Effect of Intestinal Microbial Ecology on the Developing Brain

Abstract

The mammalian gastrointestinal tract harbors a highly diverse microbial population that plays a major role in nutrition, metabolism, protection against pathogens, and development of the immune system. It is estimated that at least 1000 different bacterial species cohabit the human intestinal tract. Most recently, the Human Microbiome Project, using new genomic technologies, has started a catalog of specific microbiome composition and its correlation with health and specific diseases. Herein we provide a brief review of the intestinal microbiome, with a focus on new studies showing that there is an important link between the microbes that inhabit the intestinal tract and the developing brain. With future research, an understanding of this link may help us to treat various neurobehavioral problems such as autism, schizophrenia, and anxiety.

Gut microbiota, the immune system, and diet influence the neonatal gut–brain axis

“…While microbial colonization of the gut is important for immune system development, it also acts in concert with diet to promote healthy brain development (85,86). Human milk contains many biofactors that improve health and brain development (87).…”

“…A recent review also says probiotic bacteria release inhibitors of tumor necrosis factor-alpha and its downstream target nuclear factor-kappa B (101). Researchers also propose that probiotics prevent brain injury by blocking the transport of damaging biomolecules via the GBA (43,86).…”

Microbiome Disturbances and Autism Spectrum Disorders

“…In fact, 90% of the cells contained in most mammalian organisms are of prokaryotic origin. The gut microbiota population is comprised of 500-1000 denizen species representing 7000-40,000 bacterial strains spanning 1800 genera (Luckey, 1972;Ley et al, 2006;Frank and Pace, 2008;Qin et al, 2010;Clemente et al, 2012;Douglas-Escobar et al, 2013;Forsythe and Kunze, 2013;Gilbert et al, 2013). The 1 Â 10 3 to 1 Â 10 4 microorganism gut inhabitants possess a diverse and complex genome encompassing approximately 150 times more genes than the human genome (Gill et al, 2006;Qin et al, 2010).…”

“…The bacterial-derived SCFAs may serve as a fuel source for enterocytes lining the intestinal system; however, these chemicals can also alter the intercellular spaces between the cells, resulting in a leaky gut that allows for more metabolites and bacteria to pass through the epithelial barrier, which as discussed subsequently can lead to detrimental neurologic effects. Furthermore, disturbances in the gut and other microbiomes (dysbiosis) can affect host immunity and neurobehavioral responses (Cryan and Dinan, 2012;Douglas-Escobar et al, 2013;Ding and Schloss, 2014;Galland, 2014;Stilling et al, 2014;Sherman et al, 2015). In this review, we will primarily focus on how alterations in microbiomes, especially in the gut, and their products affect the risk for ASD and related neurobehavioral disorders.…”

Recent findings within the microbiota–gut–brain–endocrine metabolic interactome

“…In one example, a probiotic Bacteroides fragilis that was given in early adolescence has been shown to ameliorate some behavioral deficits in a rodent autism model. [36][37][38] Whether neurodevelopmental disorders, such as schizophrenia and attention-deficit hyperactivity disorder (ADHD), are associated with microbiota changes is unclear and remains under investigation.…”