we knew for a while that depression is associated with inflammation. this is one elegant theory describing why:
https://www.scientif...ess-depression/
fight-or-flight response places extreme demands on the mitochondria. All of a sudden, they need to produce much more energy to fuel a faster heartbeat, expanding lungs and tensing muscles, which leaves them vulnerable to damage. Unlike DNA in the cell’s nucleus, though, mitochondria have limited repair mechanisms. And recent animal studies have shown chronic stress not only leads to mitochondrial damage in brain regions such as the hippocampus, hypothalamus and cortex, it also results in mitochondria releasing their DNA into the cell cytoplasm, and eventually into the blood.
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mitochondrial DNA, when released into the blood after an injury, mobilized a pro-inflammatory immune response. Because of mitochondria’s bacterial origin and its circular DNA structure, immune cells think it’s a foreign invader. When circulating mitochondrial DNA binds to a particular receptor, TLR9, on immune cells, they respond as if they were reacting to a foreign invader such as a flu virus or an infected wound. The immune cells release chemicals called cytokines telling other white blood cells they need to report for duty at sites of infection, inflammation or trauma.