Gut Microbes and Neuropathology: Is There a Causal Nexus?

The gut microbiota is a virtual organ which produces a myriad of molecules that the brain and other organs require. Humans and microbes are in a symbiotic relationship, we feed the microbes, and in turn, they provide us with essential molecules. Bacteroidetes and Firmicutes phyla account for around 80% of the total human gut microbiota, and approximately 1000 species of bacteria have been identified in the human gut. In adults, the main factors influencing microbiota structure are diet, exercise, stress, disease and medications. In this narrative review, we explore the involvement of the gut microbiota in Parkinson's disease, Alzheimer's disease, multiple sclerosis and autism, as these are such high-prevalence disorders. We focus on preclinical studies that increase the understanding of disease pathophysiology. We examine the potential for targeting the gut microbiota in the development of novel therapies and the limitations of the currently published clinical studies. We conclude that while the field shows enormous promise, further large-scale studies are required if a causal link between these disorders and gut microbes is to be definitively established.

Automated summary

The gut microbiota is a virtual organ that produces essential molecules for the brain and other organs. It plays a symbiotic role with humans, as we provide them with food and they provide us with necessary molecules. Factors such as diet, exercise, stress, disease, and medications affect the structure of the gut microbiota. This review explores the involvement of the gut microbiota in high-prevalence disorders such as Parkinson's disease, Alzheimer's disease, multiple sclerosis, and autism. While there is potential for developing novel therapies targeting the gut microbiota, further large-scale studies are needed to establish a definitive causal link between these disorders and gut microbes.