Parkinsons disease is caused by the loss of dopamine stimulation to the basal ganglia of the midbrain, resulting in tremor at rest and bradykinesia. In some rare forms, protein aggregation of alpha-synuclein and parkin can elicit symptoms of Parkinsons disease. For a variety of drugs, restoring dopamine to the central nervous system remains the target therapy. Because dopamine cannot pass the blood brain barrier on its own, the dopamine precursor L-DOPA is used in its stead. However, synaptic plasticity renders this treatment decreasingly effective with time. Another treatment option is bromocriptine, which directly stimulates D Dopamine Receptors. Bromocriptine is less effective than L-Dopa in reducing symptoms, but provides less dyskinesia. Often, the two drugs are used in concert with one another.
New approaches to treatment include deep brain simulation and cell transplantation with stem cells. Deep brain stimulation offsets symptoms rather than cures, and stem cell studies have been extremely disappointing, despite relative success with animal models. Gene therapy may provide a novel route to introduce new dopamine production via viral-medicated gene transfection, but clinical trials are yet to be completed.