Two brain circuits help you decide whether you’re eating too little or too much salt.
Alexander Zubkov/Getty Images
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Alexander Zubkov/Getty Images
Two brain circuits help you decide whether you’re eating too little or too much salt.
Alexander Zubkov/Getty Images
If your turkey seems over-salted this year, blame your brain.
The question of when salty food becomes too salty is determined by a special set of neurons in the front of the brain, researchers say report in a diary cell.
In a series of experiments in mice, researchers showed that another set of neurons in the back of the brain regulates salt appetite.
“Sodium craving and sodium tolerance are controlled by completely different types of neurons,” he says. Yuki Okastudy author and professor of biology at the California Institute of Technology.
He said the findings could have health implications, as salt intake is a “major problem” in many countries, including the United States. Nirupa Chaudharyprofessor of physiology and biology at the University of Miami Miller School of Medicine.
Chaudhary, who was not involved in the study, said too much salt can cause high blood pressure and increase the risk of heart disease and stroke.
some degree of craving
This study sought to explain the complex relationship humans and animals have with salt, also known as sodium chloride.
We happily drink soda, sports drinks, and even tap water that contains a small amount of salt, Oka says. “But when you imagine very high concentrations of sodium, like in seawater, you really don’t like it.”
This aversion to extremely salty foods and drinks is maintained unless the body is truly deficient in salt, which is extremely rare in people these days. However, experiments using mice have shown that when the salinity drops rapidly, the mice become more tolerant of salty water.
“Animals start to like saltwater,” Oka says.
Oka’s team found that the reason for this change involves at least two different interactions between the body and the brain.
When sodium levels in the bloodstream begin to fall below healthy levels, a set of neurons in the back of the brain responds by increasing the animal’s desire for salt.
“When you stimulate these neurons, the animal runs to the sodium source and starts eating,” Oka says.
Meanwhile, another set of neurons in the front of the brain monitors the salinity of the food and water the mice consume. And these neurons typically set the upper limit for salty taste.
However, when salt levels become extremely low, the body sends a signal that disables these salt-limiting neurons. This allows the mice to tolerate the salinity of seawater.
Scientists were able to mimic this phenomenon in the lab by stimulating these neurons.
connect body and brain
The discovery advances scientists’ understanding of interoception, which involves sensations such as hunger, pain and thirst and tells the brain what’s going on inside the body. This is a relatively undeveloped form of sensory information, unlike the sensory information we get from our eyes, ears, nose, tongue, and skin.
“The brain receives a large amount of sensory information from the heart, lungs, stomach, and intestines.” stephen libeles, professor at Harvard Medical School and researcher at the Howard Hughes Medical Institute. “And how these functions are accomplished remains even more of a mystery.”
A new study has found evidence that brain cells involved in salt tolerance respond to hormone-like substances called prostaglandins. These substances circulating in the bloodstream are well known for their role in causing inflammation, fever, and pain.
It is now increasingly clear that they also play a role in changes in salt tolerance.
“The question is, how can the same chemical, the same prostaglandin molecule, be reused in different contexts?” Liberez says.
Answering this question may make it possible to develop prostaglandin drugs that suppress excessive salt intake.
Chaudhary says humans evolved in an era when salt was scarce, so excessive salt intake is a global problem.
“Just a few centuries ago, there were wars over salt,” she says. “We think that sodium chloride and table salt are abundant in our diets and environment, but that hasn’t always been the case.”
Understanding how the brain processes salty tastes could help food companies develop tasty salt alternatives, she says.
At least one previous effort failed, she says, for a simple reason. “Because it tasted really bad.”
So research into how the brain monitors salt intake may not be enough to find better options, she says. Scientists also need to understand how the alternatives interact with our taste buds.
