Use of [18F]FDOPA-PET for in vivo evaluation of dopaminergic dysfunction in unilaterally 6-OHDA-lesioned rats

Background: We evaluated the utility of L-3,4-dihydroxy-6-[F-18]fluoro-phenylalanine ([F-18]FDOPA) positron emission tomography (PET) as a method for assessing the severity of dopaminergic dysfunction in unilaterally 6-hydroxydopamine (6-OHDA)-lesioned rats by comparing it with quantitative biochemical, immunohistochemical, and behavioral measurements. Methods: Different doses of 6-OHDA (0, 7, 14, and 28 mu g) were unilaterally injected into the right striatum of male Sprague-Dawley rats. Dopaminergic functional activity in the striatum was assessed by [F-18]FDOPA-PET, measurement of striatal dopamine (DA) and DA metabolite levels, tyrosine hydroxylase (TH) immunostaining, and methamphetamine-induced rotational testing. Results: Accumulation of [F-18]FDOPA in the bilateral striatum was observed in rats pretreated with both aromatic L-amino acid decarboxylase and catechol-O-methyltransferase (COMT) inhibitors. Unilateral intrastriatal injection of 6-OHDA produced a significant site-specific reduction in [F-18]FDOPA accumulation. The topological distribution pattern of [F-18]FDOPA accumulation in the ipsilateral striatum agreed well with the pattern in TH-stained corresponding sections. A significant positive relationship was found between Patlak plot K-i values and striatal levels of DA and its metabolites (r = 0.958). A significant negative correlation was found between both K-i values (r = -0.639) and levels of DA and its metabolites (r = -0.719) and the number of methamphetamine-induced rotations. Conclusions: K-i values determined using [F-18]FDOPA-PET correlated significantly with the severity of dopaminergic dysfunction. [F-18]FDOPA-PET makes it possible to perform longitudinal evaluation of dopaminergic function in 6-OHDA-lesioned rats, which is useful in the development of new drugs and therapies for Parkinson's disease (PD).