According to a study by Harvard University, a small population of neutrons near the base of the brain can induce symptoms of sickness, including fever, appetite loss, and warm-seeking behaviour. When people get an infection, most people think it’s the immune system kicking into gear when they feel some of the body’s natural defences like fever, chills, or fatigue. However, what most people don’t know is that it’s actually the brain behind all of this.
The study states that the nervous system talks to the immune system to figure out that the body has an infection and then orchestrates a series of behavioural and physiological alterations that manifest as the unpleasant symptoms of sickness. For neuroscientists, long-standing questions have been: How and where does this happen 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 behaviour.
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. "What's happening is that the cells of the blood-brain barrier that are in contact with the blood and with the peripheral immune system get activated and these non-neuronal cells secrete cytokines and chemokines that, in turn, activate the population of neurons that we found," said Dulac, Lee and Ezpeleta Professor of Arts and Sciences and Higgins Professor of Molecular and Cellular Biology.