The mechanism by which the heart causes the brain to lose consciousness has been uncovered
Scientists have identified the genetic pathway that connects the heart to the brain and controls fainting.Researchers at the University of California, San Diego, have for the first time identified the exact genetic pathway connecting the heart to the brain that causes loss of consciousness or fainting. The results open a new avenue for finding treatments for conditions in which fainting occurs regularly.
Scientists have studied the neural mechanisms involved in the Bezold-Jarisch reflex, a cardiac function that was identified in 1867. The BJR, characterized by a decrease in heart rate, blood pressure and breathing, was thought to be associated with fainting, but this has never been proven.
The researchers studied in a mouse model the genetic makeup of the sensory cluster, which is part of the vagus nerves that transmit signals between the brain and heart. They found that vagal sensory neurons expressing the neuropeptide NPY2R have a significant association with the physiology of the Bezold-Jarisch reflex and fainting.
Using optogenetics to target specific neurons, the researchers induced NPY2R expression in vagal sensory neurons in mice. In doing so, the animals instantly lost consciousness. Moreover, when these neurons were activated, the mice exhibited dilated pupils and fainting "eye rolling," as well as a slowing of heart rate, breathing, and a drop in blood pressure.
When the NPY2R gene was removed from the vagal sensory neurons, the Bezold-Jarisch reflex and fainting stopped in the mice. "Neuroscientists traditionally believe that the body simply follows the brain, but now it's becoming quite clear that the body sends signals to the brain and then the brain changes function," says Vinet Augustine, co-author of the study. The discovery will help develop treatments for conditions and diseases associated with frequent fainting.