Today, it is well known that our intestine harbors a comunity of bacteria with whom we dinamically and mutually interact. Over the years, studies have demonstrated a correlation between behavioural and gastrointestinal symptoms, suggesting a link between the gut and the brain neurodevelopment. Furthermore, the composition of the gut microbiota differs from individuals with neurodevelopment diseases and neurotypical ones. For example, Clostridial species were increased in the stools of children with autism than compared to the stools of control (Real-time PCR Quantitation of Clostridia in feces of Autistic Children, Song et. Al., 2004). In addition, it was found out that the metabolism of tryptophan was modulated by B. infantis, suggesting that the microbiota can influence the pool of serotonin. As a consequence of this, the interaction between gut and brain seems to be crucial for the understanding of neuropsychiatric disorders such as autism, schizophrenia, depression, anxiety, Alzheimer disease and Parkinson disease.
It has been demonstrated that, through fermentation of dietary fibre, intestinal microorganisms produce short-chain fatty acids which are lipids that contribute to neuroplasticity and have impact on behaviours (The role of gut microbiota in the gut-brain axis: current challenges and perspectives, Chen et al., 2013). Moreover, the gut microbiota is able to produce neurotransmitters. For example, Bifidobacterium is known to produce GABA while Lactobacillus plantarum and Klebsiella pneumonia produce serotonin starting from metabolites such as indole and tyramine (Associations of neurotransmitters and the gut microbiome with emotional distress in mixed type of irritable bowel syndrome, Barandouzi et. Al., 2022).
Today there are diverse high throughput identification methods for elucidation of microbes constituting gut microbiota and NGS (Next Generation Sequencing approaches) are the best one. Recent studies have also focused on the “metagenomic systems biology” which can make us appreciate the complex interactions among parts. By annotating the metabolic sequence data to identify the enzymatic genes, it is possible to construct the community-level metabolic network of the gut microbiota and associate bacteria with the specific host phenotypes (Metagenomic systems biology of the human gut microbiome reveals topological shifts associated with obesity and inflammatory bowel disease, Greenblum et al., 2012).
All in all, we could say that by acquiring a deep knowledge into our microbiota composition, it would be possible to learn more about the origin of some behaviours and conducts!
Written by: Camilla Vitagliano, Junior scientist, Early Stage Researcher @NAICONS