Unlike conventional Parkinson’s treatments, this neuroprosthesis targets the spinal cord region responsible for activating the leg muscles. © CHUV

Neuroscientists from Inserm, CNRS and Université de Bordeaux in France, along with Swiss researchers and neurosurgeons (EPFL/CHUV/UNIL), have designed and tested a “neuroprosthesis” to correct the gait disorders associated with Parkinson’s disease. In a study published in Nature Medicine, the scientists describe the development process of the device they used to treat a Parkinson’s disease patient for the first time, enabling him to walk fluidly, confidently, and without falling.

Disabling gait disorders occur in around 90% of people with advanced Parkinson’s disease and are often resistant to the treatments currently available. Developing new strategies that enable patients to walk fluidly again, avoiding the risk of falls, is therefore a priority for the research teams that have been studying this disease for many years.

This is the case of Erwan Bézard, a neuroscientist at Inserm, and his team at the Institute of Neurodegenerative Diseases (CNRS/Université de Bordeaux), who are working to understand the pathogenic mechanisms behind Parkinson’s and to develop strategies to restore motricity in various diseases. For several years, he has been working with a Swiss team led by neuroscientist Prof. Grégoire Courtine and neurosurgeon Prof. Jocelyne Bloch, who specialize in the development of spinal cord neuromodulation strategies.

In 2016, the Franco-Swiss team had already published research in Nature showing the effectiveness of a brain-spine interface – known as a “neuroprosthesis” – to restore the function of a limb paralyzed following a spinal cord injury. Its promising results had encouraged the scientists to pursue their efforts, suggesting beneficial effects in Parkinson’s disease with a similar device.

Avoiding Falls and Freezing

In this new study, the team developed a similar neuroprosthesis to compensate for falls and the phenomenon of freezing – when the feet remain glued to the ground during walking – that is sometimes associated with Parkinson’s disease.

Unlike conventional treatments for Parkinson’s, which target the brain regions directly affected by the loss of dopamine-producing neurons, this neuroprosthesis targets the spinal cord region responsible for activating the leg muscles during walking, which is not believed to be directly affected by the disease. However, the spinal cord is under the voluntary control of the motor cortex, whose activity is modified by the loss of dopaminergic neurons.

Drawing on their complementary expertise, the French and Swiss teams were able to develop and test the neuroprosthesis in a non-human primate model reproducing the locomotor deficits caused by Parkinson’s disease. The system not only reduced the locomotor deficits, but also restored walking capacity in this model by reducing freezing.

“The idea of developing a neuroprosthesis that electrically stimulates the spinal cord to harmonize gait and correct the locomotor disorders of Parkinson’s patients is the result of several years of research on the treatment of paralysis caused by spinal cord lesions”, explains Erwan Bézard, Inserm research director at the Institute of Neurodegenerative Diseases (Université de Bordeaux/CNRS).

“Previous attempts to stimulate the spinal cord have failed because they provide blanket stimulation of the locomotor centers without taking physiology into account. In our case, the stimulation overlays the natural functioning of the spinal cord neurons to target, with spatiotemporal coordination, the different muscle groups responsible for walking,” add Courtine and Bloch, co-directors of NeuroRestore, the research center based in French-speaking Switzerland.

These promising results paved the way for clinical development, to test the device in a patient.

Improvement Thanks to the Neuroprosthesis

A first patient, aged 62, who has been living with the disease for three decades, underwent surgery two years ago at Vaud University Hospital (CHUV) in Lausanne. During a precision neurosurgical procedure, Marc, originally from Bordeaux, was fitted with this new neuroprosthesis, consisting of a field of electrodes placed against the region of his spinal cord that controls gait, and an electrical-impulse generator implanted under the skin of his abdomen.

Thanks to the targeted programming of spinal-cord stimulations that adapt to his movements in real time, Marc has quickly seen his gait problems improve. After a few weeks of rehabilitation with the device, his walking has almost returned to normal.

This neuroprosthesis therefore opens up new prospects for treating the gait disorders suffered by many people with Parkinson’s disease. However, at this stage, this therapeutic concept has only demonstrated its efficacy in one person, with an implant that still has to be optimized for large-scale deployment.

The scientists are therefore working to develop a commercial version of the device[1] that incorporates all the essential features for optimal daily use. Clinical trials on more patients are also due to start early next year[2].

“Our ambition is to enable widespread access to this innovative technology in order to significantly improve the quality of life of patients with Parkinson’s disease, throughout the world”, conclude the researchers.

[1] In partnership with ONWARD Medical, a company based in Switzerland that will develop these implants.

[2] Thanks to a one-million-dollar donation from the Michael J. Fox Foundation for Parkinson’s research, NeuroRestore will embark on clinical trials on six new patients early next year. These trials aim not only to validate the technology developed in collaboration with ONWARD, but also to identify the patient profiles most likely to benefit from this innovative therapy. Founded by actor Michael J. Fox (Back to the Future), who himself has Parkinson’s disease, this foundation is the leading private donor in the field of Parkinson’s disease research.

Sleep is generally defined as a period during which the body and mind are at rest, as if disconnected from the world. © Nicolas Decat

When we sleep we are not completely cut off from our environment: we are still able to hear and understand words. These observations, resulting from the close collaboration between researchers from Inserm, CNRS, Sorbonne Université and AP-HP at the Brain Institute and the Department of Sleep Disorders at Pitié-Salpêtrière Hospital in Paris, call into question the very definition of sleep and the clinical criteria that distinguish between its different stages. They are detailed in a new study published in Nature Neuroscience.

Sleep is generally defined as a period during which the body and mind are resting, as if disconnected from the world. However, a new study led by Delphine Oudiette, Inserm researcher, Isabelle Arnulf (Sorbonne Université, AP-HP) and Lionel Naccache (Sorbonne Université, AP-HP) at the Brain Institute, shows that the boundary between wakefulness and sleep is much more porous than it would appear.

The scientists have shown that sleepers with no particular disorders are able to capture verbal information transmitted by a human voice and respond to it by contracting facial muscles. What is more, this astonishing ability manifests itself intermittently during almost all stages of sleep — as if windows to the outside world were temporarily opened.

These new data on sleep behavior suggest that it may eventually be possible to develop standardized protocols for communication with sleepers in order to better understand how mental activity changes during sleep.

On the horizon: a new access route to the cognitive processes that underpin normal and pathological sleep.

A Thousand and One Variations in Consciousness

“Even if it seems familiar to us because we do it every night, sleep is a very complex phenomenon. Our research has taught us that wakefulness and sleep are not stable states: both resemble a kaleidoscope of conscious moments… and moments that do not appear to be so,” explains Prof. Lionel Naccache, neurologist at Pitié-Salpêtrière Hospital AP-HP and neuroscience researcher.

It is essential to improve our understanding of the brain mechanisms that underlie these intermediate states between wakefulness and sleep.

“When out of sync, they can be associated with disorders such as sleepwalking, sleep paralysis, hallucinations, the feeling of not sleeping at night or, on the contrary, sleeping with the eyes open“, explains Prof. Isabelle Arnulf, head of the Sleep Disorders Department at Pitié-Salpêtrière Hospital AP-HP.

However, in order to distinguish between wakefulness and the different stages of sleep, we have so far used simple and inaccurate physiological indicators, such as specific brain waves made visible through electroencephalography. Such indicators do not capture in detail what is going on inside the heads of sleepers, especially as they are sometimes in contradiction with what the sleepers tell us themselves.

“We need more refined physiological measurements that are aligned with the sleeper’s feelings and ability to respond to the outside world; this is to better define their level of vigilance“, adds Delphine Oudiette, Inserm researcher in cognitive neuroscience.

A Game Between Unconsciousness and Lucidity

The research team[1] therefore explored this avenue and recruited 22 people without sleep disorders and 27 narcoleptic patients — i.e. victims of irrepressible sleep episodes.

People with narcolepsy have the particularity of having many lucid dreams, namely in which they are aware of being asleep and can sometimes shape the scenario. In addition, they easily and quickly reach REM sleep (the stage where the lucid dream emerges) during the day, making them good candidates for studying consciousness during sleep under experimental conditions.

“One of our previous studies had shown that two-way communication, between the scientist and the dreamer and vice versa, is possible during lucid REM sleep, explains Oudiette. For our latest study, we wanted to know if these findings could be extrapolated to other sleep stages and to individuals who do not have lucid dreams. “

The study participants were asked to take a nap. The researchers had them do a “lexical decision” test in which a human voice uttered a series of words, both real and made up. The participants had to respond by smiling or frowning, in order to place the words in one of the two categories. Throughout the experiment, the participants were monitored using polysomnography—a comprehensive examination to record their brain and heart activity, eye movements, and muscle tone. Finally, upon waking, they had to report whether or not they had a lucid dream during their nap, and whether they remembered interacting with someone.

“Most of the participants, whether narcoleptic or not, managed to respond correctly to the verbal stimuli while sleeping. These events were admittedly more frequent during episodes of lucid dreams, characterized by a high level of consciousness; however, we observed them occasionally in both groups, during all sleep phases”, specifies Arnulf.

By combining these physiological and behavioral data with the subjective reports of the participants, the researchers also show that it is possible to predict the opening of these windows of connection with the environment, i.e. the times when the sleepers were able to respond to stimuli. These were heralded by an acceleration of brain activity, and by physiological indicators usually associated with rich cognitive activity.

“In people who had a lucid dream during their nap, the ability to dialog with the investigator and talk about this experience on waking was also characterized by a specific electrophysiological signature, adds Naccache. Our data suggest that lucid dreamers have privileged access to their inner world, and that this increased awareness also extends to the outside world. “

Further research will be needed to determine whether the increase in these windows is correlated with sleep quality, and whether they could be used to improve certain sleep disorders or promote learning.

“More advanced neuroimaging techniques, such as magnetoencephalography and intracranial recording of brain activity, will help us to better understand the brain mechanisms that orchestrate sleep behaviors“, concludes Oudiette.

Finally, these new data could help to revise the definition of sleep, a state that is ultimately very active, perhaps more conscious than we thought, and open to the world and others.

This study was funded by the French National Research Agency and the French Society for Sleep Research and Medicine (SFRMS).

[1] Including PhD students Başak Türker, Esteban Munoz Musat and Emma Chabani, whose participation was essential to the conduct of this study. 

Illustration of SARS-CoV-2 infection (immunoreactivity for the S-protein in white) in the olfactory neurons expressing the olfactory marker protein (OMP, in red) in the human nasal epithelium. © Vincent Prévot/Inserm

The brain impacts of infection with SARS-CoV-2, responsible for COVID-19, are increasingly well documented in the scientific literature. Researchers from Inserm, Lille University Hospital and Université de Lille, at the Lille Neuroscience & Cognition unit, in collaboration with their colleagues at Imperial College London, focused more specifically on the impacts of this infection on a population of neurons known for regulating sexual reproduction via the hypothalamus (the neurons that express the GnRH hormone). Their findings suggest that SARS-CoV-2 infection can lead to the death of these neurons and cause certain symptoms that persist over time. The findings of this study have been published in eBioMedicine.

Numerous scientific studies have documented the brain impacts of SARS-CoV-2 infection. One such effect is that a significant proportion of men have low testosterone levels that persist over time. Persistence beyond a period of four weeks is referred to as “long COVID”.

For many years, a research team from Inserm, Lille University Hospital and Université de Lille has been studying the role of certain neurons that express gonadotropin-releasing hormone (GnRH). From the hypothalamus, these neurons control all the processes associated with reproductive function: puberty, acquisition of secondary sexual characteristics, and fertility in adulthood.

These are the same scientists who had, for example, previously revealed that GnRH neuron dysfunction in an animal model of Down syndrome could affect the cognitive function impairment associated with this condition.

In this latest study, the scientists wanted to test the hypothesis that SARS-CoV-2 infection may have harmful consequences on this population of neurons that regulate reproduction.

The Virus Penetrates GnRH Neurons and Alters Their Functions

Following hormone measurements (testosterone and luteinizing hormone) performed three months and then one year after infection in a small group of 47 men[1], the scientists observed that contact with the virus could alter the functions of GnRH neurons, leading to a fall in testosterone levels in certain patients some time after the infectious episode.

The scientists then wanted to verify whether the infection of the GnRH neurons and the subsequently observed hormone abnormalities could be associated with cognitive deficits. To do this, they listed the cognitive symptoms reported by the cohort patients, who underwent extensive testing three months and then one year after the infection.

The outcome was that the proportion of patients reporting memory or attention disorders, regardless of frequency or severity, and also concentration difficulties, tended to be slightly higher in the patients with abnormal hormone measurements, characterized by a decrease in testosterone levels.

“Although these were measurements made on a small sample of only male patients, these findings are very interesting and warrant further exploration in other larger-scale studies,” explains Waljit Dhillo, professor at Imperial College London and co-last author of this study.

To supplement their analyses, the researchers went on to study the cortexes of patients who died as a result of COVID-19. They identified the presence of the virus in the hypothalamus and the death of part of the GnRH neuron population.

“These findings may be worrying on several levels in terms of the role of these neurons in reproduction and their involvement in certain cognitive functions. They point to the necessity to optimize and generalize the medical follow-up of people with persistent symptoms following COVID-19 infection,” concludes Vincent Prévot, Inserm research director and co-last author of this study.

The study also encourages further research into the neurological impacts of long COVID.

[1]These data were collected as part of a larger study evaluating adrenal and thyroid function following Sars-CoV-2 infection: https://pubmed.ncbi.nlm.nih.gov/34008009/

The image shows the brain region where demyelination is typically induced. The red cells correspond to all of the microglial cells with inflammatory properties when demyelination has just occurred. If the spontaneous regeneration process of myelin is effective, their inflammatory nature then diminishes in favor of an anti-inflammatory and pro-regenerative nature. The green cells are a subpopulation of these microglial cells that become anti-inflammatory.© Zahaf et al.

Multiple sclerosis (MS), an autoimmune disease for which there is no cure as yet, affects three women for every one man. Faced with this observation, scientists are studying the role of the sex hormones in order to better understand the differences between men and women in relation to the disease and its progression. A team led by Inserm researcher Elisabeth Traiffort in Unit U1195 “Diseases and hormones of the nervous system” (Inserm/Université Paris-Saclay) has recently shown that although male hormones – androgens – are present at very low levels in women, their presence is necessary to regenerate the myelin sheath which is destroyed in MS. These findings have been published in Nature Communications.

Multiple sclerosis (MS) is an autoimmune disease. In its most common form, relapsing-remitting MS[1], which accounts for 85% of cases, it manifests as inflammatory flares during which the patient’s immune cells attack and destroy the myelin in the central nervous system (see box). This phenomenon causes lesions that lead to motor, sensory, and visual disorders.

These symptoms are reversible at the beginning of the disease, thanks to the spontaneous repair of the destroyed myelin. However, over time, symptoms gradually become irreversible, reflecting the failure of the repair process, marking entry to the progressive phase of the disease. While current treatments reduce the frequency and severity of the inflammatory flares, thereby improving patient quality of life, they remain ineffective against the progression of the disease.

Current research aims to gain a better understanding of the mechanisms of the disease and develop new therapeutic avenues that would prevent patients from entering the progressive phase, particularly by promoting the regeneration of myelin. Inserm researcher Elisabeth Traiffort and her team at the “Diseases and hormones of the nervous system” unit (Inserm/Université Paris-Saclay) are working for example to better understand the differences between women and men in MS, in order to determine whether it could be beneficial or even necessary to adapt therapeutic management to the patient’s sex. Remember that the disease is predominantly female, since three out of every four patients are women.

Investigating the Role of Androgens in Women

While the hormonal environments of men and women are very different, they cannot be restricted to high androgen levels in men and fluctuating levels of estrogen and progesterone in women. We know that men also produce estrogens, particularly in the brain where an enzyme is found that converts androgens into estrogens, while women produce small amounts of androgens. It was on this last aspect that Inserm researcher Traiffort and her colleagues focused their latest study.

Research has already shown that androgens protect neurons in the central nervous system of men with relapsing-remitting forms of MS and induce the regeneration of myelin sheaths destroyed in males, in animal models of the disease. But what is the role of the small amounts of androgens that are also found in the central nervous system of women? Can these androgens present at much lower levels than in men also impact the progression of the disease in female patients?

The scientists worked with animal models of the disease and also on tissues from patients supplied by organ donation banks. They first showed that in regions where myelin is destroyed, the AR receptor that enables androgens to transmit their signal is strongly expressed in the nervous tissue of women with MS, as it is in the female mouse models of the disease. This observation would suggest the existence of an essential role of androgens in the demyelinated tissue of the affected women.

In accordance with this hypothesis, the scientists have shown that despite only being present in small quantities in female mice, androgens still have a beneficial effect on the optimal regeneration of the destroyed myelin. Indeed, when the signals transmitted by the androgens are completely absent, this regeneration is greatly reduced.

Finally, other findings in animals and in human tissues suggest that these same androgens also have major anti-inflammatory effects on demyelinated nerve tissue in females unlike what is observed in males. The beneficial effects of androgens in women with MS could therefore also be linked to a decrease in the level of local inflammation, in areas where myelin is destroyed. This finding is interesting if we consider the current hypothesis that disease progression could be closely associated with the inflammatory cells residing in nervous tissue.

“While the low levels of androgens detected in women could point to a minor role for these hormones in the disease, we show that this is not the case. Our data suggest the use of appropriate doses of androgens in women with MS and the need to consider the patient’s sex when treating this and in all likelihood other conditions involving the destruction of myelin in the central nervous system,” concludes Traiffort.

This research was carried out with the support of the ARSEP Foundation.

[1] There are two active forms of the disease. The most common is the relapsing-remitting form, which accounts for 85% of MS cases at diagnosis. It is characterized by flares, in which symptoms appear within a few hours or days, often associated with the extreme and unusual fatigue suggestive of the diagnosis. Then the symptoms disappear completely or partially within a few weeks. The “primary” progressive form accounts for only 15% of cases. It is characterized by the slow and continuous worsening of the neurological symptoms, with no flares or remission.

Images showing the human brain anatomy in two axial slices obtained by MRI (left), then the corresponding molecular images showing a larger number of mGluR5 receptors in the brain of an adult subject with ASD (right) compared to a control subject (middle). © Laurent Galineau

While great progress has been made in recent years in the understanding of autism spectrum disorder (ASD), its underlying molecular mechanisms remain fairly poorly documented. Several hypotheses have been put forward regarding the possible dysfunction of certain neurotransmitters in the brain, but rigorous scientific studies are still lacking in order to validate them. In a new publication, researchers from Inserm and Université de Tours at the Imaging & Brain unit have shown that specific receptors of glutamate, one of the most important neurotransmitters in the nervous system, are expressed in large quantities in the brains of adults with ASD. However, this overexpression of the receptors does not occur at earlier stages of development. The study, sponsored by Tours university hospital and published in Molecular Psychiatry, paves the way for a better understanding of ASD to help refine therapeutic research.

Autism spectrum disorder (ASD) is caused by neurodevelopmental particularities and affects around 700 000 people in France. This term brings together a large variety of clinical realities and as such a large variety of specific individual needs. The development of treatments that specifically target severe autism-related disorders has long been hampered by a piecemeal understanding of the underlying molecular and genetic mechanisms.

At present, those affected may therefore use treatments for potential comorbidities such as sleep disorders or epilepsy, but there is no therapeutic solution to improve behavioral disorders or the associated alterations in social interactions.

One avenue put forward to explain the development of ASD is dysfunction of glutamate – the main excitatory neurotransmitter of the central nervous system. Studies have recently suggested that glutamate receptors called mGluR5 (see inset) are expressed in increased quantities in certain brain regions in people with ASD.

Compensatory mechanism

In order to further understand the molecular mechanisms of ASD, Frédérique Bonnet-Brilhault’s team at the Imaging & Brain unit (unit 1253 Inserm/Université de Tours) sought to better characterize glutamate dysfunction in the brains of adults with ASD.

They started by quantifying the glutamate levels in the cingulate cortex of 12 adults with ASD and 14 adults without ASD (referred to as “control” participants), using several methodological approaches. Next, they looked at the expression of the mGluR5 receptors in the participants’ brains.

The scientists observed that the glutamate levels varied widely in the adults with ASD. However, they found that the quantity of mGluR5 receptors expressed was particularly high in the brains of all these individuals, compared to the controls.

Then, to better understand how the quantity of mGluR5 varies at different stages of development, the team also quantified these receptors in the brains of young rats, grouped into animal models of ASD and “control” animals.

Their analyses show that the quantities of mGluR5 in the “ASD rats” and the “control rats” did not differ during childhood. However, in adolescence, larger quantities of these receptors were present in certain brain regions of the “ASD rats”.

The fact that mGluR5 receptors are expressed in large quantities in the adult human participants with ASD, but not at the earliest stages of development in the animal models, suggests that the overexpression of these receptors is not a cause of this disorder, but rather a consequence that emerges progressively throughout life.

“Our findings suggest that the changes in the quantity of mGluR5 receptors expressed during development could be a compensatory mechanism for the early dysfunction in the brain communication systems, rather than a primary element that causes the development of ASD,” explains Bonnet-Brilhault.

At a time when research in adults with ASD is a real priority, this work points to the need to understand the development trajectory of each individual with ASD to distinguish the causes of the adaptation mechanisms.

Fluorescent marking of the Tau protein in a human cell hNT; the Tau protein, has a role in Alzheimer’s disease, particularly in its familial forms ©Inserm/U837

An international consortium has identified rare variants in two new genes that markedly increase the risk of developing Alzheimer’s disease (AD). The work was led by two research groups in France (headed respectively by Gaël Nicolas, Rouen and Jean-Charles Lambert, Lille) and a group in the Netherlands (headed by Henne Holstege, Amsterdam). The new results provide a better understanding of the genetics of AD and open up new research themes on more relevant in vitro and in vivo models. The consortium’s findings are also likely to catalyze the development of new strategies for treating AD. The results were published in the journal Nature Genetics in November 2022.

As the most prevalent neurodegenerative disease, AD affects about 55 million people across the world – 4% of whom are under the age of 65. It is a complex, multifactorial disease caused by interactions between many genetic and non-genetic predisposing factors. Given that AD has a large genetic component, the characterization of these factors is a major challenge for basic research and therapeutic development.

Our knowledge of the involvement of common gene variants (those present in more than 1% of the general population) in AD has improved enormously over recent last years, through the discovery of 75 chromosomal/gene regions associated with the risk of developing the disease. However, the role of rare or even very rare variants has not been extensively studied. In fact, these variants might contribute significantly to genetic predisposition to AD as a result of their direct biological effects and their great diversity.

Two new genes identified

It is in this context that a large international consortium has identified a number of rare mutations in two genes that markedly increase the risk of developing AD. Along with their European and American colleagues, researchers from the INSERM, the Pasteur Institute in Lille, Lille University Medical Centre, the University of the Lille, the University of Rouen Normandy, and the French National Reference Centre for Patients with Early-Onset Alzheimer’s Disease (Centre national de référence pour les malades Alzheimer jeunes (CNRMAJ)) at Rouen University Medical Centre and from the Amsterdam University Medical Center performed a high-throughput sequencing study of 16,032 AD patients and 16,522 controls. This sequencing approach provides the most precise possible picture of an individual’s genetic variants.

By specifically studying the DNA regions that code for the proteins in our body (the exons), the researchers were able to map deleterious, rare variants that might change the corresponding proteins’ biological functions. The researchers confirmed the pathological role of rare variants in the SORL1, TREM2 and ABCA7 genes and, for the first time, highlighted potentially pathological variants in two other genes (ATP8B4 and ABCA1). The potentially pathological role of variants in one other gene (ADAM10) remains to be confirmed.

Better understanding the mechanisms of AD

The identification of the effects of these rare variants should provide a better understanding of the mechanisms that underlie AD.

In fact, two disease pathways have already been well documented in the AD brain: the accumulation of beta-amyloid peptides, and changes in and the accumulation of Tau protein. Importantly, some of the genes studied by the researchers are involved in the production or aggregation of beta-amyloid peptides – confirming the latter’s central role in the development of AD. Furthermore, the present research confirmed previous reports of the importance of microglial cells (cells that help to remove waste from the brain) in AD.

These results from the largest yet sequencing study in this field constitute a major step forward in our understanding of the genetics of AD and the underlying biological mechanisms. Furthermore, these results will open up new research themes on more relevant in vitro and in vivo models in which the newly identified genes are knocked out. By continuing this work, the consortium’s scientists’ also hope to foster the development of new strategies for treating AD.