Researchers from the University of California San Diego, along with colleagues at The Scripps Research Institute and other institutions, have made a groundbreaking discovery in the field of genetics and neuroscience. In a study published in the journal Nature, they have identified the genetic pathway connecting the heart and brain, shedding light on the mechanisms behind fainting spells.

The study focused on investigating the Bezold-Jarisch reflex (BJR) and the nodose ganglia, which are part of the vagus nerves responsible for carrying signals between the brain and visceral organs, including the heart. By analyzing the genetics of the nodose ganglia, the researchers found a link between vagal sensory neurons (VSNs) expressing the neuropeptide Y receptor Y2 (NPY2R) and BJR responses.

Using optogenetics, a technique that stimulates and controls neurons, the researchers activated NPY2R VSNs in mice, leading to fainting episodes. They observed rapid pupil dilation, suppressed heart-rate, blood pressure, and breathing rate, as well as reduced blood flow to the brain. The study also revealed that fainting is caused by a reduction in brain blood flow and that brain activity plays a vital role in the condition.

"This 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," said the paper's senior author, School of Biological Sciences Assistant Professor Vineet Augustine.

The researchers took a unique approach by considering the heart as a sensory organ rather than solely being controlled by signals from the brain. They found that the heart also sends signals back to the brain, influencing brain function. This discovery could have significant implications for understanding and treating various psychiatric and neurological disorders associated with brain-heart connections.

The study brings together the expertise of neuroscientists and cardiologists, highlighting the importance of studying the heart and brain in conjunction. By further investigating the triggers for the activation of vagal sensory neurons, the researchers aim to gain a deeper understanding of the conditions under which fainting occurs.

In addition, the researchers hope to use their findings as a model to develop targeted treatments for conditions associated with fainting. This breakthrough in unraveling the genetic pathway linking the heart and brain could pave the way for personalized therapies for individuals affected by fainting episodes.

The coauthors of the Nature paper include Jonathan Lovelace, Jingrui Ma, Saurabh Yadav, Karishma Chhabria, Hanbing Shen, Zhengyuan Pang, Tianbo Qi, Ruchi Sehgal, Yunxiao Zhang, Tushar Bali, Thomas Vaissiere, Shawn Tan, Yuejia Liu, Gavin Rumbaugh, Li Ye, David Kleinfeld, Carsen Stringer, and Vineet Augustine.