The brain-gut axis: a target for treating stress-related disorders.

The brain-gut axis provides a bidirectional means of communication between the microbiota within the gut and the brain. Stress acting via the brain can result in alteration of the microbial composition of the gut, but increasing evidence indicates that bacteria within the gut can influence brain neurochemistry and behaviour. It is clear that post-natal colonisation of the gut plays a key role in regulating the development of the hypothalamic-pituitary-adrenal axis and the development of pivotal neurotransmitter systems. Probiotics are defined as live bacteria which confer a health benefit. Recent studies in rodents have demonstrated the capacity of a probiotic, Lactobacillus rhamnosus, to alter the expression of GABA receptors centrally whilst producing anxiolytic type effects. Preliminary studies in humans are yielding encouraging findings. It may in the future be possible to use probiotic bacteria to treat depression and other stress-related disorder but we await the results of appropriately designed placebo-controlled trials.