Continuous Dopaminergic Stimulation as a Treatment for Parkinson's Disease: Current Status and Future Opportunities.

Levodopa-induced motor complications remain an important source of disability for many patients with Parkinson's disease. Substantial laboratory evidence indicates that motor complications relate to the nonphysiological restoration of brain dopamine with intermittent doses of standard oral levodopa. Dopamine levels are normally maintained at a relatively constant level, even following a dose of levodopa. However, in the Parkinsonian state, where dopamine terminals have degenerated with a loss of their buffering capacity, intermittent doses of levodopa lead to dramatic peak and trough fluctuations in striatal dopamine levels. This results in pulsatile stimulation of dopamine receptors, molecular changes in striatal neurons, physiological changes in pallidal neurons, and ultimately the development of motor complications. These observations led to the hypothesis that continuous delivery of levodopa might be associated with a reduced risk of motor complications. This concept is known as continuous dopamine stimulation (CDS). Preliminary studies in animal models and patients with Parkinson's disease supported this hypothesis, suggesting a reduced risk of both motor fluctuations and dyskinesias. The present review considers the scientific advances and the more definitive clinical trials testing this concept that have taken place during the past decade and considers ongoing experimental studies and future opportunities.