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Background Parkinson's disease (PD) psychosis is a distressing condition that affects up to 60% of patients at the advanced stages of the disease. It significantly impairs patients' and caregivers' quality of life. Current therapeutic options are limited, with only 2 drugs, clozapine and pimavanserin, demonstrating efficacy in randomised controlled trials. These 2 drugs harbour significant affinity for serotonin 2A (5-HT 2A ) receptors, at which they act as antagonists. Mianserin is a non-selective, clinically-available, anti-depressant that blocks 5-HT 2A receptors. Here, we hypothesised that mianserin would effectively alleviate PD psychosis. Methods We tested the anti-psychotic potential of mianserin in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned common marmoset. Six MPTP-lesioned marmosets exhibiting psychosis-like behaviours (PLBs) were administered l -3,4-dihydroxyphenylalanine ( l -DOPA) in combination with mianserin (0.3, 1 and 3 mg/kg) or vehicle, after which the severity of PLBs was rated. We also assessed the effect of mianserin on l -DOPA-induced dyskinesia and parkinsonian disability. Results The addition of mianserin 3 mg/kg to l -DOPA led to a 23% reduction of PLBs ( P < 0.05), when compared to l -DOPA/vehicle. Dyskinesia was reduced, by ≈ 41% ( P < 0.01), when mianserin 3 mg/kg was added to l -DOPA, compared to l -DOPA/vehicle. However, mianserin 3 mg/kg reduced duration of l -DOPA anti-parkinsonian action, by ≈ 18% ( P < 0.05), when compared to l -DOPA/vehicle. Conclusions Our results suggest that mianserin, a clinically-available anti-depressant, may be effective to alleviate both PD psychosis and dyskinesia, but may hinder l -DOPA anti-parkinsonian action, which limits its potential clinical usefulness. [ABSTRACT FROM AUTHOR]

l -3,4-dihydroxyphenylalanine ( l -DOPA) is the most effective anti-parkinsonian agent available, but upon chronic administration, patients with Parkinson's disease (PD) experience abnormal involuntary movements, dyskinesia. Modulation of serotonin 1A (5-HT 1A ) receptors is regarded as an effective way to alleviate dyskinesia, yet this approach has been marred by a reduction of the therapeutic effectiveness of l -DOPA. We hypothesised that highly-selective 5-HT 1A stimulation might be a way to alleviate dyskinesia without compromising l -DOPA anti-parkinsonian action. F15599 (also known as NLX-101) is a highly-selective 5-HT 1A agonist that displays over 1000 × selectivity over off-target receptors. Seven cynomolgus macaques were administered MPTP and developed severe parkinsonism. Following chronic administration of l -DOPA, they developed severe and reproducible dyskinesia. F15599 (0.003, 0.01, 0.03 and 0.1 mg/kg) or vehicle was administered in combination with l -DOPA and its effect on dyskinesia and l -DOPA anti-parkinsonian was assessed. In combination with l -DOPA, F15599 (0.1 mg/kg) reduced the severity of peak-dose dyskinesia, by ≈45% ( P < 0.001), compared to l -DOPA alone. F15599 (any dose) had no effect on duration of on-time or motor activity counts compared to l -DOPA alone. F15599 at 0.03 and 0.1 mg/kg significantly reduced duration of on-time with disabling dyskinesia (by ≈49% and ≈71%, P < 0.05 and P < 0.001, respectively). These results suggest that F15599, a highly-selective 5-HT 1A receptor agonist, alleviates dyskinesia without exerting a deleterious effect on l -DOPA anti-parkinsonian action. [ABSTRACT FROM AUTHOR]

l -3,4-Dihydroxyphenylalanine (L-DOPA) is currently the most effective drug available to treat the symptoms of Parkinson's disease (PD). A limitation is that chronic administration of L-DOPA almost invariably, but not universally, leads to the development of abnormal involuntary movements, dyskinesia. Research suggests that striatal dopamine depletion is an important aetiological factor leading to dyskinesia development. However, in studies where L-DOPA was administered to normal animals and human subjects not afflicted by PD, abnormal involuntary movements were sometimes elicited. These studies are reviewed here and their potential significance for the pathophysiology of dyskinesia is discussed. It is concluded that, if striatal dopamine depletion may not be a requisite for the development of dyskinesia, it probably acts as a permissive factor, at least with the doses commonly employed in the clinic. [ABSTRACT FROM AUTHOR]

Abstract: L-3,4-Dihydroxyphenylalanine (l-DOPA) is the most effective treatment for Parkinson's disease (PD), but its long-term administration is complicated by wearing-off and dyskinesia. UWA-101, a dual, equipotent inhibitor of dopamine (DAT) and serotonin (SERT) transporters, has previously been shown to successfully extend duration of anti-parkinsonian benefit of l-DOPA (ON-time), without exacerbating dyskinesia, in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned marmoset. However, UWA-101 is racemic and it is unclear whether one or both enantiomers contribute to its actions, and whether a better therapeutic effect might be attained by using a single antipode. In the current study, we synthesised the two enantiomers of UWA-101, R-101 (UWA-121) and S-101 (UWA-122), characterised their pharmacological profiles and administered them to MPTP-lesioned marmosets. Parkinsonism, dyskinesia, psychosis-like behaviours and duration of ON-time were evaluated. UWA-121 is a dual DAT > SERT inhibitor, with an approximate 10:1 DAT:SERT affinity ratio (inhibitory constants (Ki) of 307 and 3830 nM, respectively). In combination with l-DOPA, UWA-121 extended duration of ON-time when compared to l-DOPA/vehicle treatment (by 40%, P < 0.01). UWA-121 also extended duration of ON-time without dyskinesia (by 215%, P < 0.05) and ON-time without psychosis-like behaviours when compared to l-DOPA/vehicle treatment (by 345%, P < 0.01). UWA-121 did not worsen the severity of dyskinesia or psychosis-like behaviours (P > 0.05). UWA-122 is a selective SERT inhibitor (Ki 120 nM, Ki at DAT > 50 μM) and, in combination with l-DOPA, had no effect on ON-time, dyskinesia or psychosis-like behaviours (P > 0.05). These data indicate that dual DAT and SERT inhibitors effectively enhance l-DOPA anti-parkinsonian action without worsening dyskinesia and that compounds with such a pharmacological profile represent promising agents against wearing-off in PD. [Copyright &y& Elsevier]

Abstract: Long-term l-DOPA treatment for Parkinson's disease (PD) is limited by motor complications, particularly l-DOPA-induced dyskinesia (LID). A therapy with the ability to ameliorate LID without reducing anti-parkinsonian benefit would be of great value. We assessed the ability of TC-8831, an agonist at nicotinic acetylcholine receptors (nAChR) containing α6β2/α4β2 subunit combinations, to provide such benefits in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine- (MPTP) lesioned macaques with established LID. Animals were treated orally for consecutive 14-day periods with twice-daily vehicle (weeks 1–2) or TC-8831 (0.03, 0.1 or 0.3 mg/kg, weeks 3–8). l-DOPA was also administered, once-daily, (weeks 1–12, median-dose 30 mg/kg, p.o.). For the following two-weeks (weeks 9–10), TC-8831 was washed out, while once-daily l-DOPA treatment was maintained. The effects of once-daily amantadine (3 mg/kg, p.o.) were then assessed over weeks 11–12. LID, parkinsonism, duration and quality of ON-time were assessed weekly by a neurologist blinded to treatment. TC-8831 reduced the duration of ‘bad’ ON-time (ON-time with disabling dyskinesia) by up to 62% and decreased LID severity (median score 18 cf. 34 (vehicle), 0.1 mg/kg, 1–3 h period). TC-8831 also significantly reduced choreiform and dystonic dyskinesia (median scores 6 and 31 cf. 19 and 31 respectively (vehicle), both 0.03 mg/kg, 1–3 h). At no time did TC-8831 treatment result in a reduction in anti-parkinsonian benefit of l-DOPA. By comparison, amantadine also significantly reduced dyskinesia and decreased ‘bad’ ON-time (up to 61%) but at the expense of total ON-time (reduced by up to 23%). TC-8831 displayed robust anti-dyskinetic actions and improved the quality of ON-time evoked by l-DOPA without any reduction in anti-parkinsonian benefit. [Copyright &y& Elsevier]

Abstract: 3,4-Dihydroxyphenylalanine (L-DOPA) treatment of Parkinson''s disease (PD) is compromised by motor side effects, such as dyskinesia and non-motor problems, including psychosis. Because of the marked reduction in brain dopamine in PD and the resultant dopamine D2 receptor supersensitivity, it is impossible to use standard potent dopamine D2 receptor antagonists such as haloperidol to alleviate side effects without compromising the anti-parkinsonian benefits of L-DOPA. Haloperidol antagonizes D2 receptors with high affinity and slowly dissociates from D2 receptors (50% dissociation at 38min). We hypothesized that a rapidly dissociating D2 antagonist might allow some functional dopaminergic transmission and thus have a profile, with respect to reduction of dyskinesia and anti-parkinsonian effects, that was more useful therapeutically. The present study tested the principle of using a fast-off-D2 drug, CLR151 (50% dissociation at 23s) to modify L-DOPA actions in cynomolgus macaques with MPTP-parkinsonism. CLR151 (100mg/kg p.o.) reduced L-DOPA-induced dyskinesia and activity in the parkinsonian macaque by 86% and 52% respectively during peak action. CLR151 (100mg/kg) also reduced psychosis-like behaviour (i.e. reduced apparent visual hallucinations by 78%). Nevertheless, this dose of CLR151 significantly reduced the duration of anti-parkinsonian action of L-DOPA, ON-time (by 90%), and increased parkinsonian disability (by 57%). These data suggest that fast-off-D2 dopamine receptor antagonists, with D2-off-rate values close to those for CLR151, are unlikely to be useful in the treatment of dyskinesia and psychosis in PD. However, fast-off-D2 drugs could provide benefit if new congeners would have an even faster dissociation rate. Such drugs are now becoming available. [Copyright &y& Elsevier]

Abstract: Background: l-3,4-dihydroxyphenylalanine (l-DOPA)-induced dyskinesia (LID) are a complication of chronic dopamine replacement therapy in Parkinson''s disease (PD). Recent studies have suggested that the mechanisms underlying development and expression of LID in PD may involve epigenetic changes that include deacetylation of striatal histone proteins. We hypothesised that inhibition of histone deacetylase, the enzyme responsible of histone deacetylation, would alleviate LID. Methods: Four female common marmoset (Callithrix jacchus) were rendered parkinsonian by administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Following stabilisation of the parkinsonian phenotype, marmosets were primed to exhibit dyskinesia with chronic administration of l-DOPA. We then investigated the effects of the brain-penetrant histone deacetylase inhibitor, RGFP109 (30 mg/kg p.o. once daily for 6 days), on LID and l-DOPA anti-parkinsonian efficacy. Results: RGFP109 had no acute effects on dyskinesia after single or 6 days once-daily treatment (both P > 0.05). However, one week following cessation of RGFP109, dyskinesia and duration of ON-time with disabling dyskinesia were reduced by 37% and 50%, respectively (both P < 0.05), compared to that seen previously with l-DOPA alone. There was no change in anti-parkinsonian actions of, or ON-time duration afforded by, l-DOPA (P > 0.05). Conclusions: Histone deacetylation inhibition may represent a novel approach to reverse established LID in PD and improve quality of the anti-parkinsonian benefit provided by l-DOPA. [Copyright &y& Elsevier]

Abstract: Objective: The 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned non-human primate is widely used to model Parkinson''s disease (PD) and to evaluate the efficacy of new therapies. However, some doubts have been raised about the translatability of findings in the MPTP-lesioned monkey, because the doses of l-3,4-dihydroxyphenylalanine (l-DOPA) required to alleviate parkinsonism and elicit dyskinesia are high, on a mg/kg basis, when compared to clinical practice. Thus, in the MPTP-lesioned macaque, doses ranging from 20 to 40 mg/kg might be used, while in the clinic single l-DOPA administrations ranging from 100 to 200 mg are more typical. However, bioavailability of drugs varies between species and it is unknown how plasma l-DOPA levels providing therapeutic benefit in the non-human primate compare to those having similar actions in PD patients. Methods: We administered acute challenges of l-DOPA 30 mg/kg orally to MPTP-lesioned macaques with established dyskinesia, and determined plasma, brain and cerebrospinal fluid (CSF) levels of l-DOPA using high-performance liquid chromatography–mass spectrometry/mass spectrometry. Results: The maximal plasma concentration of l-DOPA (C max) was 18.2 ± 3.8 nmol/ml and was achieved 1.6 ± 0.3 h after administration (t max). Half-life was 58.8 ± 22.7 min. l-DOPA levels in the caudate nucleus at peak behavioural effect were 3.3 ± 0.7 μg/g tissue protein while they were 1.5 ± 0.1 nmol/ml in the CSF. Conclusions: Although therapeutically-active doses of l-DOPA administered to the MPTP-lesioned macaque are higher on a mg/kg basis than those administered in clinical settings, they lead to l-DOPA C max similar to those achieved with 200 mg l-DOPA in clinic. l-DOPA t max and half-life are also similar to those reported in human. [Copyright &y& Elsevier]

Abstract: Although the cardinal manifestations of Parkinson''s disease (PD) are attributed to a decline in dopamine levels in the striatum, a breadth of non-motor features and treatment-related complications in which the serotonergic system plays a pivotal role are increasingly recognised. Serotonin (5-HT)-mediated neurotransmission is altered in PD and the roles of the different 5-HT receptor subtypes in disease manifestations have been investigated. The aims of this article are to summarise and discuss all published preclinical and clinical studies that have investigated the serotonergic system in PD and related animal models, in order to recapitulate the state of the current knowledge and to identify areas that need further research and understanding. [Copyright &y& Elsevier]

Abstract: The striatum harbors a population of dopaminergic interneurons that increases in number in animal models of Parkinson''s disease (PD), presumably to compensate for dopamine (DA) depletion. The purpose of the present study was to determine the fate of striatal dopaminergic neurons in parkinsonian monkeys in which striatal DA depletion had been alleviated by systemic administration of l-dopa. The number of striatal dopaminergic neurons, visualized with tyrosine hydroxylase (TH) immunohistochemistry, was measured in three groups of cynomolgus (Macaca fascicularis) monkeys: (1) normal untreated monkeys; (2) monkeys rendered parkinsonian following systemic injection of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), but otherwise untreated; and (3) MPTP-intoxicated monkeys that received oral l-dopa on a chronic basis. In agreement with previous studies, the number of striatal TH-positive (TH+) neurons in l-dopa-free parkinsonian monkeys was significantly higher (p <0.05) than in normal (non-parkinsonian) monkeys. However, this increase was abolished in parkinsonian monkeys that received l-dopa treatment. In fact, the number of striatal TH+ neurons in l-dopa-treated parkinsonian monkeys was not significantly different (p >0.05) from values obtained in normal monkeys. These findings suggest that the DA concentration regulates the numerical density of this ectopic neuronal population, a phenomenon that is more likely the result of a shift in the phenotype of preexistent striatal interneurons rather than the recruitment of newborn neurons that would eventually develop a DA phenotype. Our data also reinforce the hypothesis that striatal TH+ neurons act as local DA source and, as such, are part of a compensatory mechanism that could be artificially enhanced to alleviate or delay PD symptoms. [Copyright &y& Elsevier]

Abstract: Serotonergic 1A (5-HT1A) receptor agonists reduce L-3,4-dihydroxyphenylalanine (L-DOPA)-induced dyskinesia in Parkinson''s disease (PD), though the mechanism(s) and site(s) of action remain unclear. We employed [3H]-WAY 100,635 autoradiographic receptor binding to measure 5-HT1A receptor levels in 4 groups of macaques: normal (vehicle-vehicle); 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned, without exposure to L-DOPA, i.e., untreated parkinsonian (MPTP-vehicle); MPTP-lesioned, receiving a single administration of L-DOPA to alleviate parkinsonism (MPTP-L-DOPA-acute); and MPTP-lesioned, chronically treated with L-DOPA, parkinsonism alleviated but exhibiting dyskinesia (MPTP-L-DOPA-chronic). We demonstrate that 5-HT1A receptor binding decreases (by 10%–20%, p < 0.05) in the external layers, but increases (by 80%–100%, p < 0.05) in the middle layers, of the premotor and motor cortex of all MPTP-lesioned macaques. In the striosomes of the caudate nucleus, 5-HT1A receptor binding increases in MPTP-vehicle macaques (by 50%, p < 0.05), compared with normal macaques. While 5-HT1A receptor binding is low in the matrix of the caudate nucleus in normal macaques, it increases (by 200%, p < 0.05) in MPTP-L-DOPA-chronic macaques. These data suggest that 5-HT1A receptors are involved in the pathophysiology of both parkinsonism and complications of L-DOPA therapy. [Copyright &y& Elsevier]

Abstract: Long-term L-3,4-dihydroxyphenylalanine (L-DOPA) treatment in Parkinson''s disease (PD) is associated with motor complications such as dyskinesia. There are clear functional interactions between dopaminergic and serotonergic type 2A receptors (5-HT2A)-mediated neurotransmission. Moreover, 5-HT2A receptor antagonists can reduce L-DOPA-induced dyskinesia (LID). We hypothesized that enhanced 5-HT2A-mediated neurotransmission may be involved in the genesis of L-DOPA-induced dyskinesia. Radioligand binding autoradiography, using [3H]-ketanserin, was performed to define 5-HT2A receptor levels in brain tissue from macaques: 6 normal; 5 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned, parkinsonian macaques, without exposure to L-DOPA; 6 MPTP-lesioned, parkinsonian macaques, receiving a single administration of L-DOPA, and exhibiting no dyskinesia; and 6 MPTP-lesioned, parkinsonian, macaques chronically treated with L-DOPA, and exhibiting dyskinesia. 5-HT2A receptor binding was increased in the caudate, putamen, and middle layers of the motor cortex in chronically L-DOPA-treated animals, by 50%, 50%, and 45% respectively, compared with normal macaques. 5-HT2A binding was not significantly altered in parkinsonian, untreated, or parkinsonian, single treatment, nondyskinetic macaques, compared with normal. These data provide an anatomical basis for mechanisms to explain the efficacy of 5-HT2A antagonists against dyskinesia. [Copyright &y& Elsevier]

• Mechanism underlying anti-dyskinetic efficacy of 5-HT 3 receptor antagonists is unclear. • Dyskinetic hemi-parkinsonian rats showed increased 5-HT 3 levels in the STN, EP and thalamus. • Dyskinesia severity negatively correlated with 5-HT 3 levels in the striatum and STN. • Changes in 5-HT 3 levels in the basal ganglia may modulate l -DOPA induced dyskinesia. L-3,4-dihydroxyphenylalanine (l -DOPA) is the mainstay treatment for Parkinson's disease, but its effectiveness during early disease is marred by the eventual development of l -DOPA induced dyskinesia. In hemi-parkinsonian rats, the serotonin type 3 (5-HT 3) antagonists ondansetron and granisetron alleviated dyskinesia induced by l -DOPA without impeding its anti-parkinsonian action; in parkinsonian marmosets, ondansetron alleviated dyskinesia and enhanced l -DOPA anti-parkinsonian action. Here, we sought to gain insight into the mechanisms governing the anti-dyskinetic action of 5-HT 3 antagonists and measured 5-HT 3 receptor levels across different brain, using [3H]GR65630 autoradiographic binding. Brain sections were chosen from 6-hydroxydopamine (6-OHDA)-lesioned rats exhibiting abnormal involuntary movements (AIMs), as well as l -DOPA-naïve 6−OHDA and sham-lesioned animals. [3H]GR65630 binding increased in the ipsilateral subthalamic nucleus of 6-OHDA-lesioned rats with mild and severe AIMs, (3-fold changes, P < 0.001). [3H]GR65630 binding also increased in the ipsilateral entopeduncular nucleus and thalamus of 6-OHDA-lesioned rats with severe AIMs (75 % and 88 %, P < 0.05). AIMs scores negatively correlated with [3H]GR65630 binding in the ipsilateral dorsolateral striatum and contralateral subthalamic nucleus (P < 0.05). These results suggest that alterations in 5-HT 3 mediated neurotransmission may contribute to the pathophysiology of l -DOPA induced dyskinesia. [ABSTRACT FROM AUTHOR]

• Stereotaxic atlases of the marmoset brain limit accurate identification of targets. • Co-registration of imaging data located the surgical target in each subject. • Frameless stereotaxic surgery with a robotic arm led to injection in the putamen. • Combined approach accurately locates target; useful for longitudinal studies. The common marmoset has emerged as a popular model in neuroscience research, in part due to its reproductive efficiency, genetic and neuroanatomical similarities to humans and the successful generation of transgenic lines. Stereotaxic procedures in marmosets are guided by 2D stereotaxic atlases, which are constructed with a limited number of animals and fail to account for inter-individual variability in skull and brain size. Here, we developed a frameless imaging-guided stereotaxic system that improves upon traditional approaches by using subject-specific registration of computed tomography (CT), magnetic resonance imaging (MRI) and positron emission tomography (PET) data to identify a surgical target, namely the putamen, in two marmosets. The skull surface was laser-scanned to create a point cloud that was registered to the 3D reconstruction of the skull from CT. Reconstruction of the skull, as well as of the brain from MR images, was crucial for surgical planning. Localisation and injection into the putamen was done using a 6-axis robotic arm controlled by a surgical navigation software (Brainsight™). Integration of subject-specific registration and frameless stereotaxic navigation allowed target localisation specific to each animal. Injection of alpha-synuclein fibrils into the putamen triggered progressive neurodegeneration of the nigro-striatal system, a key feature of Parkinson's disease. Four months post-surgery, a PET scan found evidence of nigro-striatal denervation, supporting accurate targeting of the putamen during co-registration and subsequent surgery. Our results suggest that this approach, coupled with frameless stereotaxic neuronavigation, is accurate in localising surgical targets and can be used to assess endpoints for longitudinal studies. [ABSTRACT FROM AUTHOR]

Blockade of serotonin 2A (5-HT 2A ) receptors is regarded as an anti-dyskinetic and anti-psychotic strategy in Parkinson's disease (PD). However, the 5-HT 2A antagonists tested so far exhibited affinity for other receptors, which might have played a role in their action. EMD-281,014 is the most selective 5-HT 2A antagonist available, with approximately 2,000-fold selectivity over serotonin 2C (5-HT 2C ) receptors. EMD-281,014 was previously tested in the clinic and has high translational potential. In the present study, we assessed the effect of EMD-281,014 on dyskinesia and psychosis in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned common marmoset. We first determined the pharmacokinetic profile of EMD-281,014 in the marmoset, after which doses leading to clinically-relevant plasma levels (0.01, 0.03 and 0.1 mg/kg) or vehicle were administered to MPTP-lesioned marmosets, in combination with L-3,4-dihydroxyphenylalanine ( l -DOPA). The effects of EMD-281,014 on dyskinesia, psychosis-like behaviours (PLBs) and parkinsonism were then evaluated. When added to l -DOPA, EMD-281,014 (0.03 and 0.1 mg/kg) reduced peak dose dyskinesia, by 41.8% and 54.5% ( P  < 0.05 and P  < 0.001), when compared to l -DOPA/vehicle. EMD-281,014 (0.03 and 0.1 mg/kg) also significantly reduced the severity of peak dose PLBs, by 42.5% and 45.9% ( P  < 0.05 and P  < 0.001), when compared to vehicle. The anti-dyskinetic and anti-psychotic effects of EMD-281,014 were achieved without interfering with l -DOPA anti-parkinsonian action. Our results suggest that highly-selective 5-HT 2A receptor blockade with EMD-281,014 is an effective way to alleviate both dyskinesia and psychosis in PD, without adversely affecting parkinsonian disability. [ABSTRACT FROM AUTHOR]

LY-354,740 (eglumegad) is a selective and potent agonist of the metabotropic glutamate group II receptors (mGluR2,3) that has already entered clinical trials as a potential anti-psychotic agent and therefore has well-documented pharmacokinetic (PK), safety and tolerability profiles in human. Whereas its development as an anti-psychotic agent has not been pursued, LY-354,740 may have potential in other neuroscience-related fields, notably anxiety and neuro-protection. The common marmoset is a small primate that has long been used in neuroscience. However, given its small size and small circulating blood volume, conducting PK studies to determine the therapeutic effectiveness of LY-354,740 at clinically-relevant doses is challenging. Here, we have developed and validated a simple, sensitive and selective analytical method that enables quantification of LY-354,740 using a small volume of plasma. The analytical method consisted of protein precipitation followed by high-performance liquid chromatography with heat assisted electrospray ionisation mass spectrometry (UHPLC-HESI–MS/MS). The chromatographic separation was achieved using gradient elution with a mobile phase consisting of acetonitrile and 10 mM ammonium formate (pH 3) on a Thermo Scientific Acclaim Trinity P1 analytical column (100 x 3.0 mm I.D., 3 μm) operating at 45 °C and at a flow rate of 900 μl/min. The method displays a linear relationship ranging from 20.0 to 5000 ng/ml. Intra- and inter-day relative standard deviations are less than 5.7% and 7.0%, respectively and the accuracy ranged from 91.0 to 106.0%. The UHPLC-HESI–MS/MS analytical method we describe here is simple, sensitive, specific and capable of quantifying LY-354,740 in both rat and marmoset plasma, and is suitable to conduct PK studies after a single sub-cutaneous dose of 1.0 mg/kg or lower in both species. [ABSTRACT FROM AUTHOR]

Dyskinesia remains an unmet need in Parkinson's disease (PD). We have previously demonstrated that glycine transporter 1 (GlyT1) inhibition with ALX-5407 reduces dyskinesia and slightly improves parkinsonism in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned marmoset. Here, we sought to determine the effect of bitopertin, a clinically-tested GlyT1 inhibitor, on parkinsonism and dyskinesia in the 6-hydroxydopamine (6-OHDA)-lesioned rat. To do so, we assessed the effect of bitopertin on parkinsonism as monotherapy and as adjunct to a low dose of L-3,4-dihydroxyphenylalanine (L-DOPA). We then assessed the efficacy of bitopertin on dyskinesia in the context of acute challenge and chronic administration studies. Lastly, we evaluated whether de novo treatment with bitopertin, started concurrently with L-DOPA, would diminish the development of dyskinesia. We discovered that bitopertin (0.3 mg/kg), when administered alone, reduced the severity of parkinsonism by 35% (P < 0.01). As adjunct to a low dose of L-DOPA, bitopertin (3 mg/kg) enhanced the anti-parkinsonian effect of L-DOPA by 36% (P < 0.05). Moreover, the acute addition of bitopertin (0.03 mg/kg) to L-DOPA reduced dyskinesia by 27% (P < 0.001), and there was no tolerance to the anti-dyskinetic benefit after 4 weeks of daily administration. Lastly, bitopertin (0.03 mg/kg) started concurrently with L-DOPA, also attenuated the development of dyskinesia, by 33% (P < 0.01), when compared to L-DOPA alone. Our results suggest that GlyT1 inhibition may simultaneously reduce parkinsonism and L-DOPA-induced dyskinesia and represents a novel approach to treat, possibly prevent, motor complications in PD. [ABSTRACT FROM AUTHOR]

Dyskinesia and psychosis are complications encountered in advanced Parkinson's disease (PD) following long-term therapy with L-3,4-dihydroxyphenylalanine (L-DOPA). Disturbances in the glutamatergic system have been associated with both dyskinesia and psychosis, making glutamatergic modulation a potential therapeutic approach for these. Treatments thus far have sought to dampen glutamatergic transmission, for example through blockade of N -methyl-D-aspartate (NMDA) receptors or modulation of metabotropic glutamate receptors 5. In contrast, activation of the glycine-binding site on NMDA receptors is required for their physiological response. Here, we investigated whether indirectly enhancing glutamatergic transmission through inhibition of glycine re-uptake would be efficacious in diminishing both dyskinesia and psychosis-like behaviours (PLBs) in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned common marmoset. Six marmosets were rendered parkinsonian by MPTP injection. Following repeated administration of L-DOPA to induce dyskinesia and PLBs, they underwent acute challenges of the glycine transporter 1 (GlyT 1) inhibitor ALX-5407 (0.01, 0.1 and 1 mg/kg) or vehicle, in combination with L-DOPA, after which the severity of dyskinesia, PLBs and parkinsonian disability was evaluated. In combination with L-DOPA, ALX-5407 0.1 and 1 mg/kg significantly reduced the severity of dyskinesia, by 51% and 41% (both P < 0.001), when compared to vehicle. ALX-5407 0.01, 0.1 and 1 mg/kg also decreased the severity of global PLBs, by 25%, 51% and 38% (all P < 0.001), when compared to vehicle. The benefits on dyskinesia and PLBs were achieved without compromising the therapeutic effect of L-DOPA on parkinsonism. Our results suggest that GlyT 1 inhibition may be a novel strategy to attenuate dyskinesia and PLBs in PD, without interfering with L-DOPA anti-parkinsonian action. Inhibition of glycine transporter 1 reduces the expression of established dyskinesia and psychosis in MPTP-lesioned marmosets. [ABSTRACT FROM AUTHOR]

Antagonising the serotonin 2A (5-HT 2A) receptor is an efficacious way to alleviate dyskinesia and psychosis in Parkinson's disease (PD). However, previous research indicates that there might be a limit to the effects conferred by this approach. 5-HT 2A receptors were shown to form hetero-dimers with metabotropic glutamate 2 (mGlu 2) receptors, in which 5-HT 2A blockade and mGlu 2 activation elicit equivalent effects at the downstream signalling level. We have previously shown that mGlu 2 activation reduces both dyskinesia and psychosis-like behaviours (PLBs) induced by L-3,4-dihydroxyphenylalanine (l -DOPA), in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned primate. Here, we hypothesised that concurrent 5-HT 2A antagonism and mGlu 2 activation would provide greater anti-dyskinetic and anti-psychotic benefits than either approach alone. We conducted 3 series of experiments in the MPTP-lesioned marmoset. In the first series of experiments, the mGlu 2 positive allosteric modulator LY-487,379 and the 5-HT 2A antagonist EMD-281,014, either alone or in combination, were added to l -DOPA. In the second series of experiments, the mGlu 2/3 orthosteric agonist LY-354,740 and EMD-281,014, either alone or in combination, were added to l -DOPA. In the last series of experiments, we investigated whether mGlu 2 blockade would diminish the effects of antagonising 5-HT 2A receptors. To this end, the mGlu 2/3 orthosteric antagonist LY-341,495 and EMD-281,014, either alone or in combination, were added to l -DOPA. We found that the anti-dyskinetic effect of the combination LY-487,379/EMD-281,014 was greater than the ones conferred by LY-487,379 (by 35%, P < 0.05) and EMD-281,014 (by 38%, P < 0.01). The anti-dyskinetic and anti-psychotic effects of the combination LY-354,740/EMD-281,014 were also greater than the ones conferred by LY-354,740 (by 57% for dyskinesia and 54% for PLBs, both P < 0.001) and EMD-281,014 (by 61% for dyskinesia and 53% for PLBs, both P < 0.001). The anti-parkinsonian action of l -DOPA was maintained with all treatments. Lastly, the addition of LY-341,495 abolished the therapeutic effects of EMD-281,014 on dyskinesia and PLBs. Our results suggest that mGlu 2 activation may enhance the anti-dyskinetic and anti-psychotic effects of 5-HT 2A blockade and could provide relief to PD patients with dyskinesia and psychotic symptoms beyond what can be achieved with current therapies. • An additive anti-dyskinetic effect is achieved upon concurrent mGlu 2 activation and 5-HT 2A blockade. • An additive anti-psychotic effect is achieved upon concurrent mGlu 2 activation and 5-HT 2A blockade. • Combined mGlu 2 activation and 5-HT 2A blockade does not hamper l -DOPA anti-parkinsonian action. • mGlu 2 blockade hinders the anti-dyskinetic and anti-psychotic effects of 5-HT 2A antagonism. [ABSTRACT FROM AUTHOR]

• 5-HT 3 receptors were not encountered in the substantia nigra pars compacta. • 5-HT 3 receptors did not co-localise with TH-positive cells in the substantia nigra pars reticulata. • 5-HT 3 receptors were not encountered in the dorsal raphe nucleus. Serotonin (5-HT) is a common neurotransmitter in mammals, playing a central role in the regulation of various processes such as sleep, perception, cognitive and autonomic functions in the nervous system. Previous studies have demonstrated that 5-HT type 3 (5-HT 3) receptors are expressed in either or both the substantia nigra (SN) and the dorsal raphe nucleus (DRN) in humans, marmosets, rats and Syrian hamsters. Here, we quantify the distribution of 5-HT 3 receptors across these regions in the adult rat. Fluorescent immunohistochemistry was performed on sections of rat brain covering the entire rostro-caudal extent of the SN and DRN with antibodies specific to the 5-HT 3A receptor subunit, as well as others targeting the monoaminergic markers tyrosine hydroxylase (TH) and the 5-HT transporter (SERT). The number of 5-HT 3A receptor-positive, TH-positive (n = 28,428 ± 888, Gundersen's m = 1 coefficient of error [CE] = 0.05) and SERT-positive (n = 12,852 ± 462, CE = 0.06) cells were estimated in both the SN and the DRN using stereology. We found that 5-HT 3A receptor-positive cells are present in the SNr (n = 1250 ± 64, CE = 0.24), but they did not co-localise with TH-positive cells, nor were they present in the SNc. In contrast, no 5-HT 3A receptor-positive cells were found in the DRN. These results support the presence of 5-HT 3 receptors in the SN, but not in the DRN, and do not support their expression on monoaminergic cells within these two brain areas. [ABSTRACT FROM AUTHOR]

In Parkinson's disease (PD), management of L-3,4-dihydroxyphenylalanine (l -DOPA)-related complications, such as l -DOPA induced dyskinesia and psychosis, remains inadequate, which poses a significant burden on the quality of life of patients. We have shown, in the hemi-parkinsonian rat model of PD, that the selective serotonin type 3 (5-HT 3) receptor antagonists ondansetron and granisetron decreased the severity of established dyskinesia, and ondansetron even attenuated the development of dyskinesia. Here, we seek to confirm these favourable data on dyskinesia and to explore the effect of ondansetron on the severity of psychosis-like behaviours (PLBs) in the gold standard model of PD, the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned non-human primate. We first determined the pharmacokinetic profile of ondansetron in the marmoset. Subsequently, six MPTP-lesioned marmosets were administered l -DOPA chronically until they exhibited stable and reproducible dyskinesia and PLBs upon each administration of l -DOPA. On behavioural assessment days, ondansetron (0.01, 0.1 and 1 mg/kg) or vehicle was administered in conjunction with l -DOPA, and the severity of dyskinesia, PLBs and parkinsonism was evaluated. Ondansetron 0.1 mg/kg alleviated global dyskinesia severity by 73% (P < 0.0001) and decreased duration of on-time with disabling dyskinesia by 88% (P = 0.0491). Ondansetron 0.1 mg/kg reduced the severity of global PLBs by 80% (P < 0.0001) and suppressed on-time with disabling PLBs (P = 0.0213). Ondansetron enhanced the anti-parkinsonian action of l -DOPA, reducing global parkinsonism by 53% compared to l -DOPA (P = 0.0004). These results suggest that selective blockade of the 5-HT 3 receptor with ondansetron may be an effective approach to alleviate l -DOPA-related complications. • The pharmacokinetic profile of ondansetron was assessed in the marmoset. • 5-HT 3 blockade alleviates l -DOPA-induced dyskinesia in the MPTP-lesioned marmoset. • 5-HT 3 blockade alleviates psychosis-like behaviours in the MPTP-lesioned marmoset. • 5-HT 3 blockade enhances anti-parkinsonian benefit conferred by l -DOPA. [ABSTRACT FROM AUTHOR]

Psychosis and dyskinesia significantly diminish the quality of life of patients with advanced Parkinson's disease (PD). Available treatment options are unfortunately few and their use is limited by adverse effects. We have recently shown that activation of metabotropic glutamate 2 and 3 (mGlu2/3) receptors produced significant relief of L-3,4-dihydroxyphenylalanine (L-DOPA)-induced psychosis-like behaviours (PLBs) and dyskinesia in experimental models of PD. Here, using the highly-selective mGlu2 positive allosteric modulator (PAM) LY-487,379, we seek to determine the contribution of selective mGlu2 activation on both L-DOPA-induced PLBs and dyskinesia, in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned primate. We first determined the pharmacokinetic (PK) profile of LY-487,379 in the common marmoset, following which we administered it (0.1, 1 and 10 mg/kg) or its vehicle to 6 MPTP-lesioned marmosets previously exposed to L-DOPA to elicit stable PLBs and dyskinesia. We found that LY-487,379 provided a ≈45% reduction of the global PLBs observed and reduced global dyskinesia score by ≈ 55%. Moreover, LY-487,379 enhanced the anti-parkinsonian effect of L-DOPA, by reducing global parkinsonian score by ≈ 15%. Our data suggest that selective mGlu2 positive allosteric modulation with LY-487,379 may represent a potential therapeutic approach to alleviate both L-DOPA-induced PLBs and dyskinesia in PD. [ABSTRACT FROM AUTHOR]

L-3,4-dihydroxyphenylalanine (L-DOPA) has been the standard treatment for Parkinson's disease (PD), despite that its chronic use leads to motor fluctuations and dyskinesia in as many as 95% of patients. Previous studies have shown that serotonin type 3 (5-HT 3) receptor blockade reduces dopamine levels within the striatum, suggesting that it could potentially lead to a reduction of dyskinesia. Here, we assessed the effects of ondansetron on L-DOPA-induced abnormal involuntary movements (AIMs) in the 6-hydroxydopamine (6-OHDA)-lesioned rat. We performed two series of experiments. First, rats exhibiting stable AIMs were administered ondansetron (0.0001, 0.001, 0.01, 0.1 and 1 mg/kg) or vehicle in combination with L-DOPA, following which the effect of ondansetron on AIMs was assessed. In the second series of experiments, following 6-OHDA lesion, rats received daily administration of ondansetron (0.0001, 0.001 mg/kg) or vehicle, started concurrently with the first L-DOPA dose, and treatments were continued for 22 days. After a washout period, an acute L-DOPA challenge was administered and AIMs severity was assessed. The effect of ondansetron on L-DOPA anti-parkinsonian action was also determined. We found that the addition of ondansetron 0.0001 mg/kg to L-DOPA resulted in a significant reduction of AIMs severity (by 31%, P < 0.001), when compared to vehicle. Ondansetron 0.0001 mg/kg, when started concurrently with L-DOPA, also attenuated the development of AIMs, with AIMs being 64% less severe (P < 0.05), when compared to L-DOPA/vehicle. Ondansetron did not impair L-DOPA anti-parkinsonian action. Our results suggest that selective 5-HT 3 blockade is a promising strategy to reduce the severity of L-DOPA-induced dyskinesia and may also attenuate its development. [ABSTRACT FROM AUTHOR]

Selective blockade of serotonin 2A (5-HT 2A) receptors is a promising strategy to reduce L-3,4-dihydroxyphenylalanine (l -DOPA)-induced dyskinesia and has shown efficacy in a Phase III clinical trial for dopaminergic psychosis in Parkinson's disease (PD). However, pre-clinical and clinical evidence suggest that, while this approach may be effective and well tolerated, there might be a ceiling beyond which no further therapeutic benefit might be achieved. There is mounting evidence that 5-HT 2A receptors form a functional hetero-complex with metabotropic glutamate 2 (mGlu 2) receptors, with antagonism of 5-HT 2A receptors and activation of mGlu 2 receptors producing similar effects on the Gi/Gq signalling ratio at the intra-cellular level. Based on this interaction between 5-HT 2A and mGlu 2 receptors, we hypothesised that activation of mGlu 2 receptors would alleviate dyskinesia and psychosis in PD. LY-354,740 is a selective mGlu 2/3 orthosteric agonist that was previously tested in the clinic. In experiments conducted in the 6-hydroxydopamine (6-OHDA)-lesioned rat and the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned marmoset, we found that mGlu 2/3 activation with LY-354,740 significantly reduced the expression of dyskinesia and psychosis-like behaviours, while simultaneously enhancing l -DOPA therapeutic benefit. Moreover, mGlu 2/3 activation with LY-354,740 attenuated the development of dyskinesia. These data indicate that activation of mGlu 2/3 receptors is a therapeutic strategy that may provide relief for both motor and-non-motor treatment-related complications in PD. • We have determined the pharmacokinetic profile of LY-354,740 in the marmoset. • LY-354,740 reduces l -DOPA-induced dyskinesia in the 6-OHDA-lesioned rat. • LY-354,740 reduces l -DOPA-induced dyskinesia in the MPTP-lesioned marmoset. • LY-354,740 reduces l -DOPA-induced psychosis in the MPTP-lesioned marmoset. • LY-354,740 does not interfere with the anti-parkinsonian action of l -DOPA. [ABSTRACT FROM AUTHOR]