Factors contributing to fluctuations of the dopaminergic nigro-striatal feedback system in Parkinson’s disease

Summary

The experience that the supplementation of depleted dopamine in the nigro-striatal system of parkinsonian patients with L-dopa improves the clinical triad, akinesia, rigidity and tremor, mainly applies to long-term treatment in the early phase of Parkinson’s disease. Complications in motor performance, like on-off response, wearing-off phenomena, peak-dose dyskinesia, biphasic dyskinesia, off-period dystonia and others, after more than 3 to 5 years following the onset of treatment indicate fluctuations in the dopaminergic feedback control system. It is suggested that these complications are due to progressive presynaptic degeneration and late changes in postsynaptic receptor amplification. However, as fluctuations are not imperative in all patients, an important additional aspect seems to be the topography of denervation, which involves different portions of the striatum to varying degrees. Location and extent of denervation are criteria which appear to have predictive value for the malignancy of the disease, the therapeutic response of drugs and complications in long-term treatment.