Stimulating the vagus nerve may reduce symptoms of multiple sclerosis and potentially delay the disease鈥檚 progression.
Multiple sclerosis is a chronic condition in which the body鈥檚 immune system damages the protective covering of nerve cells, called myelin sheaths, leading to symptoms such as muscle stiffness and difficulty walking. has shown that stimulating the vagus nerve, which transmits signals between the brain and organs, can help treat other autoimmune conditions like rheumatoid arthritis and Chron鈥檚 disease, suggesting it may help with multiple sclerosis.
and his colleagues at SetPoint Medical, a medical equipment company in California, implanted a device that generates electrical pulses into 33 rats with characteristics of multiple sclerosis. They had been given an injection that prompted their immune system to attack proteins of the myelin sheath, causing degradation similar to what is seen in people with multiple sclerosis.
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The device was connected to the vagus nerve in 10 of the 33 rats and used to stimulate the nerve three times a day for 15 days with a small electrical dose that rats do not appear to notice. The researchers gave an additional six rats a high daily dose of teriflunomide, a standard medication for treating multiple sclerosis, and included a further 13 rats in a control group that had no intervention.
The team assessed the severity of muscle stiffness and paralysis in the rats daily using a scale of 0 to 5, with 0 indicating no symptoms and 5 indicating death. Rats who received vagus nerve stimulation or teriflunomide had, on average, a maximum score of about 2.5, whereas rats with the sham device or no treatment had a maximum score of about 4.5, on average. The researchers also looked at samples of the rats鈥� spinal cords and found that those treated with vagus nerve stimulation had significantly less myelin sheath damage compared with those who had the device implanted but not turned on, suggesting the treatment slows the progression of the disease.
鈥淭he efficacy of vagus nerve stimulation is very close to the drug treatment, but the advantage is that there are no side effects,鈥� says Natarajan who presented these findings at a November meeting of the Society for Neuroscience in San Diego, California. Teriflunomide and other drugs used to treat multiple sclerosis can increase the risk of infection and cause serious side effects, such as liver damage. They also aren鈥檛 effective for everyone with the condition.
鈥淲hat鈥檚 exciting is that clinical trials of vagus nerve stimulation for other inflammatory conditions in humans are in advanced stages of clinical testing,鈥� says at the Feinstein Institutes for Medical Research in New York. In these human trials, the vagus nerve is stimulated with the same small, implanted device used in these rodents, which is externally controlled. 鈥淚t鈥檚 very possible that, should this work continue, clinical trials of vagus nerve stimulation in patients with multiple sclerosis could be quite feasible,鈥� says Tracey.
There are three potential explanations for how vagus nerve stimulation treats multiple sclerosis, he says. The first is that it somehow modifies immune cells to make them less likely to damage the nervous system. A second possibility is that stimulation initiates a protective, anti-inflammatory mechanism in the brain. Finally, it is also possible that it may speed up tissue repair, which would reduce the inflammation seen in multiple sclerosis.
鈥淎n experiment like this is potentially a gamechanger,鈥� says Tracey. Not only can it help researchers learn more about the potential role of the vagus nerve in multiple sclerosis and the immune system, but it also provides a new treatment option to the many people with the condition who are out of therapeutic options, he says.
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