The gut microbiome and the brain

Abstract

The enteric nervous system and the central nervous system are no longer viewed as being separate entities. They are connected to each other by the vagal nerve which allows for bi-directional communication between cells on opposite sides of the body. Local cells in the gut can also activate the release of cortisol from the hypothalamic-pituitary-adrenal-axis (HPA) during an immune challenge in order to augment the local immune response. Enteric bacteria have adapted to make use of both the vagal nerve and the HPA in order to create a metabolic niche in which they can survive. They do this by sending neural, as well as, hemocrine signals to the brain which alter behaviour in the host. Feeding behaviour, mood regulation and circadian rhythms can be influenced through cross-talk between gut bacteria and neurons which form part of central circuits. Pathogens can therefore induce a dependency in the host, in which unhealthy foods are sought and irregular sleep cycles are entrenched. This may help to explain the current epidemic of ‘fussy eaters’ and ‘difficult sleepers’ in the paediatric population. Of concern is that the emergence of this dysregulated microbiome in children may result from unregulated modern practices such as elective caesarean section and poor antibiotic stewardship. The aim of this article is to foster greater discernment in our modern practices.