Study of the Effects of Dopaminergic Medications on Dopamine Transporter Density in Subjects With Parkinson's Disease

Approximately 120 Parkinson's disease subjects will be randomized to receive either carbidopa/levodopa, cabergoline or no treatment during a twelve week period. Subjects will undergo SPECT imaging with DATscan at screening and after 12 weeks. After twelve weeks carbidopa/levodopa and cabergoline treatment will be withdrawn and all subjects will undergo SPECT imaging with DATscan after 8 weeks (20 weeks after baseline).

Approximately 120 Parkinson's disease subjects will be randomized to receive either carbidopa/levodopa, cabergoline or no treatment during a twelve week period. Subjects will undergo SPECT imaging with DATscan at screening and after 12 weeks. After twelve weeks carbidopa/levodopa and cabergoline treatment will be withdrawn and all subjects will undergo SPECT imaging with DATscan after 8 weeks (20 weeks after baseline).

Approximately 120 Parkinson's disease subjects will be randomized to receive either carbidopa/levodopa, cabergoline or no treatment during a twelve week period. Subjects will undergo SPECT imaging with DATscan at screening and after 12 weeks. After twelve weeks carbidopa/levodopa and cabergoline treatment will be withdrawn and all subjects will undergo SPECT imaging with DATscan after 8 weeks (20 weeks after baseline).