There is a growing appreciation of the impact of gut microbiota on health and diseases. Recent findings have proved the relationship between gut microbiota and common health disorders such as obesity. Moreover, the role of gut microbiota in influencing brain function, behavior and mental health has attracted the attention of neuroscientists and psychiatrists.

The article provides an overview of the presentations of last year’s symposium “Gut microbiota and brain function: Relevance to psychiatric disorders” held in Vancouver, Canada. The role of the microbiome in determining behavior and cognition is increasingly being recognized. In fact, brain development in infants has been proved to be influenced by the microbiome.

The communication of gut microbiota with the brain, referred to as the microbiota-gut-brain axis, represents a new biological focus for diet-based therapies designed to influence human behavior. Many findings on the mechanisms by which microbes can influence behavior have concluded that such mechanisms involve the immune system to some degree. Scientists have focused their attention on the mechanisms of the microbiota-gut-brain axis on which the immune system does not intervene. A study published in American Journal of Physiology in 2012 established that the microbiota is capable of the in situ production of the biologically active neuroendocrine hormones, dopamine and norepinephrine, in quantities large enough to affect host neurophysiology.

Given that bacteria are prolific producers of neuroendocrine hormones, it seems reasonable to conclude that such bacterial production of neuroactive compounds within the gut lumen could influence host-specific neural receptors. Most studies employ probiotic bacteria, such as Lactobacillus o Bifidobaterium, which are prolific producers of neurochemicals for which well-defined neural mechanisms are known and by which behavior may be modulated. A recent study from 2011 observed a reduction of anxious and depressive-like behaviors in mice fed the probiotic strain L. rhamnosus. Despite the fact that they did not quantify the amount of GABA produced by the administered L. rhamnosus strain, the demonstration of a mechanism via central GABA receptor provide evidence that the ability of bacteria to influence behavior can occur through a neurochemical-mediated route.

Nowadays, studies are being focused on people and in how microbiota can influence mental disorders—like depression, anxiety or autism—or neuronal diseases—like multiple sclerosis, Alzheimer’s disease and Parkinson’s disease. A recent report showed how probiotic ingestion affected brain functions in healthy women. The four-week study of probiotic consumption showed a reduced engagement of an extensive brain network in response to an emotion recognition task.

Despite more recent studies, the article underlines that there are still some questions that remain to be answered, such as the way in which the microbiota sends signals to the brain. Studies trying to define how microbiota affects behavior are still in the early stages. Another aspect that is being studied is the individual components of bacteria that are mediating their effects. The evolving field of metabolomics is advancing and assisting in the better understanding of the signaling cascades and roles of bacterial products.

Finally, as most trials have focused on rodents, further human studies are needed in order to determine if bacteria-based interventions or treatments can have a positive effect on mental health, the so-called psychobiotic effect. Although some preliminary studies have focused on the altered composition of the microbiota in depression or autism, now is the time of a comprehensive analysis of the microbiota in other disorders, including schizophrenia, anxiety, drug addiction and eating disorders to determine if such changes have any causal relationship to psychiatric symptomatology.

 


 

Source: Foster JA, Lyte M, Meyer E, Cryan JF. Gut microbiota and brain function: An evolving field in neuroscience. 2015. Disponible en: http://ijnp.oxfordjournals.org/content/early/2015/11/17/ijnp.pyv114