Role of gut microbiota in neuropsychiatric and neurological disorders

Complex crosstalk exists between the gut microbiome and the brain or central nervous system (CNS). A healthy gut ecosystem comprises diverse microbial compositions that ensure the normal functioning of the brain. On the other hand, the CNS regulates the functioning and physiology of GIT. These bidirectional interactions regulate neural, endocrine, immune, and humoral pathways. A growing body of evidence implicated imbalance in the gut microbiota composition also known as gut dysbiosis as a critical contributing factor in the pathogenesis of various neuropsychiatric and neurological disorders. Gut dysbiosis has been associated with persistent immune activation and increased blood-brain barrier permeability. Also, the release of cellular components and metabolites by gut microbiota act as important signaling molecules in the gut-brain axis. These chemicals not only activate gastrointestinal and neural-mediated pathways locally; but once released into the systemic circulation they eventually reach the brain and trigger a neuroinflammatory cascade. All these events disturb brain homeostasis and eventually lead to the pathogenesis of numerous neurological and psychiatric illnesses. This chapter focuses on recent research on the role of the gut microbiota-brain axis in the pathogenesis of neurological diseases such as Alzheimer's, schizophrenia, anxiety, autism, depression, epilepsy, migraine, and Parkinson's disease. The various processes or pathways involved in neuropsychiatric and neurological disorders caused by gut dysbiosis will also be examined.