[Show abstract][Hide abstract] ABSTRACT: L-DOPA is the gold-standard treatment for Parkinson’s disease (PD), but induces troublesome dyskinesia after prolonged treatment. This is associated with the ‘false neurotransmitter’ conversion of L-DOPA to dopamine by serotonin neurons projecting from the raphe to the dorsal striatum. Reducing their activity by targeting pre-synaptic 5-HT1A receptors should thus be an attractive therapeutic strategy, but previous 5-HT1A agonists have yielded disappointing results. Here, we describe the activity of a novel, highly selective and potent 5-HT1A agonist, NLX-112 (also known as befiradol or F13640) in rat models relevant to PD and its associated affective disorders.
[Show abstract][Hide abstract] ABSTRACT: L-DOPA-induced dyskinesia (LID) is a major complication of the pharmacotherapy of Parkinson's disease. Emerging approaches to the treatment of LID include negative modulation of metabotropic glutamate receptor type 5 (mGluR5) and positive modulation of serotonin receptors 5-HT1A/1B. We set out to compare the efficacy of these two approaches in alleviating the dyskinesias induced by either L-DOPA or a D1 receptor agonist. Rats with unilateral 6-OHDA lesions were treated chronically with either L-DOPA or the selective D1-class receptor agonist SKF38393 to induce abnormal involuntary movements (AIMs). Rats with stable AIM scores received challenge doses of the mGluR5 antagonist, MTEP (2.5 and 5mg/kg), or the 5-HT1A/1B agonists 8-OH-DPAT/CP94253 (0.035/0.75 and 0.05/1.0mg/kg). Treatments were given either alone or in combination. In agreement with previous studies, 5mg/kg MTEP and 0.05/1.0mg/kg 8-OH-DPAT/CP94253 significantly reduced L-DOPA-induced AIM scores. The two treatments in combination achieved a significantly greater effect than each treatment alone. Moreover, a significant attenuation of L-DOPA-induced AIM scores was achieved when combining doses of MTEP (2.5mg/kg) and 8-OH-DPAT/CP94253 (0.035/0.75mg/kg) that did not have a significant effect if given alone. SKF38393-induced AIM scores were reduced by MTEP at both doses tested, but not by 0.05/1.0mg/kg 8-OH-DPAT/CP94253. The differential efficacy of MTEP and 8-OH-DPAT/CP94253 in reducing L-DOPA- versus SKF38393-induced dyskinesia indicate that these treatments have different mechanisms of action. This contention is supported by the efficacy of subthreshold doses of these compounds in reducing L-DOPA-induced AIMs. Combining negative modulators of mGluR5 with positive modulators of 5-HT1A/1B receptors may therefore achieve greater than additive antidyskinetic effects and reduce the dose requirement for these drugs in Parkinson´s disease.
[Show abstract][Hide abstract] ABSTRACT: Major limitations to the pharmacotherapy of Parkinson's disease (PD) are the motor complications resulting from L-DOPA treatment. Abnormal involuntary movements (dyskinesia) affect a majority of the patients after a few years of L-DOPA treatment and can become troublesome and debilitating. Once dyskinesia has debuted, an irreversible process seems to have occurred, and the movement disorder becomes almost impossible to eliminate with adjustments in peroral pharmacotherapy. There is a great need to find new pharmacological interventions for PD that will alleviate parkinsonian symptoms without inducing dyskinesia. The 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned non-human primate model is an excellent symptomatic model of PD and was the first model used to reproduce L-DOPA-induced dyskinesia experimentally. As it recapitulates the motor features of human dyskinesia, that is, chorea and dystonia, it is considered a reliable animal model to define novel therapies. Over the last decade, rodent models of L-DOPA-induced dyskinesia have been developed, having both face validity and predictive validity. These models have now become the first-line experimental tool for therapeutic screening purposes. The application of classical 6-hydroxydopamine (6-OHDA) lesion procedures to produce rodent models of dyskinesia has provided the field with more dynamic tools, since the versatility of toxin doses and injection coordinates allows for mimicking different stages of PD. This article will review models developed in non-human primate and rodents to reproduce motor complications induced by dopamine replacement therapy. The recent breakthroughs represented by mouse models and the relevance of rodents in relation to non-human primate models will be discussed.
[Show abstract][Hide abstract] ABSTRACT: The transcription factor ΔFosB is a mediator of maladaptive neuroplasticity in animal models of Parkinson's disease (PD) and L-DOPA-induced dyskinesia. Using an antibody that recognizes all known isoforms of FosB and ΔFosB, we have examined the expression of these proteins in post-mortem basal ganglia sections from PD patients. The patient cases were classified as being dyskinetic or non-dyskinetic based on their clinical records. Sections from neurologically healthy controls were also included in the study. Compared to both controls and non-dyskinetic cases, the dyskinetic group showed a higher density of FosB/ΔFosB-immunopositive cells in the posterior putamen, which represents the motor region of the striatum in primates. In contrast, the number of FosB/ΔFosB-positive cells did not differ significantly among the groups in the caudate, a region primarily involved with the processing of cognitive and limbic-related information. Only sparse FosB/ΔFosB immunoreactivity was found in the in the pallidum externum and internum, and no significant group differences were detected in these nuclei. The putaminal elevation of FosB/ΔFosB-like immunoreactivity in patients who had been affected by L-DOPA-induced dyskinesia is consistent with results from both rat and non-human primate models of this movement disorder. The present findings support the hypothesis of an involvement of ΔFosB-related transcription factors in the molecular mechanisms of L-DOPA-induced dyskinesia.
[Show abstract][Hide abstract] ABSTRACT: L-DOPA remains the gold-standard treatment for Parkinson's disease but causes motor fluctuations and dyskinesia. Metabotropic glutamate receptor type 5 (mGluR5) has been proposed as a target for antidyskinetic therapies. Here, we evaluate the effects of fenobam, a noncompetitive mGluR5 antagonist already tested in humans, using rodent and nonhuman primate models of Parkinson's disease. In both animal models, acute administration of fenobam attenuated the L-DOPA-induced abnormal involuntary movements (50-70% reduction at the doses of 30mg/kg in rats and 10mg/kg in monkeys). The effect consisted in a reduction of peak-dose dyskinesia, whereas the end-dose phase was not affected. Chronic administration of fenobam to previously drug-naïve animals (de novo treatment) attenuated the development of peak-dose dyskinesia without compromising the anti-parkinsonian effect of L-DOPA. In addition, fenobam prolonged the motor stimulant effect of L-DOPA. We conclude that fenobam acts similarly in rat and primate models of L-DOPA-induced dyskinesia and represents a good candidate for antidyskinetic treatment in Parkinson's disease.
Neurobiology of Disease 05/2010; 39(3):352-61. DOI:10.1016/j.nbd.2010.05.001 · 5.20 Impact Factor