Animal models of l-dopa-induced dyskinesia in Parkinson's disease

Neurophysiological treatment effects of mesdopetam, pimavanserin and clozapine in a rodent model of Parkinson's disease psychosis

Psychosis in Parkinson's disease is a common phenomenon associated with poor outcomes. To clarify the pathophysiology of this condition and the mechanisms of antipsychotic treatments, we have here characterized the neurophysiological brain states induced by clozapine, pimavanserin, and the novel prospective antipsychotic mesdopetam in a rodent model of Parkinson's disease psychosis, based on chronic dopaminergic denervation by 6-OHDA lesions, levodopa priming, and the acute administration of an NMDA antagonist. Parallel recordings of local field potentials from eleven cortical and sub-cortical regions revealed shared neurophysiological treatment effects for the three compounds, despite their different pharmacological profiles, involving reversal of features associated with the psychotomimetic state, such as a reduction of aberrant high-frequency oscillations in prefrontal structures together with a decrease of abnormal synchronization between different brain regions. Other drug-induced neurophysiological features were more specific to each treatment, affecting network oscillation frequencies and entropy, pointing to discrete differences in mechanisms of action. These findings indicate that neurophysiological characterization of brain states is particularly informative when evaluating therapeutic mechanisms in conditions involving symptoms that are difficult to assess in rodents such as psychosis, and that mesdopetam should be further explored as a potential novel antipsychotic treatment option for Parkinson psychosis.

Cells, pathways, and models in dyskinesia research

L-DOPA-induced dyskinesia (LID) is the most common form of hyperkinetic movement disorder resulting from altered information processing in the cortico-basal ganglia network. We here review recent advances clarifying the altered interplay between striatal output pathways in this movement disorder. We also review studies revealing structural and synaptic changes to the striatal microcircuitry and altered cortico-striatal activity dynamics in LID. We furthermore highlight the recent progress made in understanding the involvement of cerebellar and brain stem nuclei. These recent developments illustrate that dyskinesia research continues to provide key insights into cellular and circuit-level plasticity within the cortico-basal ganglia network and its interconnected brain regions.

Targeting Striatal Glutamate and Phosphodiesterases to Control L-DOPA-Induced Dyskinesia

A large body of work during the past several decades has been focused on therapeutic strategies to control L-DOPA-induced dyskinesias (LIDs), common motor complications of long-term L-DOPA therapy in Parkinson's disease (PD). Yet, LIDs remain a clinical challenge for the management of patients with advanced disease. Glutamatergic dysregulation of striatal projection neurons (SPNs) appears to be a key contributor to altered motor responses to L-DOPA. Targeting striatal hyperactivity at the glutamatergic neurotransmission level led to significant preclinical and clinical trials of a variety of antiglutamatergic agents. In fact, the only FDA-approved treatment for LIDs is amantadine, a drug with NMDAR antagonistic actions. Still, novel agents with improved pharmacological profiles are needed for LID therapy. Recently other therapeutic targets to reduce dysregulated SPN activity at the signal transduction level have emerged. In particular, mechanisms regulating the levels of cyclic nucleotides play a major role in the transduction of dopamine signals in SPNs. The phosphodiesterases (PDEs), a large family of enzymes that degrade cyclic nucleotides in a specific manner, are of special interest. We will review the research for antiglutamatergic and PDE inhibition strategies in view of the future development of novel LID therapies.

Quinpirole inhibits levodopa-induced dyskinesias at structural and behavioral levels: Efficacy negated by co-administration of isradipine

Dopamine depletion associated with parkinsonism induces plastic changes in striatal medium spiny neurons (MSN) that are maladaptive and associated with the emergence of the negative side-effect of standard treatment: the abnormal involuntary movements termed levodopa-induced dyskinesia (LID). Prevention of MSN dendritic spine loss is hypothesized to diminish liability for LID in Parkinson's disease. Blockade of striatal CaV1.3 calcium channels can prevent spine loss and significantly diminish LID in parkinsonian rats. While pharmacological antagonism with FDA approved CaV1 L-type channel antagonist dihydropyridine (DHP) drugs (e.g, isradipine) are potentially antidyskinetic, pharmacologic limitations of current drugs may result in suboptimal efficacy. To provide optimal CaV1.3 antagonism, we investigated the ability of a dual pharmacological approach to more potently antagonize these channels. Specifically, quinpirole, a D2/D3-type dopamine receptor (D2/3R) agonist, has been demonstrated to significantly reduce calcium current activity at CaV1.3 channels in MSNs of rats by a mechanism distinct from DHPs. We hypothesized that dual inhibition of striatal CaV1.3 channels using the DHP drug isradipine combined with the D2/D3 dopamine receptor agonist quinpirole prior to, and in conjunction with, levodopa would be more effective at preventing structural modifications of dendritic spines and providing more stable LID prevention. For these proof-of-principle studies, rats with unilateral nigrostriatal lesions received daily administration of vehicle, isradipine, quinpirole, or isradipine + quinpirole prior to, and concurrent with, levodopa. Development of LID and morphological analysis of dendritic spines were assessed. Contrary to our hypothesis, quinpirole monotherapy was the most effective at reducing dyskinesia severity and preventing abnormal mushroom spine formation on MSNs, a structural phenomenon previously associated with LID. Notably, the antidyskinetic efficacy of quinpirole monotherapy was lost in the presence of isradipine co-treatment. These findings suggest that D2/D3 dopamine receptor agonists when given in combination with levodopa and initiated in early-stage Parkinson's disease may provide long-term protection against LID. The negative interaction of isradipine with quinpirole suggests a potential cautionary note for co-administration of these drugs in a clinical setting.

Multimodal imaging study of the 5-HT1A receptor biased agonist, NLX-112, in a model of L-DOPA-induced dyskinesia

INTRODUCTION

The leading treatment for motor signs of Parkinson's disease is L-DOPA, but, upon extended use, it can lead to levodopa-induced dyskinesia (LID). Serotonergic neurons are involved in LID etiology and previous pre-clinical studies have shown that NLX-112, a 5-HT1A biased agonist, has robust antidyskinetic effects. Here, we investigated its effects in hemiparkinsonian (HPK) rats with a unilateral nigrostriatal 6-OHDA lesion.

METHODS

We compared HPK rats with LID (i.e., sensitized to the dyskinetic effects of chronic L-DOPA) and without LID (HPK-non-LID), using [18F]FDG PET imaging and fMRI functional connectivity following systemic treatment with saline, L-DOPA, NLX-112 or L-DOPA + NLX-112.

RESULTS

In HPK-non-LID rats, [18F]FDG PET experiments showed that L-DOPA led to hypermetabolism in motor areas (cerebellum, brainstem, and mesencephalic locomotor region) and to hypometabolism in cortical regions. L-DOPA effects were also observed in HPK-LID rats, with the additional emergence of hypermetabolism in raphe nuclei and hypometabolism in hippocampus and striatum. NLX-112 attenuated L-DOPA-induced raphe hypermetabolism and cingulate cortex hypometabolism in HPK-LID rats. Moreover, in fMRI experiments NLX-112 partially corrected the altered neural circuit connectivity profile in HPK-LID rats, through activity in regions rich in 5-HT1A receptors.

CONCLUSION

This neuroimaging study sheds light for the first time on the brain activation patterns of HPK-LID rats. The 5-HT1A receptor agonist, NLX-112, prevents occurrence of LID, likely by activating pre-synaptic autoreceptors in the raphe nuclei, resulting in a partial restoration of brain metabolic and connectivity profiles. In addition, NLX-112 also rescues L-DOPA-induced deficits in cortical activation, suggesting potential benefit against non-motor symptoms of Parkinson's disease.

Radiomics and Hybrid Models Based on Machine Learning to Predict Levodopa-Induced Dyskinesia of Parkinson's Disease in the First 6 Years of Levodopa Treatment

BACKGROUND

Current research on the prediction of movement complications associated with levodopa therapy in Parkinson's disease (PD) is limited. levodopa-induced dyskinesia (LID) is a movement complication that seriously affects the life quality of PD patients. One-third of PD patients develop LID within 1 to 6 years of levodopa treatment. This study aimed to construct models based on radiomics and machine learning to predict early LID in PD.

METHODS

We extracted radiomics features from the T1-weighted MRI obtained in the baseline of 49 PD control and 54 PD with LID in the first 6 years of levodopa therapy. Six brain regions related to the onset of PD were segmented as regions of interest (ROIs). The least absolute shrinkage and selection operator (LASSO) was used for feature selection. Using the machine learning methods of support vector machine (SVM), random forest (RF), and AdaBoost, we constructed radiomics models and hybrid models. The hybrid models combined the radiomics features and the Unified Parkinson's Disease Rating Scale part III (UPDRS III) total score. The five-fold cross-validation was performed and repeated 20 times to validate the stability of the classifiers. We used sensitivity, specificity, accuracy, receiver operating characteristic (ROC) curves, and area under the ROC curve (AUC) for model validation.

RESULTS

We selected 33 out of 6138 radiomics features. In the testing set of the radiomics model, the AUC values of the SVM, RF, and AdaBoost classifiers were 0.905, 0.808, and 0.778, respectively, and the accuracies were 0.839, 0.742, and 0.710. The hybrid models had better prediction performance. In the testing set, the AUC values of SVM, RF, and AdaBoost classifiers were 0.958, 0.861, and 0.832, respectively, and the accuracies were 0.903, 0.806, and 0.774.

CONCLUSIONS

Our results indicate that T1-weighted MRI is valuable in predicting early LID in PD. This work demonstrates that the combination of radiomics features and clinical features has good potential and value for identifying early LID in PD.

Effects of hydrogen gas inhalation on L-DOPA-induced dyskinesia

L-3,4-dihydroxyphenylalanine (L-DOPA)-induced dyskinesia is a side effect of Parkinson's disease treatment and it is characterized by atypical involuntary movements. A link between neuroinflammation and L-DOPA-induced dyskinesia has been documented. Hydrogen gas (H₂) has neuroprotective effects in Parkinson's disease models and has a major anti-inflammatory effect. Our objective is to test the hypothesis that H₂ inhalation reduces L-DOPA-induced dyskinesia. 15 days after 6-hydroxydopamine lesions of dopaminergic neurons were made (microinjection into the medial forebrain bundle), chronic L-DOPA treatment (15 days) was performed. Rats were exposed to H₂ (2% gas mixture, 1 h) or air (controls) before L-DOPA injection. Abnormal involuntary movements and locomotor activity were conducted. Striatal microglia and astrocyte was analyzed and striatal and plasma samples for cytokines evaluation were collected after the abnormal involuntary movements analysis. H₂ inhalation attenuated L-DOPA-induced dyskinesia. The gas therapy did not impair the improvement of locomotor activity achieved by L-DOPA treatment. H₂ inhalation reduced activated microglia in the lesioned striatum, which is consistent with the observed reduced pro-inflammatory cytokines levels. Display of abnormal involuntary movements was positively correlated with plasma IL-1β and striatal TNF-α levels and negatively correlated with striatal IL-10 levels. Prophylactic H₂ inhalation decreases abnormal involuntary movements in a preclinical L-DOPA-induced dyskinesia model. The H₂ antidyskinetic effect was associated with decreased striatal and peripheral inflammation. This finding has a translational importance to L-DOPA-treated parkinsonian patients' well-being.

Comparison of dyskinesia profiles after L-DOPA dose challenges with or without dopamine agonist coadministration

Many patients with Parkinson's disease (PD) experiencing l-DOPA-induced dyskinesia (LID) receive adjunct treatment with dopamine agonists, whose functional impact on LID is unknown. We set out to compare temporal and topographic profiles of abnormal involuntary movements (AIMs) after l-DOPA dose challenges including or not the dopamine agonist ropinirole. Twenty-five patients with PD and a history of dyskinesias were sequentially administered either l-DOPA alone (150% of usual morning dose) or an equipotent combination of l-DOPA and ropinirole in random order. Involuntary movements were assessed by two blinded raters prior and every 30 min after drug dosing using the Clinical Dyskinesia Rating Scale (CDRS). A sensor-recording smartphone was secured to the patients' abdomen during the test sessions. The two raters' CDRS scores were highly reliable and concordant with models of hyperkinesia presence and severity trained on accelerometer data. The dyskinesia time curves differed between treatments as the l-DOPA-ropinirole combination resulted in lower peak severity but longer duration of the AIMs compared with l-DOPA alone. At the peak of the AIMs curve (60-120 min), l-DOPA induced a significantly higher total hyperkinesia score, whereas in the end phase (240-270 min), both hyperkinesia and dystonia tended to be more severe after the l-DOPA-ropinirole combination (though reaching statistical significance only for the item, arm dystonia). Our results pave the way for the introduction of a combined l-DOPA-ropinirole challenge test in the early clinical evaluation of antidyskinetic treatments. Furthermore, we propose a machine-learning method to predict CDRS hyperkinesia severity using accelerometer data.

Altered Amantadine Effects after Repetitive Treatment for l-dopa-induced Involuntary Movements in a Rat Model of Parkinson's Disease

BACKGROUND

l-3,4-dihydroxyphenylalanine (l-dopa) is the most effective drug for Parkinson's disease (PD); however, most PD patients develop motor fluctuations including wearing-off and l-dopa-induced dyskinesia (LID). Amantadine is beneficial for improving the motor symptoms, reducing "off" time, and ameliorating LID, although its long-term efficacy remains unknown.

OBJECTIVES

To investigate the effects of amantadine on PD and LID using a rat model with repetitive drug treatment.

METHOD

We utilized 6-hydroxydopamine injections to develop a hemiparkinsonian rat model. The rats were assigned to four groups: five rats received l-dopa and benserazide for 31 days, six rats received l-dopa and benserazide plus amantadine for 31 days, five rats received l-dopa and benserazide for 15 days followed by l-dopa and benserazide plus amantadine for 16 days, and five rats received l-dopa and benserazide plus amantadine for 15 days followed by l-dopa and benserazide treatment for 16 days. We evaluated the l-dopa-induced abnormal involuntary movements on treatment days 1, 7, 14, 16, 22, and 29. Subsequently, immunohistochemistry for drebrin was performed.

RESULTS

l-dopa-induced abnormal movements were reduced on the first day of amantadine treatment, and these effects disappeared with repetitive treatment. In contrast, the extension of l-dopa "on" time was observed after repetitive amantadine treatment. All groups showed enlarged drebrin immunoreactive dots in the dopamine-denervated striatum, indicating that amantadine did not prevent priming effects of repetitive l-dopa treatment.

CONCLUSION

Anti-LID effect of amantadine diminished after repetitive treatment, and the effect of amantadine on wearing-off emerged after repetitive treatment in a hemiparkinsonian rat model. Fluctuations in amantadine effects should be considered when using it in clinical settings.

Regulator of G-Protein Signalling 4 (RGS4) negatively modulates nociceptin/orphanin FQ opioid receptor signalling: Implication for l-Dopa-induced dyskinesia

BACKGROUND AND PURPOSE

Regulator of G-protein signalling 4 (RGS4) is a signal transduction protein that accelerates intrinsic GTPase activity of Gαi/o and Gαq subunits, suppressing GPCR signalling. Here, we investigate whether RGS4 modulates nociceptin/orphanin FQ (N/OFQ) opioid (NOP) receptor signalling and if this modulation has relevance for l-Dopa-induced dyskinesia.

EXPERIMENTAL APPROACH

HEK293T cells transfected with NOP, NOP/RGS4 or NOP/RGS19 were challenged with N/OFQ and the small-molecule NOP agonist AT-403, using D1-stimulated cAMP levels as a readout. Primary rat striatal neurons and adult mouse striatal slices were challenged with either N/OFQ or AT-403 in the presence of the experimental RGS4 chemical probe, CCG-203920, and D1-stimulated cAMP or phosphorylated extracellular signal regulated kinase 1/2 (pERK) responses were monitored. In vivo, CCG-203920 was co-administered with AT-403 and l-Dopa to 6-hydroxydopamine hemilesioned rats, and dyskinetic movements, striatal biochemical correlates of dyskinesia (pERK and pGluR1 levels) and striatal RGS4 levels were measured.

KEY RESULTS

RGS4 expression reduced NOFQ and AT-403 potency and efficacy in HEK293T cells. CCG-203920 increased N/OFQ potency in primary rat striatal neurons and potentiated AT-403 response in mouse striatal slices. CCG-203920 enhanced AT-403-mediated inhibition of dyskinesia and its biochemical correlates, without compromising its motor-improving effects. Unilateral dopamine depletion caused bilateral reduction of RGS4 levels, which was reversed by l-Dopa. l-Dopa acutely up-regulated RGS4 in the lesioned striatum.

CONCLUSIONS AND IMPLICATIONS

RGS4 physiologically inhibits NOP receptor signalling. CCG-203920 enhanced NOP responses and improved the antidyskinetic potential of NOP receptor agonists, mitigating the effects of striatal RGS4 up-regulation occurring during dyskinesia expression.

LINKED ARTICLES

This article is part of a themed issue on Advances in Opioid Pharmacology at the Time of the Opioid Epidemic. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v180.7/issuetoc.

Dopamine Agonist Cotreatment Alters Neuroplasticity and Pharmacology of Levodopa-Induced Dyskinesia

BACKGROUND

Current models of levodopa (L-dopa)-induced dyskinesia (LID) are obtained by treating dopamine-depleted animals with L-dopa. However, patients with LID receive combination therapies that often include dopamine agonists.

OBJECTIVE

Using 6-hydroxydopamine-lesioned rats as a model, we aimed to establish whether an adjunct treatment with the D2/3 agonist ropinirole impacts on patterns of LID-related neuroplasticity and drug responses.

METHODS

Different regimens of L-dopa monotreatment and L-dopa-ropinirole cotreatment were compared using measures of hypokinesia and dyskinesia. Striatal expression of ∆FosB and angiogenesis markers were studied immunohistochemically. Antidyskinetic effects of different drug categories were investigated in parallel groups of rats receiving either L-dopa monotreatment or L-dopa combined with ropinirole.

RESULTS

We defined chronic regimens of L-dopa monotreatment and L-dopa-ropinirole cotreatment inducing overall similar abnormal involuntary movement scores. Compared with the monotreatment group, animals receiving the L-dopa-ropinirole combination exhibited an overall lower striatal expression of ∆FosB with a distinctive compartmental distribution. The expression of angiogenesis markers and blood-brain barrier hyperpermeability was markedly reduced after L-dopa-ropinirole cotreatment compared with L-dopa monotreatment. Moreover, significant group differences were detected upon examining the response to candidate antidyskinetic drugs. In particular, compounds modulating D1 receptor signaling had a stronger effect in the L-dopa-only group, whereas both amantadine and the selective NMDA antagonist MK801 produced a markedly larger antidyskinetic effect in L-dopa-ropinirole cotreated animals.

CONCLUSIONS

Cotreatment with ropinirole altered LID-related neuroplasticity and pharmacological response profiles. The impact of adjuvant dopamine agonist treatment should be taken into consideration when investigating LID mechanisms and candidate interventions in both clinical and experimental settings. © 2023 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Multimodal Imaging of Substantia Nigra in Parkinson's Disease with Levodopa-Induced Dyskinesia

BACKGROUND

Degeneration of the substantia nigra (SN) may contribute to levodopa-induced dyskinesia (LID) in Parkinson's disease (PD), but the exact characteristics of SN in LID remain unclear.

OBJECTIVE

To further understand the pathogenesis of patients with PD with LID (PD-LID), we explored the structural and functional characteristics of SN in PD-LID using multimodal magnetic resonance imaging (MRI).

METHODS

Twenty-nine patients with PD-LID, 37 patients with PD without LID (PD-nLID), and 28 healthy control subjects underwent T1-weighted MRI, quantitative susceptibility mapping, neuromelanin-sensitive MRI, multishell diffusion MRI, and resting-state functional MRI. Different measures characterizing the SN were obtained using a region of interest-based approach.

RESULTS

Compared with patients with PD-nLID and healthy control subjects, the quantitative susceptibility mapping values of SN pars compacta (SNpc) were significantly higher (P = 0.049 and P = 0.00002), and the neuromelanin contrast-to-noise ratio values in SNpc were significantly lower (P = 0.012 and P = 0.000002) in PD-LID. The intracellular volume fraction of the posterior SN in PD-LID was significantly higher compared with PD-nLID (P = 0.037). Resting-state fMRI indicated that PD-LID in the medication off state showed higher functional connectivity between the SNpc and putamen compared with PD-nLID (P = 0.031), and the functional connectivity changes in PD-LID were positively correlated with Unified Dyskinesia Rating Scale total scores (R = 0.427, P = 0.042).

CONCLUSIONS

Our multimodal imaging findings highlight greater neurodegeneration in SN and the altered nigrostriatal connectivity in PD-LID. These characteristics provide a new perspective into the role of SN in the pathophysiological mechanisms underlying PD-LID. © 2023 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Distinctive Effects of D1 and D2 Receptor Agonists on Cortico-Basal Ganglia Oscillations in a Rodent Model of L-DOPA-Induced Dyskinesia

L-DOPA-induced dyskinesia (LID) in Parkinson's disease has been linked to oscillatory neuronal activities in the cortico-basal ganglia network. We set out to examine the pattern of cortico-basal ganglia oscillations induced by selective agonists of D1 and D2 receptors in a rat model of LID. Local field potentials were recorded in freely moving rats using large-scale electrodes targeting three motor cortical regions, dorsomedial and dorsolateral striatum, external globus pallidus, and substantial nigra pars reticulata. Abnormal involuntary movements were elicited by the D1 agonist SKF82958 or the D2 agonist sumanirole, while overall motor activity was quantified using video analysis (DeepLabCut). Both SKF82958 and sumanirole induced dyskinesia, although with significant differences in temporal course, overall severity, and body distribution. The D1 agonist induced prominent narrowband oscillations in the high gamma range (70-110 Hz) in all recorded structures except for the nigra reticulata. Additionally, the D1 agonist induced strong functional connectivity between the recorded structures and the phase analysis revealed that the primary motor cortex (forelimb area) was leading a supplementary motor area and striatum. Following treatment with the D2 agonist, narrowband gamma oscillations were detected only in forelimb motor cortex and dorsolateral striatum, while prominent oscillations in the theta band occurred in the globus pallidus and nigra reticulata. Our results reveal that the dyskinetic effects of D1 and D2 receptor agonists are associated with distinct patterns of cortico-basal ganglia oscillations, suggesting a recruitment of partially distinct networks.

Targeting G Protein-Coupled Receptors in the Treatment of Parkinson's Disease

Parkinson's disease (PD) is a progressive neurodegenerative disease characterized in part by the deterioration of dopaminergic neurons which leads to motor impairment. Although there is no cure for PD, the motor symptoms can be treated using dopamine replacement therapies including the dopamine precursor L-DOPA, which has been in use since the 1960s. However, neurodegeneration in PD is not limited to dopaminergic neurons, and many patients experience non-motor symptoms including cognitive impairment or neuropsychiatric disturbances, for which there are limited treatment options. Moreover, there are currently no treatments able to alter the progression of neurodegeneration. There are many therapeutic strategies being investigated for PD, including alternatives to L-DOPA for the treatment of motor impairment, symptomatic treatments for non-motor symptoms, and neuroprotective or disease-modifying agents. G protein-coupled receptors (GPCRs), which include the dopamine receptors, are highly druggable cell surface proteins which can regulate numerous intracellular signaling pathways and thereby modulate the function of neuronal circuits affected by PD. This review will describe the treatment strategies being investigated for PD that target GPCRs and their downstream signaling mechanisms. First, we discuss new developments in dopaminergic agents for alleviating PD motor impairment, the role of dopamine receptors in L-DOPA induced dyskinesia, as well as agents targeting non-dopamine GPCRs which could augment or replace traditional dopaminergic treatments. We then discuss GPCRs as prospective treatments for neuropsychiatric and cognitive symptoms in PD. Finally, we discuss the evidence pertaining to ghrelin receptors, β-adrenergic receptors, angiotensin receptors and glucagon-like peptide 1 receptors, which have been proposed as disease modifying targets with potential neuroprotective effects in PD.

The Potential Role of Voltage-Dependent Anion Channel in the Treatment of Parkinson’s Disease

Parkinson’s disease (PD) is a neurodegenerative disease second only to Alzheimer’s disease in terms of prevalence. Previous studies have indicated that the occurrence and progression of PD are associated with mitochondrial dysfunction. Mitochondrial dysfunction is one of the most important causes for apoptosis of dopaminergic neurons. Therefore, maintaining the stability of mitochondrial functioning is a potential strategy in the treatment of PD. Voltage-dependent anion channel (VDAC) is the main component in the outer mitochondrial membrane, and it participates in a variety of biological processes. In this review, we focus on the potential roles of VDACs in the treatment of PD. We found that VDACs are involved in PD by regulating apoptosis, autophagy, and ferroptosis. VDAC1 oligomerization, VDACs ubiquitination, regulation of mitochondrial permeability transition pore (mPTP) by VDACs, and interaction between VDACs and α-synuclein (α-syn) are all promising methods for the treatment of PD. We proposed that inhibition of VDAC1 oligomerization and promotion of VDAC1 ubiquitination as an effective approach for the treatment of PD. Previous studies have proven that the expression of VDAC1 has a significant change in PD models. The expression levels of VDAC1 are decreased in the substantia nigra (SN) of patients suffering from PD compared with the control group consisting of normal individuals by using bioinformatics tools. VDAC2 is involved in PD mainly through the regulation of apoptosis. VDAC3 may have a similar function to VDAC1. It can be concluded that the functional roles of VDACs contribute to the therapeutic strategy of PD.

D2R signaling in striatal spiny neurons modulates L-DOPA induced dyskinesia

Degeneration of dopaminergic neurons leads to Parkinson’s disease (PD), characterized by reduced levels of striatal dopamine (DA) and impaired voluntary movements. DA replacement is achieved by levodopa treatment which in long-term causes involuntary movements or dyskinesia. Dyskinesia is linked to the pulsatile activation of D1 receptors of the striatal medium spiny neurons (MSNs) forming the direct output pathway (dMSNs). The contribution of DA stimulation of D2R in MSNs of the indirect pathway (iMSNs) is less clear. Using the 6-hydroxydopamine model of PD, here we show that loss of DA-mediated inhibition of these neurons intensifies levodopa-induced dyskinesia (LID) leading to reprogramming of striatal gene expression. We propose that the motor impairments characteristic of PD and of its therapy are critically dependent on D2R-mediated iMSNs activity. D2R signaling not only filters inputs to the striatum but also indirectly regulates dMSNs mediated responses.

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D2RKO in iMSNs increases L-DOPA-induced dyskinesia (LID)

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D2R signaling in iMSNs inhibits striatal gene and PD-associated genes

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Unopposed M1R signaling is responsible for the increased LID in iMSN-D2RKO mice

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Simultaneous modulation of M1R and M4R signaling on MSNs drastically reduces LID

Dyskinesia and Parkinson's disease: animal model, drug targets, and agents in preclinical testing

INTRODUCTION

Parkinson's disease (PD) is the second most common neurodegenerative disease after Alzheimer's disease. PD patients exhibit a classic spectrum of motor symptoms, arising when dopamine neurons in the substantia nigra pars compacta are reduced by 60%. The dopamine precursor L-DOPA represents the most effective therapy for improving PD motor dysfunctions, thus far available. Unfortunately, long-term treatment with L-DOPA is associated with the development of severe side effects, resulting in abnormal involuntary movements termed levodopa-induced dyskinesia (LID). Amantadine is the only drug currently approved for the treatment of LID indicating that LID management is still an unmet need in PD and encouraging the search for novel anti-dyskinetic drugs or the assessment of combined therapies with different molecular targets.

AREAS COVERED

This review provides an overview of the main preclinical models used to study LID and of the latest preclinical evidence on experimental and clinically available pharmacological approaches targeting non-dopaminergic systems.

EXPERT OPINION

LIDs are supported by complex molecular and neurobiological mechanisms that are still being studied today. This complexity suggests the need of developing personalized pharmacological approach to obtain an effective amelioration of LID condition and improve the quality of life of PD patients.

Deep Learning Paradigm for Cardiovascular Disease/Stroke Risk Stratification in Parkinson’s Disease Affected by COVID-19: A Narrative Review

Background and Motivation: Parkinson’s disease (PD) is one of the most serious, non-curable, and expensive to treat. Recently, machine learning (ML) has shown to be able to predict cardiovascular/stroke risk in PD patients. The presence of COVID-19 causes the ML systems to become severely non-linear and poses challenges in cardiovascular/stroke risk stratification. Further, due to comorbidity, sample size constraints, and poor scientific and clinical validation techniques, there have been no well-explained ML paradigms. Deep neural networks are powerful learning machines that generalize non-linear conditions. This study presents a novel investigation of deep learning (DL) solutions for CVD/stroke risk prediction in PD patients affected by the COVID-19 framework. Method: The PRISMA search strategy was used for the selection of 292 studies closely associated with the effect of PD on CVD risk in the COVID-19 framework. We study the hypothesis that PD in the presence of COVID-19 can cause more harm to the heart and brain than in non-COVID-19 conditions. COVID-19 lung damage severity can be used as a covariate during DL training model designs. We, therefore, propose a DL model for the estimation of, (i) COVID-19 lesions in computed tomography (CT) scans and (ii) combining the covariates of PD, COVID-19 lesions, office and laboratory arterial atherosclerotic image-based biomarkers, and medicine usage for the PD patients for the design of DL point-based models for CVD/stroke risk stratification. Results: We validated the feasibility of CVD/stroke risk stratification in PD patients in the presence of a COVID-19 environment and this was also verified. DL architectures like long short-term memory (LSTM), and recurrent neural network (RNN) were studied for CVD/stroke risk stratification showing powerful designs. Lastly, we examined the artificial intelligence bias and provided recommendations for early detection of CVD/stroke in PD patients in the presence of COVID-19. Conclusion: The DL is a very powerful tool for predicting CVD/stroke risk in PD patients affected by COVID-19.

Cerebellar stimulation prevents Levodopa-induced dyskinesia in mice and normalizes activity in a motor network

Chronic Levodopa therapy, the gold-standard treatment for Parkinson's Disease (PD), leads to the emergence of involuntary movements, called levodopa-induced dyskinesia (LID). Cerebellar stimulation has been shown to decrease LID severity in PD patients. Here, in order to determine how cerebellar stimulation induces LID alleviation, we performed daily short trains of optogenetic stimulations of Purkinje cells (PC) in freely moving LID mice. We demonstrated that these stimulations are sufficient to suppress LID or even prevent their development. This symptomatic relief is accompanied by the normalization of aberrant neuronal discharge in the cerebellar nuclei, the motor cortex and the parafascicular thalamus. Inhibition of the cerebello-parafascicular pathway counteracted the beneficial effects of cerebellar stimulation. Moreover, cerebellar stimulation reversed plasticity in D1 striatal neurons and normalized the overexpression of FosB, a transcription factor causally linked to LID. These findings demonstrate LID alleviation and prevention by daily PC stimulations, which restore the function of a wide motor network, and may be valuable for LID treatment.

Cardiovascular/Stroke Risk Stratification in Parkinson's Disease Patients Using Atherosclerosis Pathway and Artificial Intelligence Paradigm: A Systematic Review

Parkinson’s disease (PD) is a severe, incurable, and costly condition leading to heart failure. The link between PD and cardiovascular disease (CVD) is not available, leading to controversies and poor prognosis. Artificial Intelligence (AI) has already shown promise for CVD/stroke risk stratification. However, due to a lack of sample size, comorbidity, insufficient validation, clinical examination, and a lack of big data configuration, there have been no well-explained bias-free AI investigations to establish the CVD/Stroke risk stratification in the PD framework. The study has two objectives: (i) to establish a solid link between PD and CVD/stroke; and (ii) to use the AI paradigm to examine a well-defined CVD/stroke risk stratification in the PD framework. The PRISMA search strategy selected 223 studies for CVD/stroke risk, of which 54 and 44 studies were related to the link between PD-CVD, and PD-stroke, respectively, 59 studies for joint PD-CVD-Stroke framework, and 66 studies were only for the early PD diagnosis without CVD/stroke link. Sequential biological links were used for establishing the hypothesis. For AI design, PD risk factors as covariates along with CVD/stroke as the gold standard were used for predicting the CVD/stroke risk. The most fundamental cause of CVD/stroke damage due to PD is cardiac autonomic dysfunction due to neurodegeneration that leads to heart failure and its edema, and this validated our hypothesis. Finally, we present the novel AI solutions for CVD/stroke risk prediction in the PD framework. The study also recommends strategies for removing the bias in AI for CVD/stroke risk prediction using the PD framework.

Striatal neuronal ensembles reveal differential actions of amantadine and clozapine to ameliorate mice L-DOPA-induced dyskinesia

Amantadine and clozapine have proved to reduce abnormal involuntary movements (AIMs) in preclinical and clinical studies of L-DOPA-Induced Dyskinesias (LID). Even though both drugs decrease AIMs, they may have different action mechanisms by using different receptors and signaling profiles. Here we asked whether there are differences in how they modulate neuronal activity of multiple striatal neurons within the striatal microcircuit at histological level during the dose-peak of L-DOPA in ex-vivo brain slices obtained from dyskinetic mice. To answer this question, we used calcium imaging to record the activity of dozens of neurons of the dorsolateral striatum before and after drugs administration in vitro. We also developed an analysis framework to extract encoding insights from calcium imaging data by quantifying neuronal activity, identifying neuronal ensembles by linking neurons that coactivate using hierarchical cluster analysis and extracting network parameters using Graph Theory. The results show that while both drugs reduce LIDs scores behaviorally in a similar way, they have several different and specific actions on modulating the dyskinetic striatal microcircuit. The extracted features were highly accurate in separating amantadine and clozapine effects by means of principal components analysis (PCA) and support vector machine (SVM) algorithms. These results predict possible synergistic actions of amantadine and clozapine on the dyskinetic striatal microcircuit establishing a framework for a bioassay to test novel antidyskinetic drugs or treatments in vitro.

Dopamine neuron stimulation induces context-dependent abnormal involuntary movements in healthy rats

With continued levodopa treatment, most patients with Parkinson disease (PD) develop levodopa-induced dyskinesias (LIDs)—abnormal involuntary movements (AIMs) characterized primarily by chorea. Clinically, LIDs depend on nigrostriatal degeneration and sensitization to repeated levodopa doses. However, the degree of dopamine denervation is correlated with levodopa-induced changes in striatal dopamine. Therefore, pulsatile dopamine release may induce AIMs independently of nigrostriatal degeneration. We optogenetically stimulated dopamine neurons in healthy rats as they engaged in skilled reaching. Repeated stimulation induced progressive AIMs whose severity was modified by behavioral context. AIMs were milder with stimulation during reaches, and more severe if stimulation occurred between reaches. Despite gradual induction, AIMs recurred immediately with subsequent dopamine neuron stimulation. Thus, nigrostriatal denervation is not necessary for fluctuating striatal dopamine to induce AIMs, and behavioral context modulates AIM expression. Furthermore, pulsatile dopamine release induces persistent changes in motor circuits that are revealed by subsequent dopamine neuron activation in appropriate contexts.

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Repeated dopamine neuron activation causes involuntary movements in healthy rats

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These movements resemble levodopa-induced dyskinesias in parkinsonian rats

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Movement severity depends on the history of prior stimulation

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Movement severity is diminished in rats actively engaged in goal-directed behavior

Dopamine D2L Receptor Deficiency Alters Neuronal Excitability and Spine Formation in Mouse Striatum

The striatum contains several types of neurons including medium spiny projection neurons (MSNs), cholinergic interneurons (ChIs), and fast-spiking interneurons (FSIs). Modulating the activity of these neurons by the dopamine D2 receptor (D2R) can greatly impact motor control and movement disorders. D2R exists in two isoforms: D2L and D2S. Here, we assessed whether alterations in the D2L and D2S expression levels affect neuronal excitability and synaptic function in striatal neurons. We observed that quinpirole inhibited the firing rate of all three types of striatal neurons in wild-type (WT) mice. However, in D2L knockout (KO) mice, quinpirole enhanced the excitability of ChIs, lost influence on spike firing of MSNs, and remained inhibitory effect on spike firing of FSIs. Additionally, we showed mIPSC frequency (but not mIPSC amplitude) was reduced in ChIs from D2L KO mice compared with WT mice, suggesting spontaneous GABA release is reduced at GABAergic terminals onto ChIs in D2L KO mice. Furthermore, we found D2L deficiency resulted in reduced dendritic spine density in ChIs, suggesting D2L activation plays a role in the formation/maintenance of dendritic spines of ChIs. These findings suggest new molecular and cellular mechanisms for causing ChIs abnormality seen in Parkinson’s disease or drug-induced dyskinesias.

Animal models of Parkinson's disease: a guide to selecting the optimal model for your research

Parkinson's disease (PD) is a complex, multisystem disorder characterised by α-synuclein (SNCA) pathology, degeneration of nigrostriatal dopaminergic neurons, multifactorial pathogenetic mechanisms and expression of a plethora of motor and non-motor symptoms. Animal models of PD have already been instructive in helping us unravel some of these aspects. However, much remains to be discovered, requiring continued interrogation by the research community. In contrast with the situation for many neurological disorders, PD benefits from of a wide range of available animal models (pharmacological, toxin, genetic and α-synuclein) but this makes selection of the optimal one for a given study difficult. This is especially so when a study demands a model that displays a specific combination of features. While many excellent reviews of animal models already exist, this review takes a different approach with the intention of more readily informing this decision-making process. We have considered each feature of PD in turn - aetiology, pathology, pathogenesis, motor dysfunctions and non-motor symptoms (NMS) - highlighting those animal models that replicate each. By compiling easily accessible tables and a summary figure, we aim to provide the reader with a simple, go-to resource for selecting the optimal animal model of PD to suit their research needs.

Induction of Ticlike Involuntary Movements in Rats by Striatotomy and Subsequent Neurochemical Sensitization

OBJECTIVE

It has been proposed that Tourette syndrome is associated with dysfunction in widespread cortical areas and globus pallidus externus hyperactivity secondary to dopaminergic hyperactivity and serotonergic/dynorphinergic hypoactivity. The main objective of this study was to test this hypothesis by developing an animal model of Tourette syndrome via striatotomy, followed by administration of drugs that mimic the neurotransmitter environment, so as to induce globus pallidus externus hyperactivity.

METHODS

Rats were assigned to 3 groups: stereotactic striatotomy (STT) and striatal sham -lesion (SHAM) groups, treated with anterior and posterior striatum procedures in both hemispheres, and a group of nonoperated animals (NAIVE). Postoperatively, all rodents were blindly administered 3 drug protocols: levodopa/benserazide; levodopa/benserazide/ergotamine/naloxone (MIX); and saline. The animals were filmed at the peak action of these drugs. The videos were evaluated by a single blinded researcher.

RESULTS

Six types of involuntary movements (IMs) were observed: cephalic, trunk jerks, oromandibular, forepaw jerks, dystonic, and locomotive. The number of animals with IM and the mean number of IM after both levodopa/benserazide and MIX was significantly higher in the STT compared with the SHAM and NAIVE groups. In the SHAM and NAIVE, MIX was superior to levodopa/benserazide in the induction of IM. In the STT, MIX was superior to levodopa/benserazide in the induction of trunk jerks. Appendicular IM were more common after posterior than after anterior striatotomy.

CONCLUSIONS

These results show that striatotomy, followed by administration of levodopa/benserazide alone or associated with ergotamine and naloxone, is efficacious in inducing IM, supporting the hypothesis that led to this study.

Functional parcellation of human and macaque striatum reveals human-specific connectivity in the dorsal caudate

A wide homology between human and macaque striatum is often assumed as in both the striatum is involved in cognition, emotion and executive functions. However, differences in functional and structural organization between human and macaque striatum may reveal evolutionary divergence and shed light on human vulnerability to neuropsychiatric diseases. For instance, dopaminergic dysfunction of the human striatum is considered to be a pathophysiological underpinning of different disorders, such as Parkinson's disease (PD) and schizophrenia (SCZ). Previous investigations have found a wide similarity in structural connectivity of the striatum between human and macaque, leaving the cross-species comparison of its functional organization unknown. In this study, resting-state functional connectivity (RSFC) derived striatal parcels were compared based on their homologous cortico-striatal connectivity. The goal here was to identify striatal parcels whose connectivity is human-specific compared to macaque parcels. Functional parcellation revealed that the human striatum was split into dorsal, dorsomedial, and rostral caudate and ventral, central, and caudal putamen, while the macaque striatum was divided into dorsal, and rostral caudate and rostral, and caudal putamen. Cross-species comparison indicated dissimilar cortico-striatal RSFC of the topographically similar dorsal caudate. We probed clinical relevance of the striatal clusters by examining differences in their cortico-striatal RSFC and gray matter (GM) volume between patients (with PD and SCZ) and healthy controls. We found abnormal RSFC not only between dorsal caudate, but also between rostral caudate, ventral, central and caudal putamen and widespread cortical regions for both PD and SCZ patients. Also, we observed significant structural atrophy in rostral caudate, ventral and central putamen for both PD and SCZ while atrophy in the dorsal caudate was specific to PD. Taken together, our cross-species comparative results revealed shared and human-specific RSFC of different striatal clusters reinforcing the complex organization and function of the striatum. In addition, we provided a testable hypothesis that abnormalities in a region with human-specific connectivity, i.e., dorsal caudate, might be associated with neuropsychiatric disorders.

Neuroinflammation and L-dopa-induced abnormal involuntary movements in 6-hydroxydopamine-lesioned rat model of Parkinson's disease are counteracted by combined administration of a 5-HT1A/1B receptor agonist and A2A receptor antagonist

Several lines of evidence have strongly implicated neuroinflammation in Parkinson's disease (PD) progression and l-dopa-induced dyskinesia. The present study investigated whether early subchronic pretreatment with the serotonin 5-HT_1A/1B receptor agonist eltoprazine plus the adenosine A_2A receptor antagonist preladenant counteracted l-dopa-induced abnormal involuntary movements (AIMs, index of dyskinesia), and neuroinflammation, in unilateral 6-hydroxydopamine(6-OHDA)-lesioned rat model of PD. The immunoreactivity of glial fibrillary acidic protein (GFAP), and the colocalization of ionized calcium binding adaptor molecule-1 (IBA-1), with interleukin (IL)-1β, tumor-necrosis-factor-α (TNF-α) and IL-10 were evaluated in the denervated caudate-putamen (CPu) and substantia nigra pars-compacta (SNc). The combined subchronic pretreatment with l-dopa plus eltoprazine and preladenant reduced AIMs induced by acute l-dopa challenge in these rats and decreased GFAP and IBA-1 immunoreactivity induced by the drug in both CPu and SNc, with reduction in IL-1β in IBA-1-positive cells in both CPu and SNc, and in TNF-α in IBA-1-positive cells in SNc. Moreover, a significant increase in IL-10 in IBA-1-positive cells was observed in SNc. Evaluation of immediate early-gene zif-268 (index of neuronal activation) after l-dopa challenge, showed an increase in its expression in denervated CPu of rats pretreated with l-dopa or l-dopa plus preladenant compared with vehicle, whereas rats pretreated with eltoprazine, with or without preladenant, had lower zif-268 expression. Finally, tyrosine hydroxylase and dopamine transporter examined to evaluate neurodegeneration, showed a significant equal decrease in all experimental groups. The present findings suggest that combination of l-dopa with eltoprazine and preladenant may be promising therapeutic strategy for delaying the onset of dyskinesia, preserving l-dopa efficacy and reducing neuroinflammation markers in nigrostriatal system of 6-OHDA-lesioned rats.

Intragastric Administration of Casein Leads to Nigrostriatal Disease Progressed Accompanied with Persistent Nigrostriatal-Intestinal Inflammation Activited and Intestinal Microbiota-Metabolic Disorders Induced in MPTP Mouse Model of Parkinson's Disease

Gut microbial dysbiosis and alteration of gut microbiota composition in Parkinson's disease (PD) have been increasingly reported, no recognized therapies are available to halt or slow progression of PD and more evidence is still needed to illustrate its causative impact on gut microbiota and PD and mechanisms for targeted mitigation. Epidemiological evidence supported an association between milk intake and a higher incidence of Parkinson's disease (PD), questions have been raised about prospective associations between dietary factors and the incidence of PD. Here, we investigated the significance of casein in the development of PD. The mice were given casein (6.75 g/kg i.g.) for 21 days after MPTP (25 mg/kg i.p. × 5 days) treatment, the motor function, dopaminergic neurons, inflammation, gut microbiota and fecal metabolites were observed. The experimental results revealed that the mice with casein gavage after MPTP treatment showed a persisted dyskinesia, the content of dopamine in striatum and the expression of TH in midbrain and ileum were decreased, the expression of Iba-1, CD4, IL-22 in midbrain and ileum increased continuously with persisted intestinal histopathology and intestinal barrier injury. Decreased intestinal bile secretion in addition with abnormal digestion and metabolism of carbohydrate, lipids and proteins were found, whereas these pathological status for the MPTP mice without casein intake had recovered after 24 days, no significant differences were observed with regard to only treated with casein. Our study demonstrates that intestinal pathologic injury, intestinal dysbacteriosis and metabolism changes promoted by casein in MPTP mice ultimately exacerbated the lesions to dopaminergic neurons.

Effects of Aging on Levo-Dihydroxyphenylalanine- Induced Dyskinesia in a Rat Model of Parkinson's Disease

Background

It remains unclear why patients with young-onset Parkinson's disease more often develop levo-dihydroxyphenylalanine (L-dopa)-induced dyskinesia (LID) and have a more severe form than patients with old-onset Parkinson's disease. Previous studies using animal models have failed to show young-onset Parkinson's disease enhances LID.

Objectives

To evaluate the association of age at dopaminergic denervation (onset age) and initiation of L-dopa treatment (treatment age) with LID development in model rats.

Methods

We established rat models of young- and old-lesioned Parkinson's disease (6-hydroxydopamine lesions at 10 and 88 weeks of age, respectively). Dopaminergic denervation was confirmed by the rotational behavior test using apomorphine. Rats in the young-lesioned group were allocated to either L-dopa treatment at a young or old age, or saline treatment. Rats in the old-lesioned group were allocated to either L-dopa treatment or saline group. We evaluated L-dopa-induced abnormal involuntary movements during the 14-day treatment period. We also examined preprodynorphin mRNA expression in the striatum (a neurochemical hallmark of LID) and the volume of the medial globus pallidus (a pathological hallmark of LID).

Results

LID-like behavior was enhanced in L-dopa-treated young-lesioned rats compared with L-dopa-treated old-lesioned rats. Preprodynorphin mRNA expression was higher in L-dopa-treated young-lesioned rats than in in L-dopa-treated old-lesioned rats. The volume of the medial globus pallidus was greater in L-dopa-treated young-lesioned rats than in L-dopa-treated old-lesioned rats. Treatment age did not affect LID-like behavior or the degree of medial globus pallidus hypertrophy in the young-lesioned model.

Conclusion

Both dopaminergic denervation and L-dopa initiation at a young age contributed to the development of LID; however, the former may be a more important factor.

Pathophysiological Mechanisms and Experimental Pharmacotherapy for L-Dopa-Induced Dyskinesia

L-dopa-induced dyskinesia (LID) is the most frequent motor complication associated with chronic L-dopa treatment in Parkinson’s disease (PD). Recent advances in the understanding of the pathophysiological mechanisms underlying LID suggest that abnormalities in multiple neurotransmitter systems, in addition to dopaminergic nigrostriatal denervation and altered dopamine release and reuptake dynamics at the synaptic level, are involved in LID development. Increased knowledge of neurobiological LID substrates has led to the development of several drug candidates to alleviate this motor complication. However, with the exception of amantadine, none of the pharmacological therapies tested in humans have demonstrated clinically relevant beneficial effects. Therefore, LID management is still one of the most challenging problems in the treatment of PD patients. In this review, we first describe the known pathophysiological mechanisms of LID. We then provide an updated report of experimental pharmacotherapies tested in clinical trials of PD patients and drugs currently under study to alleviate LID. Finally, we discuss available pharmacological LID treatment approaches and offer our opinion of possible issues to be clarified and future therapeutic strategies.

The evolution of dystonia-like movements in TOR1A rats after transient nerve injury is accompanied by dopaminergic dysregulation and abnormal oscillatory activity of a central motor network

TOR1A is the most common inherited form of dystonia with still unclear pathophysiology and reduced penetrance of 30-40%. ∆ETorA rats mimic the TOR1A disease by expression of the human TOR1A mutation without presenting a dystonic phenotype. We aimed to induce dystonia-like symptoms in male ∆ETorA rats by peripheral nerve injury and to identify central mechanism of dystonia development. Dystonia-like movements (DLM) were assessed using the tail suspension test and implementing a pipeline of deep learning applications. Neuron numbers of striatal parvalbumin⁺, nNOS⁺, calretinin⁺, ChAT⁺ interneurons and Nissl⁺ cells were estimated by unbiased stereology. Striatal dopaminergic metabolism was analyzed via in vivo microdialysis, qPCR and western blot. Local field potentials (LFP) were recorded from the central motor network. Deep brain stimulation (DBS) of the entopeduncular nucleus (EP) was performed. Nerve-injured ∆ETorA rats developed long-lasting DLM over 12 weeks. No changes in striatal structure were observed. Dystonic-like ∆ETorA rats presented a higher striatal dopaminergic turnover and stimulus-induced elevation of dopamine efflux compared to the control groups. Higher LFP theta power in the EP of dystonic-like ∆ETorA compared to wt rats was recorded. Chronic EP-DBS over 3 weeks led to improvement of DLM. Our data emphasizes the role of environmental factors in TOR1A symptomatogenesis. LFP analyses indicate that the pathologically enhanced theta power is a physiomarker of DLM. This TOR1A model replicates key features of the human TOR1A pathology on multiple biological levels and is therefore suited for further analysis of dystonia pathomechanism.

Differential roles of two isoforms of dopamine D2 receptors in l-dopa-induced abnormal involuntary movements in mice

l-dopa and dopamine D2 receptor (D2R) agonists are commonly used to relieve the motor deficits of Parkinson's disease. However, long-term treatment with l-dopa or D2R agonists can induce adverse effects such as abnormal involuntary movements (AIMs), which are major limiting factors in achieving long-term control of parkinsonian syndromes. The pathophysiological mechanisms involved in the development of dopaminergic agonist-induced adverse effects are not well understood. Here, we examined the role of two D2R isoforms, D2S and D2L, in l-dopa-induced AIMs using dopamine D2L knockout (D2L KO) mice (expressing purely D2S) and wild-type mice (expressing predominantly D2L). We found that D2L KO mice displayed markedly enhanced AIMs in response to chronic treatment of l-dopa compared to wild-type mice. The l-dopa-induced enhancement of AIMs in D2L KO mice was significantly reduced by the D2R antagonist eticlopride. D2L KO mice also displayed markedly enhanced AIMs in response to chronic treatment with quinpirole, a preferential D2R agonist. These results suggest that D2S contributes more than D2L to dopaminergic agonist-induced AIMs. Our findings may uncover a new factor that contributes to the pathophysiology of dopaminergic drug-induced AIMs, a characteristic manifestation of dyskinesia and also present in psychosis. There is a possibility that the increased ratio of D2S to D2L in the brain plays a significant role in the development of AIM side effects induced by l-dopa or D2R agonists. See Video Abstract, http://links.lww.com/WNR/A622.

Dyskinesia is Closely Associated with Synchronization of Theta Oscillatory Activity Between the Substantia Nigra Pars Reticulata and Motor Cortex in the Off L-dopa State in Rats

Excessive theta (θ) frequency oscillation and synchronization in the basal ganglia (BG) has been reported in elderly parkinsonian patients and animal models of levodopa (L-dopa)-induced dyskinesia (LID), particularly the θ oscillation recorded during periods when L-dopa is withdrawn (the off L-dopa state). To gain insight into processes underlying this activity, we explored the relationship between primary motor cortex (M1) oscillatory activity and BG output in LID. We recorded local field potentials in the substantia nigra pars reticulata (SNr) and M1 of awake, inattentive resting rats before and after L-dopa priming in Sham control, Parkinson disease model, and LID model groups. We found that chronic L-dopa increased θ synchronization and information flow between the SNr and M1 in off L-dopa state LID rats, with a SNr-to-M1 flow directionality. Compared with the on state, θ oscillational activity (θ synchronization and information flow) during the off state were more closely associated with abnormal involuntary movements. Our findings indicate that θ oscillation in M1 may be consequent to abnormal synchronous discharges in the BG and support the notion that M1 θ oscillation may participate in the induction of dyskinesia.

The Delta-Specific Opioid Glycopeptide BBI-11008: CNS Penetration and Behavioral Analysis in a Preclinical Model of Levodopa-Induced Dyskinesia

In previous work we evaluated an opioid glycopeptide with mixed μ/δ-opioid receptor agonism that was a congener of leu-enkephalin, MMP-2200. The glycopeptide analogue showed penetration of the blood-brain barrier (BBB) after systemic administration to rats, as well as profound central effects in models of Parkinson's disease (PD) and levodopa (L-DOPA)-induced dyskinesia (LID). In the present study, we tested the glycopeptide BBI-11008 with selective δ-opioid receptor agonism, an analogue of deltorphin, a peptide secreted from the skin of frogs (genus Phyllomedusa). We tested BBI-11008 for BBB-penetration after intraperitoneal (i.p.) injection and evaluated effects in LID rats. BBI-11008 (10 mg/kg) demonstrated good CNS-penetrance as shown by microdialysis and mass spectrometric analysis, with peak concentration levels of 150 pM in the striatum. While BBI-11008 at both 10 and 20 mg/kg produced no effect on levodopa-induced limb, axial and oral (LAO) abnormal involuntary movements (AIMs), it reduced the levodopa-induced locomotor AIMs by 50% after systemic injection. The N-methyl-D-aspartate receptor antagonist MK-801 reduced levodopa-induced LAO AIMs, but worsened PD symptoms in this model. Co-administration of MMP-2200 had been shown prior to block the MK-801-induced pro-Parkinsonian activity. Interestingly, BBI-11008 was not able to block the pro-Parkinsonian effect of MK-801 in the LID model, further indicating that a balance of mu- and delta-opioid agonism is required for this modulation. In summary, this study illustrates another example of meaningful BBB-penetration of a glycopeptide analogue of a peptide to achieve a central behavioral effect, providing additional evidence for the glycosylation technique as a method to harness therapeutic potential of peptides.

The BDNF Val66Met polymorphism (rs6265) enhances dopamine neuron graft efficacy and side-effect liability in rs6265 knock-in rats

Prevalent in approximately 20% of the worldwide human population, the rs6265 (also called ‘Val66Met’) single nucleotide polymorphism (SNP) in the gene for brain-derived neurotrophic factor (BDNF) is a common genetic variant that can alter therapeutic responses in individuals with Parkinson’s disease (PD). Possession of the variant Met allele results in decreased activity-dependent release of BDNF. Given the resurgent worldwide interest in neural transplantation for PD and the biological relevance of BDNF, the current studies examined the effects of the rs6265 SNP on therapeutic efficacy and side-effect development following primary dopamine (DA) neuron transplantation. Considering the significant reduction in BDNF release associated with rs6265, we hypothesized that rs6265-mediated dysfunctional BDNF signaling contributes to the limited clinical benefit observed in a subpopulation of PD patients despite robust survival of grafted DA neurons, and further, that this mutation contributes to the development of aberrant graft-induced dyskinesias (GID). To this end, we generated a CRISPR knock-in rat model of the rs6265 BDNF SNP to examine for the first time the influence of a common genetic polymorphism on graft survival, functional efficacy, and side-effect liability, comparing these parameters between wild-type (Val/Val) rats and those homozygous for the variant Met allele (Met/Met). Counter to our hypothesis, the current research indicates that Met/Met rats show enhanced graft-associated therapeutic efficacy and a paradoxical enhancement of graft-derived neurite outgrowth compared to wild-type rats. However, consistent with our hypothesis, we demonstrate that the rs6265 genotype in the host rat is strongly linked to development of GID, and that this behavioral phenotype is significantly correlated with neurochemical signatures of atypical glutamatergic neurotransmission by grafted DA neurons.

Rho kinase inhibitor fasudil reduces l-DOPA-induced dyskinesia in a rat model of Parkinson's disease

BACKGROUND AND PURPOSE

Rho kinase (ROCK) activation is involved in neuroinflammatory processes leading to progression of neurodegenerative diseases such as Parkinson's disease. Furthermore, ROCK plays a major role in angiogenesis. Neuroinflammation and angiogenesis are mechanisms involved in developing l-DOPA-induced dyskinesias (LID). However, it is not known whether ROCK plays a role in LID and whether ROCK inhibitors may be useful against LID.

EXPERIMENTAL APPROACH

In rats, we performed short- and long-term dopaminergic lesions using 6-hydroxydopamine and developed a LID model. Effects of dopaminergic lesions and LID on the RhoA/ROCK levels were studied by western blot, real-time PCR analyses and ROCK activity assays in the substantia nigra and striatum. The effects of the ROCK inhibitor fasudil on LID were particularly investigated.

KEY RESULTS

Short-term 6-hydroxydopamine lesions increased nigrostriatal RhoA/ROCK expression, apparently related to the active neuroinflammatory process. However, long-term dopaminergic denervation (completed and stabilized lesions) led to a decrease in RhoA/ROCK levels. Rats with LID showed a significant increase of RhoA and ROCK expression. The development of LID was reduced by the ROCK inhibitor fasudil (10 and 40 mg·kg^-1 ), without interfering with the therapeutic effect of l-DOPA. Interestingly, treatment of 40 mg·kg^-1 of fasudil also induced a significant reduction of dyskinesia in rats with previously established LID.

CONCLUSION AND IMPLICATIONS

The present results suggest that ROCK is involved in the pathophysiology of LID and that ROCK inhibitors such as fasudil may be a novel target for preventing or treating LID. Furthermore, previous studies have revealed neuroprotective effects of ROCK inhibitors.

Preclinical evidence in support of repurposing sub-anesthetic ketamine as a treatment for L-DOPA-induced dyskinesia

Parkinson's disease (PD) is the second most common neurodegenerative disease. Pharmacotherapy with L-DOPA remains the gold-standard therapy for PD, but is often limited by the development of the common side effect of L-DOPA-induced dyskinesia (LID), which can become debilitating. The only effective treatment for disabling dyskinesia is surgical therapy (neuromodulation or lesioning), therefore effective pharmacological treatment of LID is a critical unmet need. Here, we show that sub-anesthetic doses of ketamine attenuate the development of LID in a rodent model, while also having acute anti-parkinsonian activity. The long-term anti-dyskinetic effect is mediated by brain-derived neurotrophic factor-release in the striatum, followed by activation of ERK1/2 and mTOR pathway signaling. This ultimately leads to morphological changes in dendritic spines on striatal medium spiny neurons that correlate with the behavioral effects, specifically a reduction in the density of mushroom spines, a dendritic spine phenotype that shows a high correlation with LID. These molecular and cellular changes match those occurring in hippocampus and cortex after effective sub-anesthetic ketamine treatment in preclinical models of depression, and point to common mechanisms underlying the therapeutic efficacy of ketamine for these two disorders. These preclinical mechanistic studies complement current ongoing clinical testing of sub-anesthetic ketamine for the treatment of LID by our group, and provide further evidence in support of repurposing ketamine to treat individuals with PD. Given its clinically proven therapeutic benefit for both treatment-resistant depression and several pain states, very common co-morbidities in PD, sub-anesthetic ketamine could provide multiple therapeutic benefits for PD in the future.

Actively targeted gold nanoparticle composites improve behavior and cognitive impairment in Parkinson's disease mice

Parkinson's disease (PD) is characterized by motor and non-motor symptoms, primarily affecting dopaminergic neurons (DAergic neurons) in substantia nigra (SN). However, it is still very challenging to identify new drugs that not only inhibit motor dysfunction but also improve non-motor dysfunction. It has been identified as a potential PD treatment that the inhibition of α-syn aggregation could decrease the death of DAergic neurons in SN. In this study, we synthesized gold nanoparticle composites (NPs) that were loaded with plasmid DNA (pDNA) to inhibit α-syn expression. In vivo, our results showed that NPs improved tyrosine hydroxylase (TH) levels and decreased aggregation of α-syn in the SN. Additionally, NPs attenuated motor dysfunction and exploration ability declined. Moreover, NPs reversed the inhibition of long-term potentiation (LTP) and improved non-motor dysfunction in PD mice. These results indicated that NPs had significantly neuroprotective effects not only in motor, but also in non-motor dysfunction to PD mice, providing a new strategy for gene therapy in PD.

Cortico-Striatal Oscillations Are Correlated to Motor Activity Levels in Both Physiological and Parkinsonian Conditions

Oscillatory neural activity in the cortico-basal ganglia-thalamocortical (CBGTC) loop is associated with the motor state of a subject, but also with the availability of modulatory neurotransmitters. For example, increased low-frequency oscillations in Parkinson’s disease (PD) are related to decreased levels of dopamine and have been proposed as biomarkers to adapt and optimize therapeutic interventions, such as deep brain stimulation. Using neural oscillations as biomarkers require differentiating between changes in oscillatory patterns associated with parkinsonism vs. those related to a subject’s motor state. To address this point, we studied the correlation between neural oscillatory activity in the motor cortex and striatum and varying degrees of motor activity under normal and parkinsonian conditions. Using rats with bilateral or unilateral 6-hydroxydopamine lesions as PD models, we correlated the motion index (MI)—a measure based on the physical acceleration of the head of rats—to the local field potential (LFP) oscillatory power in the 1–80 Hz range. In motor cortices and striata, we observed a robust correlation between the motion index and the oscillatory power in two main broad frequency ranges: a low-frequency range [5.0–26.5 Hz] was negatively correlated to motor activity, whereas a high-frequency range [35.0–79.9 Hz] was positively correlated. We observed these correlations in both normal and parkinsonian conditions. In addition to these general changes in broad-band power, we observed a more restricted narrow-band oscillation [25–40 Hz] in dopamine-denervated hemispheres. This oscillation, which seems to be selective to the parkinsonian state, showed a linear frequency dependence on the concurrent motor activity level. We conclude that, independently of the parkinsonian condition, changes in broad-band oscillatory activities of cortico-basal ganglia networks (including changes in the relative power of low- and high-frequency bands) are closely correlated to ongoing motions, most likely reflecting he operations of these neural circuits to control motor activity. Hence, biomarkers based on neural oscillations should focus on specific features, such as narrow frequency bands, to allow differentiation between parkinsonian states and physiological movement-dependent circuit modulation.

L-DOPA-Induced Dyskinesia in a Genetic Drosophila Model of Parkinson's Disease

Motor symptoms in Parkinson’s disease (PD) are directly related to the reduction of a neurotransmitter dopamine. Therefore, its precursor L-DOPA became the gold standard for PD treatment. However, chronic use of L-DOPA causes uncontrollable, involuntary movements, called L-DOPA-induced dyskinesia (LID) in the majority of PD patients. LID is complicated and very difficult to manage. Current rodent and non-human primate models have been developed to study LID mainly using neurotoxins. Therefore, it is necessary to develop a LID animal model with defects in genetic factors causing PD in order to study the relation between LID and PD genes such as α-synuclein. In this study, we first showed that a low concentration of L-DOPA (100 µM) rescues locomotion defects (i.e., speed, angular velocity, pause time) in Drosophila larvae expressing human mutant α-synuclein (A53T). This A53T larval model of PD was used to further examine dyskinetic behaviors. High concentrations of L-DOPA (5 or 10 mM) causes hyperactivity such as body bending behavior (BBB) in A53T larva, which resembles axial dyskinesia in rodents. Using ImageJ plugins and other third party software, dyskinetic BBB has been accurately and efficiently quantified. Further, we showed that a dopamine agonist pramipexole (PRX) partially rescues BBB caused by high L-DOPA. Our Drosophila genetic LID model will provide an important experimental platform to examine molecular and cellular mechanisms underlying LID, to study the role of PD causing genes in the development of LID, and to identify potential targets to slow/reverse LID pathology.

Striatal Nurr1, but not FosB expression links a levodopa-induced dyskinesia phenotype to genotype in Fisher 344 vs. Lewis hemiparkinsonian rats

Numerous genes, and alterations in their expression, have been identified as risk factors for developing levodopa-induced dyskinesia (LID). However, our understanding of the complexities of molecular changes remains insufficient for development of clinical treatment. In the current study we used gene array, in situ hybridization, immunohistochemistry, and microdialysis to provide a unique compare and contrast assessment of the relationship of four candidate genes to LID, employing three genetically distinct rat strains (Sprague-Dawley (SD), Fischer-344 (F344) and Lewis-RT.1) showing differences in dyskinesia susceptibility and 'first-ever LID' versus 'chronic LID' expression in subjects displaying equal dyskinesia severity. In these studies, rat strains were easily distinguishable for their LID propensity with: 1) a majority of SD rats expressing LID (LID+) and a subset being resistant (LID-); 2) all F344 rats readily developing (LID+); and 3) all Lewis rats being LID-resistant (LID-). Following chronic levodopa, LID+ SD rats showed significant increases in candidate gene expression: Nr4a2/(Nurr1) > > Trh > Inhba = Fosb. However, SD rats with long-standing striatal dopamine (DA) depletion treated with first-ever versus chronic high-dose levodopa revealed that despite identical levels of LID severity: 1) Fosb and Nurr1 transcripts but not protein were elevated with acute LID expression; 2) FOSB/ΔFOSB and NURR1 proteins were elevated only with chronic LID; and 3) Trh transcript and protein were elevated only with chronic LID. Strikingly, despite similar levodopa-induced striatal DA release in both LID-expressing F344 and LID-resistant Lewis rats, Fosb, Trh, Inhba transcripts were significantly elevated in both strains; however, Nurr1 mRNA was significantly increased only in LID+ F344 rats. These findings suggest a need to reevaluate currently accepted genotype-to-phenotype relationships in the expression of LID, specifically that of Fosb, a transcription factor generally assumed to play a causal role, and Nurr1, a transcription factor that has received significant attention in PD research linked to its critical role in the survival and function of midbrain DA neurons but who's striatal expression, generally below levels of detection, has remained largely unexplored as a regulator of LID. Finally these studies introduce a novel 'model' (inbred F344 vs inbred Lewis) that may provide a powerful tool for investigating the role for 'dyskinesia-resistance' genes downstream of 'dyskinesia-susceptibility' genes in modulating LID expression, a concept that has received considerably less attention and offers a new ways of thinking about antidyskinetic therapies.

Animal models for preclinical Parkinson's research: An update and critical appraisal

Animal models of Parkinson's disease (PD) are essential to investigate pathogenic pathways at the whole-organism level. Moreover, they are necessary for a preclinical investigation of potential new therapies. Different pathological features of PD can be induced in a variety of invertebrate and vertebrate species using toxins, drugs, or genetic perturbations. Each model has a particular utility and range of applicability. Invertebrate PD models are particularly useful for high throughput-screening applications, whereas mammalian models are needed to explore complex motor and non-motor features of the human disease. Here, we provide a comprehensive review and critical appraisal of the most commonly used mammalian models of PD, which are produced in rats and mice. A substantial loss of nigrostriatal dopamine neurons is necessary for the animal to exhibit a hypokinetic motor phenotype responsive to dopaminergic agents, thus resembling clinical PD. This level of dopaminergic neurodegeneration can be induced using specific neurotoxins, environmental toxicants, or proteasome inhibitors. Alternatively, nigrostriatal dopamine degeneration can be induced via overexpression of α-synuclein using viral vectors or transgenic techniques. In addition, protein aggregation pathology can be triggered by inoculating preformed fibrils of α-synuclein in the substantia nigra or the striatum. Thanks to the conceptual and technical progress made in the past few years a vast repertoire of well-characterized animal models are currently available to address different aspects of PD in the laboratory.

Integrated transcriptome expression profiling reveals a novel lncRNA associated with L-DOPA-induced dyskinesia in a rat model of Parkinson's disease

Levodopa-induced dyskinesia (LID) is a common complication of chronic dopamine replacement therapy in the treatment of Parkinson's disease (PD). Long noncoding RNAs regulate gene expression and participate in many biological processes. However, the role of long noncoding RNAs in LID is not well understood. In the present study, we examined the lncRNA transcriptome profile of a rat model of PD and LID by RNA sequence and got a subset of lncRNAs, which were gradually decreased during the development of PD and LID. We further identified a previously uncharacterized long noncoding RNA, NONRATT023402.2, and its target genes glutathione S-transferase omega (Gsto)2 and prostaglandin E receptor (Ptger)3. All of them were decreased in the PD and LID rats as shown by quantitative real-time PCR, fluorescence in situ hybridization and western blotting. Pearson's correlation analysis showed that their expression was positively correlated with the dyskinesia score of LID rats. In vitro experiments by small interfering RNA confirmed that slicing NONRATT023402 inhibited Gsto2 and Ptger3 and promoted the inflammatory response. These results demonstrate that NONRATT023402.2 may have inhibitive effects on the development of PD and LID.

In Silico and In Vivo Studies on Quercetin as Potential Anti-Parkinson Agent

Parkinson's disease (PD) is a major cause of morbidity and mortality among older individuals. Several researchers have suggested that iron chelators which cross the blood-brain barrier (BBB) might have clinical efficacy in treating PD. Therefore, efforts are made not only in order to improve the effect of L-dopa but also to introduce drugs which provide anti-parkinsonian and neuroprotective effects. In this study, quercetin, a flavonoid, exhibited noticeable neuroprotective effects via iron induced-oxidative stress-dependent apoptotic pathways. Our results suggested that quercetin significantly decreased the catalepsy and exhibited neuroprotective effects in rotenone-induced Parkinson. A model of rotenone-induced Parkinsonism in rats produced the decrease in glutathione, SOD, catalase, and serum iron concentration and the increase in H2O2 and lipid peroxidation activity. Quercetin efficiently halted the deleterious toxic effects of L-dopa, revealing normalization of catalepsy and rotarod score, in addition to amelioration of neurochemical parameters, indicating benefit of both symptomatic and neuroprotective therapies. In silico molecular docking studies have also shown that quercetin could be an ideal potential drug target for aromatic L-amino acid decarboxylase and human catechol-O-methyltransferase. In conclusion, quercetin possesses strong iron-chelating abilities and could be recommended as a disease-modifying therapy when administered in combination with L-dopa, early on in the course of Parkinson's disease.

Dyskinesia matters

Levodopa-induced dyskinesia (LID) represents a significant source of discomfort for people with Parkinson's disease (PD). It negatively affects quality of life, it is associated with both motor and nonmotor fluctuations, and it brings an increased risk of disability, balance problems, and falls. Although the prevalence of severe LID appears to be lower than in previous eras (likely owing to a more conservative use of oral levodopa), we have not yet found a way to prevent the development of this complication. Advanced surgical therapies, such as deep brain stimulation, ameliorate LID, but only a minority of PD patients qualify for these interventions. Although some have argued that PD patients would rather be ON with dyskinesia than OFF, the deeper truth is that patients would very much prefer to be ON without dyskinesia. As researchers and clinicians, we should aspire to make that goal a reality. To this end, translational research on LID is to be encouraged and persistently pursued. © 2019 International Parkinson and Movement Disorder Society.

Menagerie: A text-mining tool to support animal-human translation in neurodegeneration research

Discovery studies in animals constitute a cornerstone of biomedical research, but suffer from lack of generalizability to human populations. We propose that large-scale interrogation of these data could reveal patterns of animal use that could narrow the translational divide. We describe a text-mining approach that extracts translationally useful data from PubMed abstracts. These comprise six modules: species, model, genes, interventions/disease modifiers, overall outcome and functional outcome measures. Existing National Library of Medicine natural language processing tools (SemRep, GNormPlus and the Chemical annotator) underpin the program and are further augmented by various rules, term lists, and machine learning models. Evaluation of the program using a 98-abstract test set achieved F1 scores ranging from 0.75-0.95 across all modules, and exceeded F1 scores obtained from comparable baseline programs. Next, the program was applied to a larger 14,481 abstract data set (2008-2017). Expected and previously identified patterns of species and model use for the field were obtained. As previously noted, the majority of studies reported promising outcomes. Longitudinal patterns of intervention type or gene mentions were demonstrated, and patterns of animal model use characteristic of the Parkinson's disease field were confirmed. The primary function of the program is to overcome low external validity of animal model systems by aggregating evidence across a diversity of models that capture different aspects of a multifaceted cellular process. Some aspects of the tool are generalizable, whereas others are field-specific. In the initial version presented here, we demonstrate proof of concept within a single disease area, Parkinson's disease. However, the program can be expanded in modular fashion to support a wider range of neurodegenerative diseases.