Pershia Samadi

mGluR5 metabotropic glutamate receptors and dyskinesias in MPTP monkeys

Modulation of excessive glutamatergic transmission within the basal ganglia is considered as an alternative approach to reduce l-Dopa-induced dyskinesias (LIDs) in Parkinsons disease (PD). In this study receptor binding autoradiography of [3H]MPEP, a metabotropic glutamate receptor 5 (mGluR5) selective radioligand, was used to investigate possible changes in mGluR5 in the basal ganglia of l-Dopa-treated 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) monkeys having developed LIDs compared to animals in which LIDs was prevented by adjunct treatments. LIDs were associated with an increase of mGluR5 specific binding in the posterior putamen and pallidum (+41% and +56%) compared to controls. By contrast, prevention of dyskinesias was associated with an important decrease of mGluR5 specific binding in these areas (-37% and -48%) compared with dyskinetic animals. Moreover, an upregulation (+34%) of mGluR5 receptor binding was seen in the anterior caudate nucleus of saline treated MPTP monkeys. This study is the first to provide evidence that enhanced mGluR5 specific binding in the posterior putamen and pallidum may contribute to the pathogenesis of LIDs in PD.

Docosahexaenoic acid reduces levodopa-induced dyskinesias in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine monkeys

The objective of the present study was to investigate the effect of docosahexaenoic acid (DHA), a polyunsaturated fatty acid (omega‐3), on levodopa‐induced dyskinesias (LIDs) in parkinsonian 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine (MPTP)–treated monkeys.

Low doses of sarizotan reduce dyskinesias and maintain antiparkinsonian efficacy of L-Dopa in parkinsonian monkeys

Dyskinesia is an important complication of treatment in Parkinsons disease (PD). Sarizotan, a 5-HT(1A) agonist with high affinity for D3 and D4 receptors was investigated on L-Dopa-induced dyskinesia (LID) in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) animal model of PD. Five MPTP female cynomolgus monkeys (Macaca fascicularis) with a moderate to severe parkinsonian syndrome and LID were used. Sarizotan 0.2, 1, and 2 mg/kg administered alone did not worsen parkinsonian symptoms; there were no effect on locomotor counts or on normal behavior of the monkeys. Sarizotan 0.2, 1, and 2 mg/kg administered 30 min before a fixed dose of L-Dopa (25-30 mg/kg s.c.) + benserazide (50 mg) did not affect the antiparkinsonian response to L-Dopa. However, mean dyskinetic scores were significantly reduced with sarizotan 1 and 2 mg/kg but not at 0.2 mg/kg. Higher doses of sarizotan (4 and 8 mg/kg, administered immediately before L-Dopa) reduced L-Dopa-induced locomotor response in all monkeys. A pharmacokinetic investigation in these monkeys showed a dose-dependent increase in mean plasma sarizotan concentrations with similar mean plasma concentrations for sarizotan 1 mg/kg alone or with L-Dopa, indicating a lack of sarizotan/L-Dopa interaction. The time course of plasma sarizotan concentrations was associated with time of maximal reduction of dyskinesias. When administered daily for two weeks in combination with L-Dopa in the same MPTP monkeys, sarizotan 1 mg/kg had a sustained antidyskinetic effect while maintaining the antiparkinsonian and locomotor effect of L-Dopa. This detailed sarizotan investigation in MPTP monkeys supports the antidyskinetic activity of this drug and for 5-HT(1A) agonists.

Opioid antagonists increase the dyskinetic response to dopaminergic agents in parkinsonian monkeys: interaction between dopamine and opioid systems

The pathogenesis of levodopa-induced dyskinesias (LID) still remains obscure. It has been suggested that enhanced opioidergic transmission in striatal output pathways may play a role in the induction of LID. To test this hypothesis, we have investigated the effect of different doses of the opioid receptor antagonists, naloxone and naltrexone on the dyskinetic response to a D1 agonist SKF 82958, a D2 agonist quinpirole and L-3,4-dihydroxyphenylalanine (L-Dopa). We have used six female cynomolgus monkeys rendered parkinsonian by the toxin MPTP and presenting a stable parkinsonian syndrome. All responded to L-Dopa and had developed dyskinesias which were manifested with each dose. The parkinsonian syndrome and dyskinesias were evaluated for each animal and scored after the treatments. Locomotor activity was measured by an electronic motility monitoring system. Our results show that coadministration of naloxone or naltrexone with dopaminergic agents leads to a significant increase in the severity of dyskinesias without noticeable effect on the antiparkinsonian efficacy of the treatment. These results suggest that increased opioidergic transmission in the two major striatal output pathways in monkeys or humans with LID might be an attempt to dampen the effect of abnormal dopaminergic stimulation rather than the cause of dyskinesias.

Prolonged kynurenine 3-hydroxylase inhibition reduces development of levodopa-induced dyskinesias in parkinsonian monkeys.

Increased glutamatergic activity is believed to play a significant role in the development of levodopa-induced dyskinesias (LID). LID may therefore be attenuated by a reduction in glutamatergic function. This was tested pharmacologically in MPTP monkeys by increasing the formation of kynurenic acid (KYNA), a tryptophan metabolite that inhibits glutamate release and also blocks NMDA receptors directly. KYNA synthesis was stimulated by prolonged systemic administration of the kynurenine 3-hydroxylase inhibitor Ro 61-8048. Four MPTP cynomolgus monkeys received l-dopa (LD; 100mg) with benserazide (25 mg) for one month. Progressively, all these animals developed LID. Four other MPTP monkeys received Ro 61-8048 (50mg/kg) daily 3 h before administration of LD/benserazide for one month. The addition of Ro 61-8048 reduced the development of LID but did not affect the antiparkinsonian efficacy of LD. Moreover, Ro 61-8048 administration caused sustained increases in serum kynurenine and KYNA concentrations, which reverted to basal values 24 h after the last treatment. This effect of Ro 61-8048 was less pronounced in the CSF. These results demonstrate that long-lasting elevation of KYNA levels caused by prolonged inhibition of kynurenine 3-hydroxylase is associated with a significant reduction in LID but does not compromise the benefits of chronic LD therapy.

Basal ganglia group II metabotropic glutamate receptors specific binding in non-human primate model of L-Dopa-induced dyskinesias.

L-Dopa-induced dyskinesias (LIDs), the disabling abnormal involuntary movements induced by chronic use of L-Dopa, limit the quality of life in Parkinsons disease (PD) patients. Modulation of group II metabotropic glutamate receptors (mGluR2/3) in the basal ganglia, a brain region critically involved in motor control, is considered as an alternative approach in therapy of PD. In this study, receptor binding autoradiography of [3H]LY341495, a mGluR2/3 selective radioligand, was used to investigate possible changes in mGluR2/3 in the basal ganglia of L-Dopa-treated 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) monkeys having developed LIDs compared to animals in which LIDs were prevented by adjunct treatments with CI-1041, a selective antagonist of the NR1A/2B subtype of NMDA receptor, or low doses of the dopamine D2 receptor agonist, cabergoline. Our study is the first to provide evidence of: (1) the similar localization of [3H]LY341495 specific binding to mGluR2/3 in the primate basal ganglia as compared to receptor distribution measured by immunohistochemistry in human and rat as well as this ligand binding in intact rat brain; (2) no change of [3H]LY341495 specific binding in basal ganglia after nigrostriatal denervation by MPTP; and (3) a widespread reduction of [(3)H]LY341495 specific binding to mGluR2/3 in the caudate nucleus (-17% to -31%), putamen (-12% to -45%) and globus pallidus (-56 to -59%) of non-dyskinetic animals treated with L-Dopa+cabergoline as compared to controls, MPTP monkeys treated with saline, L-Dopa alone (dyskinetic) or L-Dopa+CI-1041 (non-dyskinetic). This study is the first to propose a close interaction between mGluR2/3 and dopamine D2 receptors activation in the basal ganglia.

The opioid agonist morphine decreases the dyskinetic response to dopaminergic agents in parkinsonian monkeys.

In parkinsonian patients as well as in primate models with levodopa-induced dyskinesias (LID), an increase in the expression of preproenkephalin in the striatal output pathways has been demonstrated. Does this increase contribute to the development of LID, or does it rather act as a protection mechanism? To clarify this question, we have investigated the effect of different doses of morphine on the dyskinetic response to L-DOPA, a D2 agonist, and a D1 agonist. We have used MPTP-treated cynomolgus monkeys with a stable parkinsonian syndrome and reproducible dyskinesias to L-DOPA. Co-administration of morphine with dopaminergic agents produces a significant reduction in the severity of dyskinesias, while it does not affect the anti-parkinsonian efficacy of the treatment. This study suggests that the increased production of opioids in the striatal projection neurons might have a protective role to compensate the changes in synaptic transmissions that are responsible for dyskinesias, rather than be the cause of dyskinesias.

Implication of NMDA Receptors in the Antidyskinetic Activity of Cabergoline, CI-1041, and Ro 61-8048 in MPTP Monkeys with Levodopa-induced Dyskinesias

This study assessed striatal N-methyl-D-aspartate (NMDA) glutamate receptors of 1-methyl 4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) monkeys with levodopa (L-DOPA)-induced dyskinesias (LID). In a first experiment, four MPTP monkeys receiving L-DOPA/Benserazide alone developed dyskinesias. Four MPTP monkeys received L-DOPA/Benserazide plus CI-1041 an NMDA antagonist selective for NR1/NR2B and four were treated with L-DOPA/Benserazide plus a small dose of cabergoline; one monkey of each group developed mild dyskinesias at the end of treatment. In a second experiment, a kynurenine 3-hydroxylase inhibitor Ro 61-8048, combined with L-DOPA/Benserazide, reduced dyskinesias in MPTP monkeys. Drug-treated MPTP monkeys were compared to intact monkeys and saline-treated MPTP monkeys. Glutamate receptors were investigated by autoradiography using [3H]CGP-39653 (NR1/NR2A antagonist) and [3H]Ro25-6981 (NR1/NR2B antagonist). In general, striatal [3H]CGP-39653 specific binding was unaltered in all experimental groups. MPTP lesion decreased striatal [3H]Ro25-6981 specific binding; these levels were enhanced in the L-DOPA-alone-treated MPTP monkeys and decreased in antidyskinetic drugs treated monkeys. Maximal dyskinesias scores of the MPTP monkeys correlated significantly with [3H]Ro25-6981 specific binding in the rostral and caudal striatum. Hence, MPTP lesion, L-DOPA treatment and prevention of LID with CI-1041 and cabergoline, or reduction with Ro 61-8048 were associated with modulation of NR2B/NMDA glutamate receptors.

Effect of non-dopaminergic drug treatment on Levodopa induced dyskinesias in MPTP monkeys : common implication of striatal neuropeptides

Dopamine denervation in Parkinsons disease and repeated Levodopa (L-DOPA) administration that induces dyskinesias are associated with an enhancement of basal ganglia neuropeptide transmission. Various adjunct non-dopaminergic treatments to Levodopa were shown to reduce and/or prevent dyskinesias. The aim of this study was to seek if non-dopaminergic drug treatments to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) lesioned monkeys combined with L-DOPA to prevent dyskinesia were associated with changes of striatal neuropeptides. Chronic treatment with Ro 61-8048 a kynurenine hydroxylase inhibitor, docosahexaenoic acid (DHA) a polyunsaturated fatty acid (omega-3), naltrexone an opioidergic antagonist and CI-1041 an N-methyl-D-aspartate (NMDA) glutamate receptor antagonist with L-DOPA prevented dyskinesias to various extents except naltrexone whereas all MPTP monkeys treated with L-DOPA alone developed dyskinesias. Striatal preproenkephalin (PPE), preprodynorphin (PPD) and preprotachykinin A (PPT-A) mRNA levels were measured by in situ hybridization. An increase of PPE and PPD mRNA levels was observed in anterior caudate nucleus of L-DOPA treated MPTP monkeys compared to controls and to Saline-treated MPTP monkeys whereas PPT-A mRNA levels were unchanged. Striatal PPE and PPD mRNA levels remained elevated in L-DOPA plus naltrexone-treated MPTP monkeys, while co-treatment with DHA, CI-1041 or Ro 61-8048 prevented their increase to various extents. Maximal dyskinesias scores of MPTP monkeys correlated significantly with striatal PPE and PPD mRNA levels but not with PPT-A mRNA levels. These results show that drugs displaying a wide range of pharmacological activities can modulate L-DOPA induced dyskinesias and this activity is correlated with striatal PPD and PPE mRNA levels suggesting a convergent mechanism.

Effect of Kynurenine 3-Hydroxylase Inhibition on the Dyskinetic and Antiparkinsonian Responses to Levodopa in Parkinsonian Monkeys

Homeostatic interactions between dopamine and glutamate are central to the normal physiology of the basal ganglia. This relationship is altered in Parkinsonism and in levodopa‐induced dyskinesias (LID), resulting in an upregulation of corticostriatal glutamatergic function. Kynurenic acid (KYNA), a tryptophan metabolite with antagonist activity at ionotropic glutamate receptors and the capability to inhibit glutamate release presynaptically, might therefore be of therapeutic value in LID. To evaluate this hypothesis, we used a pharmacological tool, the kynurenine 3‐hydroxylase inhibitor Ro 61‐8048, which raises KYNA levels acutely. Ro 61‐8048 was tested in MPTP cynomolgus monkeys with a stable parkinsonian syndrome and reproducible dyskinesias after each dose of levodopa. Serum and CSF concentrations of KYNA and its precursor kynurenine increased dose‐dependently after Ro 61‐8048 administration, alone or in combination with levodopa. Coadministration of Ro 61‐8048 with levodopa produced a moderate but significant reduction in the severity of dyskinesias while maintaining the motor benefit. These results suggest that elevation of KYNA levels through inhibition of kynurenine 3‐hydroxylase constitutes a promising novel approach for managing LID in Parkinsons disease.