An Open-Label Feasibility/Pilot Study With [123I]-IBZM SPECT (DOPA-SYN)

This is a pilot evaluation of dopaminergic function in PD using a bolus plus constant infusion protocol with \[123I\]-IBZM and SPECT to evaluate the potential for carbidopa/l-dopa alone or carbidopa/l-dopa/entacapone to produce displacement of striatal radioactivity for assessment of intrasynaptic dopamine. We will assess the feasibility of this paradigm for detecting l-dopa effects on the SPECT signal in subjects with PD with disease duration of greater than 4yrs and with a stable response to L-dopa. Each subject will undergo three \[123I\]-IBZM studies separated by 1-2 weeks. Subjects will be off medication for at least 12 h prior to study For each of the three scan days patients will receive a constant intravenous infusion of \[123I\]-IBZM over 4-5 hours to establish an equilibrium binding condition of the radiotracer at striatal D2/D3 receptors. Three baseline SPECT acquisitions will be obtained prior to medication dosing to establish a stable baseline. At approximately 5 h after the initiation of the infusion subjects will receive a single oral dose of either carbidopa/levodopa (37.5mg/150mg or 50mg/250mg), or carbidopa/levodopa/entacapone (either 37.5mg/150mg/200mg- STALEVO or 50/250mg/200mg).