A new study in Nature has pinpointed the specific nerve cells that change in response to spinal cord stimulation treatment, which recovers walking ability in people previously considered permanently paralyzed.
The research on the cellular level of damage in a mouse population was inspired by restoring mobility in nine people with severe spinal cord injuries. This study found that two separate populations of neurons in the lumbar spinal cord fight for attention in response to inputs. Every year, over 500,000 people suffer a spinal cord injury. A person’s capacity to move and walk may be lost depending on the degree of the damage.
Spinal cord injuries account for 27.3% of all paralysis occurrences, impacting an estimated 5.4 million people in the United States. Researchers at Switzerland’s École Polytechnique fédérale de Lausanne (EPFL) have found neurons that, when activated, can restore function to paralyzed muscles.
A spinal cord injury interrupts messages between the brain and the neurons in the spinal cord that control movement. Electrical stimulation devices have been developed in the last five years to assist persons recovering from paralysis caused by a spinal cord injury. These therapies have improved people’s lives when paired with motor therapy, but the why and how are still largely unclear.
A paper produced by researchers at the Swiss Federal Institute of Technology Lausanne (EPFL) and neurosurgeon Jocelyn Bloch from the Lausanne University Hospital revealed the efficacy of epidural electrical stimulation. Furthermore, when the stimulation was turned on, nine clinical experiment participants immediately increased their capacity to walk. When the stimulus was removed, some patients still demonstrated improved motor function.
This second study adds to the evidence that alterations in the functioning of spinal cord neurons are at the root of the remarkable gains observed. Grégoire Courtine, an EPFL professor of neurology, and his team frequently examine their patients’ spinal cords in detail.
The researchers were surprised to see a net drop in spinal cord activity in response to the stimulation, suggesting that the reaction was caused by individual neurons rather than a network. The researchers used mice with injured spinal cords to identify the exact types of neurons involved.
They could follow the neurons preferentially targeted by the stimulation treatment because they had created maps of gene activity in the mice’s spinal cord neurons. “Our technology enables us to observe the healing process with higher granularity – at the neuron level,” according to Courtine’s news release.
The researchers identified a set of excitatory lumbar interneurons responsible for Vsx2 production as crucial to the recovery of the mice’s walking ability. Normal mice can walk about without the assistance of any particular neurons if they are not triggered.
They proved, using cutting-edge light-based stimulation techniques, that Vsx2-expressing neurons are critical for appropriate spinal cord function and that their inactivation rendered spinal cord-injured mice unable to walk. Chronic inactivation of these neurons in mice reduced the initial response to stimulation.
The authors admit that a range of distinct neuronal populations within the brain and spinal cord regulate gait and that future studies must identify and connect these neurons.
As a result, the possibility for more focused therapy for people with paraplegia is realized. EPFL researchers, led by co-author Jordan Squair, may now aim to manipulate these neurons to recreate the spinal cord.
According to the University of Washington, people who have suffered spinal cord injuries seek physical therapy to regain some degree of movement. Several studies in recent years have indicated that paralyzed persons with an implanted stimulator that delivers an electric current to the damaged spinal cord may be able to walk again.
While this may appear to be a little step, Bloch argues it is crucial.” We’re learning more about how neurons in the spinal cord reconfigure due to this new study, which builds on our clinical trial with nine patients who experienced partial motor recovery due to our implants.”
