No change in striatal dopamine re-uptake site density in psychotropic drug naive and in currently treated Tourette's disorder patients: a [(123)I]-beta-CIT SPECt-study

The Pathophysiology of Tics; An Evolving Story

Background:

Tics, defined as quick, rapid, sudden, recurrent, non-rhythmic motor movements or vocalizations are required components of Tourette Syndrome (TS) - a complex disorder characterized by the presence of fluctuating, chronic motor and vocal tics, and the presence of co-existing neuropsychological problems. Despite many advances, the underlying pathophysiology of tics/TS remains unknown.

Objective:

To address a variety of controversies surrounding the pathophysiology of TS. More specifically: 1) the configuration of circuits likely involved; 2) the role of inhibitory influences on motor control; 3) the classification of tics as either goal-directed or habitual behaviors; 4) the potential anatomical site of origin, e.g. cortex, striatum, thalamus, cerebellum, or other(s); and 5) the role of specific neurotransmitters (dopamine, glutamate, GABA, and others) as possible mechanisms (Abstract figure).

Methods:

Existing evidence from current clinical, basic science, and animal model studies are reviewed to provide: 1) an expanded understanding of individual components and the complex integration of the Cortico-Basal Ganglia-Thalamo-Cortical (CBGTC) circuit - the pathway involved with motor control; and 2) scientific data directly addressing each of the aforementioned controversies regarding pathways, inhibition, classification, anatomy, and neurotransmitters.

Conclusion:

Until a definitive pathophysiological mechanism is identified, one functional approach is to consider that a disruption anywhere within CBGTC circuitry, or a brain region inputting to the motor circuit, can lead to an aberrant message arriving at the primary motor cortex and enabling a tic. Pharmacologic modulation may be therapeutically beneficial, even though it might not be directed toward the primary abnormality.

Dopaminergic Disturbances in Tourette Syndrome: An Integrative Account

Tourette syndrome (TS) is thought to involve dopaminergic disturbances, but the nature of those disturbances remains controversial. Existing hypotheses suggest that TS involves 1) supersensitive dopamine receptors, 2) overactive dopamine transporters that cause low tonic but high phasic dopamine, 3) presynaptic dysfunction in dopamine neurons, or 4) dopaminergic hyperinnervation. We review evidence that contradicts the first two hypotheses; we also note that the last two hypotheses have traditionally been considered too narrowly, explaining only small subsets of findings. We review all studies that have used positron emission tomography and single-photon emission computerized tomography to investigate the dopaminergic system in TS. The seemingly diverse findings from those studies have typically been interpreted as pointing to distinct mechanisms, as evidenced by the various hypotheses concerning the nature of dopaminergic disturbances in TS. We show, however, that the hyperinnervation hypothesis provides a simple, parsimonious explanation for all such seemingly diverse findings. Dopaminergic hyperinnervation likely causes increased tonic and phasic dopamine. We have previously shown, using a computational model of the role of dopamine in basal ganglia, that increased tonic dopamine and increased phasic dopamine likely increase the propensities to express and learn tics, respectively. There is therefore a plausible mechanistic link between dopaminergic hyperinnervation and TS via increased tonic and phasic dopamine. To further bolster this argument, we review evidence showing that all medications that are effective for TS reduce signaling by tonic dopamine, phasic dopamine, or both.

Striatal dopaminergic alterations in Tourette's syndrome: a meta-analysis based on 16 PET and SPECT neuroimaging studies

Despite intense research, the underlying mechanisms and the etiology of Tourette's syndrome (TS) remain unknown. Data from molecular imaging studies targeting the dopamine system in Tourette patients are inconclusive. For a better understanding of the striatal dopamine function in adult dopamine-antagonist-free patients we performed a systematic review in August 2017 identifying 49 PET and SPECT studies on the topic of TS. A total of 8 studies appraised the dopamine transporter (DAT) with 111 Tourette patients and 93 healthy controls, and could be included in a meta-analytic approach. We found a significantly increased striatal DAT binding in Tourette patients (Hedges' g = 0.49; 95% CI: (0.01-0.98)), although this effect did not remain significant after correcting for age differences between cohorts. A second meta-analysis was performed for the striatal dopamine receptor including 8 studies with a total of 72 Tourette patients and 71 controls. This analysis revealed a nonsignificant trend toward lower dopamine 2/3 receptor binding in striatum of Tourette patients. Other analyses regarding study population characteristics in both the DAT and receptor meta-analysis did not show any meaningful results. Our results indicate that dopaminergic alterations in TS are likely and thereby this data would be in line with the current pathophysiological hypotheses of a dysfunction in the dopamine system, e.g., the hypothesis of tonic-phasic dysfunction. However, these analyses suffer from low effect sizes probably due to the heterogeneity of TS and highlight the need for further large-scaled neuroimaging studies.

Dual regulating effect of Ningdong granule on extracellular dopamine content of two kinds of Tourette's syndrome rat models

Tourette's syndrome (TS) is an inherited chronic neuropsychiatric disorder characterized by involuntary stereotyped motor and phonic behaviors called tics. Its pathogenesis is still unclear and its treatment remains limited. Our previous basic and clinical studies have shown that traditional Chinese medicine (TCM) preparation Ningdong granule (NDG) is effective for the treatment of TS with little side effects. In the current study, two TS rat models (Apomorphine (Apo)- and 3,3'-iminodipropionitrile (IDPN)-induced) were used to explore the dual regulating effects and mechanisms of NDG on extracellular DA concentration. We found that NDG could regulate the extracellular DA concentration dually: it could make a gradual recovery in extracellular DA content from both an up-regulated level in Apo-induced rats and down-regulated level in IDPN-induced rats measured by high-performance liquid chromatography (HPLC). The protein expression of DA transporter (DAT) was measured by Western blot and the result showed that NDG could elevate DAT expression when DA release was up-regulated and could decrease DAT expression when extracellular DA concentration was down-regulated. The main mechanism of the dual regulating effect of NDG on extracellular DA release might be related to DAT protein expression in TS, through which the released DA is re-uptaken into nerve terminals. Taken together, compared with conventional single-target anti-tics drugs such as haloperidol (Hal), NDG with the dual regulating effect would be more significant for TS treatment.

Dual ameliorative effects of Ningdong granule on dopamine in rat models of Tourette's syndrome

Dopamine (DA) is a key neuromodulator in the brain that supports motor and cognitive functions. Here, we use apomorphine (Apo) and 3,3'-iminodipropionitrile (IDPN) to develop two rat models of Tourette's syndrome (TS), a common neuropsychiatric disorder characterized by stereotyped repetitive involuntary tics. The models enabled the assessment of unique ameliorative effects of Ningdong granule (NDG), a traditional Chinese medicine (TCM) preparation dedicated to the treatment of TS, on the striatal DA content of rats. By using high-performance liquid chromatography (HPLC), we found that long-term administration of NDG could, at least partially, restore the striatal dopamine alterations, either by increasing them after IDPN treatment or by decreasing them after Apo treatment. Taken together, our data indicated that NDG could ameliorate the abnormal striatal DA content dually, and the unique therapeutic property may be meaningful for the treatment of TS.

Dual regulating effects of gastrodin on extracellular dopamine concentration in rats models of Tourette's syndrome

PURPOSE

Evaluate the dual regulating effects of gastrodin on striatal extracellular dopamine (DA) concentration in Tourette's syndrome (TS) rat models, and explore the underlying pharmacological mechanisms.

MATERIALS AND METHODS

Seventy Wistar rats were randomly divided into control group and TS model group. The former was intraperitoneally injected with saline (0.9%), while in the later, the rats were injected with Apomorphine (Apo) and 3,3'-iminodipropionitrile (IDPN) respectively to manipulate two kinds of TS rat models. Both Apo and IDPN induced rats were further assigned to three conditions, and the related rats were treated respectively by oral gavage with saline, gastrodin and Haloperidol (Hal). Data of stereotypy of the rats were collected. After 8 weeks, the extracellular content of DA and HVA in striatum were examined by intracerebral microdialysis and follow-up high-performance liquid chromatography (HPLC), and the expression of dopamine transporter (DAT) was probed by Western blot.

RESULTS

Gastrodin improved the stereotyped behaviors in TS rats. Furthermore, it down-regulated the elevated striatal extracellular DA concentration in Apo-induced rats and up-regulated the decreased DA content in the rats exposed to IDPN. Meanwhile, a dramatic down-regulation was detected in DAT protein expression in Apo + GAS group, while an opposite profile was showed in the IDPN + GAS group.

CONCLUSIONS

The dual regulating effects of gastrodin on extracellular DA level have been established, and the related mechanisms would be the dual regulating effects of gastrodin on the expression of DAT, a glycoprotein in the regulation of the extracellular DA concentration.

Reward circuitry dysfunction in psychiatric and neurodevelopmental disorders and genetic syndromes: animal models and clinical findings

This review summarizes evidence of dysregulated reward circuitry function in a range of neurodevelopmental and psychiatric disorders and genetic syndromes. First, the contribution of identifying a core mechanistic process across disparate disorders to disease classification is discussed, followed by a review of the neurobiology of reward circuitry. We next consider preclinical animal models and clinical evidence of reward-pathway dysfunction in a range of disorders, including psychiatric disorders (i.e., substance-use disorders, affective disorders, eating disorders, and obsessive compulsive disorders), neurodevelopmental disorders (i.e., schizophrenia, attention-deficit/hyperactivity disorder, autism spectrum disorders, Tourette's syndrome, conduct disorder/oppositional defiant disorder), and genetic syndromes (i.e., Fragile X syndrome, Prader-Willi syndrome, Williams syndrome, Angelman syndrome, and Rett syndrome). We also provide brief overviews of effective psychopharmacologic agents that have an effect on the dopamine system in these disorders. This review concludes with methodological considerations for future research designed to more clearly probe reward-circuitry dysfunction, with the ultimate goal of improved intervention strategies.

Alterations of the dopamine transporter in resting lymphocytes of patients with different psychotic disorders

The aim of our study was to investigate and compare the dopamine (DA) transporter (DAT) in resting lymphocytes of 20 psychotic patients and 20 healthy control subjects, by means of both the binding parameters (Bmax and Kd) of 3H-WIN 35,428, and the reuptake parameters (Vmax and Km) of 3H-DA. The results showed that both the Bmax of 3H-WIN 35,428 binding and the Vmax of 3H-DA reuptake of the patients were significantly lower than those of healthy subjects, while the Kd or Km did not show any change. These findings, while indicating a reduced density of the lymphocyte DAT proteins, provide further support of the role of DA in psychoses and suggest that DA alterations may not be limited to brain structures.

Functional neuroimaging in Tourette syndrome

Functional neuroimaging of neuropsychiatric disorders is a complex discipline requiring skills in medical science, philosophy, and technical physics. This review first examines the broad categories of functional imaging studies that have been utilized in this area, comparing the strengths and weaknesses of each approach. This review then looks at much of the available literature on functional imaging in Tourette syndrome (TS) and provides a synthesis of data. The review will also examine the different methodologies employed and will suggest which methodologies are most likely to lead to elucidation of the pathophysiology of TS and related conditions.

Striatal [11C]dihydrotetrabenazine and [11C]methylphenidate binding in Tourette syndrome

OBJECTIVE

Tourette syndrome (TS) is a common neurodevelopmental disorder marked by tics and behavioral comorbidities. Clinical pharmacology suggests that dopaminergic signaling abnormalities are part of the pathophysiology of TS. Prior molecular imaging studies of nigrostriatal dopaminergic terminal markers report conflicting results. Our goal was to characterize the distribution of nigrostriatal dopaminergic terminals in subjects with TS.

METHODS

Thirty-three adult subjects with TS were studied with PET using [11C]dihydrotetrabenazine (DTBZ), a ligand for the type 2 vesicular monoamine transporter, and with [11C] methylphenidate (MP), a ligand for the plasmalemmal dopamine transporter. Subjects were characterized with standard rating instruments for tic severity, obsessive-compulsive behaviors, and attentional deficits.

RESULTS

We found no differences between subjects with TS and control subjects in DTBZ and MP binding in any striatal region. There was no correlation between binding measures and clinical variables. Ventral striatal DTBZ and MP binding distributions in subjects with TS were normal.

CONCLUSIONS

We found no evidence of increased striatal dopaminergic innervation in Tourette syndrome (TS). Discrepancy between our present results and those of other studies may be explained by heterogeneity of TS.

[99mTc]TRODAT-1/[123I]IBZM SPECT studies of the dopaminergic system in Tourette syndrome

The good clinical effectiveness of dopamine depleter and receptor antagonists on tics suggests dopaminergic hyperactivity in Tourette syndrome (TS). In this case-control study of 10 TS patients and 15 age-matched healthy controls, we evaluated (i) presynaptic and postsynaptic striatal dopaminergic function using [(99m)Tc]TRODAT-1/[(123)I]IBZM single photon emission computed tomography (SPECT) and (ii) correlations between dopamine transporter (DAT)/D2 receptor binding sites and tic severity scores. Patients 1-5 were pretreated with haloperidol and were drug free for at least 3 months before SPECT imaging. Patients 6-10 were drug-naïve. We found no significant difference in DAT and D2 receptor binding sites between TS patients and healthy controls nor any association between striatal DAT or D2 receptor binding sites and tic severity assessed using the Modified Rush Videotape Rating Scale. Our findings provided no direct evidence of abnormally available striatal DAT or dopamine D2 receptors in TS. However, functional abnormalities of the dopaminergic system, e.g., alterations in the synaptic release of endogenous dopamine, cannot be completely ruled out.

Tourette's syndrome is not associated with interleukin-10 receptor 1 variants on chromosome 11q23.3

Interleukin-10 receptor 1 (IL-10R1) single nucleotide polymorphisms, located on chromosome 11q23 - a strong candidate for linkage with Tourette's syndrome (TS) - have been investigated for association with TS. DNA of 77 patients with a DSM-IV (Diagnostic and Statistical Manual IV) diagnosis of TS and 250 healthy controls was genotyped. IL-10R1 was not associated with TS.

Phasic dysfunction of dopamine transmission in Tourette's syndrome evaluated with 99mTc TRODAT-1 imaging

This study investigated the complex dysregulation of the dopaminergic neurotransmitter system in Tourette's syndrome (TS) patients challenged with methylphenidate (MPH). Eight drug-naïve male patients (aged 21-25 years) who met DSM-IV criteria for TS and had a mean disease severity of 25 on the Yale Global Tic Severity Scale were recruited. Brain (99m)TC TRODAT-1 dopamine transporter (DAT) single photon emission computed tomography (SPECT) was performed 5 days before, and 2 h after 10 mg of orally administered MPH. Eight age-matched healthy males served as controls. Repeated measures analysis of variance was used to measure differences in DAT-binding ratios before and after MPH challenge between the TS patients and controls. The DAT-binding ratios decreased significantly after MPH treatment in both groups. However, a significant interaction between group and MPH effects was found only in the right caudate, which was mainly due to a smaller decline of the DAT-binding ratio after MPH in the TS group than in the controls. Such a distinction was not found in the other striatal sub-regions in the two groups. No correlation, however, was observed between the tic severity score and DAT-binding ratio measured from the whole striatum or its sub-regions. The observed change in the DAT-binding ratio might indicate a functional abnormality of the dopaminergic system in the right caudate nucleus of TS patients. Future studies exploring dopamine transmission are thus needed to understand the pathophysiology of TS.

Dopaminergic polymorphisms in Tourette syndrome: association with the DAT gene (SLC6A3)

Tourette syndrome (TS) is a chronic neuropsychiatric disorder characterized by involuntary motor and phonic tics. The pattern of inheritance and associated genetic abnormality has yet to be fully characterized. A dopaminergic abnormality in this disorder is supported by response to specific therapies, nuclear imaging, and postmortem studies. In this protocol, dopaminergic polymorphisms were examined for associations with TS and attention-deficit hyperactivity disorder (ADHD). Polymorphisms investigated included the dopamine transporter (DAT1 DdeI and DAT1 VNTR), dopamine receptor (D4 Upstream Repeat and D4 VNTR), dopamine converting enzyme (dopamine beta-hydroxylase), and the acid phosphatase locus 1 (ACP1) gene. DNA was obtained from 266 TS individuals +/- ADHD and 236 controls that were ethnicity-matched. A significant association, using a genotype-based association analysis, was identified for the TS-total and TS-only versus control groups for the DAT1 DdeI polymorphism (AG vs. AA, P = 0.004 and P = 0.01, respectively). Population structure, estimated by the genotyping of 27 informative SNP markers, identified 3 subgroups. A statistical re-evaluation of the DAT1 DdeI polymorphism following population stratification confirmed the association for the TS-total and TS-only groups, but the degree of significance was reduced (P = 0.017 and P = 0.016, respectively). This study has identified a significant association between the presence of TS and a DAT polymorphism. Since abnormalities of the dopamine transporter have been hypothesized in the pathophysiology of TS, it is possible that this could be a functional allele associated with clinical expression.

Evaluating dopamine transporter activity with 99mTc-TRODAT-1 SPECT in drug-naive Tourette's adults

OBJECTIVES

Findings on imaging of dopamine transporter (DAT) activity in patients with Tourette's syndrome remain inconclusive. The present study was carried out to observe DAT activity in patients with well-controlled Tourette's syndrome by using (99m)Tc-TRODAT-1 single photon emission computerized tomography (SPECT).

METHODS

Six drug-naive patients with Tourette's syndrome (mean age+/-SD, 21.2+/-1.5 years) were recruited. All met the criteria for Tourette's syndrome established in the DSM-IV. Seventeen age-matched and sex-matched healthy subjects served as the controls. Brain SPECT were acquired 165-195 min after administrating 740 MBq of (99m)Tc-TRODAT-1, using a double-headed camera equipped with ultra-high-resolution fan-beam collimators. The specific uptake ratio was calculated by subtracting the mean counts per pixel in the occipital cortex from the mean counts per pixel in the striatum, putamen or caudate nucleus and by dividing the result by the mean counts per pixel in the occipital cortex. Tic-severity scores were also measured and correlated with the specific uptake ratios.

RESULTS

No significant difference in DAT activity between patients with Tourette's syndrome and control subjects was found in the striatum and its sub-regions. Tic-severity scores were also not correlated with specific uptake ratios measured from the striatum and its sub-regions.

CONCLUSIONS

In conjunction with previous findings, our results suggested that functional abnormality of the dopamine system in patients with Tourette's syndrome might be evident only in its early stage. Adaptation to tic symptoms might play a role in regulating the neural system.

Neuroimaging of Tourette syndrome

Traditional neuropathologic methods have provided only limited insight into the central nervous system abnormalities underlying Tourette syndrome. In the past 20 years, investigators have turned increasingly to in vivo neuroimaging approaches to localize, quantify, and characterize neuroanatomic, functional, and neurochemical distinctions in living subjects with Tourette syndrome. Research methods have included aggregate measures of cerebral energy metabolism, assessments of cerebral structure and size, and highly specific assessments of neurochemical markers of select neurons and synapses. Although the available data have important limitations, an encouraging convergence of findings implicates abnormal function in the Tourette syndrome striatum and in associated limbic and frontal cortical systems.

Annotation: Tourette syndrome: a relentless drumbeat--driven by misguided brain oscillations

OBJECTIVE

This annotation reviews recent evidence that points to the likely role of aberrant neural oscillations in the pathogenesis of Tourette syndrome (TS).

METHODS

The available anatomic and electrophysiological findings in TS are reviewed in the context of an emerging picture of the crucial role that neural oscillations play in maintaining normal central nervous system (CNS) function.

RESULTS

Neurons form behavior-dependent oscillating networks of various sizes and frequencies that bias input selection and facilitate synaptic plasticity, mechanisms that cooperatively support temporal representation as well as the transfer and long-term consolidation of information. Coherent network activity is likely to modulate sensorimotor gating as well as focused motor actions. When these networks are dysrhythmic, there may be a loss of control of sensory information and motor action. The known electrophysiological effects of medications and surgical interventions used to treat TS likely have an ameliorative effect on these aberrant oscillations. Similarly, a strong case can be made that successful behavioral treatments involve the willful training regions of the prefrontal cortex to engage in tic suppression and the performance of competing motor responses to unwanted sensory urges such that these prefrontal regions become effective modulators of aberrant thalamocortical rhythms.

CONCLUSIONS

A deeper understanding of neural oscillations may illuminate the complex, challenging, enigmatic, internal world that is TS.

Recent advances in Tourette syndrome research

Tourette syndrome (TS) is a developmentally regulated neurobehavioral disorder characterized by involuntary, stereotyped, repetitive movements. Recent anatomical and neuroimaging studies have provided evidence for abnormal basal ganglia and dopaminergic function in TS. Basic research on striatal inhibitory mechanisms and dopaminergic function complements the recent neuroimaging and anatomical data. Parallel studies of basal ganglia participation in the normal performance and learning of stereotyped repetitive behaviors or habits has provided additional insight. These lines of research have provided new pieces to the TS puzzle, and their increasing convergence is showing how those pieces can be put together.

Serotonin and dopamine transporter imaging in patients with obsessive-compulsive disorder

In obsessive-compulsive disorder (OCD), the success of pharmacological treatment with serotonin re-uptake inhibitors and atypical antipsychotic drugs suggests that both the central serotonergic and dopaminergic systems are involved in the pathophysiology of the disorder. We applied [123I]-2beta-carbomethoxy-3beta-(4-idiophenyl)tropane (beta-CIT) and a brain-dedicated high-resolution single photon emission computed tomography (SPECT) system to quantify dopamine transporter (DAT) and serotonin transporter (SERT) availability. By comparing 15 drug-naïve patients with OCD and 10 controls, we found a significantly reduced availability (corrected for age) of striatal DAT and of thalamic/hypothalamic, midbrain and brainstem SERT in OCD patients. Severity of OCD symptoms showed a significant negative correlation with thalamic/hypothalamic SERT availability, corrected for age and duration of symptoms. Our data provide evidence for imbalanced monoaminergic neurotransmitter modulation in OCD. Further studies with more selective DAT and SERT radiotracers are needed.

The dopamine transporter and attention-deficit/hyperactivity disorder

The high incidence of attention-deficit/hyperactivity disorder (ADHD) and escalating use of ADHD medications present a compelling case for clarifying the pathophysiology of, and developing laboratory or radiologic tests for, ADHD. Currently, the majority of specific genes implicated in ADHD encode components of catecholamine signaling systems. Of these, the dopamine transporter (DAT) is a principal target of the most widely used antihyperactivity medications (amphetamine and methylphenidate); the DAT gene is associated with ADHD, and some studies have detected abnormal levels of the DAT in brain striatum of ADHD subjects. Medications for ADHD interfere with dopamine transport by brain-region- and drug-specific mechanisms, indirectly activating dopamine- and possibly norepinephrine-receptor subtypes that are implicated in enhancing attention and experiential salience. The most commonly used DAT-selective ADHD medications raise extracellular dopamine levels in DAT-rich brain regions. In brain regions expressing both the DAT and the norepinephrine transporter (NET), the relative contributions of dopamine and norepinephrine to ADHD pathophysiology and therapeutic response are obfuscated by the capacity of the NET to clear dopamine as well as norepinephrine. Thus, ADHD medications targeting DAT or NET might disperse dopamine widely and consign dopamine storage and release to regulation by noradrenergic, as well as dopaminergic neurons.

Cognitive-pharmacologic functional magnetic resonance imaging in tourette syndrome: a pilot study

BACKGROUND

Dopamine agonists and antagonists can reduce abnormal movements and vocalizations (tics) in Tourette syndrome (TS); however, dopamine-responsive abnormal function in specific brain regions has not been directly demonstrated in TS. We sought to identify dopamine-modulated brain regions that function abnormally in TS by combining functional magnetic resonance imaging (fMRI), a working memory (WM) task, and infusion of the dopamine prodrug levodopa (while blocking dopamine production outside the brain).

METHODS

We obtained complete fMRI data in 8 neuroleptic-naive adults with a chronic tic disorder and in 10 well-matched tic-free control subjects.

RESULTS

Different task-sensitive brain regions responded differently to the WM task depending on levodopa status and diagnostic group (analysis of variance [ANOVA], p <.001). Four regions showed interactions with diagnosis (ANOVA, p <.001). In TS subjects, the task induced excessive brain activity in parietal cortex, medial frontal gyrus, and thalamus. Levodopa normalized the excess activity. In left parietal cortex, the degree of normalization was greater in patients with higher levodopa plasma concentrations (n = 6; Spearman's r = -.84, p =.04) and a greater degree of diagnostic confidence of TS (r = -.71, p =.05).

CONCLUSIONS

These results are consistent with a dopamine-influenced functional abnormality of brain response in TS and suggest testable hypotheses about the mechanism by which dopamine antagonists and agonists alleviate tics.

Dopamine transporter binding in Gilles de la Tourette syndrome: a [123I]FP-CIT/SPECT study

OBJECTIVE

To investigate dopamine transporter binding in Gilles de la Tourette syndrome (GTS) with SPECT and [123I]FP-CIT.

METHOD

Ten neuroleptic naïve/free patients with GTS, and 10 age- and gender-matched normal volunteers were studied. Subjects were clinically evaluated. GTS severity and affective symptoms were measured and the presence of GTS-related behaviours were recorded.

RESULTS

The GTS group showed significantly higher binding in both caudate and putamen nuclei than the controls. No associations were found between striatal binding ratios and measures of affect or GTS-related behaviours.

CONCLUSION

Patients with GTS show higher striatal binding of FP-CIT to the striatum in comparison with age- and gender-matched control subjects, indicating that dopamine transporter abnormalities are involved in the pathophysiology of GTS. These abnormalities appear to be distributed across both caudate and putamen.

Neurobiology of Tourette's syndrome: concepts of neuroanatomic localization and neurochemical abnormalities

Despite a preponderance of evidence suggesting an organic rather than psychogenic origin for Tourette syndrome, the precise neurobiological abnormality remains speculative. Neuroanatomically, there is expanding confirmation that cortico-striato-thalamo-cortical pathways represent the site of origin for tics and accompanying neuropsychiatric problems. Pathophysiological hypothesis are generally defined based on involvement of (1) a specific anatomical site (striato-thalamic circuits, striatal compartments), (2) physiologic abnormality (excess thalamic excitation, impaired intracortical inhibition), or (3) involvement of a specific neurotransmitter or synaptic component. This review provides information essential for understanding current and future proposals pertaining to the neurobiology of this intriguing disorder.

Neurology of Tourette's syndrome (TS) TS as a developmental dopamine disorder: a hypothesis

The favorable effect of dopamine (DA) depletors or DA receptor blockers suggested the state of increased transmission of DA system as the pathophysiology of Tourette's syndrome (TS). We have analysed the neurological signs of TS and evaluated the role of levodopa on the symptoms of TS. The data were compared with age-matched patients with Hereditary Progressive Dystonia (HPD) with marked diurnal fluctuation. Neurological examination of 81 drug naive TS patients revealed the clumsiness of rapid alternating pronation-supination movements of the arms and induced rigidity in the contralateral arm, which responded to the oral levodopa, and suggested hypofunction of the nigrostriatal (NS)-DA system. Postural asymmetry or scoliosis and abnormal tilting response suggested the asymmetric involvement of DA. The rotation to the side of less affected DA neuron on stepping with closed eyes suggested DA receptor supersensitivity. The favourable effects of a small dose of levodopa on these signs suggest the existence of DA receptor supersensitivity, because a small dose of levodopa is considered to alleviate the supersensitized DA receptors.

Developmental processes and brain imaging studies in Tourette syndrome

OBJECTIVES

It is often difficult to discern how findings of a neuroimaging study relate to the pathophysiology of an illness because imaging correlates may variously represent causes, consequences, or epiphenomena of the condition. The objective of this paper is to exemplify the complexities of interpreting neuroimaging data by reviewing anatomical and functional studies of Tourette syndrome (TS).

METHODS

Medline and Psychological Abstracts (PsycInfo) databases were searched for functional and anatomical neuroimaging studies of TS.

RESULTS

9 anatomical and 21 functional cross-sectional imaging studies of TS contributed to this review. Anatomical studies comparing TS patients to age-matched controls have found that lenticular nucleus volumes are reduced in TS adults, while caudate nucleus volumes are reduced in both adults and children with TS. In a study of the cerebral cortex, prefrontal volumes in TS adults were smaller, but in TS children were larger than in those of age-matched controls. Complementing the anatomical findings of reduced volumes of the caudate nucleus in TS, functional studies have suggested that frontal-striatal projections play an important role in the regulation of tic symptoms. The majority of functional studies to date, however, have been limited to the study of adults. These functional studies have yielded variable results that have limited generalizability to the pathophysiology of children with TS.

CONCLUSIONS

Although many of the findings in TS imaging may represent pathological causes of the disease, they may also be indicative of compensatory changes in the nervous system of TS subjects. Prospective studies of young children at risk will be necessary to help clarify the relationship between brain abnormalities and the course of the disease.

Receptor and transporter imaging studies in schizophrenia, depression, bulimia and Tourette's disorder--implications for psychopharmacology

Considerable progress has been achieved over the past 15 years in uncovering the biological basis of major psychiatric disorders. To determine patterns of brain dysfunction and to uncover the mechanism of action of centrally active compounds we used single photon emission computerized tomography (SPECT) as well as positron emission tomography (PET) in patients diagnosed with schizophrenia, depression, bulimia and Tourette's disorder. Striatal D2 and 5-HT1A receptors were studied in schizophrenia and 5-HT transporters (5-HTT) in depression and bulimia. Patients were either drug-naïve or drug free, or we studied the influence of specifically acting compounds on receptor/transporter occupancy. We could demonstrate that atypical antipsychotics have a dose-dependent (with the exception of clozapine and quetiapine) lower striatal D2 receptor occupancy rate compared with typical neuroleptics, paralleling the more favourable extrapyramidal side effects of atypical antipsychotics. However, no association between striatal D2 receptor occupancy rates and antipsychotic efficacy has been found. The measurement of 5-HT1A receptors in drug-naïve schizophrenic patients using the in vivo PET methodology revealed an increase of cortical 5-HT1A receptor binding potential in schizophrenia. beta-CIT as a ligand for measurement of 5-HT transporter densities (5-HTT) revealed lower rates in depression compared to age- and sex-matching healthy controls, a measurement that has also been obtained for bulimia. We also documented seasonal variations in brain serotonergic function by our finding of reduced brain 5-HTT availability in winter (compared to summer) in healthy controls. Furthermore, displaceable [123I] beta-CIT binding in the area corresponding to the left striatum (representing predominantly the density of dopamine transporters) was significantly reduced in SAD patients compared to healthy controls. In depression as well as in bulimia, selective serotonin reuptake inhibitors significantly decreased the beta-CIT binding potential, however, no significant dose relationship has been obtained in depression. Genotyping depressed patients for the serotonin transporter promoter gene region (5-HTTLPR) did not provide evidence for in vivo functional regulation of 5-HTT availability by 5-HTTLPR in the thalamus-hypothalamus and mesencephalon-pons of healthy subjects. In patients suffering from Tourette's disorder (TD) we were unable to detect differences of dopamine transporter densities between psychotropic drug-naïve TD patients and controls. Furthermore, no difference could be found between currently treated (with antipsychotics) and psychotropic drug-naïve TD patients. Our data provide insight into the pathophysiology of neuropsychiatric disorders and may guide future psychopharmacological drug developments.

The dopamine transporter: relevance to attention deficit hyperactivity disorder (ADHD)

The dopamine transporter is elevated in adults with attention deficit hyperactivity disorder (ADHD) compared with healthy controls [Lancet 354 (1999) 2132]. The findings have been confirmed by others in a different population using a different probe for the dopamine transporter. Notwithstanding the need to confirm these findings in a multi-center trial, several hypotheses are presented to account for these observations. A premise that elevated transporter levels result from medication is not supported by current data. Other possibilities, including hypertrophy of dopamine neuronal terminals in the striatum, dysfunctional regulation of dopamine or dopamine receptors, or anomalies in the dopamine transporter gene are presented as hypotheses. The feasibility of exploring these mechanisms in animal models or in human subjects is explored.