Most people may "attribute" this change in the body to the immune system, thinking that the feeling of fever, chills or weakness means that the immune system automatically opens its defense.
This is not the case, but the brain is behind all this. More specifically, the nervous system has been "docking" with the immune system. After confirming that the body is infected, it will coordinate a series of behavioral and physiological changes, including those symptoms that make us uncomfortable.
This week, in a research paper published in the top academic journal Nature, scientists discovered a special group of brain cells for the first time through mouse experiments: after sensing that the immune state has changed due to infection, this handful of nerve cells strategize in the brain and manipulate a series of symptoms such as fever, chills and loss of appetite.
▲ Professor Catherine Dulac of Harvard University is a correspondent, and Professor Zhuang Xiaowei, a famous scientist in China, also participated in this research.
This special group of neurons is located in the hypothalamus, which is a key brain region and is "famous" for its important functions of regulating body temperature, diet and endocrine activities. The researchers first managed to make laboratory mice have a fever due to bacterial infection, then searched their brains for neurons that were activated at this time, and finally noticed the neurons located in the ventrolateral hypothalamic area (VMPO).
In order to confirm the function of these cells, the researchers used the methods of chemical genetics and optogenetics to precisely control this group of neurons, the number of which is about 1000, and manipulated them to transmit signals. The results show that VMPO neurons are very important to produce symptoms such as fever. After activating these cells, mice's body temperature rises, they are afraid of cold, and their appetite decreases-which is very similar to a series of symptoms that often appear after human infection.
In addition, the researchers also confirmed that this group of nerve cells project to 12 brain regions, including some brain regions known to control thirst, pain sensitivity and social interaction. In other words, other common symptoms after infection may also be affected by this group of nerve cells.
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In this paper, the researchers further revealed how these nerve cells perceive the immune state of the body. They found that these nerve cells have an excellent geographical location: next to the blood-brain barrier. The blood-brain barrier separates the brain from the circulating blood, which means that this is the place where the brain and the immune system communicate with each other.
The researchers pointed out that the cells that constitute the blood-brain barrier can release immune signals, and the adjacent hypothalamic VMPO neurons are just equipped with some receptors that receive immune signals, so the cells of the blood-brain barrier trigger nerve cells that control symptoms such as fever through a mechanism called "paracrine signals".