in 'tonic' inhibition that lead to a reduction in the 'gain' of motor excitability.

In vivo effects of ketamine on glutamate-glutamine and gamma-aminobutyric acid in obsessive-compulsive disorder: Proof of concept

We previously reported the rapid and robust clinical effects of ketamine versus saline infusions in a proof-of-concept crossover trial in unmedicated adults with obsessive-compulsive disorder (OCD). This study examined the concurrent neurochemical effects of ketamine versus saline infusions using proton magnetic resonance spectroscopy ((1)H MRS) during the clinical proof-of-concept crossover trial. Levels of the inhibitory neurotransmitter gamma-aminobutyric acid (GABA) and the excitatory neurochemicals glutamate+glutamine (Glx) were acquired in the medial prefrontal cortex (MPFC), a region implicated in OCD pathology. Seventeen unmedicated OCD adults received two intravenous infusions at least 1 week apart, one of saline and one of ketamine, while lying supine in a 3.0 T GE MR scanner. The order of each infusion pair was randomized. Levels of GABA and Glx were measured in the MPFC before, during, and after each infusion and normalized to water (W). A mixed effects model found that MPFC GABA/W significantly increased over time in the ketamine compared with the saline infusion. In contrast, there were no significant differences in Glx/W between the ketamine and saline infusions. Together with earlier evidence of low cortical GABA in OCD, our findings suggest that models of OCD pathology should consider the role of GABAergic abnormalities in OCD symptomatology.

Tourette Syndrome: Update

Tourette Syndrome is a disorder characterized by tics. It typically begins in childhood and often improves in adult life. Tics are best described as voluntary movements made automatically so that volition is not ordinarily appreciated. There is frequently an urge, sometimes in the form of a specific sensory feeling (sensory tic), that precedes the tic. Patients say that they make the tic in order to reduce the urge, although shortly after the tic, the urge recurs. The sensory feeling may arise due to defective sensory habituation. Since tics relieve the urge, this can be considered rewarding, and repetition of this behavior may perpetuate the tic as a habit. Tourette Syndrome affects boys more than girls and is associated with attention deficit hyperactivity disorder and obsessive compulsive disorder. Although Tourette Syndrome often appears to be autosomal recessive in inheritance, it has been difficult to find any abnormal genes. There is a loss of inhibition in these patients and recent studies show abnormalities in brain GABA. Certainly there is also an abnormality in dopamine function and dopamine blocking agents are effective therapy. In severe drug-refractory patients, deep brain stimulation can be effective.

Reduced GABAergic inhibition and abnormal sensory symptoms in children with Tourette syndrome

Tourette Syndrome (TS) is characterized by the presence of chronic tics. Individuals with TS often report difficulty with ignoring (habituating to) tactile sensations, and some patients perceive that this contributes to a "premonitory urge" to tic. While common, the physiological basis of impaired tactile processing in TS, and indeed tics themselves, remain poorly understood. It has been well established that GABAergic processing plays an important role in shaping the neurophysiological response to tactile stimulation. Furthermore, there are multiple lines of evidence suggesting that a deficit in GABAergic transmission may contribute to symptoms found in TS. In this study, GABA-edited magnetic resonance spectroscopy (MRS) was combined with a battery of vibrotactile tasks to investigate the role of GABA and atypical sensory processing in children with TS. Our results show reduced primary sensorimotor cortex (SM1) GABA concentration in children with TS compared with healthy control subjects (HC), as well as patterns of impaired performance on tactile detection and adaptation tasks, consistent with altered GABAergic function. Moreover, in children with TS SM1 GABA concentration correlated with motor tic severity, linking the core feature of TS directly to in vivo brain neurochemistry. There was an absence of the typical correlation between GABA and frequency discrimination performance in TS as was seen in HC. These data show that reduced GABA concentration in TS may contribute to both motor tics and sensory impairments in children with TS. Understanding the mechanisms of altered sensory processing in TS may provide a foundation for novel interventions to alleviate these symptoms.

Pathophysiology of tic disorders

Tics are the defining symptom of Tourette syndrome and other tic disorders (TDs); however, they form only a part of their overall symptoms. The recent surge of studies addressing the underlying pathophysiology of tics has revealed an intricate picture involving multiple brain areas and complex pathways. The myriad of pathophysiological findings stem, at least partially, from the multifaceted properties of tics and the disorders that express them. Distinct brain pathways mediate the expression of tics, whereas others are involved in the generation of the premonitory urge, associated comorbidities, and other changes in brain state. Expression of these symptoms is controlled by additional networks underlying voluntary suppression by the patient or those reflecting overall behavioral state. This review aims to simplify the complex picture of tic pathophysiology by dividing it into these key components based on converging data from human and animal model studies. Thus, involvement of the corticobasal ganglia pathway and its interaction with motor, sensory, limbic, and executive networks in each of the components as well as their control by different neuromodulators is described. This division enables a focused definition of the neuronal systems involved in each of these processes and allows a better understanding of the pathophysiology of TDs as a whole.

Attention-Deficit/Hyperactivity Disorder-like Phenotype in a Mouse Model with Impaired Actin Dynamics

BACKGROUND

Actin depolymerizing proteins of the actin depolymerizing factor (ADF)/cofilin family are essential for actin dynamics, which is critical for synaptic function. Two ADF/cofilin family members, ADF and n-cofilin, are highly abundant in the brain, where they are present in excitatory synapses. Previous studies demonstrated the relevance of n-cofilin for postsynaptic plasticity, associative learning, and anxiety. These studies also suggested overlapping functions for ADF and n-cofilin.

METHODS

We performed pharmacobehavioral, electrophysiologic, and electron microscopic studies on ADF and n-cofilin single mutants and double mutants (named ACC mice) to characterize the importance of ADF/cofilin activity for synapse physiology and mouse behavior.

RESULTS

The ACC mice, but not single mutants, exhibited hyperlocomotion, impulsivity, and impaired working memory. Hyperlocomotion and impulsive behavior were reversed by methylphenidate, a psychostimulant commonly used for the treatment of attention-deficit/hyperactivity disorder (ADHD). Also, ACC mice displayed a disturbed morphology of striatal excitatory synapses, accompanied by strongly increased glutamate release. Blockade of dopamine or glutamate transmission resulted in normal locomotion.

CONCLUSIONS

Our study reveals that ADHD can result from a disturbed balance between excitation and inhibition in striatal circuits, providing novel insights into the mechanisms underlying this neurobehavioral disorder. Our results link actin dynamics to ADHD, suggesting that mutations in actin regulatory proteins may contribute to the etiology of ADHD in humans.

Abnormal neuronal activity in Tourette syndrome and its modulation using deep brain stimulation

Tourette syndrome (TS) is a common childhood-onset disorder characterized by motor and vocal tics that are typically accompanied by a multitude of comorbid symptoms. Pharmacological treatment options are limited, which has led to the exploration of deep brain stimulation (DBS) as a possible treatment for severe cases. Multiple lines of evidence have linked TS with abnormalities in the motor and limbic cortico-basal ganglia (CBG) pathways. Neurophysiological data have only recently started to slowly accumulate from multiple sources: noninvasive imaging and electrophysiological techniques, invasive electrophysiological recordings in TS patients undergoing DBS implantation surgery, and animal models of the disorder. These converging sources point to system-level physiological changes throughout the CBG pathway, including both general altered baseline neuronal activity patterns and specific tic-related activity. DBS has been applied to different regions along the motor and limbic pathways, primarily to the globus pallidus internus, thalamic nuclei, and nucleus accumbens. In line with the findings that also draw on the more abundant application of DBS to Parkinson's disease, this stimulation is assumed to result in changes in the neuronal firing patterns and the passage of information through the stimulated nuclei. We present an overview of recent experimental findings on abnormal neuronal activity associated with TS and the changes in this activity following DBS. These findings are then discussed in the context of current models of CBG function in the normal state, during TS, and finally in the wider context of DBS in CBG-related disorders.

GDNF gene is associated with tourette syndrome in a family study

BACKGROUND

Tourette syndrome is a disorder characterized by persistent motor and vocal tics, and frequently accompanied by the comorbidities attention deficit hyperactivity disorder and obsessive-compulsive disorder. Impaired synaptic neurotransmission has been implicated in its pathogenesis. Our aim was to investigate the association of 28 candidate genes, including genes related to synaptic neurotransmission and neurotrophic factors, with Tourette syndrome.

METHODS

We genotyped 506 polymorphisms in a discovery cohort from the United States composed of 112 families and 47 unrelated singletons with Tourette syndrome (201 cases and 253 controls). Genes containing significant polymorphisms were imputed to fine-map the signal(s) to potential causal variants. Allelic analyses in Tourette syndrome cases were performed to check the role in attention deficit hyperactivity disorder and obsessive-compulsive disorder comorbidities. Target polymorphisms were further studied in a replication cohort from southern Spain composed of 37 families and three unrelated singletons (44 cases and 73 controls).

RESULTS

The polymorphism rs3096140 in glial cell line-derived neurotrophic factor gene (GDNF) was significant in the discovery cohort after correction (P = 1.5 × 10(-4) ). No linkage disequilibrium was found between rs3096140 and other functional variants in the gene. We selected rs3096140 as target polymorphism, and the association was confirmed in the replication cohort (P = 0.01). No association with any comorbidity was found.

CONCLUSIONS

As a conclusion, a common genetic variant in GDNF is associated with Tourette syndrome. A defect in the production of GDNF could compromise the survival of parvalbumin interneurons, thus altering the excitatory/inhibitory balance in the corticostriatal circuitry. Validation of this variant in other family cohorts is necessary.

Prefrontal dysfunction in pediatric Tourette's disorder as measured by near-infrared spectroscopy

BACKGROUND

Tourette's disorder (TD) is a chronic childhood-onset disorder characterized by the presence of multiple motor and vocal tics. Despite strong evidence that the pathophysiology of TD involves structural and functional disturbances of the basal ganglia and cortical frontal areas, in vivo imaging studies have produced conflicting results. Recent developments in near-infrared spectroscopy (NIRS) technology have enabled noninvasive assessment of brain function in people with psychiatric disorders.

METHODS

We asked 10 individuals with pediatric TD and 10 healthy controls who were age- and sex- matched to perform the Stroop color-word task during NIRS. We used prefrontal probes and a 24-channel NIRS machine to measure the relative concentrations of oxyhemoglobin (oxy-Hb) every 0.1 s during the task.

RESULTS

We found that oxy-Hb changes in the prefrontal cortex were significantly smaller in the TD group compared with the control group, especially in the left dorsolateral prefrontal cortex.

CONCLUSIONS

Our data suggest that individuals with pediatric TD have a reduced prefrontal hemodynamic response as measured by NIRS.

Executive control signals in orbitofrontal cortex during response inhibition

Orbitofrontal cortex (OFC) lesions produce deficits in response inhibition and imaging studies suggest that activity in OFC is stronger on trials that require suppression of behavior, yet few studies have examined neural correlates at the single-unit level in a behavioral task that probes response inhibition without varying other factors, such as anticipated outcomes. Here we recorded from single neurons in lateral OFC in a task that required animals in the minority of trials to STOP or inhibit an ongoing movement and respond in the opposite direction. We found that population and single-unit firing was modulated primarily by response direction and movement speed, and that very few OFC neurons exhibited a response independent inhibition signal. Remarkably, the strength of the directional signal was not diminished on STOP trials and was actually stronger on STOP trials during conflict adaptation. Finally, directional signals were stronger during sessions in which rats had the most difficulty inhibiting behavior. These results suggest that "inhibition" deficits observed with OFC interference studies reflect deficits unrelated to signaling the need to inhibit behavior, but instead support a role for OFC in executive functions related to dissociating between two perceptually similar actions during response conflict.

Existence and control of Go/No-Go decision transition threshold in the striatum

A typical Go/No-Go decision is suggested to be implemented in the brain via the activation of the direct or indirect pathway in the basal ganglia. Medium spiny neurons (MSNs) in the striatum, receiving input from cortex and projecting to the direct and indirect pathways express D1 and D2 type dopamine receptors, respectively. Recently, it has become clear that the two types of MSNs markedly differ in their mutual and recurrent connectivities as well as feedforward inhibition from FSIs. Therefore, to understand striatal function in action selection, it is of key importance to identify the role of the distinct connectivities within and between the two types of MSNs on the balance of their activity. Here, we used both a reduced firing rate model and numerical simulations of a spiking network model of the striatum to analyze the dynamic balance of spiking activities in D1 and D2 MSNs. We show that the asymmetric connectivity of the two types of MSNs renders the striatum into a threshold device, indicating the state of cortical input rates and correlations by the relative activity rates of D1 and D2 MSNs. Next, we describe how this striatal threshold can be effectively modulated by the activity of fast spiking interneurons, by the dopamine level, and by the activity of the GPe via pallidostriatal backprojections. We show that multiple mechanisms exist in the basal ganglia for biasing striatal output in favour of either the `Go' or the `No-Go' pathway. This new understanding of striatal network dynamics provides novel insights into the putative role of the striatum in various behavioral deficits in patients with Parkinson's disease, including increased reaction times, L-Dopa-induced dyskinesia, and deep brain stimulation-induced impulsivity.

Role of the right dorsal anterior insula in the urge to tic in Tourette syndrome

BACKGROUND

The mid-posterior part of the insula is involved in processing bodily sensations and urges and is activated during tic generation in Tourette syndrome. The dorsal anterior part of the insula, however, integrates sensory and emotional information with cognitive valuation and is implicated in interoception. The right dorsal anterior insula also participates in urge suppression in healthy subjects. This study examined the role of the right dorsal anterior insula in the urge to tic in Tourette syndrome.

METHODS

Resting-state functional magnetic resonance imaging was performed in 13 adult Tourette patients and 13 matched controls. The role of the right dorsal anterior insula within the urge-tic network was investigated using graph theory-based neural network analysis. The functional connectivity of the right dorsal anterior insula was also correlated with urge and tic severity.

RESULTS

Even though the patients did not exhibit any overt tics, the right dorsal anterior insula demonstrated higher connectivity, especially with the frontostriatal nodes of the urge-tic network in patients compared with controls. The functional connectivity between the right dorsal anterior insula and bilateral supplementary motor area also correlated positively with urge severity in patients.

CONCLUSIONS

These results suggest that the right dorsal anterior insula is part of the urge-tic network and could influence the urge- and tic-related cortico-striato-thalamic regions even during rest in Tourette syndrome. It might be responsible for heightened awareness of bodily sensations generating premonitory urges in Tourette syndrome.

Similar striatal D2/D3 dopamine receptor availability in adults with Tourette syndrome compared with healthy controls: A [(11) C]-(+)-PHNO and [(11) C]raclopride positron emission tomography imaging study

Pharmacological and anatomical evidence implicates striatal dopamine receptors in Tourette syndrome (TS). Nevertheless, results of positron emission tomography (PET) studies of the dopamine system in TS have been inconsistent. We investigated striatal D2/3 dopamine receptors in TS using the radioligands [(11) C]raclopride and [(11) C]-(+)-PHNO, an agonist that binds preferentially to D3 receptors, thus allowing higher sensitivity and measurement of receptors in a high affinity state. Eleven adults with TS and 11 matched healthy control (HC) participants underwent [(11) C]raclopride and [(11) C]-(+)-PHNO PET scans. General linear model was used for voxelwise contrasts of striatal binding potentials (BPND ) between TS and HC participants. Analysis of variance was performed to investigate main effect of radioligand. In addition, BPND values were extracted for ventral, motor, and associative striatum. Finally, we examined the relationship between BPND measures and symptom severity in TS participants. Main effects analyses showed that [(11) C]-(+)-PHNO BPND was higher in ventral striatum, whereas [(11) C]raclopride BPND was higher in motor and associative striatum. There were no significant group differences between TS and HC. Furthermore, TS and HC participants had similar [(11) C]-(+)-PHNO and [(11) C]raclopride BPND in the three striatal subregions. Moreover, there was no significant correlation between BPND and symptom severity. TS and HC participants had similar striatal D2/3 receptor availability measures. These results challenge the assumption that striatal dopamine receptors have a major role in the pathophysiology of TS. Consistent with previous findings, [(11) C]-(+)-PHNO localized preferentially to ventral striatal, D3 receptor-rich regions, in contrast to [(11) C]raclopride, which localized preferentially in the dorsal striatum.