An array of scientific evidence suggest that in some cases, the bacteria in your gut–your microbiome–could be tied to neurological and psychological disorders and differences, from anxiety and autism to Parkinson's and schizophrenia. The journal Science published a survey of the field and the Cambridge, Massachusetts start-up Holobiome that hopes to use insight into this "psychobiome" to develop treatments for depression, insomnia, and other conditions with a neurological side to them. From Science:
For example, many people with irritable bowel syndrome are also depressed, people on the autism spectrum tend to have digestive problems, and people with Parkinson’s are prone to constipation.
Researchers have also noticed an increase in depression in people taking antibiotics—but not antiviral or antifungal medications that leave gut bacteria unharmed. Last year, Jeroen Raes, a microbiologist at the Catholic University of Leuven, and colleagues analyzed the health records of two groups—one Belgian, one Dutch—of more then 1000 people participating in surveys of their types of gut bacteria. People with depression had deficits of the same two bacterial species, the authors reported in April 2019 in Nature Microbiology.
Researchers see ways in which gut microbes could influence the brain. Some may secrete messenger molecules that travel though the blood to the brain. Other bacteria may stimulate the vagus nerve, which runs from the base of the brain to the organs in the abdomen. Bacterial molecules might relay signals to the vagus through recently discovered “neuropod” cells that sit in the lining of the gut, sensing its biochemical milieu, including microbial compounds. Each cell has a long “foot” that extends outward to form a synapselike connection with nearby nerve cells, including those of the vagus.
Indirect links may also exist. Increasingly, researchers see inflammation as a key factor in disorders such as depression and autism. Gut bacteria are key to proper immune system development and maintenance, and studies show that having the wrong mix of microbes can derail that process and promote inflammation. And microbial products may influence what are known as enteroendocrine cells, which reside in the lining of the gut and release hormones and other peptides. Some of those cells help regulate digestion and control insulin production, but they also release the neurotransmitter serotonin, which escapes the gut and travels throughout the body.
"Meet the ‘psychobiome’: the gut bacteria that may alter how you think, feel, and act" by Elizabeth Pennisi (Science)
image: Jean-Baptiste Marc Bourgery (CC BY-SA 3.0)
𝐆𝐫𝐮𝐦𝐩𝐲 
𝐒𝐜𝐨𝐭𝐬𝐦𝐚𝐧
