Effect of the mGlu2 positive allosteric modulator biphenyl-indanone A as a monotherapy and as adjunct to a low dose of L-DOPA in the MPTP-lesioned marmoset.

Activation of metabotropic glutamate 2 (mGlu2) receptors is a potential novel therapeutic approach for the treatment of parkinsonism. Thus, when administered as monotherapy or as adjunct to a low dose of L-3,4-dihydroxyphenylalanine (L-DOPA), the mGlu2 positive allosteric modulator (PAM) LY-487,379 alleviated parkinsonism in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned primates. Here, we sought to investigate the effect of biphenyl-indanone A (BINA), a highly selective mGlu2 PAM whose chemical scaffold is unrelated to LY-487,379, to determine if a structurally different mGlu2 PAM would also confer anti-parkinsonian benefit. In monotherapy experiments, MPTP-lesioned marmosets were injected with either vehicle, L-DOPA/benserazide (15/3.75 mg/kg, positive control) or BINA (0.1, 1, 10 mg/kg). In adjunct to a low L-DOPA dose experiments, MPTP-lesioned marmosets were injected with L-DOPA/benserazide (7.5/1.875 mg/kg) in combination with vehicle or BINA (0.1, 1, 10 mg/kg). Parkinsonism, dyskinesia and psychosis-like behaviours (PLBs) were then quantified. When administered alone, BINA 1 and 10 mg/kg decreased parkinsonism severity by ~22% (p < 0.01) and ~47% (p < 0.001), when compared with vehicle, which was comparable with the global effect of a high L-DOPA dose. When administered in combination with a low L-DOPA dose, BINA 1 and 10 mg/kg decreased global parkinsonism by ~38% (p < 0.001) and ~53% (p < 0.001). BINA 10 mg/kg decreased global dyskinesia by ~94% (p < 0.01) and global PLBs by ~92% (p < 0.01). Our results provide additional evidence that mGlu2 positive allosteric modulation elicits anti-parkinsonian effects. That this benefit is not related to a particular chemical scaffold suggests that it may be a class effect rather than the effect of a specific molecule.

Effect of mGluR2 and mGluR2/3 activators on parkinsonism in the MPTP-lesioned non-human primate.

We have previously discovered that the selective activation of metabotropic glutamate type 2 receptors (mGluR2) and concurrent stimulation of metabotropic glutamate types 2 and 3 receptors (mGluR2/3) enhance the anti-parkinsonian action of L-3,4-dihydroxyphenylalanine (L-DOPA). Here, we sought to determine the effects of the mGluR2/3 orthosteric agonists LY-354,740 and LY-404,039, as well as the effects of the mGluR2 positive allosteric modulators LY-487,379 and CBiPES on the range of movement, bradykinesia, posture and alertness as adjuncts to L-DOPA. Ten 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned marmosets entered 4 experimental streams: L-DOPA + LY-354,740 (vehicle, 0.1, 0.3 and 1 mg/kg), L-DOPA + LY-404,039 (vehicle, 0.1, 1 and 10 mg/kg), L-DOPA + LY-487,379 (vehicle, 0.1, 1 and 10 mg/kg), L-DOPA + CBiPES (vehicle, 0.1, 1 and 10 mg/kg). For each molecule, treatments were randomised, and the range of movement, bradykinesia, posture and alertness were assessed by a blinded rater. None of the tested compounds significantly altered the global range of movement. LY-404,039 and CBiPES both reduced global bradykinesia, by up to 46% (both P < 0.05). LY-354,740, LY-404,039 and CBiPES each improved global posture by 35%, 44% and 39% (each P < 0.05), respectively. LY-404,039 and CBiPES both enhanced alertness by 54% (P < 0.05) and 79% (P < 0.01), respectively. LY-487,379 did not improve any of the parameters. Our results suggest that selective mGluR2 positive allosteric modulation and combined mGluR2/3 orthosteric stimulation might benefit bradykinesia, posture and alertness in PD when added to L-DOPA, which potentially represent novel therapeutic indications for molecules acting via these mechanisms.

Positive allosteric mGluR2 modulation with BINA alleviates dyskinesia and psychosis-like behaviours in the MPTP-lesioned marmoset.

There is mounting evidence that positive allosteric modulation of metabotropic glutamate type 2 receptors (mGluR2) is an efficacious approach to reduce the severity of L-3,4-dihydroxyphenylalanine (L-DOPA)-induced dyskinesia, psychosis-like behaviours (PLBs), while conferring additional anti-parkinsonian benefit. However, the mGluR2 positive allosteric modulators (PAMs) tested so far, LY-487,379 and CBiPES, share a similar chemical scaffold. Here, we sought to assess whether similar benefits would be conferred by a structurally-distinct mGluR2 PAM, biphenylindanone A (BINA). Six 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned marmosets exhibiting dyskinesia and PLBs were administered L-DOPA with either vehicle or BINA (0.1, 1, and 10 mg/kg) in a randomised within-subject design and recorded. Behaviour was analysed by a blinded rater who scored the severity of each of parkinsonism, dyskinesia and PLBs. When added to L-DOPA, BINA 0.1 mg/kg, 1 mg/kg, and 10 mg/kg all significantly reduced the severity of global dyskinesia, by 40%, 52% and 53%, (all P < 0.001) respectively. BINA similarly attenuated the severity of global PLBs by 35%, 48%, and 50%, (all P < 0.001) respectively. Meanwhile, BINA did not alter the effect of L-DOPA on parkinsonism exhibited by the marmosets. The results of this study provide incremental evidence of positive allosteric modulation of mGluR2 as an effective therapeutic strategy for alleviating dyskinesia and PLBs, without hindering the anti-parkinsonian action of L-DOPA. Furthermore, this therapeutic benefit does not appear to be confined to a particular chemical scaffold.

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.

Antioxidant and anti-inflammatory effects of Boswellia dalzielii and Hibiscus sabdariffa extracts in alloxan-induced diabetic rats.

Diabetes mellitus (DM) is one of the leading worldwide public health problems. It is characterized by hyperglycemia which induces oxidative stress and inflammation, both involved in the pathogenesis of diabetes. We previously showed that Boswellia dalzielii (BD) and Hibiscus sabdariffa (HS) extracts reduced hyperglycemia and hyperlipidemia in alloxan-induced diabetic rats. In the present study, we evaluated the antioxidant and anti-inflammatory activities of both plants in alloxan-induced diabetic rats. Two sets of experiments were conducted in male Wistar rats subjected to a single intraperitoneal injection of alloxan monohydrate (150 mg/kg, b. w.). Then, diabetic rats were daily administered with either BD (1st set of experiments) or HS (2nd set of experiments) at 100, 200, and 400 mg/kg orally for 21 consecutive days. Glibenclamide (10 mg/kg) was also administered as a reference drug. At the end of the study, the animals were anesthetized, and blood samples were collected from each animal. Then, oxidative stress and inflammatory biomarkers in the serum were determined. We found that treatment with BD and HS significantly reduced malondialdehyde (MDA) and enhanced the levels of reduced glutathione (GSH), superoxide dismutase (SOD), and catalase (CAT). These extracts also significantly decreased the inflammatory markers tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6), and interleukin-1 beta (IL-1ß). From the results obtained, it can therefore be concluded that BD and HS have the potential to being developed as natural sources of antioxidant and anti-inflammatory agents that can be used for the prevention or treatment of DM.

The 5-HT2A/2C inverse agonist nelotanserin alleviates L-DOPA-induced dyskinesia in the MPTP-lesioned marmoset.

Nelotanserin is a serotonin 2A and 2C (5-HT2A/2C) inverse agonist that was previously tested in the clinic for rapid-eye movement sleep behaviour disorder and psychosis in patients with Parkinson's disease (PD) dementia. Its effect on L-3,4-dihydroxyphenylalanine (L-DOPA)-induced dyskinesia has however not been investigated. As 5-HT2A antagonism/inverse agonism is a validated approach to alleviate dyskinesia, we undertook the current study to evaluate the anti-dyskinetic potential of nelotanserin in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned marmoset. Parkinsonism was induced in six common marmosets (Callithrix jacchus, three females and three males) that were then chronically treated with L-DOPA to induce dyskinesia. On experimental days, they were administered L-DOPA in combination with vehicle or nelotanserin (0.1, 0.3 and 1 mg/kg) subcutaneously, in a randomised fashion. Dyskinesia and parkinsonism were rated post hoc by a blinded observer. In comparison to vehicle, the addition of nelotanserin 0.3 and 1 mg/kg to L-DOPA diminished peak dose dyskinesia by 47% (P < 0.05) and 69% (P < 0.001). Nelotanserin 0.3 and 1 mg/kg also reduced the severity of global dyskinesia, by 40% (P < 0.01) and 55% (P < 0.001), when compared to vehicle. Nelotanserin 0.1 mg/kg did not alleviate peak dose or global dyskinesia severity. Nelotanserin had no impact on the anti-parkinsonian action of L-DOPA. Our results highlight that nelotanserin may represent an efficacious anti-dyskinetic drug and provide incremental evidence of the potential benefit of 5-HT2A/2C antagonism/inverse agonism for drug-induced dyskinesia in PD.

The mGluR2/3 orthosteric agonist LY-404,039 reduces dyskinesia, psychosis-like behaviours and parkinsonism in the MPTP-lesioned marmoset.

LY-404,039 is an orthosteric agonist of metabotropic glutamate 2 and 3 receptors (mGluR2/3) that may harbour additional agonist effect at dopamine D2 receptors. LY-404,039 and its pro-drug, LY-2140023, have previously entered clinical trials as treatment options for schizophrenia. They could therefore be repurposed, if proven efficacious, for other conditions, notably Parkinson's disease (PD). We have previously shown that the mGluR2/3 orthosteric agonist LY-354,740 alleviated L-3,4-dihydroxyphenylalanine (L-DOPA)-induced dyskinesia and psychosis-like behaviours (PLBs) in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned marmoset. Unlike LY-404,039, LY-354,740 does not stimulate dopamine D2 receptors, suggesting that LY-404,039 may elicit broader therapeutic effects in PD. Here, we sought to investigate the effect of this possible additional dopamine D2-agonist action of LY-404,039 by assessing its efficacy on dyskinesia, PLBs and parkinsonism in the MPTP-lesioned marmoset. We first determined the pharmacokinetic profile of LY-404,039 in the marmoset, in order to select doses resulting in plasma concentrations known to be well tolerated in the clinic. Marmosets were then injected L-DOPA with either vehicle or LY-404,039 (0.1, 0.3, 1 and 10 mg/kg). The addition of LY-404,039 10 mg/kg to L-DOPA resulted in a significant reduction of global dyskinesia (by 55%, P < 0.01) and PLBs (by 50%, P < 0.05), as well as reduction of global parkinsonism (by 47%, P < 0.05). Our results provide additional support of the efficacy of mGluR2/3 orthosteric stimulation at alleviating dyskinesia, PLBs and parkinsonism. Because LY-404,039 has already been tested in clinical trials, it could be repurposed for indications related to PD.

Effect of the mGlu4 positive allosteric modulator ADX-88178 on parkinsonism, psychosis-like behaviours and dyskinesia in the MPTP-lesioned marmoset.

RATIONALE: Positive allosteric modulation of metabotropic glutamate type 4 (mGlu4) receptors is a promising strategy to alleviate parkinsonian disability and L-3,4-dihydroxyphenylalanine (L-DOPA) induced dyskinesia. ADX-88178 is a highly selective mGlu4 positive allosteric modulator (PAM) that previously enhanced the anti-parkinsonian action of L-DOPA in the 6-hydroxydopamine-lesioned rat model of Parkinson's disease (PD). OBJECTIVES: We sought to explore the effects of ADX-88178 on psychosis-like behaviours (PLBs) in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned marmoset. We also aimed to determine the effect of ADX-88178 on parkinsonism and dyskinesia. METHODS: Six MPTP-lesioned marmosets were administered L-DOPA chronically to induce stable PLBs and dyskinesias. They were then administered ADX-88178 (0.01, 0.1 and 1 mg/kg) or vehicle, in combination with L-DOPA/benserazide (15/3.75 mg/kg), both sub-cutaneously, in a randomised fashion. PLBs, parkinsonism and dyskinesia were then measured. RESULTS: ADX-88178 mildly worsened global PLBs at the dose of 1 mg/kg (by 13%, P = 0.020). L-DOPA alone conferred 158 min of on-time, while the duration of on-time was 212 min (34% increase, P = 0.011), after adding ADX-88178 1 mg/kg to L-DOPA. Accordingly, ADX-88178 1 mg/kg reduced global parkinsonian disability, by 38% (P = 0.0096). ADX-88178 1 mg/kg diminished peak dose dyskinesia by 34% (P = 0.015). Minimal effects were provided by lower doses. CONCLUSIONS: Whereas these results provide additional evidence of the anti-parkinsonian and anti-dyskinetic effects of mGlu4 positive allosteric modulation as an adjunct to L-DOPA, they also suggest that ADX-88178 may exacerbate dopaminergic psychosis. Further studies are needed to evaluate this possible adverse effect of mGlu4 PAMs on PD psychosis.

Distribution of [11C]-JNJ-42491293 in the marmoset brain: a positron emission tomography study.

JNJ-42491293 is a metabotropic glutamate 2 (mGlu2) positive allosteric modulator (PAM) that was radiolabelled with [11C]- to serve as a positron emission tomography (PET) ligand. Indeed, in vitro, the molecule displays high selectivity at mGlu2 receptors. However, PET experiments performed in rats, macaques and humans, have suggested that [11C]-JNJ-42491293 could interact with an unidentified, non-mGlu2 receptor binding site. The brain distribution of [11C]-JNJ-42491293 has not been determined in the brain of the common marmoset, a small non-human primate increasingly used in neuroscience research. Here, we investigated the distribution of [11C]-JNJ-42491293 in the marmoset brain. Three marmosets underwent brain magnetic resonance imaging (MRI) and 90-min dynamic PET scans with [11C]-JNJ-42491293 in combination with vehicle or the mGlu2 PAM AZD8529 (0.1, 1 and 10 mg/kg). In the scans in which [11C]-JNJ-42491293 was co-administered with vehicle, the brain areas with the highest standardised uptake values (SUVs) were the midbrain, cerebellum and thalamus, while the lowest SUVs were found in the pons. The addition of AZD8529 (0.1, 1 and 10 mg/kg) to [11C]-JNJ-42491293 did not modify the SUVs obtained with [11C]-JNJ-42491293 alone, and ex vivo blocking autoradiography with PAM AZD8529 (10, 100, 300 µM) on marmoset brain sections showed increased signals in the blocking conditions compared to vehicle, suggesting that no competition occurred between the 2 ligands. The results we obtained here do not suggest that [11C]-JNJ-42491293 interacts selectively, or even at all, with mGlu2 receptors in the marmoset, in agreement with findings previously reported in macaque and human.

Pharmacokinetic profile of bitopertin, a selective GlyT1 inhibitor, in the rat.

Bitopertin, a selective glycine transporter 1 (GlyT1) inhibitor, has been extensively studied for the treatment of schizophrenia, with known safety and tolerability profiles in the clinic. Whereas several rodent experiments have been reported, the pharmacokinetic (PK) profile of bitopertin in rodents has not been extensively reported, as only two studies disclosed limited PK parameters in male rats after oral administration. Here, we determined the PK profile of bitopertin in female Sprague-Dawley rats. Blood samples were taken serially, before and after sub-cutaneous (0.03, 0.1, 0.3, 1, and 3 mg/kg) or intra-venous (0.1 mg/kg) administration. Plasma levels were determined by high-performance liquid chromatography coupled with heat-assisted electrospray ionisation tandem mass spectrometry (HPLC-HESI MS/MS). Subsequently, PK parameters were calculated using non-compartmental analysis, including area under the curve (AUC), time (Tmax) to maximal plasma concentration (Cmax), clearance (CL), volume of distribution (Vz), as well as half-life (T1/2). Following sub-cutaneous injection, bitopertin exhibited dose-dependent AUC0-∞ (439.6-34,018.9 ng/mL) and Tmax (3.7-24.0 h), a very long terminal T1/2 (35.06-110.32 h) and low CL (0.07-0.13 L/h/kg), suggesting that bitopertin is slowly absorbed and eliminated in the rat. The observed relationship between dose and the extent of drug exposure (AUC) was linear. Following administration of all sub-cutaneous doses, measured bitopertin plasma levels were comparable to levels achieved with doses already administered in the clinic. We hope that our results will be useful in the design of pre-clinical experiments in which this drug will eventually be administered sub-cutaneously.

Anti-parkinsonian effect of the mGlu2 positive allosteric modulator LY-487,379 as monotherapy and adjunct to a low L-DOPA dose in the MPTP-lesioned marmoset.

In previous experiments, we have discovered that positive allosteric modulation of metabotropic glutamate 2 (mGlu2) receptors enhances the anti-parkinsonian action of an optimal dose of L-3,4-dihydroxyphenylalanine (L-DOPA). Whether selective mGlu2 positive allosteric modulation would also alleviate parkinsonian disability as monotherapy or as adjunct to a sub-optimal dose of L-DOPA has not been determined. Here, we assessed the anti-parkinsonian effect of mGlu2 positive allosteric modulation as monotherapy and adjunct to a sub-optimal dose of L-DOPA in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned marmosets. The highly selective positive allosteric modulator (PAM) LY-487,379 was utilised to activate mGlu2 receptors. When administered as monotherapy, LY-487,379 10 mg/kg diminished global parkinsonism by 48% (P < 0.001) and increased duration of on-time by 7-fold, when compared to vehicle treatment (P < 0.05). When added to a sub-optimal dose of L-DOPA, LY-487,379 10 mg/kg decreased global parkinsonism by 44% (P < 0.001) and extended duration of on-time by 2.5-fold (P < 0.01). Our results indicate that selective mGlu2 positive allosteric modulation elicits anti-parkinsonian benefits as monotherapy and as adjunct to sub-optimal dose of L-DOPA paradigms, potentially suggesting that mGlu2 PAMs may have a therapeutic niche early in the treatment of PD as DOPA-sparing agents.

Effect of glycine transporter 1 inhibition with bitopertin on parkinsonism and L-DOPA induced dyskinesia in the 6-OHDA-lesioned rat.

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.

Effect of galvanic vestibular stimulation applied at the onset of stance on muscular activity and gait cycle duration in healthy individuals.

Locomotion requires the complex involvement of the spinal and supraspinal systems. So far, the role of vestibular input in gait has been assessed mainly with respect to gait stability. The noninvasive technique of galvanic vestibular stimulation (GVS) has been reported to decrease gait variability and increase gait speed, but the extent of its effect on spatiotemporal gait parameters is not fully known. Objective: Characterize vestibular responses during gait and determine the influence of GVS on cycle duration in healthy young participants. Methods: Fifteen right-handed individuals participated in the study. Electromyography (EMG) recordings of the bilateral soleus (SOL) and tibialis anterior muscles (TA) were performed. First, to determine stimulation intensity, an accelerometer placed on the vertex recorded the amplitude of the head tilts evoked by the GVS (1-4 mA, 200 ms) to establish a motor threshold (T). Second, while participants walked on a treadmill, GVS was applied at the onset of the stance phase during the treadmill gait with an intensity of 1 and 1.5 T with the cathode behind the right (RCathode) or left ear (LCathode). EMG traces were rectified, averaged (n = 30 stimuli), and analyzed. Latency, duration, and amplitude of vestibular responses as well as the mean duration of the gait cycles were measured. Results: GVS mainly induced long-latency responses in the right SOL, right TA and left TA. Only short-latency responses were triggered in the left SOL. Responses in the right SOL, left SOL and left TA were polarity dependent, being facilitatory with RCathode and inhibitory with LCathode, whereas responses in the right TA remained facilitatory regardless of the polarity. With the RCathode configuration, the stimulated cycle was prolonged compared with the control cycle at both 1 and 1.5 T, due to prolonged left SOL and TA EMG bursts, but no change was observed in right SOL and TA. With LCathode, GVS did not modify the cycle duration. Conclusion: During gait, a brief, low-intensity GVS pulse delivered at the right stance onset induced mainly long-latency polarity-dependent responses. Furthermore, a RCathode configuration increased the duration of the stimulated gait cycle by prolonging EMG activity on the anodic side. A similar approach could be explored to influence gait symmetry in individuals with neurological impairment.

Co-registration of Imaging Modalities (MRI, CT and PET) to Perform Frameless Stereotaxic Robotic Injections in the Common Marmoset.

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.

Autoradiographic labelling of 5-HT3 receptors in the hemi-parkinsonian rat brain.

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-HT3) 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-HT3 antagonists and measured 5-HT3 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-HT3 mediated neurotransmission may contribute to the pathophysiology of l-DOPA induced dyskinesia.

Combined 5-HT2A and mGlu2 modulation for the treatment of dyskinesia and psychosis in Parkinson's disease.

Antagonising the serotonin 2A (5-HT2A) 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-HT2A receptors were shown to form hetero-dimers with metabotropic glutamate 2 (mGlu2) receptors, in which 5-HT2A blockade and mGlu2 activation elicit equivalent effects at the downstream signalling level. We have previously shown that mGlu2 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-HT2A antagonism and mGlu2 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 mGlu2 positive allosteric modulator LY-487,379 and the 5-HT2A antagonist EMD-281,014, either alone or in combination, were added to l-DOPA. In the second series of experiments, the mGlu2/3 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 mGlu2 blockade would diminish the effects of antagonising 5-HT2A receptors. To this end, the mGlu2/3 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 mGlu2 activation may enhance the anti-dyskinetic and anti-psychotic effects of 5-HT2A blockade and could provide relief to PD patients with dyskinesia and psychotic symptoms beyond what can be achieved with current therapies.

Granisetron, a selective 5-HT3 antagonist, reduces L-3,4-dihydroxyphenylalanine-induced abnormal involuntary movements in the 6-hydroxydopamine-lesioned rat.

Administration of L-3,4-dihydroxyphenylalanine (L-DOPA) provides Parkinson's disease patients with effective symptomatic relief. However, long-term L-DOPA therapy is often marred by complications such as dyskinesia. We have previously demonstrated that serotonin type 3 (5-HT3) receptor blockade with the clinically available and highly selective antagonist ondansetron alleviates dyskinesia in the 6-hydroxydopamine (6-OHDA)-lesioned rat. Here, we sought to explore the antidyskinetic efficacy of granisetron, another clinically available 5-HT3 receptor antagonist. Rats were rendered hemi-parkinsonian by 6-OHDA injection in the medial forebrain bundle. Following induction of stable abnormal involuntary movements (AIMs), granisetron (0.0001, 0.001, 0.01, 0.1 and 1 mg/kg) or vehicle was acutely administered in combination with L-DOPA and the severity of AIMs, both duration and amplitude, was determined. We also assessed the effect of granisetron on L-DOPA antiparkinsonian action by performing the cylinder test. Adding granisetron (0.0001, 0.001, 0.01, 0.1 and 1 mg/kg) to L-DOPA resulted in a significant reduction of AIMs duration and amplitude, with certain parameters being reduced by as much as 38 and 45% (P < 0.05 and P < 0.001, respectively). The antidyskinetic effect of granisetron was not accompanied by a reduction of L-DOPA antiparkinsonian action. These results suggest that 5-HT3 blockade may reduce L-DOPA-induced dyskinesia without impairing the therapeutic efficacy of L-DOPA. However, a U-shaped dose-response curve obtained with certain parameters may limit the therapeutic potential of this strategy and require further investigation.

Effect of the mGlu2 positive allosteric modulator CBiPES on dyskinesia, psychosis-like behaviours and parkinsonism in the MPTP-lesioned marmoset.

Advanced Parkinson's disease (PD) is often complicated by the occurrence of dyskinesia, motor fluctuations and psychosis. To this day, few treatment options are available for each of these phenomena, and they are at times not effective or elicit adverse events, leaving some patients short of therapeutic options. We have recently shown that positive allosteric modulation of metabotropic 2 (mGlu2) receptors with the prototypical positive allosteric modulator (PAM) LY-487,379 is efficacious at alleviating both dyskinesia and psychosis-like behaviours (PLBs), while simultaneously enhancing the anti-parkinsonian action of L-3,4-dihydroxyphenylalanine (L-DOPA), in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned marmoset. Here, we assessed the effects of CBiPES, a mGlu2 PAM derived from LY-487,379, but with improved pharmacokinetic properties. Six MPTP-lesioned marmosets with reproducible dyskinesia and PLBs were administered L-DOPA in combination with vehicle or CBiPES (0.1, 1 and 10 mg/kg), after which their behaviour was rated. CBiPES 10 mg/kg reduced global dyskinesia by 60% (P < 0.0001), while peak dose dyskinesia was reduced by 66% (P < 0.001), compared to L-DOPA/vehicle. CBiPES 10 mg/kg also diminished global PLBs by 56% (P < 0.0001), while peak dose PLBs were reduced by 64% (P < 0.001), compared to L-DOPA/vehicle. Lastly, CBiPES enhanced the anti-parkinsonian action of L-DOPA, by reducing global parkinsonian disability by 43% (P < 0.01), compared to L-DOPA/vehicle. Our results provide further evidence that mGlu2 positive allosteric modulation may be an approach that could be efficacious for the treatment of dyskinesia, psychosis and motor fluctuations in PD.

Stereological investigation of 5-HT3 receptors in the substantia nigra and dorsal raphe nucleus in the rat.

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-HT3) 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-HT3 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-HT3A receptor subunit, as well as others targeting the monoaminergic markers tyrosine hydroxylase (TH) and the 5-HT transporter (SERT). The number of 5-HT3A receptor-positive, TH-positive (n = 28,428 ±â€¯888, Gundersen's m = 1 coefficient of error [CE] = 0.05) and SERT-positive (n = 12,852 ±â€¯462, CE = 0.06) cells were estimated in both the SN and the DRN using stereology. We found that 5-HT3A receptor-positive cells are present in the SNr (n = 1250 ±â€¯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-HT3A receptor-positive cells were found in the DRN. These results support the presence of 5-HT3 receptors in the SN, but not in the DRN, and do not support their expression on monoaminergic cells within these two brain areas.

Monoamine oxidase A inhibition with moclobemide enhances the anti-parkinsonian effect of L-DOPA in the MPTP-lesioned marmoset.

Whereas monoamine oxidase (MAO) type B inhibitors are used as adjunct to L-3,4-dihydroxyphenylalanine (L-DOPA) in the treatment of Parkinson's disease (PD), the enzyme MAO type A (MAO-A) also participates in the metabolism of dopamine in the human and primate striatum. Here, we sought to assess the effect of the selective reversible MAO-A inhibitor moclobemide on L-DOPA anti-parkinsonian in the gold standard animal model of PD, the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned primate. We also assessed the effect of moclobemide on L-DOPA-induced dyskinesia and psychosis-like behaviours (PLBs). Experiments were performed in six MPTP-lesioned marmosets chronically treated with L-DOPA and exhibiting stable dyskinesia and PLBs upon each administration. In a randomised within-subject design, animals were administered a therapeutic dose of L-DOPA in combination with moclobemide (0.1, 1 and 10 mg/kg) or its vehicle, after which the severity of parkinsonism, dyskinesia, and PLBs was rated by an experienced blinded rater. Moclobemide significantly reduced the global parkinsonian disability (- 36% with 0.1 mg/kg, P < 0.05; - 38% with 1 mg/kg, P < 0.01; - 47% with 10 mg/kg, P < 0.01), when compared with its vehicle. This reduction of parkinsonism was not accompanied by an exacerbation of dyskinesia or PLBs. Reversible MAO-A inhibition with moclobemide appears as an effective way to increase the anti-parkinsonian action of L-DOPA, without negatively affecting dyskinesia or dopaminergic psychosis.