Animal Models of Tourette Syndrome-From Proliferation to Standardization

Rats Lacking the Dopamine Transporter Display Inflexibility in Innate and Learned Behavior

Playing a key role in the organization of striatal motor output, the dopamine (DA)-ergic system regulates both innate and complex learned behaviors. Growing evidence clearly indicates the involvement of the DA-ergic system in different forms of repetitive (perseverative) behavior. Some of these behaviors accompany such disorders as obsessive-compulsive disorder (OCD), Tourette's syndrome, schizophrenia, and addiction. In this study, we have traced how the inflexibility of repetitive reactions in the recently developed animal model of hyper-DA-ergia, dopamine transporter knockout rats (DAT-KO rats), affects the realization of innate behavior (grooming) and the learning of spatial (learning and reversal learning in T-maze) and non-spatial (extinction of operant reaction) tasks. We found that the microstructure of grooming in DAT-KO rats significantly differed in comparison to control rats. DAT-KO rats more often demonstrated a fixed syntactic chain, making fewer errors and very rarely missing the chain steps in comparison to control rats. DAT-KO rats' behavior during inter-grooming intervals was completely different to the control animals. During learning and reversal learning in the T-maze, DAT-KO rats displayed pronounced patterns of hyperactivity and perseverative (stereotypical) activity, which led to worse learning and a worse performance of the task. Most of the DAT-KO rats could not properly learn the behavioral task in question. During re-learning, DAT-KO rats demonstrated rigid perseverative activity even in the absence of any reinforcement. In operant tasks, the mutant rats demonstrated poor extinction of operant lever pressing: they continued to perform lever presses despite no there being reinforcement. Our results suggest that abnormally elevated DA levels may be responsible for behavioral rigidity. It is conceivable that this phenomenon in DAT-KO rats reflects some of the behavioral traits observed in clinical conditions associated with endogenous or exogenous hyper-DA-ergia, such as schizophrenia, substance abuse, OCD, patients with Parkinson disease treated with DA mimetics, etc. Thus, DAT-KO rats may be a valuable behavioral model in the search for new pharmacological approaches to treat such illnesses.

Medical Cannabis for Gilles de la Tourette Syndrome: An Open-Label Prospective Study

Objectives. Assessing the effectiveness and tolerability of medical cannabis (MC) treatment on Gilles de la Tourette syndrome (GTS) patients. Methods. We report on an open-label, prospective study on the effect of MC on adult GTS patients. MC mode of use was decided by the treating neurologist and the patient. Δ9-Tetrahydrocannabinol (Δ9-THC) and cannabidiol (CBD) content within MC product and monthly dose were titrated during the study. Following treatment initiation, patients were assessed after 4 and 12 weeks for efficacy, tolerability, and side effects. Results. Eighteen patients entered the study. Baseline Yale Global Tic Severity Scale- (YGTSS) Total (range 0-100) was $60.3\pm 17.1$ . Three patients did not reach the end of follow-up period. The most common mode of administration was smoking (80%). Following twelve weeks of treatment, a significant 38% average reduction ( $p=0.002$ ) of YGTSS-Total and a 20% reduction ( $p=0.043$ ) of Premonitory Urge for Tic Scale (PUTS) were observed. Common side effects were dry mouth (66.7%), fatigue (53.3%), and dizziness (46.7%). Three patients suffered from psychiatric side effects including worsening of obsessive compulsive disorder (stopped treatment), panic attack, and anxiety (resolved with treatment modification). Six patients (40%) reported cognitive side effects regarding time perception, visuospatial disorientation, confusion, slow processing speed, and attention. Conclusions. MC treatment demonstrates good efficacy and tolerability in adult GTS patients. Predilection for smoking rather than using oil drops requires further comparative studies to evaluate the efficacy of each. Cognitive and psychiatric side effects have to be monitored and addressed.

Cerebellin-2 regulates a serotonergic dorsal raphe circuit that controls compulsive behaviors

Cerebellin-1 (Cbln1) and cerebellin-2 (Cbln2) are secreted glycoproteins that are expressed in distinct subsets of neurons throughout the brain. Cbln1 and Cbln2 simultaneously bind to presynaptic neurexins and postsynaptic GluD1 and GluD2, thereby forming trans-synaptic adhesion complexes. Genetic associations link cerebellins, neurexins and GluD's to neuropsychiatric disorders involving compulsive behaviors, such as Tourette syndrome, attention-deficit hyperactivity disorder (ADHD), and obsessive-compulsive disorder (OCD). Extensive evidence implicates dysfunction of serotonergic signaling in these neuropsychiatric disorders. Here, we report that constitutive Cbln2 KO mice, but not Cbln1 KO mice, display robust compulsive behaviors, including stereotypic pattern running, marble burying, explosive jumping, and excessive nest building, and exhibit decreased brain serotonin levels. Strikingly, treatment of Cbln2 KO mice with the serotonin precursor 5-hydroxytryptophan or the serotonin reuptake-inhibitor fluoxetine alleviated compulsive behaviors. Conditional deletion of Cbln2 both from dorsal raphe neurons and from presynaptic neurons synapsing onto dorsal raphe neurons reproduced the compulsive behaviors of Cbln2 KO mice. Finally, injection of recombinant Cbln2 protein into the dorsal raphe of Cbln2 KO mice largely reversed their compulsive behaviors. Taken together, our results show that Cbln2 controls compulsive behaviors by regulating serotonergic circuits in the dorsal raphe.

Dissociation of tic generation from tic expression during the sleep-wake cycle

Motor tics, the hallmark of Tourette syndrome (TS), are modulated by different behavioral and environmental factors. A major modulating factor is the sleep-wake cycle in which tics are attenuated to a large extent during sleep. This study demonstrates a similar reduction in tic expression during sleep in an animal model of chronic tic disorders and investigates the underlying neural mechanism. We recorded the neuronal activity during spontaneous sleep-wake cycles throughout continuous GABA_A antagonist infusion into the striatum. Analysis of video streams and concurrent kinematic assessments indicated tic reduction during sleep in both frequency and intensity. Extracellular recordings in the striatum revealed a state-dependent dissociation between motor tic expression and their macro-level neural correlates ("LFP spikes") during the sleep-wake cycle. Local field potential (LFP) spikes, which are highly correlated with tic expression during wakefulness, persisted during tic-free sleep and did not change their properties despite the reduced behavioral expression. Local, micro-level, activity near the infusion site was time-locked to the LFP spikes during wakefulness, but this locking decreased significantly during sleep. These results suggest that whereas LFP spikes encode motor tic generation and feasibility, the behavioral expression of tics requires local striatal neural activity entrained to the LFP spikes, leading to the propagation of the activity to downstream targets and consequently their motor expression. These findings point to a possible mechanism for the modulation of tic expression in patients with TS during sleep and potentially during other behavioral states.

The role of Hipk2-p53 pathways in arsenic-induced autistic behaviors: A translational study from rats to humans

Previous studies have associated the risk of autism spectrum disorder (ASD) with increased exposures to metals and metalloids such as arsenic. In this study, we used an animal-to-human translational strategy to identify key molecular changes that potentially mediated the effects of arsenic exposures on ASD development. In a previously established rat model, we have induced autistic behaviors in rat pups with gestational arsenic exposures (10 and 45 μg/L As₂O₃ in drinking water). Neuronal apoptosis and the associated epigenetic dysregulations in frontal cortex were assayed to screen potential mediating pathways, which were subsequently validated with qPCR, western blotting, and immunohistochemistry analyses. Furthermore, the identified pathway, along with serum levels of 26 elements including arsenic, were characterized in a case-control study with 21 ASD children and 21 age-matched healthy controls. In animals, we found that arsenic exposures caused difficulties of social interaction and increased stereotypic behaviors in a dose-dependent manner, accompanied by increased neuronal apoptosis and upregulation of Hipk2-p53 pathway in the frontal cortex. In humans, we found that serum levels of Hipk2 and p53 were 24.7 (95%CI: 8.5 to 43.4) % and 23.7 (95%CI: 10.5 to 38.5) % higher in ASD children than in healthy controls. ASD children had significantly higher serum levels of 15 elements, among which arsenic, silicon, strontium, and vanadium were positively associated with both Hipk2 and p53. Results from both the rat arsenic exposure and human case-control studies suggest a likely role of Hipk2-p53 pathway in ASD development induced by exposures to environmental pollutants such as arsenic.

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.

Rhynchophyllin attenuates neuroinflammation in Tourette syndrome rats via JAK2/STAT3 and NF-κB pathways

The aim of this study was designed to investigate the effects of rhynchophyllin (RH) on neuroinflammation in Tourette syndrome (TS) rats. TS model was established in rats by the injection of selective 5-HT2A/2C agonist 1-(2, 5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI). Behavior in DOI-induced rats was tested. Inflammatory cytokines levels such as interleukin-1β (IL-1β), interleukin-6 (IL-6), and tumor necrosis factor-α (TNF-α) in serum and striatum were detected. The expression levels of janus kinase 2 (JAK2)/signal transducer and transcription activator 3 (STAT3) and nuclear factor (NF)-κB pathways in striatum were measured by Western blot. Data indicated that RH can significantly reduce the numbers of nodding experiment of TS rats. RH significantly decreased IL-6, IL-1β, and TNF-α in serum and striatum of TS rats, with altered expression of P-JAK2, P-STAT3, P-NF-κBp65, and P-IκBα in TS rats, as evidenced by Western blot analysis and immunohistochemistry, suggesting that the regulation of JAK2/STAT3 and NF-κB pathways might be involved in the mechanism of RH on TS.

The Potential of Cannabinoid-Based Treatments in Tourette Syndrome

Novel pharmacological treatments are needed for Tourette syndrome. Our goal was to examine the current evidence base and biological rationale for the use of cannabis-derived medications or medications that act on the cannabinoid system in Tourette syndrome. We conducted a comprehensive literature search of PubMed for randomized controlled trials or clinical trials of cannabis-derived medications in Tourette syndrome. Data regarding the population, intervention, safety profile, and outcomes for each trial were extracted and reported and the evidence supporting use of individual cannabis-derived medications was critiqued. There is a strong biological rationale regarding how cannabis-derived medications could affect tic severity. Anecdotal case reports and series have noted that many patients report that their tics improve after using cannabis. However, only two small randomized, placebo-controlled trials of Δ⁹-tetrahydrocannabinol have been published; these suggested possible benefits of cannabis-derived agents for the treatment of tics. Trials examining other agents active on the cannabinoid system for tic disorders are currently ongoing. Cannabinoid-based treatments are a promising avenue of new research for medications that may help the Tourette syndrome population. However, given the limited research available, the overall efficacy and safety of cannabinoid-based treatments is largely unknown. Further trials are needed to examine dosing, active ingredients, and optimal mode of administration of cannabis-derived compounds, assuming initial trials suggest efficacy. Clinical use for refractory patients should at the very least be restricted to adult populations, given the uncertain efficacy and risk of developmental adverse effects that cannabinoids may have in children. Even in adult populations, cannabis-derived medications are associated with significant issues such as the effects they have on driving safety and the fact that they cause positive urine drug screens that can affect employment.

Altered dopaminergic regulation of the dorsal striatum is able to induce tic-like movements in juvenile rats

Motor tics are sudden, repetitive, involuntary movements representing the hallmark behaviors of the neurodevelopmental disease Tourette’s syndrome (TS). The primary cause of TS remains unclear. The initial observation that dopaminergic antagonists alleviate tics led to the development of a dopaminergic theory of TS etiology which is supported by post mortem and in vivo studies indicating that non-physiological activation of the striatum could generate tics. The striatum controls movement execution through the balanced activity of dopamine receptor D1 and D2-expressing medium spiny neurons of the direct and indirect pathway, respectively. Different neurotransmitters can activate or repress striatal activity and among them, dopamine plays a major role. In this study we introduced a chronic dopaminergic alteration in juvenile rats, in order to modify the delicate balance between direct and indirect pathway. This manipulation was done in the dorsal striatum, that had been associated with tic-like movements generation in animal models. The results were movements resembling tics, which were categorized and scored according to a newly developed rating scale and were reduced by clonidine and riluzole treatment. Finally, post mortem analyses revealed altered RNA expression of dopaminergic receptors D1 and D2, suggesting an imbalanced dopaminergic regulation of medium spiny neuron activity as being causally related to the observed phenotype.

Tourette’s syndrome and its borderland

The Gilles de la Tourette syndrome (or Tourette’s syndrome) has a prevalence of 1% of children with a wide range of severity and associated comorbidities. The last 20 years have seen advances in the understanding of the syndrome’s complex genetics and underlying neurobiology. Investigation with imaging and neurophysiology techniques indicate it is a neurodevelopmental condition with dysfunction of basal ganglia–cortical interactions, which are now also being studied in animal models. There is also increasing evidence for treatments although it often remains difficult to manage. First-line options include neuroleptics, other drugs and specialised behavioural treatments. Deep brain stimulation is an evolving field, not yet fully established. This review focuses on the phenomenology of tics, how to assess and manage the syndrome, and uses examples of atypical cases to explore the characteristics and limits of its clinical spectrum.

Global network modulation during thalamic stimulation for Tourette syndrome

Background and objectives

Deep brain stimulation (DBS) of the thalamus is a promising therapeutic alternative for treating medically refractory Tourette syndrome (TS). However, few human studies have examined its mechanism of action. Therefore, the networks that mediate the therapeutic effects of thalamic DBS remain poorly understood.

Methods

Five participants diagnosed with severe medically refractory TS underwent bilateral thalamic DBS stereotactic surgery. Intraoperative fMRI characterized the blood oxygen level-dependent (BOLD) response evoked by thalamic DBS and determined whether the therapeutic effectiveness of thalamic DBS, as assessed using the Modified Rush Video Rating Scale test, would correlate with evoked BOLD responses in motor and limbic cortical and subcortical regions.

Results

Our results reveal that thalamic stimulation in TS participants has wide-ranging effects that impact the frontostriatal, limbic, and motor networks. Thalamic stimulation induced suppression of motor and insula networks correlated with motor tic reduction, while suppression of frontal and parietal networks correlated with vocal tic reduction. These regions mapped closely to major regions of interest (ROI) identified in a nonhuman primate model of TS.

Conclusions

Overall, these findings suggest that a critical factor in TS treatment should involve modulation of both frontostriatal and motor networks, rather than be treated as a focal disorder of the brain. Using the novel combination of DBS-evoked tic reduction and fMRI in human subjects, we provide new insights into the basal ganglia-cerebellar-thalamo-cortical network-level mechanisms that influence the effects of thalamic DBS. Future translational research should identify whether these network changes are cause or effect of TS symptoms.

Aripiprazole Selectively Reduces Motor Tics in a Young Animal Model for Tourette's Syndrome and Comorbid Attention Deficit and Hyperactivity Disorder

Tourette’s syndrome (TS) is a neurodevelopmental disorder characterized primarily by motor and vocal tics. Comorbidities such as attention deficit and hyperactivity disorder (ADHD) are observed in over 50% of TS patients. We applied aripiprazole in a juvenile rat model that displays motor tics and hyperactivity. We additionally assessed the amount of ultrasonic vocalizations (USVs) as an indicator for the presence of vocal tics and evaluated the changes in the striatal neurometabolism using in vivo proton magnetic resonance spectroscopy (1H-MRS) at 11.7T. Thirty-one juvenile spontaneously hypertensive rats (SHRs) underwent bicuculline striatal microinjection and treatment with either aripiprazole or vehicle. Control groups were sham operated and sham injected. Behavior, USVs, and striatal neurochemical profile were analyzed at early, middle, and late adolescence (postnatal days 35 to 50). Bicuculline microinjections in the dorsolateral striatum induced motor tics in SHR juvenile rats. Acute aripiprazole administration selectively reduced both tic frequency and latency, whereas stereotypies, USVs, and hyperactivity remained unaltered. The striatal neurochemical profile was only moderately altered after tic-induction and was not affected by systemic drug treatment. When applied to a young rat model that provides high degrees of construct, face, and predictive validity for TS and comorbid ADHD, aripiprazole selectively reduces motor tics, revealing that tics and stereotypies are distinct phenomena in line with clinical treatment of patients. Finally, our 1H-MRS results suggest a critical revision of the striatal role in the hypothesized cortico-striatal dysregulation in TS pathophysiology.

Modeling tics in rodents: Conceptual challenges and paths forward

BACKGROUND

Recent advances in our understanding of the neurobiology of tics have led to the development of novel rodent models capturing different pathophysiological and phenotypic aspects of Tourette syndrome. The proliferation of these models, however, raises vexing questions on what standards should be adopted to assess their theoretical validity and empirical utility. Assessing the homology of a rodent motoric burst with a tic remains problematic, due to our incomplete knowledge of the underpinnings of tics, their high phenotypic complexity and variability, limitations in our ability test key aspects of tic phenomenology (such as premonitory sensory phenomena) in animals, and between-species differences in neuroanatomy and behavioral repertoire. These limitations underscore that any interpretation of behavioral output in an animal model cannot exclusively rely on the recognition of features that bear superficial resemblance with tics, but must be supported by other etiological and convergent phenomenological criteria.

NEW METHOD

Here, we discuss two complementary approaches for the study and validation of tic-like manifestations in rodents, based respectively on the use of contextual modulators and accompanying features of repetitive motor manifestations and on the reproduction of pathogenic factors.

RESULTS

Neither strategy can by itself provide convincing evidence that a model informatively recapitulates tic pathophysiology. Their combination holds promise to enhance the rigorous evaluation and translational relevance of rodent models of tic disorders.

CONCLUSIONS

This systematic consideration of different approaches to the validation and study of animal models of tic pathophysiology provides a framework for future work in this area.