Parkinson's disease is characterized by loss of neurons that produce dopamine in a region of the brain called the substantia nigra. In the early stages of the disease, the disease responds to agents that replace dopamine such as levodopa. Patients with more advanced disease have wide fluctuations in their response to levodopa, exhibiting on and off periods. This is due to continued degeneration of neurons. Recombinant-methionyl human glial cell line-derived neurotrophic factor (r-metHuGDNF or GDNF) is a neurotrophic factor that promotes survival of dopaminergic neurons. This is a protein produced by recombinant technology that is almost identical to the naturally produced factor. Results of animal studies indicate that GDNF has the potential to benefit patients with advanced Parkinson's disease.

The purpose of this clinical trial is to determine whether GDNF works to relieve symptoms of advanced Parkinson's disease. The study will also test the delivery of GDNF using a catheter implanted into the putamen, the area of the brain associated with Parkinson's disease, and an infusion pump that is implanted under the skin in the abdomen or chest. GDNF will be placed into the pump and delivered through the catheter to the brain. The purposes of this study are to determine the potential benefits and side effects of GDNF. The performance and safety of the catheter/infusion pump system will also be assessed. The study will last for 6 months. Subjects will undergo neurological testing, computerized gait assessment and neurological imaging.