Striatal cholinergic interneurons and D2 receptor-expressing GABAergic medium spiny neurons regulate tardive dyskinesia

Enhancement of adenosine A2A signaling improves dopamine D2 receptor antagonist-induced dyskinesia via β-arrestin signaling

Repeated administration of dopamine D₂ receptor (D2R) antagonists, which is the treatment for psychosis, often causes tardive dyskinesia (TD). Despite notable clinical demand, effective treatment for TD has not been established yet. The neural mechanism involving the hyperinhibition of indirect pathway medium spiny neurons (iMSNs) in the striatum is considered one of the main causes of TD. In this study, we focused on adenosine A_2A receptors (A2ARs) expressed in iMSNs and investigated whether pharmacological activation of A2ARs improves dyskinetic symptoms in a TD mouse model. A 21-day treatment with haloperidol increased the number of vacuous chewing movements (VCMs) and decreased the number of c-Fos⁺/ppENK⁺ iMSNs in the dorsal striatum. Haloperidol-induced VCMs were reduced by acute intraperitoneal administration of an A2AR agonist, CGS 21680A. Consistently, haloperidol-induced VCMs and decrease in the number of c-Fos⁺/ppENK⁺ iMSNs were also mitigated by intrastriatal injection of CGS 21680A. The effects of intrastriatal CGS 21680A were not observed when it was concomitantly administered with a β-arrestin inhibitor, barbadin. Finally, intrastriatal injection of an arrestin-biased D2R agonist, UNC9994, also inhibited haloperidol-induced VCMs. These results suggest that A2AR agonists mitigate TD symptoms by activating striatal iMSNs via β-arrestin signaling.

The effects of cannabidiol on behavioural and oxidative stress parameters induced by prolonged haloperidol administration

OBJECTIVES

We investigated the influence of oral cannabidiol (CBD) on vacuous chewing movements (VCM) and oxidative stress parameters induced by short- and long-term administration of haloperidol in a rat model of tardive dyskinesia (TD).

METHODS

Haloperidol was administered either sub-chronically via the intraperitoneal (IP) route or chronically via the intramuscular (IM) route to six experimental groups only or in combination with CBD. VCM and oxidative stress parameters were assessed at different time points after the last dose of medication.

RESULTS

Oral CBD (5 mg/kg) attenuated the VCM produced by sub-chronic administration of haloperidol (5 mg/kg) but had minimal effects on the VCM produced by chronic administration of haloperidol (50 mg/kg). In both sub-chronic and chronic haloperidol groups, there were significant changes in brain antioxidant parameters compared with CBD only and the control groups. The sub-chronic haloperidol-only group had lower glutathione activity compared with sub-chronic haloperidol before CBD and the control groups; also, superoxide dismutase, catalase, and 2,2-diphenyl-1-picrylhydrazyl activities were increased in the sub-chronic (IP) haloperidol only group compared with the CBD only and control groups. Nitric oxide activity was increased in sub-chronic haloperidol-only group compared to the other groups; however, the chronic haloperidol group had increased malondialdehyde activity compared to the other groups.

CONCLUSIONS

Our findings indicate that CBD ameliorated VCM in the sub-chronic haloperidol group before CBD, but marginally in the chronic haloperidol group before CBD. There was increased antioxidant activity in the sub-chronic group compared to the chronic group.

Striatal TRPV1 activation by acetaminophen ameliorates dopamine D2 receptor antagonist-induced orofacial dyskinesia

Antipsychotics often cause tardive dyskinesia, an adverse symptom of involuntary hyperkinetic movements. Analysis of the US Food and Drug Administration Adverse Event Reporting System and JMDC insurance claims revealed that acetaminophen prevented the dyskinesia induced by dopamine D₂ receptor antagonists. In vivo experiments further showed that a 21-day treatment with haloperidol increased the number of vacuous chewing movements (VCMs) in rats, an effect that was inhibited by oral acetaminophen treatment or intracerebroventricular injection of N-(4-hydroxyphenyl)-arachidonylamide (AM404), an acetaminophen metabolite that acts as an activator of the transient receptor potential vanilloid 1 (TRPV1). In mice, haloperidol-induced VCMs were also mitigated by treatment with AM404 applied to the dorsal striatum, an effect not seen in TRPV1-deficient mice. Acetaminophen prevented the haloperidol-induced decrease in the number of c-Fos⁺preproenkephalin⁺ striatal neurons in wild-type mice but not in TRPV1-deficient mice. Finally, chemogenetic stimulation of indirect pathway medium spiny neurons in the dorsal striatum decreased haloperidol-induced VCMs. These results suggest that acetaminophen activates the indirect pathway neurons by activating TRPV1 channels via AM404.

Leveraging VGLUT3 Functions to Untangle Brain Dysfunctions

Vesicular glutamate transporters (VGLUTs) were long thought to be specific markers of glutamatergic excitatory transmission. The discovery, two decades ago, of the atypical VGLUT3 has thoroughly modified this oversimplified view. VGLUT3 is strategically expressed in discrete populations of glutamatergic, cholinergic, serotonergic, and even GABAergic neurons. Recent reports show the subtle, but critical, implications of VGLUT3-dependent glutamate co-transmission and its roles in the regulation of diverse brain functions and dysfunctions. Progress in the neuropharmacology of VGLUT3 could lead to decisive breakthroughs in the treatment of Parkinson's disease (PD), addiction, eating disorders, anxiety, presbycusis, or pain. This review summarizes recent findings on VGLUT3 and its vesicular underpinnings as well as on possible ways to target this atypical transporter for future therapeutic strategies.

Alterations in the intrinsic properties of striatal cholinergic interneurons after dopamine lesion and chronic L-DOPA

Changes in striatal cholinergic interneuron (ChI) activity are thought to contribute to Parkinson's disease pathophysiology and dyskinesia from chronic L-3,4-dihydroxyphenylalanine (L-DOPA) treatment, but the physiological basis of these changes is unknown. We find that dopamine lesion decreases the spontaneous firing rate of ChIs, whereas chronic treatment with L-DOPA of lesioned mice increases baseline ChI firing rates to levels beyond normal activity. The effect of dopamine loss on ChIs was due to decreased currents of both hyperpolarization-activated cyclic nucleotide-gated (HCN) and small conductance calcium-activated potassium (SK) channels. L-DOPA reinstatement of dopamine normalized HCN activity, but SK current remained depressed. Pharmacological blockade of HCN and SK activities mimicked changes in firing, confirming that these channels are responsible for the molecular adaptation of ChIs to dopamine loss and chronic L-DOPA treatment. These findings suggest that targeting ChIs with channel-specific modulators may provide therapeutic approaches for alleviating L-DOPA-induced dyskinesia in PD patients.

The role of glutamate receptors and their interactions with dopamine and other neurotransmitters in the development of tardive dyskinesia: preclinical and clinical results

Tardive dyskinesia is a serious, disabling, movement disorder associated with the ongoing use of antipsychotic medication. Current evidence regarding the pathophysiology of tardive dyskinesia is mainly based on preclinical animal models and is still not completely understood. The leading preclinical hypothesis of tardive dyskinesia development includes dopaminergic imbalance in the direct and indirect pathways of the basal ganglia, cholinergic deficiency, serotonin receptor disturbances, neurotoxicity, oxidative stress, and changes in synaptic plasticity. Although, the role of the glutamatergic system has been confirmed in preclinical tardive dyskinesia models it seems to have been neglected in recent reviews. This review focuses on the role and interactions of glutamate receptors with dopamine, acetylcholine, and serotonin in the neuropathology of tardive dyskinesia development. Moreover, preclinical and clinical results of the differentiated effectiveness of N-methyl-D-aspartate (NMDA) receptor antagonists are discussed with a special focus on antagonists that bind with the GluN2B subunit of NMDA receptors. This review also presents new combinations of drugs that are worth considering in the treatment of tardive dyskinesia.

Influence of magnesium supplementation and L-type calcium channel blocker on haloperidol-induced movement disturbances

Haloperidol (Hal) is an antipsychotic related to movement disorders. Magnesium (Mg) showed benefits on orofacial dyskinesia (OD), suggesting its involvement with N-methyl-D-aspartate receptors (NMDAR) since it acts blocking calcium channels. Comparisons between nifedipine (NIF; a calcium channel blocker) and Mg were performed to establish the Mg mechanism. Male rats concomitantly received Hal and Mg or NIF for 28 days, and OD behaviors were weekly assessed. Both Mg and NIF decreased Hal-induced OD. Hal increased Ca²⁺-ATPase activity in the striatum, and Mg reversed it. In the cortex, both Mg and NIF decreased such activity. Dopaminergic and glutamatergic immunoreactivity were modified by Hal and treatments: i) in the cortex: Hal reduced D1R and D2R, increasing NMDAR immunoreactivity. Mg and NIF reversed this Hal influence on D1R and NMDAR, while only Mg reversed Hal effects on D2R levels; ii) in the striatum: Hal decreased D2R and increased NMDAR while Mg and NIF decreased D1R and reversed the Hal-induced decreasing D2R levels. Only Mg reversed the Hal-induced increasing NMDAR levels; iii) in the substantia nigra (SN): while Hal increased D1R, D2R, and NMDAR, both Mg and NIF reversed this influence on D2R, but only Mg reversed the Hal-influence on D1R levels. Only NIF reversed the Hal effects on NMDAR immunoreactivity. These findings allow us to propose that Mg may be useful to minimize Hal-induced movement disturbances. Mg molecular mechanism seems to be involved with a calcium channel blocker because the NIF group showed less expressive effects than the Mg group.

New Insights Into Cholinergic Neuron Diversity

Cholinergic neurons comprise a small population of cells in the striatum but have fundamental roles in fine tuning brain function, and in the etiology of neurological and psychiatric disorders such as Parkinson’s disease (PD) or schizophrenia. The process of developmental cell specification underlying neuronal identity and function is an area of great current interest. There has been significant progress in identifying the developmental origins, commonalities in molecular markers, and physiological properties of the cholinergic neurons. Currently, we are aware of a number of key factors that promote cholinergic fate during development. However, the extent of cholinergic cell diversity is still largely underestimated. New insights into the biological basis of their specification indicate that cholinergic neurons may be far more diverse than previously thought. This review article, highlights the physiological features and the synaptic properties that segregate cholinergic cell subtypes. It provides an accurate picture of cholinergic cell diversity underlying their organization and function in neuronal networks. This review article, also discusses current challenges in deciphering the logic of the cholinergic cell heterogeneity that plays a fundamental role in the control of neural processes in health and disease.

Receptor Ligands as Helping Hands to L-DOPA in the Treatment of Parkinson's Disease

Levodopa (LD) is the most effective drug in the treatment of Parkinson’s disease (PD). However, although it represents the “gold standard” of PD therapy, LD can cause side effects, including gastrointestinal and cardiovascular symptoms as well as transient elevated liver enzyme levels. Moreover, LD therapy leads to LD-induced dyskinesia (LID), a disabling motor complication that represents a major challenge for the clinical neurologist. Due to the many limitations associated with LD therapeutic use, other dopaminergic and non-dopaminergic drugs are being developed to optimize the treatment response. This review focuses on recent investigations about non-dopaminergic central nervous system (CNS) receptor ligands that have been identified to have therapeutic potential for the treatment of motor and non-motor symptoms of PD. In a different way, such agents may contribute to extending LD response and/or ameliorate LD-induced side effects.

Coordination of rapid cholinergic and dopaminergic signaling in striatum during spontaneous movement

Interplay between dopaminergic and cholinergic neuromodulation in the striatum is crucial for movement control, with prominent models proposing pro-kinetic and anti-kinetic effects of dopamine and acetylcholine release, respectively. However, the natural, movement-related signals of striatum cholinergic neurons and their relationship to simultaneous variations in dopamine signaling are unknown. Here, functional optical recordings in mice were used to establish rapid cholinergic signals in dorsal striatum during spontaneous movements. Bursts across the cholinergic population occurred at transitions between movement states and were marked by widespread network synchronization which diminished during sustained locomotion. Simultaneous cholinergic and dopaminergic recordings revealed distinct but coordinated sub-second signals, suggesting a new model where cholinergic population synchrony signals rapid changes in movement states while dopamine signals the drive to enact or sustain those states.

Potential Therapeutic Application for Nicotinic Receptor Drugs in Movement Disorders

Emerging studies indicate that striatal cholinergic interneurons play an important role in synaptic plasticity and motor control under normal physiological conditions, while their disruption may lead to movement disorders. Here we discuss the involvement of the cholinergic system in motor dysfunction, with a focus on the role of the nicotinic cholinergic system in Parkinson's disease and drug-induced dyskinesias. Evidence for a role for the striatal nicotinic cholinergic system stems from studies showing that administration of nicotine or nicotinic receptor drugs protects against nigrostriatal degeneration and decreases L-dopa-induced dyskinesias. In addition, nicotinic receptor drugs may ameliorate tardive dyskinesia, Tourette's syndrome and ataxia, although further study is required to understand their full potential in the treatment of these disorders. A role for the striatal muscarinic cholinergic system in movement disorders stems from studies showing that muscarinic receptor drugs acutely improve Parkinson's disease motor symptoms, and may reduce dyskinesias and dystonia. Selective stimulation or lesioning of striatal cholinergic interneurons suggests they are primary players in this regulation, although multiple central nervous systems appear to be involved.

IMPLICATIONS

Accumulating data from preclinical studies and clinical trials suggest that drugs targeting CNS cholinergic systems may be useful for symptomatic treatment of movement disorders. Nicotinic cholinergic drugs, including nicotine and selective nAChR receptor agonists, reduce L-dopa-induced dyskinesias, as well as antipsychotic-induced tardive dyskinesia, and may be useful in Tourette's syndrome and ataxia. Subtype selective muscarinic cholinergic drugs may also provide effective therapies for Parkinson's disease, dyskinesias and dystonia. Continued studies/trials will help address this important issue.

VMAT2 Inhibitors in Neuropsychiatric Disorders

The basal ganglia and dopaminergic pathways play a central role in hyperkinetic movement disorders. Vesicular monoamine transporter 2 (VMAT2) inhibitors, which deplete dopamine at presynaptic striatal nerve terminals, are a class of drugs that have long been used to treat hyperkinetic movement disorders, but have recently gained more attention following their development for specific indications in the United States. At present, there are three commercially available VMAT2 inhibitors: tetrabenazine, deutetrabenazine, and valbenazine. Pharmacokinetics, metabolism, and dosing vary significantly between the three drugs, and likely underlie the more favorable side effect profile of the newer agents (deutetrabenazine and valbenazine). Tetrabenazine and deutetrabenazine have demonstrated safety and efficacy in the treatment of chorea associated with Huntington's disease, including in randomized controlled trials, although direct comparison studies are limited. Both deutetrabenazine and valbenazine have demonstrated safety and efficacy in the treatment of tardive dyskinesia, with multiple double-blind, placebo-controlled trials, whereas tetrabenazine has been studied less rigorously. There have been no blinded, prospective trials with tetrabenazine in Tourette's syndrome (TS); however, double-blind, placebo-controlled trials in TS are ongoing for both deutetrabenazine and valbenazine. Given the favored side effect profile of newer VMAT2 inhibitors, clinicians should be aware of the distinctions between agents and become familiar with differences in their use, especially as there is potential for their utilization to increase across the range of hyperkinetic movement disorders.

Cannabidiol prevents haloperidol-induced vacuos chewing movements and inflammatory changes in mice via PPARγ receptors

The chronic use of drugs that reduce the dopaminergic neurotransmission can cause a hyperkinetic movement disorder called tardive dyskinesia (TD). The pathophysiology of this disorder is not entirely understood but could involve oxidative and neuroinflammatory mechanisms. Cannabidiol (CBD), the major non-psychotomimetic compound present in Cannabis sativa plant, could be a possible therapeutic alternative for TD. This phytocannabinoid shows antioxidant, anti-inflammatory and antipsychotic properties and decreases the acute motor effects of classical antipsychotics. The present study investigated if CBD would attenuate orofacial dyskinesia, oxidative stress and inflammatory changes induced by chronic administration of haloperidol in mice. Furthermore, we verified in vivo and in vitro (in primary microglial culture) whether these effects would be mediated by PPARγ receptors. The results showed that the male Swiss mice treated daily for 21 days with haloperidol develop orofacial dyskinesia. Daily CBD administration before each haloperidol injection prevented this effect. Mice treated with haloperidol showed an increase in microglial activation and inflammatory mediators in the striatum. These changes were also reduced by CBD. On the other hand, the levels of the anti-inflammatory cytokine IL-10 increased in the striatum of animals that received CBD and haloperidol. Regarding oxidative stress, haloperidol induced lipid peroxidation and reduced catalase activity. This latter effect was attenuated by CBD. The combination of CBD and haloperidol also increased PGC-1α mRNA expression, a co-activator of PPARγ receptors. Pretreatment with the PPARγ antagonist, GW9662, blocked the behavioural effect of CBD in our TD model. CBD also prevented LPS-stimulated microglial activation, an effect that was also antagonized by GW9662. In conclusion, our results suggest that CBD could prevent haloperidol-induced orofacial dyskinesia by activating PPARγ receptors and attenuating neuroinflammatory changes in the striatum.

Investigation of the HSPG2 Gene in Tardive Dyskinesia - New Data and Meta-Analysis

Tardive dyskinesia (TD) is a movement disorder that may occur after extended use of antipsychotic medications. The etiopathophysiology is unclear; however, genetic factors play an important role. The Perlecan (HSPG2) gene was found to be significantly associated with TD in Japanese schizophrenia patients, and this association was subsequently replicated by an independent research group. To add to the evidence for this gene in TD, we conducted a meta-analysis specific to the relationship of HSPG2 rs2445142 with TD occurrence, while also adding our unpublished genotype data. Overall, we found a significant association of the G allele with TD occurrence (p = 0.0001); however, much of the effect appeared to originate from the discovery dataset. Nonetheless, most study samples exhibit the same trend of association with TD for the G allele. Our findings encourage further genetic and molecular studies of HSPG2 in TD.

Unilateral Botulinum Neurotoxin-A Injection into the Striatum of C57BL/6 Mice Leads to a Different Motor Behavior Compared with Rats

Different morphological changes in the caudate-putamen (CPu) of naïve rats and mice were observed after intrastriatal botulinum neurotoxin-A (BoNT-A) injection. For this purpose we here studied various motor behaviors in mice (n = 46) longitudinally up to 9 months after intrastriatal BoNT-A administration as previously reported for rats, and compared both outcomes. Apomorphine- and amphetamine-induced rotational behavior, spontaneous motor behavior, as well as lateralized neglect were studied in mice after the injection of single doses of BoNT-A into the right CPu, comparing them with sham-injected animals. Unilateral intrastriatal injection of BoNT-A in mice induced significantly increased contralateral apomorphine-induced rotations for 1 to 3 months, as well as significantly increased contralateral amphetamine-induced rotations 1 to 9 months after injection. In rats (n = 28), unilateral BoNT-A injection also induced significantly increased contralateral apomorphine-induced rotations 3 months after injection, but did not provoke amphetamine-induced rotations at all. Lateralized sensorimotor integration, forelimb preference, and forelimb stepping were significantly impaired on the left side. The differences in motor behaviors between rats and mice may be caused by different BoNT-A effects on cholinergic and catecholaminergic fibers in rat and mouse striata, interspecies differences in striatal receptor densities, and different connectomes of the basal ganglia.

Genetics of tardive dyskinesia: Promising leads and ways forward

Tardive dyskinesia (TD) is a potentially irreversible and often debilitating movement disorder secondary to chronic use of dopamine receptor blocking medications. Genetic factors have been implicated in the etiology of TD. We therefore have reviewed the most promising genes associated with TD, including DRD2, DRD3, VMAT2, HSPG2, HTR2A, HTR2C, and SOD2. In addition, we present evidence supporting a role for these genes from preclinical models of TD. The current understanding of the etiogenesis of TD is discussed in the light of the recent approvals of valbenazine and deutetrabenazine, VMAT2 inhibitors, for treating TD.

Antipsychotic-induced Tardive dyskinesia: from biological basis to clinical management

INTRODUCTION

Tardive dyskinesia (TD) is a chronic and disabling movement disorder with a complex pathophysiological basis. A significant percentage of patients does not receive correct diagnosis, resulting in delayed or inaccurate treatment and poor outcome. Therefore, there is a critical need for prompt recognition, implementation of efficacious treatment regimens and long-term follow up of patients with TD. Areas covered: The current paper provides an overview of emerging data concerning proposed pathophysiology theories, epidemiology, risk factors, and therapeutic strategies for TD. Expert commentary: Despite considerable research efforts, TD remains a challenge in the treatment of psychosis as the available strategies remain sub-optimal. The best scenario will always be the prophylaxis or prevention of TD, which entails limiting the use of antipsychotics.

Botulinum Neurotoxin A Injected Ipsilaterally or Contralaterally into the Striatum in the Rat 6-OHDA Model of Unilateral Parkinson's Disease Differently Affects Behavior

Parkinson's disease (PD) is one of the most frequent neurodegenerative disorders. The loss of dopaminergic neurons in the substantia nigra leads to a disinhibition of cholinergic interneurons in the striatum. Pharmacotherapeutical strategies of PD-related hypercholinism have numerous adverse side effects. We previously showed that ipsilateral intrastriatal injections of 1 ng in unilaterally 6-hydroxydopamine (6-OHDA)-lesioned rats inhibit apomorphine-induced rotation behavior significantly up to 6 months. In this study, we extended the behavioral testing of ipsilateral botulinum neurotoxin A (BoNT-A)-injection and additionally investigated the impact of intrastriatal BoNT-A-injections contralateral to the 6-OHDA-lesioned hemisphere on the basal ganglia circuity and motor functions. We hypothesized that the interhemispheric differences of acetylcholine (ACh) concentration seen in unilateral hemi-PD should be differentially and temporally influenced by the ipsilateral or contralateral injection of BoNT-A. Hemi-PD rats were injected with 1 ng BoNT-A or vehicle substance into either the ipsilateral or contralateral striatum 6 weeks after 6-OHDA-lesion and various behaviors were tested. In hemi-PD rats intrastriatal ipsilateral BoNT-A-injections significantly reduced apomorphine-induced rotations and increased amphetamine-induced rotations, but showed no significant improvement of forelimb usage and akinesia, lateralized sensorimotor integration and also no effect on spontaneous locomotor activity. However, intrastriatal BoNT-A-injections contralateral to the lesion led to a significant increase of the apomorphine-induced turning rate only 2 weeks after the treatment. The apomorphine-induced rotation rate decreases thereafter to a value below the initial rotation rate. Amphetamine-induced rotations were not significantly changed after BoNT-A-application in comparison to sham-treated animals. Forelimb usage was temporally improved by contralateral BoNT-A-injection at 2 weeks after BoNT-A. Akinesia and lateralized sensorimotor integration were also improved, but contralateral BoNT-A-injection had no significant effect on spontaneous locomotor activity. These long-ranging and different effects suggest that intrastriatally applied BoNT-A acts not only as an inhibitor of ACh release but also has long-lasting impact on transmitter expression and thereby on the basal ganglia circuitry. Evaluation of changes of transmitter receptors is subject of ongoing studies of our group.

Nicotinic Receptor Intervention in Parkinson's Disease: Future Directions

Sufficient preclinical and epidemiological data are available to justify nicotinic intervention in Parkinson's disease (PD). Although use of nicotine patch has been suggested in some neurodegenerative disorders, including PD, the key for success with nicotinic intervention, particularly in PD, appears to rely not only on the dose but also on the mode of nicotine administration. Our aim in this short review is to provide justification for such contention. Thus, following a short introduction of nicotinic receptor pharmacology, the potential of nicotine in alleviating not only the motor symptoms, but also the mood disorders (e.g. depression) and mild cognitive impairments that are commonly co-morbid with PD will be presented. Moreover, since current PD therapy is associated with dyskinesia, the effectiveness of nicotine in ameliorating levodopa (L-Dopa)-induced dyskinesia will also be discussed. It is suggested that pulsatile nicotine administration (e.g. via inhalation or nasal spray) may be the optimal route in nicotinic intervention in PD.