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Researchers have unraveled the mystery of fainting! A genetic discovery has established the link between the heart and the brain in cases of fainting. A team of American neurobiologists has identified the sensory neurons that control fainting, paving the way for specific treatments for associated disorders.

This research represents “the first comprehensive demonstration of a genetically defined cardiac reflex that accurately reproduces the characteristics of human syncope at the physiological, behavioral, and neural levels.”

Fainting attacks, also known as syncope, affect almost 40% of people at least once in their lives. These episodes of loss of consciousness, triggered by various factors such as pain, fear, heat or hyperventilation, often lead to visits to the emergency room.

The recent study by a team at the University of California-San Diego (UCSD) has identified, for the first time, the genetic pathway that links the heart and brain in fainting.

What distinguishes this research is its innovative approach to the phenomenon. Instead of treating the heart as a passive organ that responds only to signals sent out by the brain, researchers examined the hypothesis that the heart may also send signals back to the brain, influencing brain function.

Uncovering this insight could have significant implications for understanding and treating various psychiatric and neurological disorders related to the heart-brain connection.

The research explored in depth the neural mechanisms associated with the Bezold-Jarisch reflex (BJR), a cardiac reflex first described in 1867. For a long time, researchers speculated that BJR, characterized by a decrease in heart rate, blood pressure and respiration, would it could be related to the fainting.

However, this hypothesis has remained largely unconfirmed due to a lack of knowledge regarding the neural pathways involved in this reflex.

To unravel the genetics underlying the sensory ganglia (nodose ganglia) in the vagus nerves responsible for transmitting signals between the brain and visceral organs, including the heart, researchers focused on vagal sensory neurons (VSNs).

The study revealed that VSN expressing the neuropeptide Y receptor type 2 (NPY2R) are closely related to the well-known reactions of BJR. Using mice as a model, the researchers activated the VSN NPY2R using optogenetics, a method of stimulating and controlling neurons.

The result was that the mice had fainting episodes when these neurons were activated. During these fainting episodes, the researchers monitored thousands of neurons in the brain, heart activity, changes in facial features such as pupil dilation and whisker movement.

They also used machine learning to analyze the data and found rapid pupil dilation and eye movement, typical symptoms of fainting, along with a drop in heart rate, blood pressure and breathing rate.

The researchers also observed reduced blood flow to the brain during these episodes. Deletion of NPY2R from the VSN in mice resulted in the absence of the BJR reflex and syncope episodes. This research not only confirmed the link between fainting and decreased blood flow to the brain, but also the involvement of brain activity in this condition.

These findings indicate that activation of genetically identified VSN neurons and their neural pathways not only impacts the BJR reflex, but also general physiology, specific brain networks, and behavior.

This finding is particularly significant because in the past neurologists and cardiologists generally looked at the brain and heart in isolation from each other. The study paves the way for future research into the conditions that trigger the activation of vagal sensory neurons and to investigate cerebral blood flow and neural pathways in the brain during fainting, so as to better understand this common but still enigmatic condition.

The researchers also hope that their findings can serve as a model for developing specific treatments for fainting disorders. The study was published in the journal Nature.

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Source: 360medical.ro

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2023-11-03 15:58:23
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