Brain functional connectivity in chronic tic disorders and Gilles de la Tourette syndrome

When the interoceptive and conceptual clash: The case of oppositional phenomenal self-modelling in Tourette syndrome

Tourette syndrome (TS) has been associated with a rich set of symptoms that are said to be uncomfortable, unwilled, and effortful to manage. Furthermore, tics, the canonical characteristic of TS, are multifaceted, and their onset and maintenance is complex. A formal account that integrates these features of TS symptomatology within a plausible theoretical framework is currently absent from the field. In this paper, we assess the explanatory power of hierarchical generative modelling in accounting for TS symptomatology from the perspective of active inference. We propose a fourfold analysis of sensory, motor, and cognitive phenomena associated with TS. In Section 1, we characterise tics as a form of action aimed at sensory attenuation. In Section 2, we introduce the notion of epistemic ticcing and describe such behaviour as the search for evidence that there is an agent (i.e., self) at the heart of the generative hierarchy. In Section 3, we characterise both epistemic (sensation-free) and nonepistemic (sensational) tics as habitual behaviour. Finally, in Section 4, we propose that ticcing behaviour involves an inevitable conflict between distinguishable aspects of selfhood; namely, between the minimal phenomenal sense of self-which is putatively underwritten by interoceptive inference-and the explicit preferences that constitute the individual's conceptual sense of self. In sum, we aim to provide an empirically informed analysis of TS symptomatology under active inference, revealing a continuity between covert and overt features of the condition.

New insights of metabolite abnormalities in the thalamus of rats with iminodiproprionitrile-induced tic disorders

Introduction

This study aimed to investigate pathological changes in the "Glutamate (Glu)-γ-aminobutyric acid (GABA)" loop and apply widely targeted metabolomic analysis technology to comprehensively explore metabolite abnormalities/ in the thalamus of rats with tic disorders (TD).

Methods

Wistar rats were randomized into control, TD, and tiapride (Tia) groups. Iminodipropionitrile (IDPN) was used to induce TD in rats. The Tia group was administered tiapride. Neurotransmitter levels in the thalamus of rats in the three groups were measured using UPLC-3Q MS. And, the protein expression levels of Glu decarboxylase (GAD65/67) and GABA transporter protein (GAD-T) were measured using western blotting. The mRNA expression levels of these genes were evaluated using real-time polymerase chain reaction. Lastly, other metabolites in the thalamus were detected by widely targeted metabolomic analysis between TD and Control group rats.

Results

The Glu level, Glu/GABA ratio, and Asp level in the TD group were significantly higher (all p < 0.001) than those of the Control group, whereas the GABA and Gly levels were lower (p < 0.001 and p = 0.009, respectively). The Tia group exhibited a significant reduction in the Glu level (p = 0.001) compared with the TD group. The protein expression level of GAD67 in TD group was higher (p = 0.009) and the mRNA expression levels of GAD65, GAD67, and GAT-1 were lower (p < 0.05) than those of the Control group. The Tia group did not display any differences in GAD65, GAD67, or GAT-1 expression. Widely targeted metabolomic analysis revealed that 34 substances were abnornal between the TD and Control groups (9 upregulated and 25 downregulated). Neurosteroids (progesterone, corticosterone) exhibited distinct differences. Metabolite analysis using the Kyoto encyclopedia for genes and genomes indicated that the steroid hormone biosynthesis pathway may be involved in TD pathogenesis.

Conclusion

This study revealed metabolic abnormalities in the thalamus of rats with TD. The interaction between neurotransmitters and neurosteroid biosynthesis represents a new direction for future studies.

Tourette syndrome and obsessive-compulsive disorder: A comprehensive review of structural alterations and neurological mechanisms

Currently, it is possible to study the pathogenesis of Tourette's syndrome (TS) in more detail, due to more advanced methods of neuroimaging. However, medical and surgical treatment options are limited by a lack of understanding of the nature of the disorder and its relationship to some psychiatric disorders, the most common of which is obsessive-compulsive disorder (OCD). It is believed that the origin of chronic tic disorders is based on an imbalance of excitatory and inhibitory influences in the Cortico-Striato-Thalamo-Cortical circuits (CSTC). The main CSTCs involved in the pathological process have been identified by studying structural and neurotransmitter disturbances in the interaction between the cortex and the basal ganglia. A neurotransmitter deficiency in CSTC has been demonstrated by immunohistochemical and genetic methods, but it is still not known whether it arises as a consequence of genetically determined disturbances of neuronal migration during ontogenesis or as a consequence of altered production of proteins involved in neurotransmitter production. The aim of this review is to describe current ideas about the comorbidity of TS with OCD, the involvement of CSTC in the pathogenesis of both disorders and the background of structural and neurotransmitter changes in CSTC that may serve as targets for drug and neuromodulatory treatments.

The Dysfunctional Mechanisms Throwing Tics: Structural and Functional Changes in Tourette Syndrome

Tourette Syndrome (TS) is a high-incidence multifactorial neuropsychiatric disorder characterized by motor and vocal tics co-occurring with several diverse comorbidities, including obsessive-compulsive disorder and attention-deficit hyperactivity disorder. The origin of TS is multifactorial, with strong genetic, perinatal, and immunological influences. Although almost all neurotransmettitorial systems have been implicated in TS pathophysiology, a comprehensive neurophysiological model explaining the dynamics of expression and inhibition of tics is still lacking. The genesis and maintenance of motor and non-motor aspects of TS are thought to arise from functional and/or structural modifications of the basal ganglia and related circuitry. This complex wiring involves several cortical and subcortical structures whose concerted activity controls the selection of the most appropriate reflexive and habitual motor, cognitive and emotional actions. Importantly, striatal circuits exhibit bidirectional forms of synaptic plasticity that differ in many respects from hippocampal and neocortical plasticity, including sensitivity to metaplastic molecules such as dopamine. Here, we review the available evidence about structural and functional anomalies in neural circuits which have been found in TS patients. Finally, considering what is known in the field of striatal plasticity, we discuss the role of exuberant plasticity in TS, including the prospect of future pharmacological and neuromodulation avenues.

Profiles of Proinflammatory Cytokines and T Cells in Patients With Tourette Syndrome: A Meta-Analysis

Background

Tic disorder is a neurodevelopmental disorder characterized by motor and phonic tic symptoms. Tourette syndrome (TS) is a subtype of tic disorder that shows more persistent tic symptoms. The etiological mechanism of TS concerning immune dysfunction remains unclear due to limited evidence, especially for pediatric TS patients.

Method

In the present study, a meta-analysis was performed to confirm the identified changes in proinflammatory cytokines and T cells of pediatric TS patients. A total of five databases, including PubMed, Web of Science, PsycINFO, Google Scholar and the China National Knowledge Infrastructure (CNKI), were used for the literature search. The standardized mean difference (SMD) and mean difference (MD) with a 95% confidence interval (CI) were used to present the effect size of each type of proinflammatory cytokine and T cell. Sensitivity analysis, subgroup analysis and meta-regression analysis were used to explore the heterogeneity of the meta-analysis. This meta-analysis was registered in the International Platform of Registered Systematic Review and Meta-analysis Protocols (number: INPLASY2021110079).

Results

In the 25 studies included in this meta-analysis, thirteen studies focused on the levels of T cells, and twelve studies focused on the levels of proinflammatory cytokines. Based on the random-effects model, the pooled MDs are -1.45 (95% CI: -3.44, 0.54) for CD3 cells, -4.44 (95% CI: -6.80, -2.08) for CD4 cells, and 1.94 (95% CI: -0.08, 3.97) for CD8 cells. The pooled SMDs are1.36 for IL-6 (95% CI: 0.00, 2.72) and 2.39 for tumor necrosis factor alpha (TNF-α) (95% CI: 0.93, 3.84).

Conclusion

We provided evidence of immune dysfunction in pediatric TS patients, with elevated levels of particular proinflammatory cytokines and disproportionate changes in T-cell subpopulations. Small to large effect sizes were identified for increased IL-6 levels as well as a reduced number of T helper cells, while a large effect size was identified for increased TNF-α levels. These results indicate a close association between peripheral immune activation and TS. However, the most direct and meaningful interaction between peripheral immune status and microglial activation in the central nervous system in TS patients requires further exploration.

Tourette syndrome research highlights from 2020

We present here research from 2020 relevant to Tourette syndrome (TS). The authors briefly summarize a few reports they consider most important or interesting.

Grey matter abnormalities in Tourette syndrome: an activation likelihood estimation meta-analysis

BACKGROUND

Tourette syndrome (TS) is a neurodevelopmental disorder defined by the continual presence of primary motor and vocal tics. Grey matter abnormalities have been identified in numerous studies of TS, but conflicting results have been reported. This study was an unbiased statistical meta-analysis of published neuroimaging studies of TS structures.

METHODS

A voxel quantitative meta-analysis technique called activation likelihood estimation (ALE) was used. The meta-analysis included six neuroimaging studies involving 247 TS patients and 236 healthy controls. A statistical threshold of p < 0.05 was established based on the false discovery rate and a cluster extent threshold of 50 voxels.

RESULTS

We found that grey matter volumes were significantly increased in the bilateral thalamus, right hypothalamus, right precentral gyrus, left postcentral gyrus, left inferior parietal lobule, right lentiform nucleus, and left insula of TS patients compared to those of healthy controls. In contrast, grey matter volumes were significantly decreased in the bilateral postcentral gyrus, bilateral anterior cingulate, bilateral insula, left posterior cingulate and left postcentral gyrus of TS patients compared to those of healthy controls.

CONCLUSIONS

Our present meta-analysis primarily revealed significant increases in grey matter volumes in the thalamus and lentiform nucleus, and decreased grey matter volumes in the anterior cingulate gyrus, of TS patients compared to those in healthy controls. Most of these identified regions are associated with cortico-striato-thalamo-cortical circuits. Further studies with larger sample sizes are needed to confirm these changes in grey matter volumes in TS patients.

The α6 GABAA Receptor Positive Allosteric Modulator DK-I-56-1 Reduces Tic-Related Behaviors in Mouse Models of Tourette Syndrome

Tourette syndrome (TS) is a disabling neurodevelopmental disorder characterized by multiple, recurrent tics. The pharmacological treatment of TS is currently based on dopaminergic antagonists; however, these drugs are associated with extrapyramidal symptoms and other serious adverse events. Recent evidence suggests that positive allosteric modulators (PAMs) of GABA_A receptors containing α6 subunits (α6 GABA_ARs) oppose the behavioral effects of dopamine. Building on this evidence, in the present study, we tested the efficacy of DK-I-56-1, a highly selective PAM for α6 GABA_ARs, in mouse models of TS exhibiting tic-related responses. DK-I-56-1 significantly reduced tic-like jerks and prepulse inhibition (PPI) deficits in D1CT-7 transgenic mice, a well-documented mouse model of TS. DK-I-56-1 also prevented the exacerbation of spontaneous eyeblink reflex induced by the potent dopamine D₁ receptor agonist SKF 82958, a proxy for tic-like responses. We also showed that both systemic and prefrontal cortical administration of DK-I-56-1 countered the PPI disruption caused by SKF 82958. Although the effects of DK-I-56-1 were akin to those elicited by dopaminergic antagonists, this drug did not elicit extrapyramidal effects, as measured by catalepsy. These results point to α6 GABA_AR PAMs as promising TS therapies with a better safety profile than dopaminergic antagonists.