The rationale for continuous dopaminergic stimulation in advanced Parkinson's disease.

Control of movement depends on the continuous release of dopamine by neurons in the basal ganglia of the brain. The degeneration of these neurons in Parkinson's disease (PD) interferes with the flow of dopamine, leading to classic motor symptoms. In early PD, enough dopaminergic neurons remain to store dopamine provided by periodic dosing with oral levodopa and relatively normal, tonic levels of dopamine release are maintained. PD progression leads to degeneration of remaining dopaminergic terminals and loss of buffering capacity for exogenous levodopa. As a result, there are supraphysiological levels of dopamine after dosing and troughs when the available dopamine has been depleted. These divergent levels are associated with dyskinesia and 'off' states, respectively. Treatment strategies that provide a continuous flow of dopamine and can thus mimic normal physiological dopamine stimulation have potential to improve motor control for patients with advanced PD.