The α2 adrenergic antagonist fipamezole improves quality of levodopa action in Parkinsonian primates

Reduction in the antiparkinsonian benefit of levodopa is a major complication of long‐term levodopa treatment in advanced Parkinson's disease (PD). Such loss of benefit arises because of reduced duration of action and appearance of disabling dyskinesia. We assess the potential of the α₂ adrenergic antagonist fipamezole to reduce motor complications in parkinsonian macaques. MPTP‐lesioned macaques were treated acutely with fipamezole (10 mg/kg) alone and in combination with two doses of levodopa. Fipamezole extended both duration and quality of antiparkinsonian action of levodopa. Duration of antiparkinsonian action, on time, was increased by up to 75% while “good‐quality” on time, i.e., that not associated with disabling dyskinesia, was increased by up to 98%. Combination of fipamezole with the lower dose of levodopa provided antiparkinsonian benefit at least equivalent to that provided by the higher dose levodopa alone. However, with the combination, antiparkinsonian benefit was of much better quality. The proportion of on time without disabling dyskinesia (79%) was significantly greater than that with high dose levodopa alone (45%). Increased duration and quality of levodopa action may represent therapeutically valuable actions of α₂ adrenergic antagonists. © 2010 Movement Disorder Society     

Histamine H3 receptor agonists reduce L-dopa-induced chorea, but not dystonia, in the MPTP-lesioned nonhuman primate model of Parkinson's disease.

L-dopa-induced dyskinesia (LID) remains a major complication of the treatment of Parkinson's disease. The neural mechanisms underlying LID are thought to involve overactivity of striatal glutamatergic neurotransmission, with resultant underactivation of the output regions of the basal ganglia. Histamine H3 heteroreceptors can reduce glutamate and gamma-aminobutyric acid (GABA) transmission in the striatum and substantia nigra reticulata, respectively. Thus, we tested whether the histamine H3 receptor agonists immepip and imetit can alleviate LID in the MPTP-lesioned marmoset model of Parkinson's disease. Coadministration of immepip (1 mg/kg) with L-dopa (15 mg/kg) was associated with significantly less total dyskinesia than L-dopa alone. When dyskinesia was separately rated as chorea and dystonia, coadministration of L-dopa with either immepip or imetit (both 10 mg/kg) significantly reduced chorea but had no effect on dystonia. The antidyskinetic actions of the H3 agonists were not accompanied by alteration of the antiparkinsonian actions of L-dopa. However, immepip (10 mg/kg), when administered as monotherapy, significantly increased parkinsonian disability compared to vehicle. Overall, the results obtained in this study suggest that histamine H3 receptors may be involved in the neural mechanisms underlying L-dopa-induced dyskinesia in Parkinson's disease.     

Induction of chorea and dystonia in parkinsonian primates

Administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine in primates induced a parkinsonian syndrome that could be reversed by levodopa treatment. Animals quickly developed an apparent restlessness ("akathisia") of the lower limbs after as little as five doses. After 4-10 weeks of regular levodopa therapy, animals developed "peak dose" choreiform movements in the lower limbs that spread, with time, to involve the upper limbs and orofacial musculature. With further treatment (5-21 months), animals developed "peak dose" dystonia that variably involved the limbs and orofacial musculature. These conditions represent novel models of levodopa-induced chorea and dystonia in humans. They depend on the same underlying neuropathology and treatment regimen as their human counterparts. It is to be anticipated that these models of dyskinesia will be useful in determining the mechanisms underlying chorea and dystonia in humans and are ideally suited for experimental evaluation of new treatment strategies.     

The selective mu‐opioid receptor antagonist adl5510 reduces levodopa‐induced dyskinesia without affecting antiparkinsonian action in mptp‐lesioned macaque model of Parkinson's disease

In Parkinson's disease (PD), dyskinesia develops following long‐term treatment with 3,4‐dihydroxyphenylalanine (L ‐dopa). Given the prominent role of the opioid system in basal ganglia function, nonselective opioid receptor antagonists have been tested for antidyskinetic efficacy in the clinic (naltrexone and naloxone), although without success. In the current study, ADL5510, a novel, orally active opioid antagonist with mu opioid receptor selectivity, was examined in L ‐dopa‐treated 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine (MPTP) macaques. Antidyskinetic effects were compared with those of naltrexone. Parkinsonian monkeys with established L ‐dopa‐induced dyskinesia (LID) received acute challenges with L ‐dopa (subcutaneously) in combination with either vehicle, ADL5510 (0.1, 1, 3 or 10 mg/kg by mouth), or naltrexone (1, 3, or 10 mg/kg subcutaneously). Following treatments, behavior was monitored for 6 hours. Parameters assessed were total activity, parkinsonism, and dyskinesia. ADL5510 (1, 3, and 10 mg/kg) reduced activity and LID (chorea and dystonia) without affecting the antiparkinsonian benefits of L ‐dopa. The antidyskinetic effect of ADL5510 showed a U‐shaped dose–response. It was inactive at 0.1 mg/kg, efficacious at 1 and 3 mg/kg (72% and 40% reductions, respectively), and then less effective at 10 mg/kg. The quality of ON time produced by L ‐dopa was improved, as indicated by a reduction in the percentage of ON time spent experiencing disabling dyskinesia (70% and 61% reductions with 1 and 3 mg/kg, respectively, compared with L ‐dopa). Naltrexone, in contrast, did not alleviate LID or affect the antiparkinsonian actions of L ‐dopa. Mu‐selective opioid antagonists have the potential to form the basis of novel antidyskinetic therapies for PD. © 2011 Movement Disorder Society     

Pramipexole combined with levodopa improves motor function but reduces dyskinesia in MPTP‐treated common marmosets

Reduced expression of dyskinesia is observed in levodopa‐primed MPTP‐treated common marmosets when dopamine agonists are used to replace levodopa. We now investigate whether a combination of the D‐2/D‐3 agonist pramipexole and levodopa also reduces dyskinesia intensity while maintaining the reversal of motor disability. Drug naïve, non‐dyskinetic MPTP‐treated common marmosets were treated daily for up to 62 days with levodopa (12.5 mg/kg plus carbidopa 12.5 mg/kg p.o. BID) or pramipexole (0.04–0.3 mg/kg BID) producing equivalent reversal of motor disability and increases in locomotor activity. Levodopa alone resulted in marked dyskinesia induction but little or no dyskinesia resulted from the administration of pramipexole. From day 36, some animals were treated with a combination of levodopa (3.125–6.25 mg/kg plus carbidopa 12.5 mg/kg p.o. BID) and pramipexole (0.1–0.2 mg/kg p.o. SID). This improved motor disability to a greater extent than occurred with levodopa alone. Importantly, while dyskinesia was greater than that produced by pramipexole alone, the combination resulted in less intense dyskinesia than produced by levodopa alone. These results suggest that pramipexole could be administered with a reduced dose of levodopa to minimize dyskinesia in Parkinson's disease while maintaining therapeutic efficacy. © 2010 Movement Disorder Society     

Use of catechol‐O‐methyltransferase inhibition to minimize L‐3,4‐dihydroxyphenylalanine‐induced dyskinesia in the 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine‐lesioned macaque

L‐3,4‐dihydroxyphenylalanine (L‐DOPA)‐induced dyskinesia is a complication of dopaminergic treatment in Parkinson's disease. Lowering the L‐DOPA dose reduces dyskinesia but also reduces the antiparkinsonian benefit. A therapy that could enhance the antiparkinsonian action of low‐dose L‐DOPA (LDl) without exacerbating dyskinesia would thus be of considerable therapeutic benefit. This study assessed whether catechol‐O‐methyltransferase (COMT) inhibition, as an add‐on to LDl, might be a means to achieve this goal. Cynomolgus macaques were administered 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine. Dyskinesia was established by chronic treatment with L‐DOPA. Two doses of L‐DOPA were identified – high‐dose L‐DOPA (LDh), which provided good antiparkinsonian benefit but was compromised by disabling dyskinesia, and LDl, which was sub‐threshold for providing significant antiparkinsonian benefit, without dyskinesia. LDh and LDl were administered in acute challenges in combination with vehicle and, for LDl, with the COMT inhibitor entacapone (5, 15 and 45 mg/kg). The duration of antiparkinsonian benefit (ON‐time), parkinsonism and dyskinesia were determined. The ON‐time after LDh was ～170 min and the ON‐time after LDl alone (～98 min) was not significantly different to vehicle (～37 min). In combination with LDl, entacapone significantly increased the ON‐time (5, 15 and 45 mg/kg being ～123, ～148 and ～180 min, respectively). The ON‐time after LDl/entacapone 45 mg/kg was not different to that after LDh. However, whereas the percentage ON‐time that was compromised by disabling dyskinesia was ～56% with LDh, it was only ～31% with LDl/entacapone 45 mg/kg. In addition to the well‐recognized action of COMT inhibition to reduce wearing‐OFF, the data presented suggest that COMT inhibition in combination with low doses of L‐DOPA has potential as a strategy to alleviate dyskinesia.     

Combined fenobam and amantadine treatment promotes robust antidyskinetic effects in the 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine (MPTP)‐lesioned primate model of Parkinson's disease

Amantadine, an N‐methyl‐D‐aspartate glutamate receptor antagonist, is currently the only pharmacological treatment for levodopa‐induced dyskinesia (LID) in Parkinson's disease (PD), but causes adverse effects on the central nervous system at therapeutic doses. Fenobam, a negative modulator of metabotropic glutamate receptor subtype 5, has recently been reported to attenuate LID in MPTP‐treated macaques. The aim of the current study was to investigate the treatment interactions of fenobam and amantadine on LID in the MPTP‐treated macaque model of PD. The antidyskinetic and ‐parkinsonian effects were measured after administration of fenobam (10‐30 mg/kg) and amantadine (10‐30 mg/kg) alone and in combination. Fenobam (30 mg/kg) and amantadine (30 mg/kg) alone reduced LID, whereas lower doses of either drug did not cause any significant effects. A combined treatment of fenobam and amantadine at subthreshold doses (10 and 20 mg/kg) significantly reduced LID without worsening PD disability. These data suggest that a low‐dose combination of fenobam and amantadine can be used for alleviating dyskinesia without causing adverse motor effects. Such combined therapies may offer a new therapeutic strategy for treatment of LID in PD patients. © 2014 International Parkinson and Movement Disorder Society     

The 5-HT1A-receptor agonist flibanserin reduces drug-induced dyskinesia in RGS9-deficient mice

Drug-induced dyskinesia is a major complication of dopamine replacement therapy in advanced Parkinson’s disease consisting of dystonia, chorea and athetosis. Agonists at 5-HT1A-receptors attenuate levodopa-induced motor complications in non-human primates. Mice with increased dopamine D2 receptor (DRD2) signalling due to the lack of expression of the regulator of G-protein signalling 9 (RGS9) also develop dyskinesia following levodopa treatment. We investigated whether the 5-HT1A-receptor agonist flibanserin compared with buspirone reduces motor abnormalities induced by levodopa or quinelorane, a selective dopamine D2-receptor agonist. Following dopamine depletion via reserpine, 40 mice (20 wild-type and 20 RGS9 knock-out) were treated with flibanserin or buspirone in combination with levodopa or quinelorane. Motor behaviour was analysed using open field analysis. RGS9 knock-out mice displayed significantly more drug-induced dystonia (p?<?0.04; t test) than wild type. In quinelorane-treated wild-type mice flibanserin as well as buspirone significantly reduced dystonia (p?<?0.05). In RGS9 knock-out animals again both reduced quinelorane-induced dystonia. However, flibanserin was significantly more effective (p?=?0.003). Following reserpine pretreatment and administration of levodopa wild-type and RGS 9 knock-out mice showed mild to moderate dystonia. Surprisingly, 10?mg/kg buspirone increased dystonia in both animal groups, whereas it was decreased by 10?mg/kg flibanserin. However, compared with levodopa alone only the increase of dystonia by buspirone was significant (p?<?0.04). Flibanserin showed promising antidyskinetic effects in a model of drug-induced dyskinesia. Our data underline the possible benefit of 5-HT1A agonists in drug-induced dyskinesia.     

Levodopa-induced dyskinesias improved by a glutamate antagonist in parkinsonia monkeys

Antagonists of the N-methyl-D-aspartate (NMDA) subtype of glutamate receptor have been reported to potentiate the antiparkinsonian action of levodopa and reverse levodopa-induced motor fluctuations in animal models of Parkinson's disease. To evalute the effect of NMDA receptor blockade on dyskinesias complicating the response to long-term levodopa therapy, we studied the selective antagonist LY235959 in six 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine-lesioned monkeys. Drugs were administered subcutaneously, LY235959 at doses of 0.5, 1.0, 3.0, and 5.0 mg/kg and levodopa/benserazide at doses that produced moderate dyskinesias while almost totally reversing parkinsonian signs. Compared with vehicle control injections, LY235959 (3.0 mg/kg) abolished oral dyskinesias and diminished choreic dyskinesias by 68% (P < 0.01). Lower doses had smaller effects, although still significant, on oral dyskinesias (55% reduction at 1.0 mg/kg, P < 0.05). The highest LY235959 dose (5.0 mg/kg) prolonged oral dyskinesia suppression, but tended to increase dystonia severity. LY235959 had no effect on motor function when given alone and did not reduce the antiparkinsonian response to levodopa. These findings suggest that NMDA receptor blockade may ameliorate the dyskinetic complications of long-term levodopa therapy, without diminishing the beneficial effects on parkinsonian signs.     

The course of dyskinesia induction by different treatment schedules of levodopa in Parkinsonian rats: Is continuous dopaminergic stimulation necessary?

The aim of the present study was to investigate the course of levodopa induced dyskinesia (LID) development in parkinsonian rats treated with several different levodopa dosing regiments. Administration of 6.25 mg/kg levodopa once daily did not induce any dyskinesia for the first 12.5 ± 2.5 days. Then, LID gradually increased in intensity reaching an AIMs score on day 40 of 6.3 ± 0.9. Treatment with 6.25 mg/kg of levodopa qid resulted in the rapid appearance of LID with a mean latency of 2 days and an AIMs score of 19.9 ± 2.9 on day 10. Levodopa (25 mg/kg) once daily induced severe LID from the second day of treatment reaching an AIMs score of 35 ± 3.2. In summary, the worst way for delivering levodopa was through intermittent administration of high doses. The daily cumulative dose of levodopa was found more important for LID induction than the total amount of levodopa received. In contrast, the best way to administer levodopa in respect to prevention/delay of LID was “low dopaminergic stimulation” with one low daily dose, instead of trying to achieve “continuous dopaminergic stimulation” using several levodopa doses throughout the day. The benefits of this strategy offered protection against severe dyskinesia even if subsequently subjects were switched to high dose levodopa. © 2007 Movement Disorder Society     

Antidyskinetic effect of magnesium sulfate in MPTP-lesioned monkeys

The antiparkinsonian action of an NMDA receptor antagonist, magnesium sulfate (50, 100, and 200 mg/kg), alone and in association with levodopa was explored in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned parkinsonian and control rhesus monkeys. At the three doses tested, magnesium sulfate decreased levodopa-induced dyskinesia [cumulative dyskinetic scores after levodopa: 129 +/- 13; after levodopa and magnesium sulfate: 65 +/- 14 (50 mg/kg), P < 0.001; 64 +/- 10 (100 mg/kg), P < 0.001; 66 +/- 21 (200 mg/kg), P < 0.001, compared to levodopa administration alone]. These results show that magnesium sulfate importantly reduces levodopa-induced dyskinesia.     

Effect of pulsatile administration of levodopa on dyskinesia induction in drug‐naïve MPTP‐treated common marmosets: Effect of dose,frequency of administration,and brain exposure

Levodopa (L ‐dopa) consistently primes basal ganglia for the appearance of dyskinesia in parkinsonian patients and 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine hydrochloride (MPTP) ‐treated primates. This finding may reflect its relatively short duration of effects resulting in pulsatile stimulation of postsynaptic dopamine receptors in the striatum. We have compared the relationship between L ‐dopa dose and frequency of administration on dyskinesia initiation in drug‐naïve, MPTP‐treated common marmosets. We have also studied the effect of increased brain exposure to pulsatile administration by combining a low‐dose of L ‐dopa with the peripheral catechol‐O‐methyltransferase inhibitor (COMT‐I), entacapone. Pulsatile administration of a low (dose range, 5.0–7.5 mg/kg p.o.) or a high (12.5 mg/kg) dose of L ‐dopa plus carbidopa b.i.d. produced a dose‐related reversal of motor deficits. Repeated administration of low and high doses of L ‐dopa for 26 days to drug‐naïve, MPTP‐treated animals also caused a dose‐related induction of peak‐dose dyskinesia. Repeated administration of high‐dose L ‐dopa b.i.d. compared to once daily caused a frequency‐related improvement of motor symptoms, resulting in a more rapid and initially more intense appearance of peak‐dose dyskinesia. Administration of low‐dose L ‐dopa b.i.d. for 26 days in combination with entacapone enhanced the increase in locomotor activity and reversal of disability produced by L ‐dopa alone, but with no obvious change in duration of L ‐dopa's effect. However, combining entacapone with L ‐dopa resulted in the more rapid appearance of dyskinesia, which was initially more severe than occurred with L ‐dopa alone. Importantly, increasing pulsatile exposure of brain to L ‐dopa by preventing its peripheral breakdown also increases dyskinesia induction. © 2003 Movement Disorder Society     

The highly selective mGlu2 receptor positive allosteric modulator LY‐487,379 alleviates l‐DOPA‐induced dyskinesia in the 6‐OHDA‐lesioned rat model of Parkinson's disease

l ‐3,4‐Dihydroxyphenylalanine (l ‐DOPA) is the most effective treatment for Parkinson's disease (PD), but its use over a long period is marred by motors complications such as dyskinesia. We previously demonstrated that selective metabotropic glutamate 2/3 (mGlu_2/3) receptor activation with LY‐354,740 alleviates dyskinesia in the 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine (MPTP)‐lesioned marmoset and the 6‐hydroxydopamine (6‐OHDA)‐lesioned rat. Here, we sought to determine the role played by selective mGlu₂ activation in the anti‐dyskinetic effect of mGlu_2/3 stimulation and have investigated the effect of the highly selective mGlu₂ positive allosteric modulator LY‐487,379 at alleviating established, and preventing the development of, l ‐DOPA‐induced dyskinesia in the 6‐OHDA‐lesioned rat. First, dyskinetic 6‐OHDA‐lesioned rats were administered l ‐DOPA in combination with LY‐487,379 (0.1, 1 and 10 mg/kg) or vehicle, and the severity of dyskinesia was determined. Second, 6‐OHDA‐lesioned rats were administered LY‐487,379 (0.1 or 1 mg/kg), started concurrently with l ‐DOPA, once daily for 22 days, and dyskinesia severity was evaluated weekly for four consecutive weeks. We also assessed the effect of LY‐487,379 on l ‐DOPA anti‐parkinsonian effect. We found that acute challenges of LY‐487,379 0.1 mg/kg in combination with l ‐DOPA, significantly diminished dyskinesia severity, by ≈54% (p < .01), when compared to vehicle. Moreover, animals treated with l ‐DOPA/LY‐487,379 0.1 and 1 mg/kg during the dyskinesia induction phase exhibited milder dyskinesia, by ≈74% and ≈61%, respectively (both p < .01), when compared to l ‐DOPA/vehicle. LY‐487,379 did not impair l ‐DOPA anti‐parkinsonian activity. These results suggest that mGlu₂ activation may be an effective and promising therapeutic strategy to alleviate the severity and prevent the development of dyskinesia.     

Factors predictive of the development of Levodopa‐induced dyskinesia and wearing‐off in Parkinson's disease

The Stalevo Reduction in Dyskinesia Evaluation in Parkinson's Disease (STRIDE‐PD) study compared the initiation of levodopa (l ‐dopa) therapy with l ‐dopa/carbidopa (LC) versus l ‐dopa/carbidopa/entacapone (LCE) in patients with Parkinson's disease. In the current study, the STRIDE‐PD study population was investigated to determine the effect of l ‐dopa dose and other risk factors on the development of dyskinesia and wearing‐off. Patients were randomized to receive LCE (n=373) or LC (n=372). Blinded assessments for dyskinesia and wearing‐off were performed at 3‐month intervals for the 134‐ to 208‐week duration of the study. The patients were divided into 4 dose groups based on nominal l ‐dopa dose at the time of onset of dyskinesia (or at study conclusion if there was no dyskinesia): group 1, <400 mg/day (n=157); group 2, 400 mg/day (n=310); group 3, 401 to 600 mg/day (n=201); and group 4, >600 mg/day (n=77). Similar analyses were performed with respect to wearing‐off and any motor complication. The times to onset and frequency of dyskinesia, wearing‐off, or any motor complication were compared using the log‐rank test (overall trend test) and a Cox proportional hazards model (pairwise comparisons). A stepwise Cox proportional hazards model was used to screen predictive factors in a multivariate analysis. The risk of developing dyskinesia and wearing‐off increased in an l ‐dopa dose‐dependent manner (P<0.001 for both). Analyses using l ‐dopa equivalent doses produced comparable results. Factors that were predictive of dyskinesia, in rank order, were: young age at onset, higher l ‐dopa dose, low body weight, North American geographic region, LCE treatment group, female gender, and more severe Unified Parkinson's Disease Rating Scale (UPDRS) Part II. Multivariate analyses identified similar predictors for wearing‐off but included baseline UPDRS Part III and excluded weight and treatment allocation. The risk of developing dyskinesia or wearing‐off was closely linked to l ‐dopa dose. The current results suggest that physicians should use the lowest dose of l ‐dopa that provides satisfactory clinical control to minimize the risk of both dyskinesia and wearing‐off. © 2013 Movement Disorder Society     

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

Understanding the biological mechanisms of l ‐dopa‐induced motor complications is dependent on our ability to investigate these phenomena in animal models of Parkinson's disease. The most common motor complications consist in wearing‐off fluctuations and abnormal involuntary movements appearing when plasma levels of l ‐dopa are high, commonly referred to as peak‐dose l ‐dopa‐induced dyskinesia. Parkinsonian models exhibiting these features have been well‐characterized in both rodent and nonhuman primate species. The first animal models of peak‐dose l ‐dopa‐induced dyskinesia were produced in monkeys lesioned with N‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine (MPTP) and treated chronically with l ‐dopa to elicit choreic movements and dystonic postures. Seminal studies were performed in these models using both metabolic mapping and electrophysiological techniques, providing fundamental pathophysiological insights that have stood the test of time. A decade later, it was shown possible to reproduce peak‐dose l ‐dopa‐induced dyskinesia in rats and mice rendered parkinsonian with nigrostriatal 6‐hydroxydopamine lesions. When treated with l ‐dopa, these animals exhibit abnormal involuntary movements having both hyperkinetic and dystonic components. These models have enabled molecular‐ and cellular‐level investigations into the mechanisms of l ‐dopa‐induced dyskinesia. A flourishing literature using genetically engineered mice is now unraveling the role of specific genes and neural circuits in the development of l ‐dopa‐induced motor complications. Both non‐human primate and rodent models of peak‐dose l ‐dopa‐induced dyskinesia have excellent construct validity and provide valuable tools for discovering therapeutic targets and evaluating potential treatments. © 2018 International Parkinson and Movement Disorder Society     

Pardoprunox reverses motor deficits but induces only mild dyskinesia in MPTP‐treated common marmosets

Long‐acting full dopamine D₂ agonists produce less dyskinesia in 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine (MPTP)‐treated primates and in Parkinson's disease than effective antiparkinsonian doses of levodopa. They do not however, prevent priming for dyskinesia expression on subsequent levodopa exposure. In contrast, the effects of partial D₂ receptor agonists on dyskinesia are unclear. We now examine the ability of the partial D₂ agonist pardoprunox (SLV308) to improve motor function and its propensity to prime for dyskinesia in drug naïve, MPTP‐treated common marmosets. Previously, drug naïve, MPTP‐treated common marmosets were treated with equivalent doses of either pardoprunox (SLV308) (0.1 mg/kg po), ropinirole (0.18 mg/kg po), or levodopa (10 mg/kg po BID) for 28 days. All treatments induced a similar reduction of motor disability. Dyskinesia induced by levodopa was of greater intensity than that following administration of either pardoprunox (SLV308) or ropinirole. Administration of pardoprunox (SLV308) resulted in dyskinesia that was less intense and of shorter duration than either ropinirole or levodopa. At the end of drug treatment, acute challenge with levodopa resulted in the expression of marked dyskinesia in animals that had previously received chronic levodopa or ropinirole treatment. However, animals previously treated with pardoprunox (SLV308) showed only mild dyskinesia in response to the levodopa challenge. These results suggest that the partial D₂ agonist pardoprunox (SLV308) is less likely to prime for dyskinesia or to lead to the expression of dyskinesia than either levodopa or full dopamine agonists. © 2010 Movement Disorder Society     

Onset of dyskinesia with adjunct ropinirole prolonged‐release or additional levodopa in early Parkinson's disease

Levodopa‐induced dyskinesia can result in significant functional disability and reduced quality of life in patients with Parkinson's disease (PD). The goal of this study was to determine if the addition of once‐daily ropinirole 24‐hour prolonged‐release (n = 104) in PD patients not optimally controlled with levodopa after up to 3 years of therapy with less than 600 mg/d delays the onset of dyskinesia compared with increasing doses of levodopa (n = 104). During the study, 3% of the ropinirole prolonged‐release group (mean dose 10 mg/d) and 17% of the levodopa group (mean additional dose 284 mg/d) developed dyskinesia (P < 0.001). There were no significant differences in change in Unified Parkinson's Disease Rating Scale activities of daily living or motor scores, suggesting comparable efficacy between the two treatments. Adverse events were comparable in the two groups with nausea, dizziness, insomnia, back pain, arthralgia, somnolence, fatigue, and pain most commonly reported. Ropinirole prolonged‐release delayed the onset of dyskinesia with comparable efficacy to increased doses of levodopa in early PD patients not optimally controlled with levodopa. © 2010 Movement Disorder Society     

Antiparkinsonian effects of the novel D3/D2 dopamine receptor agonist, S32504, in MPTP-lesioned marmosets: Mediation by D2, not D3, dopamine receptors.

L-dopa remains the most common treatment for Parkinson's disease. However, there is considerable interest in D3/D2 receptor agonists such as the novel agent S32504, since they exert antiparkinsonian properties in the absence of dyskinesia. An important question concerns the roles of D2 vs. D3 receptors, an issue we addressed with the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned nonhuman primate model of Parkinson's disease. In L-dopa-primed animals, S32504 (0.16-2.5 mg/kg p.o.) dose-dependently enhanced locomotor activity. This action was abolished by the D2 antagonist, L741,626 (2.5 mg/kg), but potentiated by the D3 antagonist, S33084 (0.63 mg/kg). Both antagonists were inactive alone. In drug-naive animals, a maximally effective dose of S32504 (2.5 mg/kg p.o.) displayed pronounced antiparkinsonian properties from the third day of administration, and its actions were expressed rapidly and durably. Thus, on day 33, antiparkinsonian properties of S32504 were apparent within 5 minutes and present for > 4 hours. Moreover, they were associated with neither wearing off nor significant dyskinesia. In conclusion, the novel D3/D2 agonist S32504 may offer advantages over L-dopa in the treatment of newly diagnosed parkinsonian patients. Its actions are expressed primarily by activation of D2, not D3, receptors.     

The acute antiparkinsonian and antidyskinetic effect of AFQ056, a novel metabotropic glutamate receptor type 5 antagonist, in L-Dopa-treated parkinsonian monkeys

Overactivity of glutamatergic transmission has been implicated in Parkinson's disease (PD) and levodopa (L-Dopa)-induced dyskinesias. Striatal metabotropic glutamate receptors type 5 (mGluR5) are abundant and provide specific targets to modulate glutamatergic activity. This study investigated the acute effects of the novel mGluR5 antagonist AFQ056 on motor behavior in L-Dopa-treated monkeys with a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) lesion to model PD. Six Macaca fascicularis MPTP monkeys were treated repeatedly with L-Dopa; this treatment increased their locomotion and reduced their parkinsonian scores, but also induced dyskinesias. When AFQ056 (doses of 5, 25, 125 or 250mg/kg) was administered one hour prior to a high dose of L-Dopa, the antiparkinsonian activity of L-Dopa was maintained as measured with locomotion and antiparkinsonian scores, whereas dyskinesias were significantly reduced at 25, 125 and 250mg/kg AFQ056 for peak dyskinesia score and at 125 and 250mg/kg for the 1h peak period of dyskinesia score. Administration of AFQ056 one hour before L-Dopa led to peak or elevated plasma AFQ056 concentrations occurring close to L-Dopa peak-dose dyskinesias. We next investigated AFQ056 25mg/kg combined with a low dose of L-Dopa. The antiparkinsonian activity of L-Dopa was increased as measured with locomotion, while dyskinesias remained low at these doses. Our results show a beneficial motor effect of AFQ056 with L-Dopa in MPTP monkeys. This supports the therapeutic use of an mGluR5 antagonist to restore normal glutamatergic neurotransmission in PD and decrease dyskinesias.     

Unilateral pallidotomy in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated common marmosets exhibiting levodopa-induced dyskinesia

Pallidotomy paradoxically reduces the intensity of levodopa-induced dyskinesia without worsening motor symptoms. The reasons for this are not clear and no experimental study has investigated this phenomenon. The objective of this investigation was to evaluate the effects of unilateral pallidotomy on locomotor activity, motor disability and levodopa-induced dyskinesia in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated levodopa-primed common marmosets. Animals were primed to exhibit dyskinesia by daily administration of levodopa until stable dyskinesia was evoked by each dose. Locomotor activity, motor disability and dyskinesia were assessed weekly at baseline and following an acute levodopa challenge. Prior to pallidotomies, two distinct groups of animals emerged: poor responders to levodopa with mild dyskinesia (Group 1) and those exhibiting a marked increase in motor activity and pronounced dyskinesia (Group 2). Electrolytic lesions were placed in the left internal segment of the globus pallidus. Pallidotomy had no effect on basal or levodopa-induced motor activity in either group but significantly improved basal motor disability in Group 2. Following pallidotomy, the ability of levodopa to reduce motor disability was significantly increased in both groups. Pallidotomy improved dyskinesia in both Groups 1 and 2 but it was more effective in reducing dystonia compared with chorea. The effect of pallidotomy on dyskinesia in Group 2 was transient, with the intensity of involuntary movements reverting to presurgery levels 4 weeks later. This study shows that in levodopa-primed, parkinsonian marmosets, placement of discrete globus pallidus lesions can ameliorate levodopa-induced dyskinesia but not akinesia. This model allows the evaluation of pallidotomy-induced biochemical changes in dyskinetic primates.