Gut-Brain Axis or Brain-Gut Axis?
Your gut is now considered to be your second brain. A two-way connection exists between the gut and the brain through a complex network of neurons, hormones and neurotransmitters. Let’s look at these in a bit more detail…
Your brain is connected to your gut via the involuntary part of your nervous system - the autonomic nervous system. Signals through this pathway influence the speed at which food moves through the tract, the amount of stomach acid secreted and the production of mucus in the gut wall.
The hypothalamic-pituitary-adrenal axis is a feedback loop that involves two parts of your brain and the small adrenal glands that are above your kidneys. Hormones are secreted as part of this circuitry and impact your feelings of hunger and satiety influencing the gut microbiota.
Gut microbes synthesise neurotransmitters, these are chemical signaling molecules that influence mood and behaviour. For example gut microbes influence the amount of the neurotransmitter serotonin, which regulates the feeling of happiness.
These complex communication circuits send information about the status of your gut to your brain. The brain responds by altering what it can - food transit time, acid and/or mucus production. There is also a complex interplay between psychological symptoms, the microbiota and the immune system. At this point we think that improving your microbiota could have a positive impact on your psychological wellbeing.
New research is looking at probiotics (Lactobacillus plantarum strain) and their potential effects on psychological symptoms of depression. These are called “psychobiotics” and could potentially affect levels of dopamine and serotonin. (Tsai, 2017).