Viva the Vagus: Stimulation Boosts SCI Recovery

Posted by Sam Maddox in Research News on March 18, 2016 # Health, Research

Stimulation of the vagus nerve is being investigated as a way to treat migraine, tinnitus, inflammatory bowel disease, hiccups, stroke, diabetes, brain injury and multiple sclerosis. Add spinal cord injury to the list

The vagus nerve is one of the major nerve highways connecting the brain and the rest of the body. It winds from brain to neck and then the heart and all they way down to the abdomen; it controls several muscle groups, including those related to speech. The vagus nerve is a major pipeline for sensory information going toward the brain, but provides neural input to the heart and gastrointestinal system, and is related to sweating, vomiting, and orgasm* -- of course not necessarily all at once.

Doctors have since 1997 been stimulating the vagus nerve to treat drug-resistant epilepsy. In 2005 the FDA approved vagal stimulation to treat depression in people unresponsive to the usual therapies (that indication, however, has never gotten anywhere because Medicare and private insurance reimbursement disagree with the FDA’s controversial approval and doubt the treatment’s purported effectiveness; they won’t pay for it).

Photo courtesy of UT Dallas.

A few weeks ago, attention was called to a project that pairs vagal nerve stimulation (VNS) with rehabilitation to restore function after spinal cord injury. Research scientist Patrick Ganzer from the Texas Biomedical Device Center (TxBCD) at the University of Texas, Dallas won a best paper award at the International Spinal Cord Repair (ISCORE)** meeting for work that showed how VNS might enhance neuroplasticity -- the remodeling of the nervous system as it responds to change. Ganzer’s study found that, after a cervical spinal cord injury in an animal model, VNS therapy plus rehab helped rats recover 75 percent more forelimb strength than those who got rehabilitation alone.

Ganzer’s paper was presented to a small gathering of researchers in Spain but has not been published in the literature yet, so we can’t get at all the details. In the world of restorative neuroscience, this sounds promising.

TxBCD posted a news release, quoting Robert Rennaker, executive director of TxBDC and head of the Department of Bioengineering in the Erik Jonsson School of Engineering and Computer Science. “This work provides an initial glimpse into the significance of neural plasticity in functional recovery following spinal cord injuries. Not only do the subjects regain useful motor function, but improved strength and sensory restoration.”

From the release:

VNS is an FDA-approved therapy for various neurological disorders, such as depression and epilepsy. It involves sending a mild electric pulse through the vagus nerve, which allows precise control of neurotransmitter release throughout the nervous system.

Clinical trials at UT Southwestern Medical Center are underway for VNS as a potential treatment for stroke patients and individuals suffering from tinnitus, or constant ringing in the ears. University researchers are also exploring VNS as a potential treatment for post-traumatic stress disorder. Their work on cervical spinal cord injury is the first assessment of VNS therapy after an injury outside of the forebrain.

High-resolution brain maps revealed that VNS therapy led to an enhancement of connections to muscles controlling grasping, the magnitude of which was correlated to recovery of function.

Said Ganzer:

VNS therapy significantly enhanced forelimb recovery and enabled new motor connections from the brain to spinal cord. To our knowledge, this is the first time VNS therapy has been shown effective at restoring lost motor function after an injury outside of the forebrain. This represents a significant opportunity to identify new patient populations who can benefit from targeted plasticity therapy using VNS.

How does it work? Stimulating the vagus nerve seems to affect neurotransmitters, the chemicals that facilitate nerve communication.

More from Ganzer, via TxBCD:

Spinal cord injuries disrupt communication between the brain and the damaged area. ... Even though the brain and spinal cord are two distant but connected structures, our findings show that the brain is functionally engaged in recovery from cervical spinal cord injury driven by VNS therapy.

The next step in the research is to assess the efficacy of VNS therapy after injuries damaging both sides of the spinal cord, and eventually move to clinical trials in humans.

*Regarding vagus and orgasm, an interesting sidebar from the SCI clinical view. Research in the late 1990s by a group from Rutgers showed that nerve pathways related to sexual stimulation are outside the spinal cord and remain intact, even after complete SCI. The vagus nerve is apparently the key to female orgasm.

Said the paper:

Women diagnosed with complete spinal cord injury (SCI) at T10 or higher report sensations generated by vaginal-cervical mechanical self-stimulation (CSS). In this paper we review brain responses to sexual arousal and orgasm in such women, and further hypothesize that the afferent pathway for this unexpected perception is provided by the vagus nerves, which bypass the spinal cord. We conclude that the vagus nerves provide a spinal cord-bypass pathway for vaginal-cervical sensibility and that activation of this pathway can produce analgesia and orgasm.

Here are Beverly Whipple and Barry Komisaruk, the research principals, from an article in Wired:

Whipple: We’ve documented through our research that women who have complete transection -- interruption of the spinal cord -- can experience orgasms.

"Vagus" means wanderer -- the nerve wanders through the body. Previously, it wasn't thought that it goes as far as the pelvic region. But our research and that of other laboratories is showing that it does in fact go to the cervix and uterus and probably the vagina. It carries the impulses from those regions, travels up through the abdomen, goes through the diaphragm, through the thorax (chest cavity), up the neck outside the spinal cord, and into the brain.

Komisaruk: Men and women have described an orgasmic experience from stimulation of the skin region around the level of the spinal cord injury. The injury creates an area of heightened sensitivity. They've told us if the right person stimulates that skin in the right way, it can produce very pleasurable sensation, including what they describe as orgasms.

We studied one such woman who had a spinal cord injury near her shoulders. She stimulated her neck with a vibrator, and she said that elicited an orgasm for her. We observed her blood pressure and heart rate, and they became elevated just as if it were a genital orgasm.

Wired: Professor Whipple, you had a very emotional moment with one subject who had a spinal-cord injury.

Whipple: That particular woman had not tried any sexual stimulation, either with herself or a partner, in the two years since she had an injury. When she was in the laboratory, this woman experienced six orgasms through self-simulation. It was extremely emotional. She was crying, I was crying. She didn't think this was possible, and she was so pleased that she had volunteered to be a research subject. This had helped open up her essential pleasure again.

** ISCORE is a biennial SCI research meeting held in Barcelona, and staged by the Step by Step Foundation, a non-profit which states as its principal objectives “the treatment of spinal cord injuries and research for a future cure.” Step by Step has set up a recovery center, “based on the methodology and equipment of the U.S. based organization, Project Walk, a pioneer and leader in this innovative treatment.” Project Walk is an activity-based gym/sports training model, started near San Diego, with franchises now in five other states.

ISCORE has met three times, most recently in November. That meeting included scientists well known to the SCI research community, including Reggie Edgerton, UCLA; Leif Havton, UC Irvine; Jerry Silver, Case Western; Phil Popovich, Ohio State; Jim Guest, Miami Project; and Charles Tator, University of Toronto.