Experimental and computational assessment of Antiparkinson Medication effects on meiofauna: Case study of Benserazide and Trihexyphenidyl.

Two concentrations (6.25 and 1.25 mg/L) were used for two Parkinson's disease medications, Benserazide, and Trihexyphenidyl, to test their effects on the meiobenthic nematofauna. It is predicted that these highly hydrosoluble drugs will end up in marine environments. The results showed that both medications when added alone, induced (i) important changes in the numbers and (ii) taxonomic composition. The impact of Benserazide and Trihexyphenidyl was also reflected in the (iii) functional traits of nematofauna, with the most affected categories following exposure being the trophic group 1B, the clavate tails, the circular amphids, the c-p2 life history, and the body length of 1-2 mm. These results were supported by the molecular interactions of the studied drugs with both GLD-3 and SDP proteins of Caenorhabditis elegans. (iv) The mixtures of both drugs did not show any changes in the nematode communities, suggesting that no synergistic or antagonistic interactions exist between them.

Levodopa versus levodopa sparing in early parkinson's disease: can we meet halfway?

Monotherapy is the recommended initial treatment for early Parkinson's disease. The pharmacological options for initial treatment include dopaminergic agonists, monoamine oxidase B inhibitors, and levodopa formulations. Several factors should be considered when selecting the optimal treatment, such as disease severity, disease duration, age, activity level, and the risk of developing motor and non-motor complications. Early evidence on the potential role of levodopa formulations in the risk of dyskinesia led to levodopa aversion in the late 1990s and early 2000s, favoring the use of levodopa-sparing options like dopamine agonists. This shift resulted in an increase in behavioral adverse effects, such as impulse control disorders, leading to a subsequent dopamine agonist aversion in the mid-2000s. This review aims to provide a comprehensive evaluation of the existing literature regarding the benefits and drawbacks of levodopa versus levodopa-sparing strategies in drug-naive early-stage Parkinson's disease.

Targets to Search for New Pharmacological Treatment in Idiopathic Parkinson's Disease According to the Single-Neuron Degeneration Model.

One of the biggest problems in the treatment of idiopathic Parkinson's disease is the lack of new drugs that slow its progression. L-Dopa remains the star drug in the treatment of this disease, although it induces severe side effects. The failure of clinical studies with new drugs depends on the use of preclinical models based on neurotoxins that do not represent what happens in the disease since they induce rapid and expansive neurodegeneration. We have recently proposed a single-neuron degeneration model for idiopathic Parkinson's disease that requires years to accumulate enough lost neurons for the onset of motor symptoms. This single-neuron degeneration model is based on the excessive formation of aminochrome during neuromelanin synthesis that surpass the neuroprotective action of the enzymes DT-diaphorase and glutathione transferase M2-2, which prevent the neurotoxic effects of aminochrome. Although the neurotoxic effects of aminochrome do not have an expansive effect, a stereotaxic injection of this endogenous neurotoxin cannot be used to generate a preclinical model in an animal. Therefore, the aim of this review is to evaluate the strategies for pharmacologically increasing the expression of DT diaphorase and GSTM2-2 and molecules that induce the expression of vesicular monoamine transporter 2, such as pramipexole.

Discovery of novel benzimidazole derivatives as selective and reversible monoamine oxidase B inhibitors for Parkinson's disease treatment.

Parkinson's disease (PD) is a common neurodegenerative disorder characterized by the loss of dopaminergic neurons in the substantia nigra pars compacta. The development of novel scaffolds for human monoamine oxidase B (hMAO-B) inhibitors with reversible properties represents an important strategy to improve the efficacy and safety for PD treatment. In the current work, we have devised and assessed two innovative derivative series serving as hMAO-B inhibitors. These series have utilized benzimidazole as a scaffold and strategically incorporated a primary amide group, which is recognized as a pivotal pharmacophore in subsequent activity screening and reversible mode of action. Among these compounds, 16d has emerged as the most potent hMAO-B inhibitor with an IC50 value of 67.3 nM, comparable to safinamide (IC50 = 42.6 nM) in vitro. Besides, 16d demonstrated good selectivity towards hMAO-B isoenzyme with a selectivity index over 387. Importantly, in line with the design purpose, 16d inhibited hMAO-B in a competitive and reversible manner (Ki = 82.50 nM). Moreover, 16d exhibited a good safety profile in both cellular and acute toxicity assays in mice. It also displayed ideal pharmacokinetic properties and blood-brain barrier permeability in vivo, essential prerequisites for central nervous system medicines. In the MPTP-induced PD mouse model, 16d significantly alleviated the motor impairment, especially muscle relaxation and motor coordination. Therefore, 16d, serving as a lead compound, holds instructive significance for subsequent investigations regarding its application in the treatment of PD.

Antimicrobial drugs for Parkinson's disease: Existing therapeutic strategies and novel drugs exploration.

Parkinson's disease (PD), the second most common neurodegenerative disorder, is characterized by loss of dopaminergic neurons in the substantia nigra, as well as the abnormal accumulation of misfolded α-synuclein. Clinically, PD is featured by typical motor symptoms and some non-motor symptoms. Up to now, although considerable progress has been made in understanding the pathogenesis of PD, there is still no effective therapeutic treatment for the disease. Thus, exploring new therapeutic strategies has been a topic that needs to be addressed urgently. Noteworthy, with the proposal of the microbiota-gut-brain axis theory, antimicrobial drugs have received significant attention due to their effects on regulating the intestinal microbiota. Nowadays, there is growing evidence showing that some antimicrobial drugs may be promising drugs for the treatment of PD. Data from pre-clinical and clinical studies have shown that some antimicrobial drugs may play neuroprotective roles in PD by modulating multiple biochemical and molecular pathways, including reducing α-synuclein aggregation, inhibiting neuroinflammation, regulating mitochondrial structure and function, as well as suppressing oxidative stress. In this paper, we summarized the effects of some antimicrobial drugs on PD treatment from recent pre-clinical and clinical studies. Then, we further discussed the potential of a few antimicrobial drugs for treating PD based on molecular docking and molecular dynamics simulation. Importantly, we highlighted the potential of clorobiocin as the therapeutic strategy for PD owing to its ability to inhibit α-synuclein aggregation. These results will help us to better understand the potential of antimicrobial drugs in treating PD and how antimicrobial drugs may alleviate or reverse the pathological symptoms of PD.

Differential effects of opioid receptor antagonism on the anti-dyskinetic and anti-parkinsonian effects of sub-anesthetic ketamine treatment in a preclinical model.

Sub-anesthetic ketamine treatment has been shown to be an effective therapy for treatment-resistant depression and chronic pain. Our group has previously shown that sub-anesthetic ketamine produces acute anti-parkinsonian, and acute anti-dyskinetic effects in preclinical models of Parkinson's disease (PD). Ketamine is a multifunctional drug and exerts effects through blockade of N-methyl-d-aspartate receptors but also through interaction with the opioid system. In this report, we provide detailed pharmacokinetic rodent data on ketamine and its main metabolites following an intraperitoneal injection, and second, we explore the pharmacodynamic properties of ketamine in a rodent PD model with respect to the opioid system, using naloxone, a pan-opioid receptor antagonist, in unilateral 6-hydroxydopamine-lesioned male rats, treated with 6 mg/kg levodopa (l-DOPA) to establish a model of l-DOPA-induced dyskinesia (LID). As previously reported, we showed that ketamine (20 mg/kg) is highly efficacious in reducing LID and now report that the magnitude of this effect is resistant to naloxone (3 and 5 mg/kg). The higher naloxone dose of 5 mg/kg, however, led to an extension of the time-course of the LID, indicating that opioid receptor activation, while not a prerequisite for the anti-dyskinetic effects of ketamine, still exerts an acute modulatory effect. In contrast to the mild modulatory effect on LID, we found that naloxone added to the anti-parkinsonian activity of ketamine, further reducing the akinetic phenotype. In conclusion, our data show opioid receptor blockade differentially modulates the acute anti-parkinsonian and anti-dyskinetic actions of ketamine, providing novel mechanistic information to support repurposing ketamine for individuals with LID.

Levodopa modulates semantic fluency and uniqueness in non-demented patients with progressive supranuclear palsy.

INTRODUCTION: Semantic fluency is the ability to name items from a given category within a limited time, which relies on semantic knowledge, working memory, and executive function. Similar to patients with Parkinson's disease (PD), patients with progressive supranuclear palsy (PSP) scored lower than healthy adults in the well-established semantic fluency test. However, it is unclear how unique are the produced words. This study examined the relationship between semantic fluency and words' uniqueness in patients with PSP. METHODS: Twenty-seven patients with PSP Richardson's syndrome (PSP-RS), 37 patients with PD, and 41 healthy controls (HC) performed a standard semantic fluency test (animals), and their verbal responses were audio-recorded. We used the uniqueness to reflect the ability to produce both original and effective work, that is, creativity. RESULTS: The PSP-RS group produced fewer correct words and fewer unique words than the PD and HC groups. Moreover, the correlation between fluency and uniqueness was positive in the HC and PD groups but negative in the PSP-RS group. Importantly, the actual levodopa dose was positively correlated with the fluency but negatively correlated with the uniqueness in PSP-RS. The PSP-RS patients who took a greater dose of levodopa tended to produce more correct words but fewer unique words. CONCLUSIONS: These results suggested that levodopa may modulate semantic fluency and uniqueness in the early stages of PSP-RS.

5-HT4R agonism reduces L-DOPA-induced dyskinesia via striatopallidal neurons in unilaterally 6-OHDA lesioned mice.

Parkinson's disease is caused by a selective vulnerability and cell loss of dopaminergic neurons of the Substantia Nigra pars compacta and, consequently, striatal dopamine depletion. In Parkinson's disease therapy, dopamine loss is counteracted by the administration of L-DOPA, which is initially effective in ameliorating motor symptoms, but over time leads to a burdening side effect of uncontrollable jerky movements, termed L-DOPA-induced dyskinesia. To date, no efficient treatment for dyskinesia exists. The dopaminergic and serotonergic systems are intrinsically linked, and in recent years, a role has been established for pre-synaptic 5-HT1a/b receptors in L-DOPA-induced dyskinesia. We hypothesized that post-synaptic serotonin receptors may have a role and investigated the effect of modulation of 5-HT4 receptor on motor symptoms and L-DOPA-induced dyskinesia in the unilateral 6-OHDA mouse model of Parkinson's disease. Administration of RS 67333, a 5-HT4 receptor partial agonist, reduces L-DOPA-induced dyskinesia without altering L-DOPA's pro-kinetic effect. In the dorsolateral striatum, we find 5-HT4 receptor to be predominantly expressed in D2R-containing medium spiny neurons, and its expression is altered by dopamine depletion and L-DOPA treatment. We further show that 5-HT4 receptor agonism not only reduces L-DOPA-induced dyskinesia, but also enhances the activation of the cAMP-PKA pathway in striatopallidal medium spiny neurons. Taken together, our findings suggest that agonism of the post-synaptic serotonin receptor 5-HT4 may be a novel therapeutic approach to reduce L-DOPA-induced dyskinesia.

Serotonergic Regulation of Synaptic Dopamine Levels Mitigates L-DOPA-Induced Dyskinesia in a Mouse Model of Parkinson's Disease.

Background: The serotonin (5-HT) system can manipulate the processing of exogenous L-DOPA in the DA-denervated striatum, resulting in the modulation of L-DOPA-induced dyskinesia (LID). Objective: To characterize the effects of the serotonin precursor 5-hydroxy-tryptophan (5-HTP) or the serotonin transporter (SERT) inhibitor, Citalopram on L-DOPA-induced behavior, neurochemical signals, and underlying protein expressions in an animal model of Parkinson's disease. Methods: MitoPark (MP) mice at 20 weeks of age, subjected to a 14-day administration of L-DOPA/Carbidopa, displayed dyskinesia, referred to as LID. Subsequent investigations explored the effects of 5-HT-modifying agents, such as 5-HTP and Citalopram, on abnormal involuntary movements (AIMs), locomotor activity, neurochemical signals, serotonin transporter activity, and protein expression in the DA-denervated striatum of LID MP mice. Results: 5-HTP exhibited duration-dependent suppressive effects on developing and established LID, especially related to abnormal limb movements observed in L-DOPA-primed MP mice. However, Citalopram, predominantly suppressed abnormal axial movement induced by L-DOPA in LID MP mice. We demonstrated that 5-HTP could decrease L-DOPA-upregulation of DA turnover rates while concurrently upregulating 5-HT metabolism. Additionally, 5-HTP was shown to reduce the expressions of p-ERK and p-DARPP-32 in the striatum of LID MP mice. The effect of Citalopram in alleviating LID development may be attributed to downregulation of SERT activity in the dorsal striatum of LID MP mice. Conclusions: While both single injection of 5-HTP and Citalopram effectively mitigated the development of LID, the difference in mitigation of AIM subtypes may be linked to the unique effects of these two serotonergic agents on L-DOPA-derived DA and 5-HT metabolism.

Effectiveness of Continuous Dopaminergic Therapies in Parkinson's Disease: A Review of L-DOPA Pharmacokinetics/Pharmacodynamics.

Background: Parkinson's disease (PD) is characterized by striatal dopamine deficiency. Since dopamine cannot cross the digestive and blood-brain barriers, its precursor, levodopa (L-DOPA), remains the mainstay of treatment. However, the significant pharmacokinetic (Pk) and pharmacodynamic (Pd) limitations of L-DOPA, combined with the severity of PD, may trigger motor and non-motor complications, for which continuous dopaminergic delivery therapies have been developed. Objective: The aim of this study was to review the literature on the Pk/Pd limitations of L-DOPA and how current treatments of continuous dopaminergic administration ameliorate these problems, in order to identify the need for new therapeutic avenues. Methods: A comprehensive literature search was carried out using PubMed and 75 articles were initially extracted. Following independent screening by two reviewers and consideration of eligibility, 10 articles were chosen for further analysis. Information concerning the Pk/Pd of L-DOPA was classified for each article. Results: Pk/Pd problems notably include: (i) restricted digestive and cerebral absorption; (ii) unnecessary peripheral distribution; (iii) short half-life; (iv) age- and PD-induced decline of central aromatic L-amino acid decarboxylase; (v) misdistribution in many cells; and (vii) pulsatile stimulation of dopaminergic receptors. Current treatments only slightly ameliorate some of these problems. Conclusions: Many Pk/Pd constraints are not resolved by existing continuous dopaminergic delivery therapies. This highlights the significant gap between these treatments and the ideal of continuous dopaminergic stimulation.

Ganoderic acid A mitigates dopaminergic neuron ferroptosis via inhibiting NCOA4-mediated ferritinophagy in Parkinson's disease mice.

ETHNOPHARMACOLOGICAL RELEVANCE: Ganoderma lucidum, a renowned tonic traditional Chinese medicine, is widely recognized for the exceptional activity in soothing nerves and nourishing the brain. It has been extensively employed to alleviate various neurological disorders, notably Parkinson's disease (PD). AIM OF THE STUDY: To appraise the antiparkinsonian effect of GAA, the main bioactive constituent of G. lucidum, and clarify the molecular mechanism through the perspective of ferritinophagy-mediated dopaminergic neuron ferroptosis. MATERIALS AND METHODS: PD mouse and cell models were established using 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and 1-methyl-4-phenylpyridinium (MPP+), respectively. Cell viability, behavioral tests and immunofluorescence analysis were performed to evaluate the neurotoxicity, motor dysfunction and dopaminergic loss, respectively. Biochemical assay kits were used to determine the levels of iron, lipid reactive oxygen species (ROS), malondialdehyde (MDA), total ROS and glutathione (GSH). Western blot and immunofluorescence were applied to detect the expressions of nuclear receptor co-activator 4 (NCOA4), ferritin heavy chain 1 (FTH1), p62 and LC3B. Additionally, NCOA4-overexpressing plasmid vector was constructed to verify the inhibitory effect of GAA on the neurotoxicity and ferroptosis-related parameters in PD models. RESULTS: GAA significantly mitigated MPP+/MPTP-induced neurotoxicity, motor dysfunction and dopaminergic neuron loss (p＜0.01 or p＜0.05). In contrast to MPP+/MPTP treatment, GAA treatment decreased the levels of iron, MDA, lipid and total ROS, while increasing the GSH level. GAA also reduced the levels of NCOA4 and LC3B, and enhanced the expressions of FTH1 and p62 in PD models (p＜0.01 or p＜0.05). However, the protective effect of GAA against the neurotoxicity, NCOA4-mediated ferritinophagy and ferroptosis in PD model was abolished by the overexpression of NCOA4 (p＜0.01). CONCLUSION: GAA exerted a protective effect on PD, and this effect was achieved by suppressing dopaminergic neuron ferroptosis through the inhibition of NCOA4-mediated ferritinophagy.

Mitigating gut microbial degradation of levodopa and enhancing brain dopamine: Implications in Parkinson's disease.

Parkinson's disease is managed using levodopa; however, as Parkinson's disease progresses, patients require increased doses of levodopa, which can cause undesirable side effects. Additionally, the oral bioavailability of levodopa decreases in Parkinson's disease patients due to the increased metabolism of levodopa to dopamine by gut bacteria, Enterococcus faecalis, resulting in decreased neuronal uptake and dopamine formation. Parkinson's disease patients have varying levels of these bacteria. Thus, decreasing bacterial metabolism is a promising therapeutic approach to enhance the bioavailability of levodopa in the brain. In this work, we show that Mito-ortho-HNK, formed by modification of a naturally occurring molecule, honokiol, conjugated to a triphenylphosphonium moiety, mitigates the metabolism of levodopa-alone or combined with carbidopa-to dopamine. Mito-ortho-HNK suppresses the growth of E. faecalis, decreases dopamine levels in the gut, and increases dopamine levels in the brain. Mitigating the gut bacterial metabolism of levodopa as shown here could enhance its efficacy.

Effects of Continuous Dopaminergic Stimulation on Parkinson's Disease Gait: A Longitudinal Prospective Study with Levodopa Intestinal Gel Infusion.

Background: Gait issues, including reduced speed, stride length and freezing of gait (FoG), are disabling in advanced phases of Parkinson's disease (PD), and their treatment is challenging. Levodopa/carbidopa intestinal gel (LCIG) can improve these symptoms in PD patients with suboptimal control of motor fluctuations, but it is unclear if continuous dopaminergic stimulation can further improve gait issues, independently from reducing Off-time. Objective: To analyze before (T0) and after 3 (T1) and 6 (T2) months of LCIG initiation: a) the objective improvement of gait and balance; b) the improvement of FoG severity; c) the improvement of motor complications and their correlation with changes in gait parameters and FoG severity. Methods: This prospective, longitudinal 6-months study analyzed quantitative gait parameters using wearable inertial sensors, FoG with the New Freezing of Gait Questionnaire (NFoG-Q), and motor complications, as per the MDS-UPDRS part IV scores. Results: Gait speed and stride length increased and duration of Timed up and Go and of sit-to-stand transition was significantly reduced comparing T0 with T2, but not between T0-T1. NFoG-Q score decreased significantly from 19.3±4.6 (T0) to 11.8±7.9 (T1) and 8.4±7.6 (T2) (T1-T0 p = 0.018; T2-T0 p < 0.001). Improvement of MDS-UPDRS-IV (T0-T2, p = 0.002, T0-T1 p = 0.024) was not correlated with improvement of gait parameters and NFoG-Q from T0 to T2. LEDD did not change significantly after LCIG initiation. Conclusion: Continuous dopaminergic stimulation provided by LCIG infusion progressively ameliorates gait and alleviates FoG in PD patients over time, independently from improvement of motor fluctuations and without increase of daily dosage of dopaminergic therapy.

The effects of L-DOPA on gait abnormalities in a unilateral 6-OHDA rat model of Parkinson's disease.

Parkinson's Disease (PD) is a neurodegenerative movement disorder characterized by dopamine (DA) cell loss in the substantia nigra pars compacta (SNc). As PD progresses, patients display disruptions in gait such as changes in posture, bradykinesia, and shortened stride. DA replacement via L-DOPA alleviates many PD symptoms, though its effects on gait are not well demonstrated. This study aimed to assess the relationship between DA lesion, gait, and deficit-induced reversal with L-DOPA. To do so, Sprague-Dawley rats (N = 25, 14 males, 11 females) received unilateral medial forebrain bundle (MFB) DA lesions with 6-hydroxydopamine (6-OHDA). An automated gait analysis system assessed spatiotemporal gait parameters pre- and post-lesion, and after various doses of L-DOPA (0, 3, or 6 mg/kg; s.c.). The forepaw adjusting steps (FAS) test was implemented to evaluate lesion efficacy while the abnormal involuntary movements (AIMs) scale monitored the emergence of L-DOPA-induced dyskinesia (LID). High performance liquid chromatography (HPLC) assessed changes in brain monoamines on account of lesion and treatment. Results revealed lesion-induced impairments in gait, inclusive of max-contact area and step-sequence alterations that were not reversible with L-DOPA. However, the emergence of AIMs were observed at higher doses. Post-mortem, 6-OHDA lesions induced a loss of striatal DA and norepinephrine (NE), while prefrontal cortex (PFC) displayed noticeable reduction in NE but not DA. Our findings indicate that hemiparkinsonian rats display measurable gait disturbances similar to PD patients that are not rescued by DA replacement. Furthermore, non-DA mechanisms such as attention-related NE in PFC may contribute to altered gait and may constitute a novel target for its treatment.

Identification and optimization of nitrophenolic analogues as dopamine metabolic enzyme inhibitors for the treatment of Parkinson's disease.

Progressive loss of dopaminergic neurons leads to the depletion of the striatal neurotransmitter dopamine, which is the main cause of Parkinson's disease (PD) motor symptoms. Simultaneous inhibition of the two key dopamine metabolic enzymes, catechol-O-methyltransferase (COMT) and monoamine oxidase B (MAO-B), could potentially be a breakthrough in achieving clinical efficacy. Representative compound C12 exhibits good COMT inhibitory activity (IC50 = 0.37 µM), metal chelation ability, and BBB permeability. Furthermore, results from in vivo biological activity evaluations indicate that C12 can improve dopamine levels and ameliorate MPTP-induced PD symptoms in mice. Preliminary in vivo and in vitro study results highlight the potential of compound C12 in PD treatment.

OFF-times before, during, and after nighttime sleep periods in Parkinson's disease patients with motor fluctuations and the effects of opicapone: A post hoc analysis of diary data from BIPARK-1 and -2.

INTRODUCTION: In BIPARK-1 and BIPARK-2, addition of once-daily opicapone to levodopa/carbidopa significantly reduced daily "OFF"-time relative to placebo in adults with Parkinson's disease (PD) and motor fluctuations. Diary data from these studies were pooled and analyzed post hoc to characterize "OFF"-times around nighttime sleep and to explore the effects of opicapone 50 mg. METHODS: "OFF" before sleep (OBS), "OFF during the nighttime sleep period" (ODNSP), early morning "OFF" (EMO), and duration of nighttime sleep and awake periods were analyzed descriptively at baseline. Mean changes from baseline to Week 14/15 (end of double-blind treatment) were analyzed using two-sided t-tests in participants with data for both visits. RESULTS: At baseline, 88.3 % (454/514) of participants reported having OBS (34.0 %), ODNSP (17.1 %), or EMO (79.6 %). Those with ODNSP had substantially shorter mean duration of uninterrupted sleep (4.4 h) than the overall pooled population (7.1 h). At Week 14/15, mean decrease from baseline in ODNSP duration was significantly greater with opicapone than with placebo (-0.9 vs. -0.4 h, P < 0.05). In participants with ODNSP at baseline, the decrease in total time spent awake during the night-time sleep period was significantly greater with opicapone than with placebo (-1.0 vs. -0.4 h, P < 0.05), as was the reduction in percent time spent awake during the night-time sleep period (-12.8 % vs. -4.5 %, P < 0.05). CONCLUSION: "OFF"-times around nighttime sleep were common in BIPARK-1 and BIPARK-2. Opicapone may improve sleep by decreasing the amount of time spent awake during the night in patients with PD who have night-time sleep period "OFF" episodes.

Activation of mGlu 2/3 receptors with the orthosteric agonist LY-404,039 alleviates dyskinesia in experimental parkinsonism.

LY-404,039 is an orthosteric agonist at metabotropic glutamate 2 and 3 (mGlu 2/3 ) receptors, with a possible additional agonist effect at dopamine D 2 receptors. LY-404,039 and its pro-drug, LY-2140023, have previously been tested in clinical trials for psychiatric indications and could therefore be repurposed if they were shown to be efficacious in other conditions. We have recently demonstrated that the mGlu 2/3 orthosteric agonist LY-354,740 alleviated L-3,4-dihydroxyphenylalanine (L-DOPA)-induced abnormal involuntary movements (AIMs) in the 6-hydroxydopamine (6-OHDA)-lesioned rat without hampering the anti-parkinsonian action of L-DOPA. Here, we seek to take advantage of a possible additional D 2 -agonist effect of LY-404,039 and see if an anti-parkinsonian benefit might be achieved in addition to the antidyskinetic effect of mGlu 2/3 activation. To this end, we have administered LY-404,039 (vehicle, 0.1, 1 and 10 mg/kg) to 6-OHDA-lesioned rats, after which the severity of axial, limbs and oro-lingual (ALO) AIMs was assessed. The addition of LY-404,039 10 mg/kg to L-DOPA resulted in a significant reduction of ALO AIMs over 60-100 min (54%, P  < 0.05). In addition, LY-404,039 significantly enhanced the antiparkinsonian effect of L-DOPA, assessed through the cylinder test (76%, P  < 0.01). These results provide further evidence that mGlu 2/3 orthosteric stimulation may alleviate dyskinesia in PD and, in the specific case of LY-404,039, a possible D 2 -agonist effect might also make it attractive to address motor fluctuations. Because LY-404,039 and its pro-drug have been administered to humans, they could possibly be advanced to Phase IIa trials rapidly for the treatment of motor complications in PD.

Differential Activation States of Direct Pathway Striatal Output Neurons during l-DOPA-Induced Dyskinesia Development.

l-DOPA-induced dyskinesia (LID) is a debilitating motor side effect arising from chronic dopamine (DA) replacement therapy with l-DOPA for the treatment of Parkinson's disease. LID is associated with supersensitivity of striatal dopaminergic signaling and fluctuations in synaptic DA following each l-DOPA dose, shrinking the therapeutic window. The heterogeneous composition of the striatum, including subpopulations of medium spiny output neurons (MSNs), interneurons, and supporting cells, complicates the identification of cell(s) underlying LID. We used single-nucleus RNA sequencing (snRNA-seq) to establish a comprehensive striatal transcriptional profile during LID development. Male hemiparkinsonian mice were treated with vehicle or l-DOPA for 1, 5, or 10 d, and striatal nuclei were processed for snRNA-seq. Analyses indicated a limited population of DA D1 receptor-expressing MSNs (D1-MSNs) formed three subclusters in response to l-DOPA treatment and expressed cellular markers of activation. These activated D1-MSNs display similar transcriptional changes previously associated with LID; however, their prevalence and transcriptional behavior were differentially influenced by l-DOPA experience. Differentially expressed genes indicated acute upregulation of plasticity-related transcription factors and mitogen-activated protein kinase signaling, while repeated l-DOPA-induced synaptic remodeling, learning and memory, and transforming growth factor-ß (TGF-ß) signaling genes. Notably, repeated l-DOPA sensitized Inhba, an activin subunit of the TGF-ß superfamily, in activated D1-MSNs, and its pharmacological inhibition impaired LID development, suggesting that activin signaling may play an essential role in LID. These data suggest distinct subsets of D1-MSNs become differentially l-DOPA-responsive due to aberrant induction of molecular mechanisms necessary for neuronal entrainment, similar to processes underlying hippocampal learning and memory.