Anodal block, a technique based on electrical nerve stimulation, allows for the selective activation of fibers in the vagus nerve, a key nerve that runs through the neck and controls the workings of the heart and lungs, an early study in mice reported.
The study “Anodal block permits directional vagus nerve stimulation” was published in the journal Nature Scientific Reports.
Electric stimulation of peripheral nerves is seen as a potential way of treating disorders where the nervous system is affected. Vagus nerve stimulation (VNS), specifically, has been proposed to treat diseases that include PH, arrhythmias, heart failure, and high blood pressure.
VNS is an approved treatment for some forms of epilepsy and depression.
The vagus nerve, the longest of the cranial nerves, extends from the base of the brain to the abdomen. It interacts with multiple organs, including the heart, esophagus, and lungs. It contains several types of fibers, including those that carry information to the brain (afferent fibers) and from the brain (efferent fibers).
VNS may be useful in treating PH because it helps to normalize heart function, promotes the widening of blood vessels in the lungs, and suppresses inflammation. Targeting specific fibers, however, is key to maximizing the effectiveness of stimulating this nerve and to reducing off-target effects.
Anodal block is a type of electrical stimulation that allows for nerve fiber activation in either direction (from and to the brain). To apply anodal block, the vagus nerve is accessed through a minor surgery to implant electrodes.
Although some treatments in epilepsy have used this directional technique, scientific evidence supporting VNS though the use of anodal block is lacking.
Researchers at the Feinstein Institutes for Medical Research, in Manhasset, N.Y., studied the extent to which anodal block could be selective in VNS.
Using a rat model, researchers were able to apply the stimulation technique to vagus nerve fibers and measure physiological responses. Changes in heart rate were used to evaluate the correct selection of efferent fiber activation, and of breathing rate for the afferent fibers.
Stimulating efferent fibers were seen to cause a drop in the animals’ heart rate, and those of afferent fibers lowered their breathing rate. Both responses disappeared upon vagotomy (removal of part of the vagus nerve), showing responses were dependent on the fibers’ stimulation.
Measuring fiber electrical activity (action potentials) also demonstrated that anodal block allowed a correct selection of both fiber types.
Based on these results, “anodal block provides a significant degree of directional biasing in the vagus,” the researchers concluded.
“We were pleased to establish that the mechanism of anodal block, that has been assumed to provide directional vagal activation in preclinical and clinical studies, does indeed produce the intended neurophysiological and functional effects,” Stavros Zanos, PhD, the study’s lead author, said in a press release.
“We work to produce this knowledge in the hopes that it will one day benefit patients with conditions such as rheumatoid arthritis, lupus, inflammatory bowel disease, and pulmonary hypertension,” Zanos added.
The team believes that their findings support the use of bioelectronic medicine — which is based on molecular medicine, neuroscience and bioengineering — as a way of modulating electrical activity within the nervous system through specific devices.
“We have long known that the nervous system communicates with the body, and now that we are learning the language by which it communicates we have increased hope for disease management through bioelectronic medicine,” said Kevin Tracey, MD, president and CEO of the Feinstein Institutes.
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