Does Parkinson's disease start in the gut?

Parkinson's disease (PD) is pathologically characterized by the presence of intraneuronal inclusions, termed Lewy bodies and Lewy neurites, whose main component is alpha-synuclein. Based on the topographic distribution of Lewy bodies and neurites established after autopsy from PD patients, Braak and coworkers hypothesized that PD pathology may start in the gastrointestinal tract then spread through the vagus nerve to the brain. This hypothesis has been reinforced by the discovery that alpha-synuclein may be capable of spreading transcellularly, thereby providing a mechanistic basis for Braak's hypothesis. This 'gut to brain' scenario has ignited heated debates within the movement disorders community and prompted a large number of studies in both humans and animals. Here, we review the arguments for and against the gut as the origin of PD. We conclude that the human autopsy evidence does not support the hypothesis and that it is too early to draw any definitive conclusions. We discuss how this issue might be further addressed in future research.

Nitrous oxide: a unique official French addictovigilance national survey.

Introduction: Nitrous oxide has become over the last few years a public health problem in many countries. France has a dedicated health monitoring system dedicated to the surveillance of the abuse, dependence and consequences associated with the use of psychoactive substances coordinated by the French National Agency for the Safety of Medicines and Health Products.We present the French national survey of nitrous oxide. Materials and methods: We analyzed all the cases with nitrous oxide from 2012 to 2021: number of notifications, characteristics of the subjects and consumption, consequences reported and their evolutions over time. In addition, we have made a special focus on the four main complications reported. Results: A total of 525 cases were received with an exponential increase since 2019. We observed changes in the characteristics of the notifications with an increase in the proportion of women [42.7% in 2021 vs. 30.8% in 2020 (p = 0.02)]; an increase in the quantities consumed (use of cylinders); a negative evolution of the contexts of use with a search for self-therapeutic effects and use in violent contexts; an increasing trend of the severity of cases [78.1% in 2021 vs. 70.0% in 2020 (p = 0.07)].The main effects were substance use disorders and/or associated criteria (82.5%), neurological disorders (75.4%), psychiatric symptoms (15.4%) and cardiovascular events (8.6%). In terms of evolution, we observed a significant increase in cases with a use disorder and an increase in neurological complications. Moreover, new serious effects, notably cardiovascular events were reported. Discussion: The combination of high availability, varied effects from euphoria to relief of discomfort in a stressful global pandemic context and the development of dependence could explain the rapid growth of consumption and the seriousness of the cases.It must now be taken into account that (i) Substance use disorders are associated with nitrous oxide consumption; (ii) clinicians must consider "nitrous oxide" in young subjects presenting different types of manifestations; and (iii) stopping consumption is imperative and is the first treatment. In this context, an addictological assessment must also be carried out.

Characterisation of tau in the human and rodent enteric nervous system under physiological conditions and in tauopathy.

Tau is normally a highly soluble phosphoprotein found predominantly in neurons. Six different isoforms of tau are expressed in the adult human CNS. Under pathological conditions, phosphorylated tau aggregates are a defining feature of neurodegenerative disorders called tauopathies. Recent findings have suggested a potential role of the gut-brain axis in CNS homeostasis, and therefore we set out to examine the isoform profile and phosphorylation state of tau in the enteric nervous system (ENS) under physiological conditions and in tauopathies. Surgical specimens of human colon from controls, Parkinson's disease (PD) and progressive supranuclear palsy (PSP) patients were analyzed by Western Blot and immunohistochemistry using a panel of anti-tau antibodies. We found that adult human ENS primarily expresses two tau isoforms, localized in the cell bodies and neuronal processes. We did not observe any difference in the enteric tau isoform profile and phosphorylation state between PSP, PD and control subjects. The htau mouse model of tauopathy also expressed two main isoforms of human tau in the ENS, and there were no apparent differences in ENS tau localization or phosphorylation between wild-type and htau mice. Tau in both human and mouse ENS was found to be phosphorylated but poorly susceptible to dephosphorylation with lambda phosphatase. To investigate ENS tau phosphorylation further, primary cultures from rat enteric neurons, which express four isoforms of tau, were pharmacologically manipulated to show that ENS tau phosphorylation state can be regulated, at least in vitro. Our study is the first to characterize tau in the rodent and human ENS. As a whole, our findings provide a basis to unravel the functions of tau in the ENS and to further investigate the possibility of pathological changes in enteric neuropathies and tauopathies.

[Neuropathology and pathophysiology of Parkinson's disease: Focus on α-synuclein]. / Neuropathologie et physiopathologie de la maladie de Parkinson : focus sur l'α-synucléine.

The past 20 years has witnessed tremendous progress in our understanding of Parkinson's disease. It is now well established that α-synuclein, a presynaptic neuronal protein, is not only a marker but also an actor of the disease. In this review, we discuss the advances that have been obtained in neuropathology using α-synuclein immunohistochemistry and the role of this protein in the spread of the disease.