The Microbiota-Gut-Brain Axis: From Motility to Mood

Role of microbes in the pathogenesis of neuropsychiatric disorders

Microbes inhabit different anatomical sites of the human body including oral cavity, gut, and skin. A growing literature highlights how microbiome variation is associated with human health and disease. There is strong evidence of bidirectional communication between gut and brain mediated by neurotransmitters and microbial metabolites. Here, we review the potential involvement of microbes residing in the gut and in other body sites in the pathogenesis of eight neuropsychiatric disorders, discussing findings from animal and human studies. The data reported provide a comprehensive overview of the current state of the microbiome research in neuropsychiatry, including hypotheses about the mechanisms underlying the associations reported and the translational potential of probiotics and prebiotics.

Impact of the Gut Microbiota Balance on the Health-Disease Relationship: The Importance of Consuming Probiotics and Prebiotics

Gut microbiota is a group of microorganisms that are deposited throughout the entire gastrointestinal tract. Currently, thanks to genomic tools, studies of gut microbiota have pointed towards the understanding of the metabolism of important bacteria that are not cultivable and their relationship with human homeostasis. Alterations in the composition of gut microbiota could explain, at least in part, some epidemics, such as diabetes and obesity. Likewise, dysbiosis has been associated with gastrointestinal disorders, neurodegenerative diseases, and even cancer. That is why several studies have recently been focused on the direct relationship that these types of conditions have with the specific composition of gut microbiota, as in the case of the microbiota-intestine-brain axis. In the same way, the control of microbiota is related to the diet. Therefore, this review highlights the importance of gut microbiota, from its composition to its relationship with the human health-disease condition, as well as emphasizes the effect of probiotic and prebiotic consumption on the balance of its composition.

Deep Transcranial Magnetic Stimulation Affects Gut Microbiota Composition in Obesity: Results of Randomized Clinical Trial

Growing evidence highlights the crucial role of gut microbiota in affecting different aspects of obesity. Considering the ability of deep transcranial magnetic stimulation (dTMS) to modulate the cortical excitability, the reward system, and, indirectly, the autonomic nervous system (ANS), we hypothesized a potential role of dTMS in affecting the brain-gut communication pathways, and the gut microbiota composition in obesity. In a hospital setting, 22 subjects with obesity (5 M, 17 F; 44.9 ± 2.2 years; BMI 37.5 ± 1.0 kg/m²) were randomized into three groups receiving 15 sessions (3 per week for 5 weeks) of high frequency (HF), low frequency (LF) dTMS, or sham stimulation. Fecal samples were collected at baseline and after 5 weeks of treatment. Total bacterial DNA was extracted from fecal samples using the QIAamp DNA Stool Mini Kit (Qiagen, Italy) and analyzed by a metagenomics approach (Ion Torrent Personal Genome Machine). After 5 weeks, a significant weight loss was found in HF (HF: −4.1 ± 0.8%, LF: −1.9 ± 0.8%, sham: −1.3 ± 0.6%, p = 0.042) compared to LF and sham groups, associated with a decrease in norepinephrine compared to baseline (HF: −61.5 ± 15.2%, p < 0.01; LF: −31.8 ± 17.1%, p < 0.05; sham: −35.8 ± 21.0%, p > 0.05). Furthermore, an increase in Faecalibacterium (+154.3% vs. baseline, p < 0.05) and Alistipes (+153.4% vs. baseline, p < 0.05) genera, and a significant decrease in Lactobacillus (−77.1% vs. baseline, p < 0.05) were found in HF. Faecalibacterium variations were not significant compared to baseline in the other two groups (LF: +106.6%, sham: +27.6%; p > 0.05) as well as Alistipes (LF: −54.9%, sham: −15.1%; p > 0.05) and Lactobacillus (LF: −26.0%, sham: +228.3%; p > 0.05) variations. Norepinephrine change significantly correlated with Bacteroides (r² = 0.734; p < 0.05), Eubacterium (r² = 0.734; p < 0.05), and Parasutterella (r² = 0.618; p < 0.05) abundance variations in HF. In conclusion, HF dTMS treatment revealed to be effective in modulating gut microbiota composition in subjects with obesity, reversing obesity-associated microbiota variations, and promoting bacterial species representative of healthy subjects with anti-inflammatory properties.

Postbiotic Supplementation for Children and Newborn's Health

It is now well known how the microbiota can positively or negatively influence humans health, depending on its composition. The microbiota's countless beneficial effects have allowed it to be defined as a genuine symbiont for our species. In an attempt to positively influence the microbiota, research has focused on probiotics and prebiotics. Probiotics are viable beneficial bacteria of various strains. Prebiotics are specific substances able to favor the development of advantageous bacteria strains. Postbiotics are a new category of compounds capable of affecting the microbiota. According to the different definitions, postbiotics include both nonviable bacteria and substances deriving from bacterial metabolism. Postbiotics are particularly promising in pediatric settings, as they offer some advantages over probiotics, including the absence of the risk of intestinal translocation or worsening of local inflammation. For these reasons, their use in fragile population categories such as newborns, and even more prematures, seems to be the best solution for improving microbiota's health in this population. This narrative review aims to collect the research conducted so far on postbiotics' potential in the first stages of life.