Introducing the brain: fainting involves a heart reflex (Introduction)

by David Turell , Wednesday, November 01, 2023, 21:26 (177 days ago) @ David Turell
edited by David Turell, Wednesday, November 01, 2023, 21:41

The heart actively informs the brain:

https://medicalxpress.com/news/2023-11-brain-heart.html

"Nearly 40% of people experience syncope, or fainting spells, at least once in their lives. These brief losses of consciousness, whether brought by pain, fear, heat, hyperventilation or other causes, account for a significant portion of hospital emergency room visits. Yet the exact root mechanisms at play when people "pass out" largely have remained a mystery.

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"'What we are finding is that the heart also sends signals back to the brain, which can change brain function," said Augustine. Information resulting from the study could be relevant to better understanding and treating various psychiatric and neurological disorders linked with brain-heart connections, the researchers note in their paper. "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."

"Augustine,... studied neural mechanisms related to Bezold-Jarisch reflex (BJR), a cardiac reflex first described in 1867. For decades researchers have hypothesized that the BJR, which features reduced heart rate, blood pressure and breathing, may be associated with fainting. But information lacked in proving the idea since the neural pathways involved in the reflex were not well known.

"The researchers focused on the genetics behind a sensory cluster known as the nodose ganglia, which is part of the vagus nerves that carry signals between the brain and visceral organs, including the heart. Specifically, vagal sensory neurons, or VSNs, project signals to the brainstem and are thought to be associated with BJR and fainting. In their search for a novel neural pathway, they discovered that VSNs expressing the neuropeptide Y receptor Y2 (known as NPY2R) are tightly linked to the well-known BJR responses.

"Studying this pathway in mice, the researchers were surprised to find that when they proactively triggered NPY2R VSNs using optogenetics, a method of stimulating and controlling neurons, mice that had been freely moving about immediately fainted. During these episodes, they recorded data from thousands of neurons in the brains of the mice, as well as heart activity and changes in facial features, including pupil diameter and whisking.

" Once NPY2R neurons were activated, the researchers found, mice exhibited rapid pupil dilation and the classic "eye-roll" seen during human fainting, as well as suppressed heart rate, blood pressure and breathing rate. They also measured reduced blood flow to the brain, an area of collaboration with Professor David Kleinfeld's laboratory in the UC San Diego Departments of Neurobiology and Physics.

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"The findings therefore implicate the activation of the newly genetically identified VSNs and their neural pathways not only with BJR, but more centrally in overall animal physiology, certain brain networks and even behavior.

"Such findings were difficult to tease out previously because neuroscientists study the brain and cardiologists study the heart, but many do so in isolation of the other. "Neuroscientists traditionally think the body just follows the brain, but now it is becoming very clear that the body sends signals to the brain and then the brain changes function," said Augustine." (my bold)

Comment: note my bold. Augustine's revelation that the brain and body send signals back and forth in both directions is not a new concept. I was taught it in Med school. This article confirms:

https://www.the-scientist.com/ts-digest/issue/bacterial-time-capsules-21-5?utm_campaign...

"Evidence suggested that the aryl hydrocarbon receptor (AHR) is essential for airway epithelia and gut barrier immunity.1,2 So, Wack led a team of scientists to investigate the function of AHR in the lung endothelium. In the journal Nature, he and his collaborators described how AHR signaling prevents endothelium damage after an infection and pinpointed the contribution of dietary AHR ligands to this end."

"AHR ligands come from the diet (mainly from cruciferous vegetables) or from the metabolism of gut bacteria, so the team next tested whether adding an AHR ligand to the mouse food would affect AHR activity and disease progression. The enriched diet led to fewer signs of lung damage, which according to Wack, provides an example of how gut-derived molecules can affect barrier integrity in other parts of the body.

“'A lesson for all immunologists is that you want to embed your lung immune response research into a bigger context,” said Wack. “The lung is clearly communicating with other barrier sites and organs, and we need to think about this.'”

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The other form of fainting is orthostatic hypotension fainting: a soldier at very still attention suddenly keels over. It is due to much blood pooling in his legs. It also occurs in some folks. My brother as a young child had to get up from a night's sleep very slowly, and not just jump out of bed, which often led him to be out cold flat on the floor. When a person gets up a Vagus nerve reflex tells the leg veins to contract.