Dopamine agonist therapy in early Parkinson's disease.

BACKGROUND: Dopamine agonists are being used increasingly as first line treatment for Parkinson's disease, but there remains uncertainty about their clinical and cost-effectiveness relative to levodopa. OBJECTIVES: This meta-analysis aims to quantify more reliably the benefits and risks of dopamine agonists compared to placebo or levodopa in early Parkinson's disease. SEARCH STRATEGY: We searched CENTRAL (The Cochrane Library), MEDLINE, EMBASE, PubMed, LILACS and Web of Science, plus major journals in the field, abstract books, conference proceedings and reference lists of retrieved publications. SELECTION CRITERIA: Randomised trials comparing an orally administered dopamine agonist (with or without levodopa) versus placebo or levodopa or both placebo and levodopa in participants with early Parkinson's disease. DATA COLLECTION AND ANALYSIS: Two authors independently extracted data on clinician-rated disability, motor complications, other side-effects, treatment concordance, levodopa dose and mortality. MAIN RESULTS: Twenty-nine eligible trials, involving 5247 participants, were identified. Participants randomised to a dopamine agonist were less likely to develop dyskinesia (odds ratio (OR) 0.51, 95% confidence interval (CI) 0.43 to 0.59; P < 0.00001), dystonia (OR 0.64, 95% CI 0.51 to 0.81; P = 0.0002) and motor fluctuations (OR 0.75, 95% CI 0.63 to 0.90; P = 0.002) than levodopa-treated participants. However, various 'non-motor' side-effects, including oedema (OR 3.68, 95% CI 2.62 to 5.18; P < 0.00001), somnolence (OR 1.49, 95% CI 1.12 to 2.00; P = 0.007), constipation (OR 1.59, 95% CI 1.11 to 2.28; P = 0.01), dizziness (OR 1.45, 95% CI 1.09 to 1.92; P = 0.01), hallucinations (OR 1.69, 95% CI 1.13 to 2.52; P = 0.01) and nausea (OR 1.32, 95% CI 1.05 to 1.66; P = 0.02) were all increased in agonist-treated participants (compared with levodopa-treated participants). Agonist-treated participants were also significantly more likely to discontinue treatment due to adverse events (OR 2.49, 95% CI 2.08 to 2.98; P < 0.00001). Finally symptomatic control of Parkinson's disease was better with levodopa than with agonists, but data were reported too inconsistently and incompletely to meta-analyse. AUTHORS' CONCLUSIONS: This meta-analysis confirms that motor complications are reduced with dopamine agonists compared to levodopa, but also establishes that other important side-effects are increased and symptom control is poorer with agonists. Larger, long-term comparative trials assessing patient-rated quality of life are needed to assess more reliably the balance of benefits and risks of dopamine agonists compared to levodopa.

Surgery for Parkinson's disease: lack of reliable clinical trial evidence.

There has been a striking resurgence of interest in surgery for Parkinson's disease (PD) with new targets identified and new procedures developed. This systematic review identified over 500 studies of surgery for PD published since 1990, including over 10 000 patients. However, the authors were unable to assess the value of PD surgery reliably because only seven randomised trials were identified including just 196 patients. Studies of surgery for PD have generally been of poor quality with too few patients, too short follow up, inappropriate choice of outcome measures, and lack of control groups. Much larger, randomised, controlled trials are needed to assess the longer term effects of surgery on patient rated quality of life and cost effectiveness.

Selective labelling of 5-HT7 receptor recognition sites in rat brain using [3H]5-carboxamidotryptamine.

The aim of the present study was to establish a radioligand binding assay to selectively label the native 5-HT7 receptor expressed in rat brain. In rat whole brain (minus cerebellum and striatum) homogenate, (+/-)-pindolol (10 microM)-insensitive [3H]5-CT ([3H]5-carboxamidotryptamine; 0.5 nM) specific binding (defined by 5-HT, 10 microM) displayed a pharmacological profile similar to the recombinant 5-HT7 receptor, although the Hill coefficients for competition curves generated by methiothepin, ritanserin, sumatriptan, clozapine and pimozide were significantly less than unity. In homogenates of rat hypothalamus, (+/-)-pindolol (10 microM)-insensitive [3H]5-CT recognition sites also resembled, pharmacologically, the 5-HT7 receptor, although pimozide still generated Hill coefficients significantly less than unity. Subsequent studies were performed in the additional presence of WAY100635 (100 nM) to prevent [3H]5-CT binding to residual, possibly, 5-HT1A sites. Competition for this [3H]5-CT binding indicated the labelling in whole rat brain homogenate of a homogenous population of sites with the pharmacological profile of the 5-HT7 receptor. Saturation studies also indicated that (+/-)-pindolol (10 microM)/WAY 100635 (100 nM)-insensitive [3H]5-CT binding to homogenates of whole rat brain was saturable and to an apparently homogenous population of sites which were labelled with nanomolar affinity (Bmax=33.2+/-0.7 fmol mg(-1) protein, pKd=8.78+/-0.05, mean+/-S.E.M., n=3). The development of this 5-HT7 receptor binding assay will aid investigation of the rat native 5-HT7 receptor.

Ability of 5-HT4 receptor ligands to modulate rat striatal dopamine release in vitro and in vivo.

1. The ability of 5-HT4 (5-hydroxytryptamine4) receptor ligands to modify dopamine release from rat striatal slices in vitro and in the striatum of freely moving rats was assessed by the microdialysis technique. 2. The release of dopamine from slices of rat striatum continually perfused with Krebs buffer was enhanced by 5-HT4 receptor agonists; 5-HT (10 microM), 5-methoxytryptamine (5-MeOT; 10 microM), renzapride (10 microM) and (S)-zacopride (10 microM) maximally increased dopamine release by 133 +/- 5, 214 +/- 25, 232 +/- 29 and 264 +/- 69%, respectively (mean +/- s.e.mean, n = 3-8). The drug-induced responses were maximal within the first 2 min of drug application, and subsequently declined. The non-selective 5-HT3/5-HT4 receptor antagonist, SDZ205-557 (10 microM), failed to modify basal dopamine release from striatal slices but completely antagonized the (S)-zacopride (10 microM)-induced increase in dopamine release. 3. To allow faster drug application, the modulation of dopamine release from rat striatal slices in a static release preparation was also investigated. The 5-HT4 receptor agonist, renzapride (10 microM) also enhanced dopamine release in this preparation (maximal increase = 214 +/- 35%, mean +/- s.e.mean, n = 14), whilst a lower concentration of renzapride (3 microM) was less effective. The renzapride-induced response was maximal within the first 2 min of drug application, before declining. In this preparation, the stimulation of dopamine release by renzapride (10 microM), was completely antagonized by the selective 5-HT4 receptor antagonist, GR113808 (100 nM). In addition, both the Na+ channel blocker, tetrodotoxin (100 nM) and the non-selective protein kinase A inhibitor, H7 (100 nM) completely prevented the stimulation of dopamine release induced by renzapride (10 microM). 4. In vivo microdialysis studies demonstrated that the 5-HT4 receptor agonists, 5-MeOT (10 microM), renzapride (100 microM) and (S)-zacopride (100 microM) maximally elevated extracellular levels of dopamine in the striatum by 220 +/- 20, 161 +/- 10 and 189 +/- 53%, respectively (mean +/- s.e.mean, n = 5-9). A lower concentration of renzapride (10 microM) was less effective. The elevation of extracellular striatal dopamine levels induced by either renzapride (100 microM) or (S)-zacopride (100 microM) were completely antagonized by the non-selective 5-HT4 receptor antagonist, SDZ205-557 (100 microM). In addition, the elevation of extracellular levels of dopamine induced by either 5-MeOT (10 microM) or renzapride (100 microM) was completely prevented by the selective 5-HT4 receptor antagonist, GR113808 (1 microM) and the renzapride (100 microM)-induced response was also completely prevented by the non-selective protein kinase A inhibitor, H7 (1 microM). In this in vivo preparation, both GR113808 (1 microM) and H7 (1 microM), when perfused alone, reduced extracellular levels of dopamine. 5. In conclusion, the present study provides evidence that the 5-HT4 receptor facilitates rat striatal dopamine release in vitro and in vivo.