Have you ever fainted for no reason?In fact, fainting is a sudden, transient, transient loss of consciousness that affects nearly 40 percent of the world's population.
Previous studies have hypothesized that symptoms of decreased heart rate, blood pressure and respiratory frequency, known as Bay-Sub reflexes, can lead to fainting.But scientists and doctors have long disputed the hypothesis.
In a study published in Nature, neuroscientists looked at a nerve pathway between the heart and brain that triggers a Bay-Sub reflex that causes mice to fainting.This proves the existence of a fainting caused by the controversial Baya reflex.The study is expected to help humans find a cure for fainting.
In the study, neuroscientist Vineet Augustine and colleagues at the University of California, San Diego (UCSD) examined different types of nerve fibers that make up the vagus nerve in mice.
The so-called vagus nerve, is a kind of mixed nerve, it is the brain and the heart, digestive system, lung and other key signal pathways.
Augustine et al. used fluorescence imaging and genetic analysis to identify NPY2R vagus sensory nerve cells and track their path from the lower ventricle of the heart to the final region of the brainstem.These special neurons express a receptor that acts in vasoconstriction.
To test the effects of activating the pathway, the researchers inserted a tiny fiber into each mouse's brain and used pulsed lasers to stimulate the last part of the brain.Results The heart rate, blood pressure and respiration rate of the mice decreased sharply and remained unconscious for 7 to 8 seconds.When the nerve pathway was blocked, the same stimulation did not make the mice unconscious.
This is the first gene-defined neuronal pathway that regulates fainting by triggering a Bay-subreflection.”Augustine说。
In addition, the researchers found that vagus nerve cells in the aortic arch of the heart that help regulate blood pressure were not part of the pathway.Although NPY2R vasovagal nerve cells in these cells and the cardio-brain pathway regulate blood pressure, they are genetically different.
Researchers also used imaging to rule out the possibility that cells in the newly defined cardiac and brain pathways would receive signals from other organs, said co-author Ma Jingrui, a neuroscientist at UCSD.There is "nearly no overlap" between this neural pathway and other known pathways.
Robert Sheldon, a cardiologist and syncope specialist at the University of Calgary in Canada who did not participate in the study, said it was unclear why NPY2R vagus nerve cells in the newly defined pathway were stimulated during syncope.
But some researchers questioned the study.David Goldstein, an autonomic nervous system specialist at the National Institute of Neurology and Stroke, says it's not clear how relevant the fainting mouse model is to humans.
In addition, Goldstein notes, the cardio-brain pathway is only part of the fainting process. The study does not explore the full role of the body's sympathetic nervous system, which controls reactions that can lead to fainting.