Sodium nitroprusside enhances stepping test performance and increases medium spiny neurons responsiveness to cortical inputs in a rat model of Levodopa-induced dyskinesias.

Levodopa (L-DOPA) is the classical gold standard treatment for Parkinson's disease. However, its chronic administration can lead to the development of L-DOPA-induced dyskinesias (LIDs). Dysregulation of the nitric oxide-cyclic guanosine monophosphate pathway in striatal networks has been linked to deficits in corticostriatal transmission in LIDs. This study investigated the effects of the nitric oxide (NO) donor sodium nitroprusside (SNP) on behavioural and electrophysiological outcomes in sham-operated and 6-hydroxydopamine-lesioned rats chronically treated with vehicle or L-DOPA, respectively. In sham-operated animals, systemic administration of SNP increased the spike probability of putative striatal medium spiny neurons (MSNs) in response to electrical stimulation of the primary motor cortex. In 6-hydroxydopamine-lesioned animals, SNP improved the stepping test performance without exacerbating abnormal involuntary movements. Additionally, SNP significantly increased the responsiveness of putative striatal MSNs in the dyskinetic striatum. These findings highlight the critical role of the NO signalling pathway in facilitating the responsiveness of striatal MSNs in both the intact and dyskinetic striata. The study suggests that SNP has the potential to enhance L-DOPA's effects in the stepping test without exacerbating abnormal involuntary movements, thereby offering new possibilities for optimizing Parkinson's disease therapy. In conclusion, this study highlights the involvement of the NO signalling pathway in the pathophysiology of LIDs.

Diametric neural ensemble dynamics in parkinsonian and dyskinetic states.

Loss of dopamine in Parkinson's disease is hypothesized to impede movement by inducing hypo- and hyperactivity in striatal spiny projection neurons (SPNs) of the direct (dSPNs) and indirect (iSPNs) pathways in the basal ganglia, respectively. The opposite imbalance might underlie hyperkinetic abnormalities, such as dyskinesia caused by treatment of Parkinson's disease with the dopamine precursor L-DOPA. Here we monitored thousands of SPNs in behaving mice, before and after dopamine depletion and during L-DOPA-induced dyskinesia. Normally, intermingled clusters of dSPNs and iSPNs coactivated before movement. Dopamine depletion unbalanced SPN activity rates and disrupted the movement-encoding iSPN clusters. Matching their clinical efficacy, L-DOPA or agonism of the D2 dopamine receptor reversed these abnormalities more effectively than agonism of the D1 dopamine receptor. The opposite pathophysiology arose in L-DOPA-induced dyskinesia, during which iSPNs showed hypoactivity and dSPNs showed unclustered hyperactivity. Therefore, both the spatiotemporal profiles and rates of SPN activity appear crucial to striatal function, and next-generation treatments for basal ganglia disorders should target both facets of striatal activity.

A novel giant non-cholinergic striatal interneuron restricted to the ventrolateral striatum coexpresses Kv3.3 potassium channel, parvalbumin, and the vesicular GABA transporter.

The striatum is the main input structure of the basal ganglia. Distinct striatal subfields are involved in voluntary movement generation and cognitive and emotional tasks, but little is known about the morphological and molecular differences of striatal subregions. The ventrolateral subfield of the striatum (VLS) is the orofacial projection field of the sensorimotor cortex and is involved in the development of orofacial dyskinesias, involuntary chewing-like movements that often accompany long-term neuroleptic treatment. The biological basis for this particular vulnerability of the VLS is not known. Potassium channels are known to be strategically localized within the striatum. In search of possible molecular correlates of the specific vulnerability of the VLS, we analyzed the expression of voltage-gated potassium channels in rodent and primate brains using qPCR, in situ hybridization, and immunocytochemical single and double staining. Here we describe a novel, giant, non-cholinergic interneuron within the VLS. This neuron coexpresses the vesicular GABA transporter, the calcium-binding protein parvalbumin (PV), and the Kv3.3 potassium channel subunit. This novel neuron is much larger than PV neurons in other striatal regions, displays characteristic electrophysiological properties, and, most importantly, is restricted to the VLS. Consequently, the giant striatal Kv3.3-expressing PV neuron may link compromised Kv3 channel function and VLS-based orofacial dyskinesias.

Striatal Synaptic Dysfunction in Dystonia and Levodopa-Induced Dyskinesia.

This review provides an overview of the synaptic dysfunctions of neuronal circuits and underlying neurochemical alterations observed in the hyperkinetic movement disorders, dystonia and dyskinesia. These disorders exhibit similar changes in expression of synaptic plasticity and neuromodulation. This includes alterations in physical attributes of synapses, synaptic protein expression, and neurotransmitter systems, such as glutamate and gamma-aminobutyric acid (GABA), and neuromodulators, such as dopamine, acetylcholine, serotonin, adenosine, and endocannabinoids. A full understanding of the mechanisms and consequences of disruptions in synaptic function and plasticity will lend insight into the development of these disorders and new ways to combat maladaptive changes.

Cardiac Noradrenaline Turnover and Heat Shock Protein 27 Phosphorylation in Dyskinetic Monkeys.

BACKGROUND: Autonomic dysfunction is a well-known dominant symptom in the advanced stages of Parkinson's disease. However, the role of cardiac sympathetic nerves still needs to be elucidated. OBJECTIVES: To evaluate cardiac sympathetic response in Parkinsonian and dyskinetic monkeys. METHODS: Adult male monkeys were divided into 1 of the following 3 groups: controls, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated monkeys, and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine+levodopa-treated animals. Noradrenaline, its metabolite normetanephrine, and phospho-Heat shock proten 27 (p-Hsp27) at serine 82 levels were analyzed in the left and right ventricles of the heart. Tyrosine hydroxylase immunohistochemistry was performed in the ventral mesencephalon. RESULTS: The results were the following: (1) 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine intoxication significantly increased normetanephrine levels and decreased noradrenaline turnover in the right ventricle without changes in the left ventricle; however, (2) levodopa treatment decreased noradrenaline levels and enhanced the normetanephrine/noradrenaline ratio in parallel with a very significant increase of Hsp27 activity in both ventricles. CONCLUSIONS: Levodopa treatment could induce protective cardiac effects through the increased Hsp27 activity. © 2019 International Parkinson and Movement Disorder Society.

Presynaptic dopamine depletion determines the timing of levodopa-induced dyskinesia onset in Parkinson's disease.

PURPOSE: Reduced presynaptic dopaminergic activity plays an important role in the development of levodopa-induced dyskinesia (LID) in Parkinson's disease (PD). In this study, we investigated whether dopaminergic function in the nigrostriatal system is associated with the timing of LID onset. METHODS: From among 412 drug-naive PD patients who underwent a dopamine transporter (DAT) PET scan during their baseline evaluation, we enrolled 65 patients who developed LID during a follow-up period of >2 years. Based on the time from PD onset, LID was classified as early, intermediate or late onset. We then compared DAT availability in the striatal subregions of the patients in the three groups. RESULTS: The demographic characteristics did not differ among the three patient groups except for earlier intervention of levodopa therapy in the early LID onset group (p = 0.001). After adjusting for age at PD onset, gender, timing of levodopa therapy from PD onset, and the severity of PD motor symptoms, DAT activity in the posterior putamen was found to be significantly lower in the early LID onset group than in the late LID onset group (p = 0.017). Multivariate linear regression analysis showed that low DAT activity in the posterior putamen was significantly associated with the early appearance of LID in the early LID onset group (ß = 16.039, p = 0.033). CONCLUSION: This study demonstrated that low DAT activity in the posterior putamen at baseline is a major risk factor for the early onset of LID in patients with PD, suggesting that the degree of presynaptic dopaminergic denervation plays an important role in determining the timing of LID onset.

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.

Effects of Fish and Grape Seed Oils as Core of Haloperidol-Loaded Nanocapsules on Oral Dyskinesia in Rats.

Haloperidol is a widely used antipsychotic, despite the severe motor side effects associated with its chronic use. This study was carried out to compare oral dyskinesia induced by different formulations of haloperidol-loaded nanocapsules containing caprylic/capric triglycerides, fish oil or grape seed oil (GSO) as core, as well as free haloperidol. Haloperidol-loaded lipid-core nanocapsules formulations were prepared, physicochemical characterized and administered (0.5 mg kg-1-ip) to rats for 28 days. Oral dyskinesia was evaluated acutely and subchronically and after that cell viability and free radical generation in cortex and substantia nigra. All formulations presented satisfactory physicochemical parameters. Acutely, all formulations were able to prevent oral dyskinesia development in comparison to free haloperidol, except haloperidol-loaded nanocapsules containing GSO, whose effect was only partial. After subchronic treatment, all haloperidol-loaded nanocapsules formulations prevented oral dyskinesia in relation to free drug. Also, haloperidol-loaded nanocapsules containing fish oil and GSO were more effective than caprylic/capric triglycerides nanocapsules and free haloperidol in cell viability preservation and control of free radical generation. Our findings showed that fish oil formulation may be considered as the best formulation of haloperidol-loaded lipid-core nanocapsules, being able to prevent motor side effects associated with chronic use of antipsychotic drugs, as haloperidol.

Targeting ß-arrestin2 in the treatment of L-DOPA-induced dyskinesia in Parkinson's disease.

Parkinson's disease (PD) is characterized by severe locomotor deficits and is commonly treated with the dopamine (DA) precursor l-3,4-dihydroxyphenylalanine (L-DOPA), but its prolonged use causes dyskinesias referred to as L-DOPA-induced dyskinesias (LIDs). Recent studies in animal models of PD have suggested that dyskinesias are associated with the overactivation of G protein-mediated signaling through DA receptors. ß-Arrestins desensitize G protein signaling at DA receptors (D1R and D2R) in addition to activating their own G protein-independent signaling events, which have been shown to mediate locomotion. Therefore, targeting ß-arrestins in PD L-DOPA therapy might prove to be a desirable approach. Here we show in a bilateral DA-depletion mouse model of Parkinson's symptoms that genetic deletion of ß-arrestin2 significantly limits the beneficial locomotor effects while markedly enhancing the dyskinesia-like effects of acute or chronic L-DOPA treatment. Viral rescue or overexpression of ß-arrestin2 in knockout or control mice either reverses or protects against LIDs and its key biochemical markers. In other more conventional animal models of DA neuron loss and PD, such as 6-hydroxydopamine-treated mice or rats and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated nonhuman primates, ß-arrestin2 overexpression significantly reduced dyskinesias while maintaining the therapeutic effect of L-DOPA. Considerable efforts are being spent in the pharmaceutical industry to identify therapeutic approaches to block LIDs in patients with PD. Our results point to a potential therapeutic approach, whereby development of either a genetic or pharmacological intervention to enhance ß-arrestin2- or limit G protein-dependent D1/D2R signaling could represent a more mechanistically informed strategy.

Cortical areas involved in behavioral expression of external pallidum dysfunctions: A PET imaging study in non-human primates.

The external pallidum (GPe) is a component of the indirect pathway centrally placed in the basal ganglia. Studies already demonstrated that the pharmacological disinhibition of the sensorimotor, associative, and limbic GPe produced dyskinesia, hyperactivity, and compulsive behaviors, respectively. The aim of this study was to investigate the cortical regions altered by the disinhibition of each GPe functional territory. Thus, 5 macaques were injected with bicuculline in sensorimotor, associative, and limbic sites of the GPe producing dyskinesia, hyperactivity, and compulsive behaviors, and underwent in vivo positron tomography with 18F-2-fluoro-2-deoxy-D-glucose to identify cortical dysfunctions related to GPe disinhibition. Blood cortisol levels were also quantified as a biomarker of anxiety for each condition. Our results showed that pallidal bicuculline injections in anesthetized animals reproducibly modified the activity of specific ipsilateral and contralateral cortical areas depending on the pallidal territory targeted. Bicuculline injections in the limbic GPe led to increased ipsilateral activations in limbic cortical regions (anterior insula, amygdala, and hippocampus). Injections in the associative vs. sensorimotor GPe increased the activity in the ipsilateral midcingulate vs. somatosensory and parietal cortices. Moreover, bicuculline injections increased blood cortisol levels only in animals injected in their limbic GPe. These are the first functional results supporting the model of opened cortico-striato-thalamo-cortical loops where modifications in a functional pallidal territory can impact cortical activities of the same functional territory but also cortical activities of other functional territories. This highlights the importance of the GPe as a crucial node in the top-down control of the cortico-striato-thalamo-cortical circuits from the frontal cortex to influence the perception, attention, and emotional processes at downstream (or non-frontal) cortical levels. Finally, we showed the implication of the ventral pallidum with the amygdala and the insular cortex in a circuit related to aversive processing that should be crucial for the production of anxious disorders.

A new target for Parkinson's disease: Small molecule SERCA activator CDN1163 ameliorates dyskinesia in 6-OHDA-lesioned rats.

Endoplasmic reticulum (ER) stress is intimately linked to Parkinson's disease (PD) pathophysiology. Disrupted intracellular calcium homeostasis is a major cause of the ER stress seen in dopaminergic neurons, leading to the cell death and subsequent loss of movement and coordination in patients. Dysfunctional calcium handling proteins play a major role in the promulgation of ER stress in PD. Specifically, compromised sarco/endoplasmic reticulum Ca2+-ATPase (SERCA) has been identified as a major cause of ER stress and neuron loss in PD. We have identified a small molecule activator of SERCA that increases ER calcium content, rescues neurons from ER stress-induced cell death in vitro, and shows significant efficacy in the rat 6-hydroxydopamine (6-OHDA) model of PD. Together, these results support targeting SERCA activation as a viable strategy to develop disease-modifying therapeutics for PD.

Clinical and molecular analysis of 6 Chinese patients with isoleucine metabolism defects: identification of 3 novel mutations in the HSD17B10 and ACAT1 gene.

Hydroxysteroid (17ß) dehydrogenase 10 (HSD10) and mitochondrial acetoacetyl-CoA thiolase (ß-KT) are two adjacent enzymes for the degradation of isoleucine, thus HSD10 and ß-KT deficiencies are confusing at an early stage because of nearly the same elevation of typical metabolites in urine, such as 2-methyl-3-hydroxybutyric acid (2M3HBA) and tiglylglycine (TG). In order to better understand the differences between these two disorders, we described the clinical and molecular characteristics of two HSD10 deficiency patients and four ß-KT deficiency patients. ß-KT deficiency patients had a much more favorable outcome than that of HSD10 deficiency patients, indicating that the multifunction of HSD10, especially neurosteroid metabolic activity, other than only enzymatic degradation of isoleucine, is involved in the pathogenesis of HSD10 deficiency. Two different mutations, a novel mutation p.Ile175Met and a reported mutation p.Arg226Gln, were detected in the HSD17B10 gene of HSD10 deficiency patients. Six different mutations, including four known mutations: p.Ala333Pro, p.Thr297Lys, c.83_84delAT, c.1006-1G > C, and two novel mutations: p.Thr277Pro and c.121-3C > G were identified in the ACAT1 gene of ß-KT deficiency patients. In general, DNA diagnosis played an important role in distinguishing between these two disorders.

Glutamatergic pathways as a target for the treatment of dyskinesias in Parkinson's disease.

PD (Parkinson's disease) is characterized by some typical motor features that are caused by striatal dopamine depletion and respond well to dopamine-replacement therapy with L-dopa. Unfortunately, the majority of PD patients treated with L-dopa develop abnormal involuntary movements (dyskinesias) within a few years. The mechanisms underlying the development of LIDs (L-dopa-induced dyskinesias) involve, on one hand, a presynaptic dysregulation of dopamine release and clearance and, on the other hand, an abnormal postsynaptic response to dopamine in the brain. There is a large amount of evidence that these dopamine-dependent mechanisms are modulated by glutamatergic pathways and glutamate receptors. The present article summarizes the pathophysiological role of glutamatergic pathways in LID and reviews pre-clinical and clinical results obtained using pharmacological modulators of different classes and subtypes of glutamate receptors to treat parkinsonian dyskinesias.

Enhanced striatal cholinergic neuronal activity mediates L-DOPA-induced dyskinesia in parkinsonian mice.

Treatment of Parkinson disease (PD) with L-3,4-dihydroxyphenylalanine (L-DOPA) dramatically relieves associated motor deficits, but L-DOPA-induced dyskinesias (LID) limit the therapeutic benefit over time. Previous investigations have noted changes in striatal medium spiny neurons, including abnormal activation of extracellular signal-regulated kinase1/2 (ERK). Using two PD models, the traditional 6-hydroxydopamine toxic lesion and a genetic model with nigrostriatal dopaminergic deficits, we found that acute dopamine challenge induces ERK activation in medium spiny neurons in denervated striatum. After repeated L-DOPA treatment, however, ERK activation diminishes in medium spiny neurons and increases in striatal cholinergic interneurons. ERK activation leads to enhanced basal firing rate and stronger excitatory responses to dopamine in striatal cholinergic neurons. Pharmacological blockers of ERK activation inhibit L-DOPA-induced changes in ERK phosphorylation, neuronal excitability, and the behavioral manifestation of LID. In addition, a muscarinic receptor antagonist reduces LID. These data indicate that increased dopamine sensitivity of striatal cholinergic neurons contributes to the expression of LID, which suggests novel therapeutic targets for LID.

Regulation of the dopaminergic system in a murine model of aromatic L-amino acid decarboxylase deficiency.

Aromatic l-amino acid decarboxylase (AADC) is responsible for the syntheses of dopamine and serotonin. Children with AADC deficiency exhibit compromised development, particularly with regard to their motor functions. Currently, no animal model of AADC deficiency exists. We inserted an AADC gene mutation (IVS6+4A>T) and a neomycin-resistance gene into intron 6 of the mouse AADC (Ddc) gene. In the brains of homozygous knock-in (KI) mice (Ddc(IVS6/IVS6)), AADC mRNA lacked exon 6, and AADC activity was <0.3% of that in wild-type mice. Half of the KI mice were born alive but grew poorly and exhibited severe dyskinesia and hindlimb clasping after birth. Two-thirds of the live-born KI mice survived the weaning period, with subsequent improvements in their growth and motor functions; however, these mice still displayed cardiovascular dysfunction and behavioral problems due to serotonin deficiencies. The brain dopamine levels in the KI mice increased from 9.39% of the levels in wild-type mice at 2weeks of age to 37.86% of the levels in wild-type mice at 8weeks of age. Adult KI mice also exhibited an exaggerated response to apomorphine and an elevation of striatal c-Fos expression, suggesting post-synaptic adaptations. Therefore, we generated an AADC deficient mouse model, in which compensatory regulation allowed the mice to survive to adulthood. This mouse model will be useful both for developing gene therapies for AADC deficiency and for designing treatments for diseases associated with neurotransmitter deficiency.

Topography of dyskinesias and torticollis evoked by inhibition of substantia nigra pars reticulata.

GABAergic neurons of the substantia nigra pars reticulata (SNpr) and globus pallidus pars interna (GPi) constitute the output pathways of the basal ganglia. In monkeys, choreiform limb dyskinesias have been described after inhibition of the GPi, but not the SNpr. Given the anatomical and functional similarities between these structures, we hypothesized that choreiform dyskinesias could be evoked by inhibition of an appropriate region within the SNpr. The GABAA receptor agonist, muscimol, was infused into various sites within the SNpr and the adjacent STN of freely moving macaques. The effect of the GABAA antagonist, bicuculline (BIC), was also examined. Muscimol (MUS) in SNpr evoked the following: (1) choreiform dyskinesias of the contralateral arm and/or leg from central and lateral sites; (2) contralaterally directed torticollis from central and posterior sites; and (3) contraversive quadrupedal rotation from anterior and lateral sites. MUS infusions into the adjacent SN pars compacta or STN were without effect, ruling out a contribution of drug spread to adjacent structures. BIC in SNpr induced ipsiversive postures without choreiform dyskinesia or torticollis, whereas in the STN, it evoked ballistic movements. This is the first report of choreiform dyskinesia evoked by inhibition of the SNpr. This highly site-specific effect was obtained from a restricted region within the SNpr distinct from that responsible for inducing torticollis. These results suggest that overactivity of different SNpr outputs mediates choreiform dyskinesia and torticollis. These abnormalities are symptoms of dystonia, Huntington's disease, and iatrogenic dyskinesias, suggesting that these conditions may result, in part, from a loss of function in SNpr efferent projections.

Amino acid transporter Asc-1 (SLC7A10) expression is altered in basal ganglia in experimental Parkinsonism and L-dopa-induced dyskinesia model mice.

In Parkinson's disease (PD), a decrease in dopamine levels in the striatum causes abnormal circuit activity in the basal ganglia, resulting in increased output via the substantia nigra pars reticulata (SNr). A characteristic feature of glutamatergic synaptic transmission in the basal ganglia circuitry under conditions of dopamine depletion is enhanced synaptic activity of NMDA receptors. However, the cause of this NMDA receptor hyperactivity is not fully understood. We focused on Asc-1 (SLC7A10), an alanine-serine-cysteine transporter, as one of the factors that regulate NMDA receptor activity by modulating D-serine and glycine concentration in synaptic clefts. We generated PD model mice by injection of 6-hydroxydopamine into the unilateral medial forebrain bundle and analyzed the expression level of Asc-1 mRNA in the nuclei of basal ganglia (the external segment of the globus pallidus (GPe), subthalamic nucleus (STN), and SNr) compared to control mice. Each nucleus was dissected using laser microdissection, and RNA was extracted and quantified by quantitative PCR. Asc-1 mRNA expression was significantly higher in the GPe and lower in the SNr under the PD state than that in control naïve mice. The STN showed no change in Asc-1 mRNA expression. We further modeled L-dopa-induced dyskinesia by administering L-dopa continuously for 14 days to the PD model mice and found that Asc-1 mRNA expression in the GPe and SNr became close to that of control mice, regardless of the presence of abnormal involuntary movements. The present study revealed that Asc-1 mRNA expression is differentially regulated in the basal ganglionic nuclei in response to striatal dopamine concentration (depleted or replenished) and suggests that Asc-1 can be a therapeutic target for the amelioration of motor symptoms of PD.

Delayed postnatal loss of P/Q-type calcium channels recapitulates the absence epilepsy, dyskinesia, and ataxia phenotypes of genomic Cacna1a mutations.

Inherited loss of P/Q-type calcium channel function causes human absence epilepsy, episodic dyskinesia, and ataxia, but the molecular "birthdate" of the neurological syndrome and its dependence on prenatal pathophysiology is unknown. Since these channels mediate transmitter release at synapses throughout the brain and are expressed early in embryonic development, delineating the critical circuitry and onset underlying each of the emergent phenotypes requires targeted control of gene expression. To visualize P/Q-type Ca(2+) channels and dissect their role in neuronal networks at distinct developmental stages, we created a novel conditional Cacna1a knock-in mouse by inserting the floxed green fluorescent protein derivative Citrine into the first exon of Cacna1a and then crossed it with a postnatally expressing PCP2-Cre line for delayed Purkinje cell (PC) gene deletion within the cerebellum and sparsely in forebrain (purky). PCs in purky mice lacked P/Q-type calcium channel protein and currents within the first month after birth, displayed altered spontaneous firing, and showed impaired neurotransmission. Unexpectedly, adult purky mice exhibited the full spectrum of neurological deficits seen in mice with genomic Cacna1a ablation. Our results show that the ataxia, dyskinesia, and absence epilepsy caused by inherited disorders of the P/Q-type channel arise from signaling defects beginning in late infancy, revealing an early window of opportunity for therapeutic intervention.

Effects of L-DOPA and STN-HFS dyskinesiogenic treatments on NR2B regulation in basal ganglia in the rat model of Parkinson's disease.

Dyskinesia is a major side effect of chronic levodopa (L-DOPA) administration, the reference treatment for Parkinson's disease (PD). High-frequency stimulation of the subthalamic nucleus (STN-HFS) alleviates parkinsonian motor symptoms and indirectly improves dyskinesia by decreasing L-DOPA requirement. However, inadequate stimulation can also trigger dyskinetic movements in PD patients and animal models. Here, we investigated the possible association between L-DOPA- and STN-HFS-induced dyskinesia and regulation of the NR2B subunit of NMDA receptors in the rodent model of PD. We subjected 6-OHDA-lesioned rats to HFS for 1h, at an intensity triggering forelimb dyskinesia. Other 6-OHDA-lesioned rats were treated with chronic high doses of L-DOPA for ten days, to induce abnormal involuntary movements. The 6-OHDA lesion regulated NR2B only in the SNr, where the activation of NR2B was observed (as assessed by phosphorylation of the Tyr1472 residue). Both STN-HFS and L-DOPA dyskinesiogenic treatments induced NR2B activation in the STN and EP, but only L-DOPA triggered NR2B hyperphosphorylation in the striatum. Finally, the use of CP-101,606 exacerbated L-DOPA-induced motor behavior and associated NR2B hyperphosphorylation in the striatum, STN and EP. Thus, NR2B activation in basal ganglia structures is correlated with dyskinesia.

L-745,870 reduces L-DOPA-induced dyskinesia in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-lesioned macaque model of Parkinson's disease.

L-DOPA-induced dyskinesia remains an unmet challenge in the treatment of Parkinson's disease (PD). Here, we investigate the potential antidyskinetic efficacy of 3-([4-(4-chlorophenyl)piperazin-1-yl]methyl)-1H-pyrrolo[2,3-b]pyridine (L-745,870), a potent and selective dopamine D(4) receptor antagonist with a good toxicology profile and an excellent safety and tolerability record in phase I/II clinical studies, for non-PD indications. Six macaques were rendered parkinsonian by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine administration. After induction of stable and marked dyskinesia, animals were administered acute challenges of L-745,870 in combination with L-DOPA. To guarantee D(4) selectivity at the doses used in the study, we determined the plasma, cerebrospinal fluid, and brain levels of L-745,870. Coadministration of L-745,870 (1 mg/kg) and L-DOPA significantly reduced the severity of dyskinesia, by up to 59%, in comparison with L-DOPA alone (P < 0.01). L-745,870 had no effect on the duration of antiparkinsonian benefit (ON-time) (P > 0.05). However, L-745,870 (1 mg/kg) significantly increased the duration of ON-time without disabling dyskinesia (+204%; P < 0.001) and decreased duration of ON-time with disabling dyskinesia compared with L-DOPA alone (-56%; P < 0.01). Brain levels of L-745,870 (∼600 ng/g) were within the range at which L-745,870 provides selective D(4) receptor antagonism. Plasma levels were comparable with those demonstrated to be well tolerated in human studies. These data suggest that selective D(4) receptor antagonists represent a potential therapeutic approach for L-DOPA-induced dyskinesia. It is noteworthy that L-745,870 has already undergone significant clinical development, has an excellent profile for a therapeutic candidate, and could be advanced rapidly to phase IIa clinical studies for dyskinesia in PD.