Pathophysiology of motor response complications in Parkinson's disease: hypotheses on the why, where, and what

Levodopa response motor complications--GABA receptors and preproenkephalin expression in human brain

Post-mortem studies in human brain of patients with Parkinson's disease have greatly contributed to our understanding of the disease. However, few human brain studies have focused on levodopa-induced dyskinesias, which considerably limit the beneficial effect of levodopa (LD) in the treatment of Parkinson's disease. We have taken advantage of the fact that some patients develop dyskinesias and other do not to compare biochemical markers between them. In post-mortem samples from LD-treated parkinsonian patients, increased preproenkephalin expression in the putamen and increased GABA(A) receptors content in the internal globus pallidus (GPi) are found in dyskinetic parkinsonian patients compared to non-dyskinetic patients. These data are consistent with previous observations in MPTP monkeys developing dyskinesias following LD or dopamine agonist treatment. This combination of data in an animal model and in humans strongly suggests that increased enkephalinergic activity in the putamen and increased sensitivity of GABA(A) receptors in the GPi are implicated in the pathogenesis of LD-induced dyskinesias in Parkinson's disease.

Clinical-pathological study of levodopa complications

We sought to determine the continued benefit and the pattern of motor complications of long-term levodopa treatment in Parkinson's disease. Patients were evaluated between 1968 and 1996. Only those who had an adequate levodopa trial and in whom autopsy revealed Lewy body Parkinson's disease were included. Total levodopa and mean daily dose were calculated in each case. Dyskinesia, wearing-off and on-off were collectively classified as motor adverse effects and reported as cumulative incidence. Forty-two patients (male, 30; female, 12) with mean 15.9 years of illness and 9.1 years follow-up received on average 500-mg levodopa daily over 9.8 years. Seventeen of 21 patients assessed during the last 18 months of life reported some motor benefit. Adverse effects were seen in 71.4% of patients. The most common was dyskinesia, in 61.9%; wearing-off in 35.7%; and on-off in 16.7% of patients. The earliest adverse effect was dyskinesia and the last to emerge was on-off. Isolated dyskinesia was seen in 35.7% and wearing-off in 7.1% of patients; 15.5% of patients developed dyskinesia after 2.6 years and 31% after 6.4 years on levodopa. We concluded that levodopa benefit declined and adverse effects increased with time. Dyskinesia was the earliest and the most common isolated adverse effect.

Levodopa-induced dyskinesias and continuous subcutaneous infusions of apomorphine: results of a two-year, prospective follow-up

Twelve patients with levodopa-induced dyskinesias were treated with continuous subcutaneous apomorphine. A markedly significant reduction in peak dose dyskinesias occurred over a two-year follow-up.

Alteration of glutamate receptors in the striatum of dyskinetic 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated monkeys following dopamine agonist treatment

The effects of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced nigrostriatal lesion and dopaminomimetic treatment on parameters of glutamatergic activity within the basal ganglia of monkeys were studied in relation with the development of dyskinesias. Drug-naive controls, saline-treated MPTP monkeys, as well as MPTP monkeys treated with either a long-acting D2 agonist (cabergoline) or a D1 agonist (SKF-82958) given by intermittent injections or continuous infusion, were included in this study. 3H-L-glutamate, 3H-alpha-amino-3-hydroxy-5-methylisoxasole-4-propionate (AMPA), 3H-glycine, 3H-CGP39653 (an N-methyl-D-aspartate, NMDA, antagonist selective for NR1/NR2A assembly) and 3H-Ro 25-6981 (an NMDA antagonist selective for NR1/NR2B assembly), specific binding to glutamate receptors, the expression of the NR1 subunit of NMDA receptors and glutamate, glutamine and glycine concentrations were studied by autoradiography, in situ hybridization and high-performance liquid chromatography (HPLC), respectively. Pulsatile SKF-82958 and cabergoline treatment relieved parkinsonian symptoms, whereas animals continuously treated with SKF-82958 remained akinetic. Pulsatile SKF-82958 induced dyskinesias in two of the three animals tested, whereas cabergoline did not. MPTP induced no significant changes of striatal specific binding of the radioligands used, NR1 mRNA expression and amino acid concentrations. In the putamen, pulsatile SKF-82958 treatment was associated with decreased content of glycine and glutamate, whereas only glycine was decreased in cabergoline-treated monkeys. Cabergoline and continuous administration of SKF-82958 led to lower levels of NR1 mRNA in the caudate in comparison to pulsatile SKF-82958 administration. The development of dyskinesias following a D1 agonist treatment was associated with an upregulation of 3H-glutamate [+49%], 3H-AMPA [+38%], 3H-CGP39653 [+ 111%], 3H-glycine [+ 26%, nonsignificant] and 3H-Ro 25-6981 [+ 33%] specific binding in the striatum in comparison to nondyskinetic MPTP monkeys. Our data suggest that supersensitivity to glutamatergic input in the striatum might play a role in the pathogenesis of dopaminomimetic-induced dyskinesias and further support the therapeutic potential of glutamate antagonists in Parkinson's disease.

Anatomy and function of dopamine receptors: understanding the pathophysiology of fluctuations in Parkinson's disease

The principal dopamine (DA) receptors mediating the antiparkinson effects of levodopa are D1 and D2, which are anatomically and functionally segregated. We hypothesize that DA receptor-mediated effects are critical for the development of treatment-related fluctuations in Parkinson's disease (PD). We suggest that two sequential processes occur to permit the emergence of the so-called short duration response and dyskinesias: (1) functional uncoupling of D1 and D2 receptor-mediated effects with shift to the left of the dose-response curve; and, (2) sensitization of the D1-mediated striatal output due to repetitive, primarily D1 receptor stimulation by DA. These mechanisms result in excessive, pathological inhibition of basal ganglia output neurons in the GPi producing dyskinesias and the short duration response.

Continuous transdermal dopaminergic stimulation in advanced Parkinson's disease

The objective of the study was to determine the safety and efficacy of increasing doses of Rotigotine CDS in patients with advanced Parkinson's disease. The development of motor complications in Parkinson's disease has been linked to intermittent stimulation of dopamine receptors. Continuous, noninvasive, dopaminergic stimulation has not been available to date. Rotigotine CDS is a lipid-soluble D2 dopamine agonist in a transdermal delivery system that could fill this void. This inpatient study consisted of a 2-week dose escalation phase followed by a 2-week dose maintenance phase at the highest dose (80 cm2). Each individual's L-Dopa dose was back-titrated as feasible. The primary outcome measure was L-Dopa dose, and secondary outcome measures included early morning "off"-L-Dopa Unified Parkinson's Disease Rating Scale motor scores by a blinded evaluator and motor fluctuation data obtained from patient diaries ("on" without dyskinesia, "on" with dyskinesia, and "off"). Seven of 10 subjects provided data that could be evaluated. There were two administrative dropouts, and one individual was eliminated from the study because of recrudescence of hallucinations. The median daily L-Dopa dose decreased from 1,400 to 400 mg (p = 0.018, Wilcoxon test). Unified Parkinson's Disease Rating Scale motor scores were unchanged. Although diary variables improved in most individuals, only the reduction in "off" time attained statistical significance. Adverse effects were mild and consisted mainly of dopaminergic side effects and local skin reactions. The data suggest that Rotigotine CDS is an effective treatment for advanced Parkinson's disease and permits patients to substantially lower L-Dopa doses without loss of antiparkinsonian efficacy. Full-scale controlled clinical trials are warranted. In addition to potential therapeutic benefits, this drug can be used to test the hypothesis that continuous dopaminergic stimulation from the initiation of Parkinson's disease therapy will limit the development of motor complications.

Transdermal dopaminergic D(2) receptor agonist therapy in Parkinson's disease with N-0923 TDS: a double-blind, placebo-controlled study

N-0923 is a non-ergot, dopaminergic D(2) agonist designed to be transdermally available. It has anti-parkinsonian effects when infused intravenously. An adhesive matrix patch was developed to deliver N-0923 transdermally (N-0923 TDS). In this phase II trial, we evaluated the effectiveness of various doses of N-0923 TDS at replacing levodopa. Eighty-five Parkinson's disease (PD) patients were randomized to placebo or one of four doses of N-0923 TDS for 21 days. Change in daily levodopa dose was the primary efficacy measure. Significantly greater reductions in levodopa dose were achieved as compared to placebo for the two highest doses of N-0923 TDS. Patients treated with 33.5 mg and 67 mg N-0923 TDS decreased levodopa use by 26% and 28%, vs. 7% for placebo. N-0923 TDS was safe and well tolerated.

Dopamine-receptor stimulation: biobehavioral and biochemical consequences

The MPTP monkey is a well-characterized animal model of parkinsonism and provides an exceptional tool for the study of dyskinesias induced by dopamine-like agents. Several such agents have been tested during the past 15 years, and it has been found that the duration of action of these compounds is the most reliable variable with which to predict their dyskinesiogenic profile. It is proposed that L-dopa-induced dyskinesias represent a form of pathological learning caused by chronic pulsatile (nonphysiological) stimulation of dopamine receptors, which activates a cascade of molecular and biochemical events. These events include defective regulation of Fos proteins that belong to the deltaFosB family, increased expression of neuropeptides, and defective GABA- and glutamate-mediated neurotransmission in the output structures of the basal ganglia.