Researching the influence of intestinal bacteria on the brain

‘Adults have around a hundred-thousand billion bacteria in their guts, weighing almost one-and-a-half kilos. It is gradually becoming clear that these intestinal bacteria, known collectively as the microbiota, have a huge influence on the body. Work in my laboratory focuses on how the effect of intestinal bacteria on the gut can influence our brain. Gut flora and the brain seem to be talking to each other all the time’.

‘I chose the word “talking” carefully – it is a dialogue. And it’s a two-way dialogue: the intestinal bacteria influence our health and behaviour, but our behaviour can also change our gut flora.
The intestines have a direct link with the brain via the vagus nerve, an important neural pathway that transmits signals in both directions between the gut and the brain. Bacteria influence this communication. Intestinal bacteria are like tiny factories for neuroactive substances. They produce the same chemical substances – neurotransmitters – that our nervous system uses to communicate. These include serotonin, dopamine and noradrenalin. Since the bacterial population influences this production, it has a direct impact on the behaviour and mood of the host.
In other words, it is important to ensure a good variety of intestinal bacteria. Having adequate gut flora starts at birth. During delivery, a baby comes into contact with the mother’s vaginal microbiota. The composition of this microbiota largely determines the composition of the baby’s gut flora, which in turn influences the development of the infant’s immune system, metabolism and brain. An abnormal composition due to stress, diet, infections or the use of antibiotics will therefore affect the health of the child.
To understand these effects, researchers are studying the gut flora of mice. They examine how prenatal stress in pregnant mice, for example, affects the gut flora of newborn mice. Their gut flora shows signs of abnormality immediately after birth, but by adulthood, the microbiota of these mice is no different from that of “normal mice”. However, as soon as these mice are put under stress, their gut flora shows a strong reaction. It seems that mice whose mothers were stressed are themselves more sensitive to stress. So the bacteria in our gut appear to be one of the factors that determine whether we will become anxious or depressed.
I also study another important factor that affects our gut flora: nutrition. Our diet is very different from that of our ancestors. A prehistoric diet would have contained many more indigestible ingredients, which then served as food for the intestinal bacteria. Our current diet is threatening the existence of many of these ancient bacteria. We want to understand the implications. And whether we can limit the damage by eating more indigestible food.

Research into the interaction between intestinal bacteria and the brain is relatively new. We still understand very little about this highly complex relationship. Looking to the distant future, I think that this field may provide starting points for developing new drugs to treat mental health problems. We’ve noticed, for example, that many behavioural disorders occur in people with intestinal problems or food allergies. Take ADHD, autism or depression, for example, or certain brain diseases, such as Parkinson’s disease or Alzheimer’s disease. There is still a lot to discover in this particular field’.