Nature News: What makes paralyzed people walk again? Scientists have made a new discovery

Paralysis refers to the reduction or loss of voluntary movement function.

The cause of paralysis is generally damage to the nervous system, especially the spinal cord.

However, as long as a connection can be established between the brain and the motor neurons in the damaged spinal cord, with the help of certain scientific methods, paralyzed people may be able to regain the ability to walk.

Electrical stimulation of the spinal cord, such as epidural electrical stimulation (EES), has been shown to be effective in helping paralyzed people regain the ability to walk, but the underlying mechanism behind this therapy is still unclear.

(Source: Pixabay)

Now, scientists have finally made a new discovery——

Neuroscientist Grégoire Courtine, professor at EPFL, and his colleagues have identified neurons that promote recovery after paralysis, a discovery that adds to our understanding of how to regain mobility after paralysis.

Figure ｜Growing neurons.

The related research paper, titled “The neurons that restore walking after paralysis”, was published today in the authoritative scientific journal Nature.

Remodeling spinal cord neurons

The spinal cord is an extension of the central nervous system originating from the brain. It is located in the vertebral canal of the spine and is protected by the vertebrae. It is mainly responsible for the reflex actions of the trunk and limbs, and for transmitting neural information between the brain and the periphery.

Once the spinal cord is injured, the connection between the brain and spinal cord neurons will be passively interrupted, causing partial sensory loss in mild cases and hemiplegia, quadriplegia, or even total paralysis in severe cases .

Therefore, discovering new ways to treat paralysis and understanding the underlying mechanisms behind it are important research topics for scientists in the future to help paralyzed people move better or even recover completely.

In most cases, some connections still remain between the brain and the motor neurons in the damaged spinal cord, but these tiny connections may not be enough to allow the paralyzed to walk again. Stimulation from outside the body may be able to reconnect the brain and spinal cord .

As early as 2018, Courtine's team helped three spinal cord injury patients regain leg muscle control and improve their walking through electrical stimulation therapy.

In this work, 9 patients with severe or complete paralysis due to spinal cord injury were enrolled and received EES treatment. They immediately recovered or improved their walking ability during the treatment, and their mobility was further improved after 5 months of EES treatment and rehabilitation.

Video | Nine patients with chronic spinal cord injury who received electrical stimulation therapy in this study regained the ability to walk.

Going further, Courtine et al. are trying to explore whether electrical stimulation can restore one or more specific neurons and whether these neurons are essential in helping paralyzed people walk again .

To this end, Courtine et al. established a mouse model that replicated key features of human EES neurorehabilitation and constructed a single-cell atlas of gene expression for different neurons in the mouse spinal cord.

By combining this model with molecular profiling, they identified a specific class of excitatory neurons that are important for recovery of walking ability after spinal cord injury but are not essential for walking ability in individuals without spinal cord injury.

However, the research team also pointed out that other neurons in the brain and spinal cord can also promote the recovery of walking ability, so further research is still needed.

In a commentary article published at the same time, Eiman Azim, associate professor in the Molecular Neurobiology Laboratory of the Salk Institute for Biological Studies, and postdoctoral researcher Kee Wui Huang commented that this discovery can help people further understand the rehabilitation mechanism of EES, but the whole process of how the spinal cord is reorganized remains to be studied.

Furthermore, they say that despite the challenges, the development of enhanced neurorehabilitation methods and the rapid growth of tools for accessing specific cell types in the nervous system make the prospect of targeted, circuit-based treatments for spinal cord injury look more promising.

Marc Ruitenberg, associate professor and neurologist at the School of Biomedical Sciences at the University of Queensland, said walking is usually not the first thing people with paralysis consider, and the loss of bladder control, bowel control and sexual function will have a greater impact on the quality of life of people with paralysis. "It will be very interesting to see if these functions can also be improved by this technology."

Spinal cord injury should not be underestimated

Spinal cord injuries may be caused by damage to the vertebrae, ligaments or discs, or to the spinal cord itself.

Traumatic spinal cord injury may be caused by a sudden violent impact on the spine that results in fracture, displacement, crushing or compression of one or more vertebrae, such as traffic accidents, smashes, falls, sports injuries, and disasters such as earthquakes and mining accidents; while non-traumatic spinal cord injury may be caused by arthritis, cancer, inflammation, infection or spinal disc degeneration.

Patients with spinal cord injuries not only lose the ability to move, but also lose control of their bowels or bladder, experience loss or changes in sensation (including the ability to feel heat, cold and touch), excessive reflex activity or spasms, and pain or intense tingling caused by damage to the spinal nerve fibers.

The paralysis caused by spinal cord injury makes it difficult for the unfortunate to take care of themselves in daily life, which places a huge burden on the family. According to data from Mayo Clinic, the most common causes of spinal cord injury in the United States include : Motor vehicle accidents: Car and motorcycle accidents are the main cause of spinal cord injury, accounting for almost half of the new spinal cord injury cases each year;

Falls: Spinal cord injuries that occur after age 65 are usually caused by falls;

Violence: About 12% of spinal cord injuries are caused by violent encounters;

Injuries from sports and leisure activities: Sports activities, such as impact sports and diving in shallow water, account for about 10%;

Disease: Cancer, arthritis, osteoporosis and inflammation of the spinal cord can also cause spinal cord injury. Therefore, safe driving, preventing falls, and taking precautions before exercise can reduce the risk of spinal cord injury.

Academics, protect your spinal cord~

References:

https://www.nature.com/articles/s41586-022-05385-7

https://www.nature.com/articles/d41586-022-02234-5

https://www.nature.com/articles/d41586-022-03605-8

https://www.nature.com/articles/s41593-018-0262-6

https://en.wikipedia.org/wiki/Spinal_cord

https://www.mayoclinic.org/zh-hans/diseases-conditions/spinal-cord-injury/symptoms-causes/syc-20377890