Food for thought: Role of gut health in mental health

A TOPIC that dealt with the implications of the gut and the microbiota in human response to stress and anxiety was a rare occasion for neurobiologists, behavioural experts, microbiologists, gastroenterologists and even animal nutritionists to gather in the same room. Indeed, as leading experts shared at the Second Scientific Exchange on the Gut-Brain Axis in Chantilly, France, the communication between the brain and the gut – sometimes called "the second brain" – is a bi-directional dialogue that co-ordinates brain and gut functions.

Whilst the relationship between the brain and the gut, which harbours 70 per cent of our nervous cells (the enteric nervous system), has been known for a long time, new developments and findings are emerging. As symposium chair Dr Vassilia Theodorou from INRA (Institut National de la Recherche Agronomique) in Toulouse explained in her introduction, new "players" have emerged along the way: the immune system (also largely represented in the digestive tract since 60-70 per cent of our immune cells are associated with our gut) and, more recently, the microbiota, which has certainly been overlooked until now.

Let's not forget that our guts harbour around 10 times more bacteria than the number of cells in our body, and 100 times more genes than our own genome. Several animal studies and hypothesis around digestive pathologies prove the implication of the microbiota in the gutbrain cross-talk, or Gut-Brain Axis; however, Dr Theodorou admitted that the exact mechanisms involved are still a "black box" needing further investigations.

Exciting data were presented about the great potential of probiotics to modulate the Gut-Brain Axis and, for example, to impact our response to stress and anxiety. For Lallemand, this meeting
was also a great opportunity to gather the companies who distribute its stress targeting probiotic, Probio'Stick?, as part of the company's strategy to offer its partners worldwide sustained marketing and scientific support. Following the Scientific Exchange, a Partner's Exchange session was an opportunity for the partners to share marketing strategies used to promote this unique probiotic in their own market.

The chicken and egg dilemma
Some scientists have recently noticed that, in certain behavioural conditions –such as autism, anxiety or depression – the microbiota is altered, and they are trying to link the condition to a particular microbiota profile. But is it the microbiota that determines the behaviour or the other way round?  Prof Stephen M. Collins of McMaster University (Hamilton, Canada) presented another perspective to this chicken and egg dilemma by showing that stress, by altering the gut environment, can alter the microbiota. In an animal model for anxiety and depression, his team showed how behavioural changes or stress alter gut microbiota. Specifically, they found that a particular neurotransmitter involved in the stress-response, the corticotrophin releasing
hormone – CRH, could play a role by altering the gut physiology and hence the habitat of the microbiota.

Probiotics – anti-depressor of tomorrow?
Several studies presented during the meeting showed that an alteration of the microbiota could affect the behaviour of animals or modify the stress response and visceral sensitivity. In particular, Professor Collins presented some microbiota transfer experiments in mice, which lead to a "behavioural transfer". The Gut-Brain Axis is essential for maintaining intestinal equilibrium (homeostasis) and wellness, and we now know that the disruptions of this axis could be implicated in certain patholNike Benassi Slide