Does salt intake affect blood flow to the brain? Scientists reveal for the first time the relationship between neural activity and blood flow in deep brain regions

　　Salt is a “must eat” food for people every day. While adding flavor to food, excessive intake of salt may bring health risks to people. For example, heart disease, stroke, etc., about 3 million people die each year due to these two diseases.
　　According to the World Health Organization, adults should consume no more than 5 grams of salt per day. However, due to the inability to accurately assess salt intake, people have different levels of “excessive” salt intake. Recently, a research team found that salt intake may affect blood flow in the brain.
　　The Georgia State University team’s study of how blood flow in the hypothalamus changes with salt intake has for the first time uncovered a link between neuronal activity and blood flow deep in the brain, and how salt intake affects salt intake. effects on brain activity.
　　A related paper was published under the title “Inverse neurovascular coupling contributes to positive feedback firing of vasopressin neurons during systemic homeostatic challenges.”
Surprising discovery: reverse neurovascular coupling

　　Typically, once neurons are activated, small arteries through the brain dilate, causing blood flow to rise in that area for a short period of time, a process known as “neurovascular coupling” or “functional hyperemia.”
　　So how do experts diagnose brain disorders? They used functional magnetic resonance imaging with the aforementioned “neurovascular coupling” in areas of the brain where blood flow was weaker to determine the presence of brain disease.
　　However, previous studies of neurovascular coupling have mainly focused on the superficial regions of the brain (such as the cerebral cortex), and their main direction has focused on how blood flow changes and rules in response to sensory stimuli (such as visual or auditory stimuli) from the environment. Has blood flow been coordinated with stimuli (called “interoceptive signals”) from the body in deeper regions of the brain? There are not many conclusions to refer to.

Two-photon imaging of SON microvasculature

Javier Stern

　　Javier Stern, the corresponding author of the paper, is a professor of neuroscience and director of the Center for Neurological and Cardiometabolic Diseases at Georgia State University. a new method.
　　This approach uses state-of-the-art neuroimaging followed by a combination of relevant surgical techniques and states. The team’s research focused on key bodily functions involved in drinking, eating, thermoregulation and reproduction, a region deep in the brain called the hypothalamus.
　　So how did they come up with the idea of ​​looking at the relationship with brain blood flow by studying salt intake?
　　To this, Stern gave the answer: “We chose salt as one of the elements of the study because the human body needs to control the amount of sodium very precisely. The human body even has specific cells that can detect the amount of salt in the blood. When people eat salty food, the brain senses it and activates a series of compensatory mechanisms to reduce sodium levels.” The
　　body activates neurons, turning on the ‘switch’ of vasopressin to facilitate this ‘compensatory mechanism’ . Vasopressin is one of the antidiuretic hormones and plays an important role in the balance regulation of salt concentration.
　　Previously, scientists had concluded that in the cerebral cortex, neuronal activity increases with blood flow, which means there is a positive correlation between the two. The team found experimentally that blood flow decreased as neurons were activated in the hypothalamus. The results came as a surprise to them, and the researchers dubbed this phenomenon “reverse neurovascular coupling,” which means that oxygen-deprived blood flow decreases as neuronal activity increases.
　　”This finding came as a surprise to us because in the study we observed vasoconstriction, which is the opposite of how the cerebral cortex responds to sensory stimuli as described in most studies. After Alzheimer’s disease, stroke or ischemia, the human body can usually A decrease in blood flow was observed in the cerebral cortex,” Stern said.
　　They also observed other different phenomena in the cerebral cortex and hypothalamic regions: in the cerebral cortex, the blood vessels have a limited response to stimulation, which allows their dilation to occur rapidly in a short period of time; while in the hypothalamus, the blood vessels respond to stimulation by Diffuse, in terms of the rate of expansion, occurs slowly and over a long period of time.
　　”When we eat a lot of salt, our sodium levels remain elevated for an extended period of time,” Stern said. “We believe hypoxia is a mechanism that enhances the ability of neurons to respond to sustained salt stimulation, enabling They can stay active for a long time.”
May lead to further research into depression, obesity and neurodegenerative diseases

　　One of Stern’s research priorities is to elucidate how structural and functional remodeling within key neuronal networks plays a role in the pathophysiology of hypertension, heart failure, diabetes and obesity.
　　Generally, high blood pressure is considered to be 50% to 60% of the factors caused by excessive intake of salt, which means that high blood pressure is closely related to salt intake. These new findings inspired him to propose a topic for further research—is hypertension related to this mechanism?
　　Therefore, the team hopes to confirm whether the “reverse neurovascular coupling mechanism” contributes to the pathology of hypertension in animal models in the future. They also plan to use this method to study other brain diseases, such as depression, obesity and neurodegenerative diseases.
　　”If the human body consumes a lot of salt for a long time, the neurons that stimulate the release of vasopressin become overactive. This mechanism can lead to excessive hypoxia in the brain and even tissue damage. If we can better understand this process, we can Designing new targets to block this phenomenon may improve outcomes in patients with salt-dependent hypertension,” Stern said.