Researchers from the University of California (UC) San Diego have, for the first time, identified the precise genetic pathway linking the heart to the brain that triggers fainting, aka syncope. As well as a generally fascinating discovery, it also paves the way to finding effective treatments for conditions in which fainting is prevalent and persistent.

Traditionally, it was thought the brain sent out a signal to the heart, which swiftly followed directions. But the team, led by Biological Sciences Assistant Professor Vineet Augustine, was able to show this pathway was only half the story.

"What we are finding is that the heart also sends signals back to the brain, which can change brain function," said Augustine. "Our study is the first comprehensive demonstration of a genetically defined cardiac reflex, which faithfully recapitulates characteristics of human syncope at physiological, behavioral and neural network levels."

The team looked at neural mechanisms related to Bezold-Jarisch reflex (BJR), the cardiac function that was identified in 1867. BJR, which features reduced heart rate, blood pressure and breathing, has been thought to be associated with fainting but never proven.

Here, the researchers looked at the genetic makeup of a sensory cluster known as the nodose ganglia, which is part of the vagus nerves that transports signals between the brain and the heart. Here, vagal sensory neurons (VSNs) send signals up to the brainstem and have been linked to BJR and fainting.

And it was here they found that VSNs expressing neuropeptide Y receptor Y2 (NPY2R) have a significant connection to BJR physiology