Potential Role of Gut Microbes in Psychiatry
Understanding the influence of gut microbiota on host health, including brain health, is one of the most exciting areas in medicine. Emerging research from both animal and human studies suggests that the function and health of the brain, along with the rest of the central nervous system, is modulated by complex interactions with our gut microbiota. Although research into the complex signaling pathways involved is still in its infancy, studies lead researchers to conclude the gut microbiota plays an important role in cognitive function, sociality, hippocampal-dependent memory, anxiety, depression, temperament, and stress response.
Multiple routes of communication between the gut and brain have been recognized. Many researchers consider the vagus nerve to be the principal communication route. Other routes in the gut-brain axis include neurotransmitters, the immune system, spinal pathways, and short chain fatty acids.
Research has demonstrated that we are dependent on a spectrum of essential neurochemicals produced by microbes. For example, germ-free rodents, who were raised without exposure to bacteria, display altered sociability with autistic-like patterns of behavior. Researchers have also found that the serotonergic system does not develop appropriately in the absence of microbes. (The serotonergic system is a system of nerve cells that uses serotonin as its neurotransmitter. It plays a key role in emotional health.) (Dinan)
Furthermore, animal studies have demonstrated that long-term stress triggers low-grade inflammation that disturbs gut microbiota. And murine studies have shown that the presence or absence of exposure to certain microorganisms contributes to individual differences in stress vulnerability. (Langgartner)
Research on human subjects has demonstrated that dysbiosis can be reversed and reversal has measurable effects on cognitive performance. For example, a recent small-scale human study tested the effect of a probiotic (a strain of Bifidobacterium longum) on stress response in 22 healthy males and found that the intervention group benefited from improved memory and reduced stress compared to controls. (Allen)