Is Your Gut Bacteria Making You Depressed?

OK, so far, they've only done this is mice, but they were the kind of mice whose bodies often respond the way human bodies do. The Wall Street Journal reports, first of all, that 90 percent of people who suffer from chronic bowel disorders also suffer from anxiety and depression. Yikes! The paper directs us to research (recently published in Gastroenterology) that suggests that such unpleasant brain activity may be related to a "disruption in the intestinal environment." That, at least is the working theory of Canadian scientists, who found that changing the bacterial composition of the colon through the administration of antibiotics resulted in increased levels of brain-derived neurotrophic factor (BDNF), a protein associated with memory, learning and mood. When the researchers switched out the bacteria in colons of very passive and lethargic mice, the mice perked up, immediatly becoming more curious and more adventurous. Sound good so far, but there is also some evidence that the researchers have their causes and effects flipped. Psychology Today reports that other experiments have shown that psychological stress causes immediate changes to the gut bacterial population. Researchers in those experiments exposed mice to social disruption, which altered bacterial counts of some gut bacteria sub-populations. So the next question is, which came first, the anxiety or the bacteria?