Paula Ravenscroft

Alterations of striatal NMDA receptor subunits associated with the development of dyskinesia in the MPTP-lesioned primate model of Parkinson's disease

The development of dyskinesias and other motor complications greatly limits the use of levodopa therapy in Parkinsons disease (PD). Studies in rodent models of PD suggest that an important mechanism underlying the development of levodopa-related motor complications is alterations in striatal NMDA receptor function. We examined striatal NMDA receptors in the MPTP-lesioned primate model of PD. Quantitative immunoblotting was used to determine the subcellular abundance of NR1, NR2A and NR2B subunits in striata from unlesioned, MPTP-lesioned (parkinsonian) and MPTP-lesioned, levodopa-treated (dyskinetic) macaques. In parkinsonian macaques, NR1 and NR2B subunits in synaptosomal membranes were decreased to 66 +/- 11% and 51.2 +/- 5% of unlesioned levels respectively, while the abundance of NR2A was unaltered. Levodopa treatment eliciting dyskinesia normalized NR1 and NR2B and increased NR2A subunits to 150 +/- 12% of unlesioned levels. No alterations in receptor subunit tyrosine phosphorylation were detected. These results demonstrate that altered synaptic abundance of NMDA receptors with relative enhancement in the abundance of NR2A occurs in primate as well as rodent models of parkinsonism, and that in the macaque model, NR2A subunit abundance is further increased in dyskinesia. These data support the view that alterations in striatal NMDA receptor systems are responsible for adaptive and maladaptive responses to dopamine depletion and replacement in parkinsonism, and highlight the value of subtype selective NMDA antagonists as novel therapeutic approaches for PD.

The NR2B-selective NMDA receptor antagonist CP-101,606 exacerbates L-DOPA-induced dyskinesia and provides mild potentiation of anti-parkinsonian effects of L-DOPA in the MPTP-lesioned marmoset model of Parkinson's disease

In Parkinsons disease (PD), degeneration of the dopaminergic nigrostriatal pathway leads to enhanced transmission at NMDA receptors containing NR2B subunits. Previous studies have shown that some, but not all, NR2B-containing NMDA receptor antagonists alleviate parkinsonian symptoms in animal models of PD. Furthermore, enhanced NMDA receptor-mediated transmission underlies the generation of L-DOPA-induced dyskinesia (LID). The subunit content of NMDA receptors responsible for LID is not clear. Here, we assess the actions of the NMDA antagonist CP-101,606 in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned marmoset model of Parkinsons disease. CP-101,606 is selective for NMDA receptors containing NR2B subunits, with higher affinity for NR1/NR2B complexes compared to ternary NR1/NR2A/NR2B complexes. CP-101,606 had no significant effect on parkinsonian symptoms when administered as monotherapy over a range of doses (0.1-10 mg/kg). CP-101,606 provided a modest potentiation of the anti-parkinsonian actions of L-DOPA (8 mg/kg), although, at doses of 1 and 3 mg/kg, CP-101,606 exacerbated LID. Results of this study provide further evidence of differences in the anti-parkinsonian activity and effects on LID of the NR2B subunit selective NMDA receptor antagonists. These distinctions may reflect disparities in action on NR1/NR2B as opposed to NR1/NR2A/NR2B receptors.

Ropinirole versus L-DOPA effects on striatal opioid peptide precursors in a rodent model of Parkinson's disease: implications for dyskinesia.

The dopamine precursor, L-3,4-dihydroxyphenylalanine (L-DOPA), remains the most common treatment for Parkinsons disease. However, following long-term treatment, disabling side effects, particularly L-DOPA-induced dyskinesias, are encountered. Conversely, D2/D3 dopamine receptor agonists, such as ropinirole, exert an anti-parkinsonian effect while eliciting less dyskinesia when administered de novo in Parkinsons disease patients. Parkinsons disease and L-DOPA-induced dyskinesia are both associated with changes in mRNA and peptide levels of the opioid peptide precursors preproenkephalin-A (PPE-A) and preproenkephalin-B (PPE-B). Furthermore, a potential role of abnormal opioid peptide transmission in dyskinesia is suggested due to the ability of opioid receptor antagonists to reduce the L-DOPA-induced dyskinesia in animal models of Parkinsons disease. In this study, the behavioural response, striatal topography and levels of expression of the opioid peptide precursors PPE-A and PPE-B were assessed, following repeated vehicle, ropinirole, or L-DOPA administration in the 6-OHDA-lesioned rat model of Parkinsons disease. While repeated administration of L-DOPA significantly elevated PPE-B mRNA levels (313% cf. vehicle, 6-OHDA-lesioned rostral striatum; 189% cf. vehicle, 6-OHDA-lesioned caudal striatum) in the unilaterally 6-OHDA-lesioned rat model of Parkinsons disease, ropinirole did not. These data and previous studies suggest the involvement of enhanced opioid transmission in L-DOPA-induced dyskinesia and that part of the reason why D2/D3 dopamine receptor agonists have a reduced propensity to elicit dyskinesia may reside in their reduced ability to elevate opioid transmission.

Calcium-permeable AMPA receptors are involved in the induction and expression of L-DOPA-induced dyskinesia in Parkinson's disease

J. Neurochem. (2010) 114, 409–511.

Phenotype of Striatofugal Medium Spiny Neurons in Parkinsonian and Dyskinetic Nonhuman Primates: A Call for a Reappraisal of the Functional Organization of the Basal Ganglia

The classic view of anatomofunctional organization of the basal ganglia is that striatopallidal neurons of the “indirect” pathway express D2 dopamine receptors and corelease enkephalin with GABA, whereas striatopallidal neurons of the “direct” pathway bear D1 dopamine receptors and corelease dynorphin and substance P with GABA. Although many studies have investigated the pathophysiology of the basal ganglia after dopamine denervation and subsequent chronic levodopa (l-dopa) treatment, none has ever considered the possibility of plastic changes leading to profound reorganization and/or biochemical phenotype modifications of medium spiny neurons. Therefore, we studied the phenotype of striatal neurons in four groups of nonhuman primates, including the following: normal, parkinsonian, parkinsonian chronically treated with l-dopa without exhibiting dyskinesia, and parkinsonian chronically treated with l-dopa exhibiting overt dyskinesia. To identify striatal cells projecting to external (indirect) or internal (direct) segments of the globus pallidus, the retrograde tracer cholera toxin subunit B (CTb) was injected stereotaxically into the terminal areas. Using immunohistochemistry techniques, brain sections were double labeled for CTb and dopamine receptors, opioid peptides, or the substance P receptor (NK1). We also used HPLC-RIA to assess opioid levels throughout structures of the basal ganglia. Our results suggest that medium spiny neurons retain their phenotype because no variations were observed in any experimental condition. Therefore, it appears unlikely that dyskinesia is related to a phenotype modification of the striatal neurons. However, this study supports the concept of axonal collateralization of striatofugal cells that project to both globus pallidus pars externa and globus pallidus pars interna. Striatofugal pathways are not as segregated in the primate as previously considered.

Synaptic recruitment of AMPA glutamate receptor subunits in levodopa-induced dyskinesia in the MPTP-lesioned nonhuman primate

MONTY A. SILVERDALE,* CHRISTOPHER KOBYLECKI, PENELOPE J. HALLETT, QIN LI, ANTHONE W. DUNAH, PAULA RAVENSCROFT, ERWAN BEZARD, AND JONATHAN M. BROTCHIE Greater Manchester Neurosciences Centre, Salford Royal Hospital, Stott Lane, Salford, United Kingdom MassGeneral Institute for Neurodegenerative Disease, Massachusetts General Hospital and Harvard Medical School, Charlestown, Massachusetts Institute of Lab Animal Sciences, China Academy of Medical Sciences, Beijing, China Université Victor Segalen-Bordeaux 2, Centre National de la Recherche Scientifique, Bordeaux Institute of Neuroscience, UMR 5227, Bordeaux, France Toronto Western Research Institute, Toronto Western Hospital, Toronto, Ontario, Canada

Striatal histone modifications in models of levodopa-induced dyskinesia.

Despite recent advances in the treatment of Parkinson disease (PD), levodopa remains the most effective and widely used therapy. A major limitation to the use of levodopa is the development of abnormal involuntary movements, termed levodopa‐induced dyskinesia (LDID), following chronic levodopa treatment. Since recent studies have suggested that modifications of chromatin structure may be responsible for many long‐lasting changes in brain function, we have examined post‐translational modifications of striatal histones in two models of LDID: an acute murine model and a chronic macaque monkey model, both exposed to 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine (MPTP). In the primate model, which closely resembles human LDID, we observed that chronic levodopa and the appearance of LDID was associated with marked deacetylation of histone H4, hyperacetylation and dephosphorylation of histone H3, and enhancement of the phosphorylation of extracellular signal‐regulated kinase (ERK). In the murine model of acutely rather than chronically induced LDID, dopamine depletion and levodopa treatment also induced deacetylation of histone H4 and phosphorylation of ERK, but histone H3 exhibited decreased trimethylation and reduced rather than enhanced acetylation. These data demonstrate striking changes in striatal histones associated with the induction of LDID in both animal models. The pattern of changes observed, as well as the behavioral features, differed in the two models. However, both models exhibit marked deacetylation of histone H4, suggesting that inhibitors of H4 deacetylation may be useful in preventing or reversing LDID.

Neuroanatomical Study of the A11 Diencephalospinal Pathway in the Non-Human Primate

Background The A11 diencephalospinal pathway is crucial for sensorimotor integration and pain control at the spinal cord level. When disrupted, it is thought to be involved in numerous painful conditions such as restless legs syndrome and migraine. Its anatomical organization, however, remains largely unknown in the non-human primate (NHP). We therefore characterized the anatomy of this pathway in the NHP. Methods and Findings In situ hybridization of spinal dopamine receptors showed that D1 receptor mRNA is absent while D2 and D5 receptor mRNAs are mainly expressed in the dorsal horn and D3 receptor mRNA in both the dorsal and ventral horns. Unilateral injections of the retrograde tracer Fluoro-Gold (FG) into the cervical spinal enlargement labeled A11 hypothalamic neurons quasi-exclusively among dopamine areas. Detailed immunohistochemical analysis suggested that these FG-labeled A11 neurons are tyrosine hydroxylase-positive but dopa-decarboxylase and dopamine transporter-negative, suggestive of a L-DOPAergic nucleus. Stereological cell count of A11 neurons revealed that this group is composed by 4002±501 neurons per side. A 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine (MPTP) intoxication with subsequent development of a parkinsonian syndrome produced a 50% neuronal cell loss in the A11 group. Conclusion The diencephalic A11 area could be the major source of L-DOPA in the NHP spinal cord, where it may play a role in the modulation of sensorimotor integration through D2 and D3 receptors either directly or indirectly via dopamine formation in spinal dopa-decarboxylase-positives cells.

Rotigotine treatment partially protects from MPTP toxicity in a progressive macaque model of Parkinson's disease.

Clinical DA agonist monotherapy trials, which used in vivo imaging of the DA transporter (DAT) to assess the rate of progression of nigrostriatal degeneration, have failed to demonstrate consistent evidence for neuroprotection. The present study aims at reconciling these experimental and clinical data by testing the protective property of the continuously delivered D3/D2/D1 dopamine receptor agonist rotigotine. Using a progressive 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-lesioned (MPTP) macaque model that mimics the progression of Parkinsons disease in vivo ([99mTc]-TRODAT-1 single photon emission computed tomography (SPECT)) and ex vivo ([125I]-nortropane DAT labelling) endpoints were evaluated. After 38 days of treatment followed by two weeks of washout, rotigotine-treated animals were significantly less parkinsonian than the vehicle-treated ones. Such behavioural difference is the consequence of a partial protection of the DA terminals as could be confirmed by ex vivo DAT labelling. However, the protection of nerve terminals was not detected using SPECT. The data suggest that rotigotine exerts partial protection but that conventional imaging would not be able to identify such protection.

Pattern of levodopa‐induced striatal changes is different in normal and MPTP‐lesioned mice

While levodopa‐induced neurochemical changes have been studied in animal models of Parkinsons disease, very little is known regarding the effects of levodopa administration in normal animals. The present study investigates the effects normal and MPTP‐lesioned mice chronically treated with two different doses of levodopa. We assess changes in striatal dopamine (DA) receptor binding, striatal DA receptor mRNA levels and striatal neuropeptide precursor levels (preproenkephalin‐A [PPE‐A]; preprotachykinin [PPT]; preproenkephalin‐B [PPE‐B]). The extent of the lesion was measured by striatal DA transporter binding and stereological estimation of the number of tyrosine hydroxylase immunoreactive neurones in the substantia nigra pars compacta (SNc). In non‐lesioned animals, chronic levodopa treatment induced an increase in PPE‐A mRNA, whereas both D3R binding and PPE‐B mRNA levels were dramatically increased in the lesioned animals in a dose dependent manner. The present results show that chronic levodopa administration may induce pathophysiological changes, even in the absence of a lesion of the nigro‐striatal pathway, suggesting that the sensitization process involves predominantly the indirect striatofugal pathway in non‐lesioned animals, whereas the direct pathway is primarily involved in lesioned animals.