Pedunculopontine Nucleus Cholinergic Deficiency in Cervical Dystonia

Abstract

Background: The etiology of cervical dystonia is unknown. Cholinergic abnormalities have been identified in dystonia animal models and human imaging studies. Some animal models have cholinergic neuronal loss in the striatum and increased acetylcholinesterase activity in the pedunculopontine nucleus.

Objectives: The objective of this study was to determine the presence of cholinergic abnormalities in the putamen and pedunculopontine nucleus in cervical dystonia human brain donors.

Methods: Formalin-fixed brain tissues were obtained from 8 cervical dystonia and 7 age-matched control brains (controls). Pedunculopontine nucleus was available in only 6 cervical dystonia and 5 controls. Neurodegeneration was evaluated pathologically in the putamen, pedunculopontine nucleus, and other regions. Cholinergic neurons were detected using choline acetyltransferase immunohistochemistry in the putamen and pedunculopontine nucleus. Putaminal cholinergic neurons were quantified. A total of 6 cervical dystonia patients and 6 age-matched healthy controls underwent diffusion tensor imaging to determine if there were white matter microstructural abnormalities around the pedunculopontine nucleus.

Results: Decreased or absent choline acetyltransferase staining was identified in all 6 pedunculopontine nucleus samples in cervical dystonia. In contrast, strong choline acetyltransferase staining was present in 4 of 5 pedunculopontine nucleus controls. There were no differences in pedunculopontine nucleus diffusion tensor imaging between cervical dystonia and healthy controls. There was no difference in numbers of putaminal cholinergic neurons between cervical dystonia and controls.

Conclusions: Our findings suggest that pedunculopontine nucleus choline acetyltransferase deficiency represents a functional cholinergic deficit in cervical dystonia. Structural lesions and confounding neurodegenerative processes were excluded by absence of neuronal loss, gliosis, diffusion tensor imaging abnormalities, and beta-amyloid, tau, and alpha-synuclein pathologies. © 2018 International Parkinson and Movement Disorder Society.

Keywords: MRI; acetylcholine; cervical dystonia; diffusion tensor imaging; neuropathology.

Figure 1.

Cholinergic Neurons in the Putamen A–D. Putamen with hematoxylin and eosin (H&E) staining (A) and choline acetyltransferase (ChAT) immunochemistry (B) from a control and putamen with H&E (C) and ChAT (D) staining from a CD brain appear similar. Inset in (B) and (D) show individual cholinergic neuron at 40x magnification. Scale bars in A-D are 100 µm. As shown in (E), there is no difference in the cholinergic neuronal density in the putamen between CD and control specimens.

Figure 2.

Choline Acetyltransferase Immunohistochemistry in the Pedunculopontine Nucleus A & B. Control pedunculopontine nucleus (PPN) with hematoxylin and eosin (H&E) staining in A and choline acetyltransferase (ChAT) immunohistochemistry in B. There is positive ChAT immunoreactivity in B; C& D. CD PPN with H&E staining in C and ChAT staining in D. While background staining is slightly higher in and around the PPN in D, there is a population of neurons with weakly positive immunoreactivity in the cytoplasm, which is the expected pattern of ChAT staining; E & F. CD PPN with H&E staining in E and ChAT staining in F. F is an example of negative immunoreactivity in PPN neurons. Scale bars in A-F are 100 μm.

Figure 3.

Pedunculopontine Nucleus Diffusion Tensor Imaging A. Axial, coronal and sagittal brain MRI in MNI space showing the location of the pedunculopontine nucleus (PPN) in blue; B. This table shows fractional anistropy values in and around the PPN in CD and control subjects. There is no difference between the groups.