Progression of regional cortical cholinergic denervation in Parkinson's disease


 Cortical cholinergic deficits contribute to cognitive decline and other deficits in Parkinson's disease. Cross-sectional imaging studies suggest a stereotyped pattern of posterior-to-anterior cortical cholinergic denervation accompanying disease progression in Parkinson's disease. We used serial acetylcholinesterase PET ligand imaging to characterize the trajectory of regional cholinergic synapse deficits in Parkinson's disease, testing the hypothesis of posterior-to-anterior progression of cortical cholinergic deficits.
 Sixteen Parkinson's disease subjects (4 females/12 males; mean age 64.4 ± 6.7 years; disease duration 5.5 ± 4.2 years; Hoehn & Yahr stage 2.3 ± 0.6 at entry) completed serial 11C-methyl-4-piperidinyl propionate acetylcholinesterase PET scans over a 4-8 year period (median 5 years). Three-dimensional stereotactic cortical surface projections and volume-of-interest analyses were performed. Cholinergic synapse integrity was assessed by the magnitude, k3, of acetylcholinesterase hydrolysis of 11C-methyl-4-piperidinyl propionate. Based on normative data, we generated Z-score maps for both k3 and the k1 parameter, the latter a proxy for regional cerebral blood flow. Compared to control subjects, baseline scans showed predominantly posterior cortical k3 deficits in Parkinson’s disease subjects. Interval change analyses showed evidence of posterior-to-anterior progression of cholinergic cortical deficits in posterior cortices. In frontal cortices, an opposite gradient of anterior-to-posterior progression of cholinergic deficits was found. The topography of k3 changes exhibited regionally specific disconnection from k1 changes. Interval change analysis based on k3/k1 ratio images (k3 adjustment for regional cerebral blood flow changes) showed interval reductions (up to 20%) in ventral frontal, anterior cingulate, and Brodmann area 6 cortices. In contrast, interval k3 reductions in posterior cortices, especially Brodmann areas 17-19, were largely proportional to k1 changes. Our results partially support the hypothesis of progressive posterior-to-cortical cholinergic denervation in Parkinson’s disease. This pattern appears characteristic of posterior cortices. In frontal cortices, an opposite pattern of anterior-to-posterior progression of cholinergic deficits was found. Progressive decline of posterior cortical acetylcholinesterase activity was largely proportional to declining regional cerebral blood flow, suggesting that posterior cortical cholinergic synapse deficits are part of generalized loss of synapses. The disproportionate decline in regional frontal cortical acetylcholinesterase activity relative to regional cerebral blood flow suggests preferential loss or dysregulation of cholinergic synapses in these regions. Our observations suggest that cortical cholinergic synapse vulnerability in Parkinson's disease is mediated by both diffuse processes affecting cortical synapses and processes specific to subpopulations of cortical cholinergic afferents.