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How the brain controls symptoms of sickness

When someone gets an infection, most people think it’s the immune system kicking into gear when they feel some of the body’s natural defenses like a fever, chills, or fatigue. What most people don’t know is that it’s actually the brain behind all of this.

Here’s what happens: The nervous system talks to the immune system to figure out that the body has an infection and then orchestrates a series of behavioral and physiological alterations that manifest as the unpleasant symptoms of sickness. For neuroscientists, long-standing questions have been: How and where does this happens in the brain? Harvard researchers from the labs of Catherine Dulac and Xiaowei Zhuang sought the answer in the brains of mice.

In a new study published in Nature, the researchers and their collaborators describe finding a small population of neurons near the base of the brain that can induce symptoms of sickness, including fever, appetite loss, and warm seeking behavior.

The neurons, which have not been previously described, are found in an area of the hypothalamus, a part of the brain known for controlling key homeostatic functions that keep the body in a balanced, healthy state. The researchers found these neurons have receptors that are capable of directly detecting molecular signals coming from the immune system, an ability most neurons don’t have.

“It was important for us to establish this general principle that the brain can even sense these immune states,” said Jessica Osterhout, a postdoctoral researcher in the Dulac Lab and the study’s lead author. “This was poorly understood before.”

The researchers found that the key area of the hypothalamus is located right next to a permeable section of the brain called the blood-brain barrier, which helps circulates blood to the brain.

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