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      Inoculation of α-synuclein preformed fibrils into the mouse gastrointestinal tract induces Lewy body-like aggregates in the brainstem via the vagus nerve

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          Abstract:

          Background

          Intraneuronal α-synuclein (α-Syn) aggregates known as Lewy bodies (LBs) and the loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc) are the pathological hallmarks of Parkinson’s disease (PD). Braak’s hypothesis based on autopsy studies suggests that Lewy pathology initially occurs in the enteric nervous system (ENS) and then travels retrogradely to the dorsal motor nucleus of the vagus nerve (dmX), proceeding from there in a caudo-rostral direction. Recent evidence that α-Syn aggregates propagate between interconnected neurons supports this hypothesis. However, there is no direct evidence demonstrating this transmission from the ENS to the dmX and then to the SNpc.

          Methods

          We inoculated α-Syn preformed fibrils (PFFs) or phosphate-buffered saline (PBS) into the mouse gastric wall and analyzed the progression of the pathology.

          Results

          The mice inoculated with α-Syn PFFs, but not with PBS, developed phosphorylated α-Syn (p-α-Syn)–positive LB-like aggregates in the dmX at 45 days postinoculation. This aggregate formation was completely abolished when vagotomy was performed prior to inoculation of α-Syn PFFs, suggesting that the aggregates in the dmX were retrogradely induced via the vagus nerve. Unexpectedly, the number of neurons containing p-α-Syn–positive aggregates in the dmX decreased over time, and no further caudo-rostral propagation beyond the dmX was observed up to 12 months postinoculation. P-α-Syn–positive aggregates were also present in the myenteric plexus at 12 months postinoculation. However, unlike in patients with PD, there was no cell-type specificity in neurons containing those aggregates in this model.

          Conclusions: These results indicate that α-Syn PFF inoculation into the mouse gastrointestinal tract can induce α-Syn pathology resembling that of very early PD, but other factors are apparently required if further progression of PD pathology is to be replicated in this animal model.

          Electronic supplementary material

          The online version of this article (10.1186/s13024-018-0257-5) contains supplementary material, which is available to authorized users.

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          Most cited references16

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          Parkinson's disease: a dual‐hit hypothesis

          Accumulating evidence suggests that sporadic Parkinson's disease has a long prodromal period during which several non‐motor features develop, in particular, impairment of olfaction, vagal dysfunction and sleep disorder. Early sites of Lewy pathology are the olfactory bulb and enteric plexus of the stomach. We propose that a neurotropic pathogen, probably viral, enters the brain via two routes: (i) nasal, with anterograde progression into the temporal lobe; and (ii) gastric, secondary to swallowing of nasal secretions in saliva. These secretions might contain a neurotropic pathogen that, after penetration of the epithelial lining, could enter axons of the Meissner's plexus and, via transsynaptic transmission, reach the preganglionic parasympathetic motor neurones of the vagus nerve. This would allow retrograde transport into the medulla and, from here, into the pons and midbrain until the substantia nigra is reached and typical aspects of disease commence. Evidence for this theory from the perspective of olfactory and autonomic dysfunction is reviewed, and the possible routes of pathogenic invasion are considered. It is concluded that the most parsimonious explanation for the initial events of sporadic Parkinson's disease is pathogenic access to the brain through the stomach and nose – hence the term ‘dual‐hit’.
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            Vagotomy and Parkinson disease

            Objective: To examine whether vagotomy decreases the risk of Parkinson disease (PD). Methods: Using data from nationwide Swedish registers, we conducted a matched-cohort study of 9,430 vagotomized patients (3,445 truncal and 5,978 selective) identified between 1970 and 2010 and 377,200 reference individuals from the general population individually matched to vagotomized patients by sex and year of birth with a 40:1 ratio. Participants were followed up from the date of vagotomy until PD diagnosis, death, emigration out of Sweden, or December 31, 2010, whichever occurred first. Vagotomy and PD were identified from the Swedish Patient Register. We estimated hazard ratios (HRs) with 95% confidence intervals (CIs) using Cox models stratified by matching variables, adjusting for country of birth, chronic obstructive pulmonary disease, diabetes mellitus, vascular diseases, rheumatologic disease, osteoarthritis, and comorbidity index. Results: A total of 4,930 cases of incident PD were identified during 7.3 million person-years of follow-up. PD incidence (per 100,000 person-years) was 61.8 among vagotomized patients (80.4 for truncal and 55.1 for selective) and 67.5 among reference individuals. Overall, vagotomy was not associated with PD risk (HR 0.96, 95% CI 0.78–1.17). However, there was a suggestion of lower risk among patients with truncal vagotomy (HR 0.78, 95% CI 0.55–1.09), which may be driven by truncal vagotomy at least 5 years before PD diagnosis (HR 0.59, 95% CI 0.37–0.93). Selective vagotomy was not related to PD risk in any analyses. Conclusions: Although overall vagotomy was not associated the risk of PD, we found suggestive evidence for a potential protective effect of truncal, but not selective, vagotomy against PD development.
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              Where does parkinson disease pathology begin in the brain?

              The substantia nigra is not the induction site in the brain of the neurodegenerative process underlying Parkinson disease (PD). Instead, the results of this semi-quantitative study of 30 autopsy cases with incidental Lewy body pathology indicate that PD in the brain commences with the formation of the very first immunoreactive Lewy neurites and Lewy bodies in non-catecholaminergic neurons of the dorsal glossopharyngeus-vagus complex, in projection neurons of the intermediate reticular zone, and in specific nerve cell types of the gain setting system (coeruleus-subcoeruleus complex, caudal raphe nuclei, gigantocellular reticular nucleus), olfactory bulb, olfactory tract, and/or anterior olfactory nucleus in the absence of nigral involvement. The topographical parcellation of the nuclear grays described here is based upon known architectonic analyses of the human brainstem and takes into consideration the pigmentation properties of a few highly susceptible nerve cell types involved in PD. In this sample and in all 58 age- and gender-matched controls, Lewy bodies and Lewy neurites do not occur in any of the known prosencephalic predilection sites (i.e. hippocampal formation, temporal mesocortex, proneocortical cingulate areas, amygdala, basal nucleus of Meynert, interstitial nucleus of the diagonal band of Broca, hypothalamic tuberomamillary nucleus).
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                Author and article information

                Contributors
                nuemura@kuhp.kyoto-u.ac.jp
                yagi@bio.tottori-u.ac.jp
                maikohs@kuhp.kyoto-u.ac.jp
                hatanaka@kuhp.kyoto-u.ac.jp
                yamakado@kuhp.kyoto-u.ac.jp
                ryosuket@kuhp.kyoto-u.ac.jp
                Journal
                Mol Neurodegener
                Mol Neurodegener
                Molecular Neurodegeneration
                BioMed Central (London )
                1750-1326
                11 May 2018
                11 May 2018
                2018
                : 13
                : 21
                Affiliations
                [1 ]ISNI 0000 0004 0372 2033, GRID grid.258799.8, Department of Neurology, , Kyoto University Graduate School of Medicine, ; 54 Shogoin-Kawaharacho, Kyoto, Sakyoku 606-8507 Japan
                [2 ]ISNI 0000 0001 0663 5064, GRID grid.265107.7, Center for Research on Green Sustainable Chemistry, , Tottori University, ; 4-101 Koyamacho-minami, Tottori, Tottori 680-8550 Japan
                Author information
                http://orcid.org/0000-0002-6251-0810
                Article
                257
                10.1186/s13024-018-0257-5
                5948849
                29751824
                3b444968-6a1d-4e47-8701-ec0516d0ab1f
                © The Author(s). 2018

                Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License ( http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver ( http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

                History
                : 9 March 2018
                : 2 May 2018
                Funding
                Funded by: Japan Agency for Medical Research and Development (JP)
                Award ID: JP17dm0207020h0004
                Award Recipient :
                Funded by: FundRef http://dx.doi.org/10.13039/501100001691, Japan Society for the Promotion of Science;
                Award ID: JP17H05698
                Award ID: JP17K16119
                Award Recipient :
                Funded by: FundRef http://dx.doi.org/10.13039/100007449, Takeda Science Foundation;
                Funded by: FundRef http://dx.doi.org/10.13039/501100008880, Kanae Foundation for the Promotion of Medical Science;
                Categories
                Research Article
                Custom metadata
                © The Author(s) 2018

                Neurosciences
                parkinson’s disease,α-synuclein,lewy bodies,propagation,enteric nervous system,vagus nerve

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