Neuroinflammation of the nigrostriatal pathway during progressive 6-OHDA dopamine degeneration in rats monitored by immunohistochemistry and PET imaging

We investigated the microglial response to progressive dopamine neuron degeneration using in vivo positron emission tomography (PET) imaging and postmortem analyses in a Parkinson's disease (PD) rat model induced by unilateral (right side) intrastriatal administration of 6-hydroxydopamine (6-OHDA). Degeneration of the dopamine system was monitored by PET imaging of presynaptic dopamine transporters using a specific ligand (11)C-CFT (2beta-carbomethoxy-3beta-(4-fluorophenyl) tropane). Binding of (11)C-CFT was markedly reduced in the striatum indicating dopaminergic degeneration. Parallel PET studies of (11)C-PK11195 (1-(2-chlorophenyl)-N-methyl-N-(1-methylpropyl)-3 isoquinoline carboxamide) (specific ligand for activated microglia) showed increased binding in the striatum and substantia nigra indicative of a microglial response. Postmortem immunohistochemical analyses were performed with antibodies against CR3 for microglia/macrophage activation. Using a qualitative postmortem index for microglial activation we found an initially focal, then widespread microglial response at striatal and nigral levels at 4 weeks postlesion. These data support the hypothesis that inflammation is a significant component of progressive dopaminergic degeneration that can be monitored by PET imaging.