Serotonin transporter binding is increased in Tourette syndrome with Obsessive Compulsive Disorder

The Role of CBGTC Synaptic Neurotransmission in the Pathophysiology of Tics

The pathophysiology of tic disorders involves an alteration in the transmission of messages through the cortico-basal ganglia-thalamo-cortical circuit. A major requirement for the passage of a message through this circuit is an intact chemically mediated synaptic neurotransmitter system (ie, neurotransmitters and second messengers). This article reviews the scientific evidence supporting the involvement of a variety of neurotransmitters (ie, dopamine, glutamate, gamma-aminobutyric acid, serotonin, acetylcholine, and the opioid system). Although there are favored neurotransmitter abnormalities, their complex interactions suggest the likelihood that several are involved in the production of tics.

Serotonergic underpinnings of obsessive-compulsive disorder: A systematic review and meta-analysis of neuroimaging findings

Obsessive-compulsive disorder (OCD) is a frequent and disabling condition, with many patients being treatment-resistant. Improved understanding of its neurobiology is vital for better therapies. Evidence is still conflicting regarding specific serotonergic-related dysfunctions in OCD. We systematically reviewed the literature to provide a quantitative assessment of the role of serotonin (5-HT) in patients with untreated OCD through imaging. We searched for neuroimaging studies investigating central 5-HT tonus in unmedicated patients with OCD, excluding studies comprising treated patients to prevent bias from antidepressant-induced changes in serotonergic tonus. We also conducted a meta-analysis using a homogeneous group of positron emission tomography and single photon emission computed tomography articles that compared 5-HT transporter (SERT) and 5-HT2A receptor (HT2AR) binding potential in different brain regions of patients with untreated OCD and healthy controls. The systematic review encompassed 18 articles, with 13 included in the subsequent meta-analysis. Risk of bias was assessed by a revised form of the Newcastle-Ottawa Scale. We provided standardized mean difference (SMD) values for SERT and 5-HT2AR binding potential measures across 15 different brain regions. Patients with OCD showed lower SERT binding potential in the brainstem (SMD = -1.13, 95% CI [-1.81 to -0.46]), midbrain (SMD = -0.54, 95% CI [-0.92 to -0.16]), and thalamus/hypothalamus regions (SMD = -0.58, 95% CI [-0.99 to -0.18]) with neglectable to moderate heterogeneity. By combining results from 2 decades of molecular imaging studies, we show that individuals with OCD exhibit lower SERT binding potential in specific brain regions, providing compelling evidence of a 5-HT system dysfunction. However, the exact mechanisms underlying this phenotype remain elusive. The limitations include heterogeneity across studies in populations, imaging techniques, and radiotracer usage.

The Use of Cannabis-Based Medicine in Selected Neurological Disorders

Cannabis-based medicine (CBM) is used in a wide variety of different neurological disorders. While the use of CBM in the treatment of pain, AIDS wasting, loss of appetite, and spasticity is well established, CBM application in movement disorders and neurodegenerative disorders is still an emerging topic. The purpose of this chapter is to summarize current evidence behind the use of CBM in selected neurological diseases, mainly movement and neurodegenerative disorders. The best evidence for efficacy of CBM is for Tourette syndrome resulting in an improvement of tics and psychiatric comorbidities. In this indication, delta-9-tetrahydrocannabinol (THC)-containing CBMs are recommended. There is limited evidence that CBMs are also effective in Parkinson's disease in which they may improve tremor, but also non-motor symptoms such as pain and sleeping problems. With respect to other neurodegenerative diseases, there is limited evidence that CBMs may improve behavioral symptoms in Huntington's disease. In addition, it has been speculated that CBMs may have neuroprotective effects, but this has not yet been confirmed in the clinical setting.

Psilocybin in pharmacotherapy of obsessive-compulsive disorder

Obsessive-compulsive disorder (OCD) is a chronic mental disease that affects approximately 2% of the population. Obsessions and compulsions are troublesome for patients and may disturb their everyday activities. The pathogenesis of this disease is still not fully elucidated, but dysfunctions of serotonin-, dopamine- and glutamate-mediated neurotransmission together with early maladaptive schemas seem of importance. Pharmacological treatment includes drugs affecting the serotoninergic, dopaminergic, and glutamatergic systems, such as selective serotonin reuptake inhibitors (SSRIs). Providing that up to 40% of patients with OCD are resistant to the currently available medications, there is a need for novel and effective therapies. Recent discoveries suggest that psilocybin, a non-physically addictive psychoactive substance, may ameliorate disease symptoms. When used in appropriate doses and under strict clinical control, psilocybin appears as a valuable treatment for OCD. This narrative article provides a thorough overview of OCD's etiology, current treatment options, and the emerging evidence supporting psilocybin's efficacy in managing OCD symptoms.

Mispatterning and interneuron deficit in Tourette Syndrome basal ganglia organoids

Tourette Syndrome (TS) is a neuropsychiatric disorder thought to involve a reduction of basal ganglia (BG) interneurons and malfunctioning of the BG circuitry. However, whether interneurons fail to develop or are lost postnatally remains unknown. To investigate the pathophysiology of early development in TS, induced pluripotent stem cell (iPSC)-derived BG organoids from TS patients and healthy controls were compared on multiple levels of measurement and analysis. BG organoids from TS individuals manifested an impaired medial ganglionic eminence fate and a decreased differentiation of cholinergic and GABAergic interneurons. Transcriptome analyses revealed organoid mispatterning in TS, with a preference for dorsolateral at the expense of ventromedial fates. Our results point to altered expression of GLI transcription factors downstream of the Sonic Hedgehog signaling pathway with cilia disruption at the earliest stages of BG organoid differentiation as a potential mechanism for the BG mispatterning in TS. This study uncovers early neurodevelopmental underpinnings of TS neuropathological deficits using organoids as a model system.

Fecal transplantation can alleviate tic severity in a Tourette syndrome mouse model by modulating intestinal flora and promoting serotonin secretion

Background

: Tourette syndrome (TS) is a neuropsychiatric disorder with onset in childhood that warrants effective therapies. Gut microbiota can affect central physiology and function via the microbiota–gut-brain axis. Therefore, the gut microbiota plays an important role in some mental illnesses. A small clinical trial showed that fecal microbiota transplantation (FMT) may alleviate TS symptoms in children. Herein, FMT effects and mechanisms were explored in a TS mouse model.

Methods

: TS mice model (TSMO) (n = 80) were established with 3,3′-iminodipropionitrile, and 80 mice were used as controls. Mice were grouped into eight groups and were subjected to FMT with feces from children or mice with or without TS, or were given probiotics. Fecal specimens were collected 3 weeks after FMT. 16S rRNA sequencing, behavioral observation, and serum serotonin (5-HT) assay were performed. Differences between groups were analyzed using Mann-Whitney U test and Kolmogorov-Smirnov (KS) tests.

Results

: A total of 18 discriminative microbial signatures (linear discriminant analysis score > 3) that varied significantly between TS and healthy mice (CONH) were identified. A significant increase in Turicibacteraceae and Ruminococcaceae in TSMO after FMT was observed (P < 0.05). Compared with non-transplanted TSMO, the symptoms of those transplanted with feces from CONH were alleviated (W = 336, P = 0.046). In the probiotic and FMT experiments, the serum 5-HT levels significantly increased in TSMO that received probiotics (KS = 1.423, P = 0.035) and in those transplanted with feces from CONH (W = 336.5, P = 0.046) compared with TSMO without transplantation.

Conclusions

: This study suggests that FMT may ameliorate TS by promoting 5-HT secretion, and it provides new insights into the underlying mechanisms of FMT as a treatment for TS.

Elevated Expression of SLC6A4 Encoding the Serotonin Transporter (SERT) in Gilles de la Tourette Syndrome

Gilles de la Tourette syndrome (GTS) is a complex neurodevelopmental disorder characterized by motor and vocal tics. Most of the GTS individuals have comorbid diagnoses, of which obsessive-compulsive disorder (OCD) and attention deficit-hyperactivity disorder (ADHD) are the most common. Several neurotransmitter systems have been implicated in disease pathogenesis, and amongst these, the dopaminergic and the serotonergic pathways are the most widely studied. In this study, we aimed to investigate whether the serotonin transporter (SERT) gene (SLC6A4) was differentially expressed among GTS individuals compared to healthy controls, and whether DNA variants (the SERT-linked polymorphic region 5-HTTLPR, together with the associated rs25531 and rs25532 variants, and the rare Ile425Val variant) or promoter methylation of SLC6A4 were associated with gene expression levels or with the presence of OCD as comorbidity. We observed that SLC6A4 expression is upregulated in GTS individuals compared to controls. Although no specific genotype, allele or haplotype was overrepresented in GTS individuals compared to controls, we observed that the LAC/LAC genotype of the 5-HTTLPR/rs25531/rs25532 three-locus haplotype was associated with higher SLC6A4 mRNA expression levels in GTS individuals, but not in the control group.

Refractory Gilles de la Tourette Syndrome-Many Pieces That Define the Puzzle

Gilles de la Tourette syndrome (GTS) is a childhood onset neuropsychiatric disorder characterized by the presence of motor and vocal tics. The clinical spectrum of GTS is heterogeneous and varies from mild cases that do not require any medical attention to cases that are refractory to standard treatments. One of the unresolved issues is the definition of what constitutes treatment-refractory GTS. While for some other neuropsychiatric disorders, such as obsessive-compulsive disorder (OCD), a clear definition has been established, there is still no consensus with regard to GTS. One important issue is that many individuals with GTS also meet criteria for one or more other neurodevelopmental and neuropsychiatric disorders. In many individuals, the severity of these comorbid conditions contributes to the degree to which GTS is treatment refractory. The scope of this paper is to present the current state-of-the-art regarding refractory GTS and indicate possible approaches to define it. In closing, we discuss promising approaches to the treatment of individuals with refractory GTS.

Tourette syndrome research highlights from 2019

This is the sixth yearly article in the Tourette Syndrome Research Highlights series, summarizing research from 2019 relevant to Tourette syndrome and other tic disorders. The highlights from 2020 is being drafted on the Authorea online authoring platform; readers are encouraged to add references or give feedback on our selections comments feature on this page. After the calendar year ends, this article is submitted as the annual update for the Tics collection F1000Research.

Effects of Jian-Pi-Zhi-Dong Decoction on the Expression of 5-HT and Its Receptor in a Rat Model of Tourette Syndrome and Comorbid Anxiety

BACKGROUND Anxiety is one of the common comorbidities of Tourette syndrome (TS). The serotonin (5-HT) system is involved in both TS and anxiety. Jian-pi-zhi-dong decoction (JPZDD) is widely used. However, the mechanism remains unknown. In this study, a rat model of TS and comorbid anxiety was used to evaluate the effect of JPZDD on 5-HT and its receptor. MATERIAL AND METHODS 48 rats were divided into 4 groups randomly (n=12). The model was established by empty water bottle stimulation plus iminodipropionitrile injection for 3 weeks. Then the control and model groups were gavaged with saline, while the treatment groups were gavaged with fluoxetine hydrochloride (Flx) or JPZDD. Body weights were measured, and behavioral tests were evaluated with stereotypy and elevated plus maze. The morphologic characters were observed by hematoxylin and eosin staining. The content of 5-HT was detected by enzyme-linked immunosorbent assay and high-performance liquid chromatography. The expression of 5-HT2C receptor was detected by western blot and quantitative polymerase chain reaction. RESULTS The stereotypy score was lower and the time spent in the open arm was longer in the JPZDD group compared with the model group. After the treatment of Flx or JPZDD, the structure of neurons became gradually normal and the cells were arranged neatly. The contents of 5-HT in the treatment groups were higher compared with the model group in the striatum. The expression of 5-HT2C mRNA in the striatum of JPZDD and Flx groups decreased compared with the model group, and the JPZDD group was lower than the Flx group. CONCLUSIONS JPZDD alleviated both tic and anxiety symptoms and the mechanism may be via reducing the expression of 5-HT2C mRNA in the striatum, increasing the concentration of 5-HT, and enhancing the activity of the 5-HT system, which in turn exerts neuro-inhibition.

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.

Treatment of tics associated with Tourette syndrome

Motor and phonic tics associated with Tourette syndrome (TS) can range in severity from barely perceptible to disabling and most patients have a variety of behavioral co-morbidities, particularly, attention deficit disorder and obsessive compulsive disorder. Therefore, therapy must be tailored to the individual needs of the patients. In addition to behavioral therapy, oral medications such as alpha agonists, dopamine depletors, anti-psychotics, and topiramate are used to control the involuntary movements and noises. Botulinum toxin injections are particularly effective in patients with troublesome focal motor and phonic tics, including coprolalia. Deep brain stimulation may be considered for patients with "malignant" TS, that is, refractory to medical therapy. When appropriate therapy is selected and implemented, most patients with TS can achieve their full potential and lead essentially normal life.