The Gut Microbiome and the Central Nervous System (CNS)

The presence of resident microbial species in the human gastrointestinal tract has been known for a long time. However, only recently have they been recognized as tremendous regulators of overall host pathophysiology. Interestingly, the central nervous system (CNS) features as a key target of the gut microflora. Recent studies indicate that the bidirectional interactions of the microbiota-gut-brain axis play critical roles in influencing a plethora of neuroendocrine and neuroinflammatory mediators, with huge implications for neurotransmitter physiology at the levels of enteric, autonomous, and central nervous systems. This chapter deals with the discussion of the pathophysiological roles of the resident microflora in the developing and adult brains, focusing on the two relevant aspects of blood-brain barrier development and adult hippocampal neurogenesis. Further, dysbiosis of the gut microbiome as a pathogenic factor for the development of CNS disorders (e.g., multiple sclerosis, Alzheimer’s and Parkinson’s diseases, amyotrophic lateral sclerosis, and stroke) is detailed. We also discuss the possibilities of harnessing the alterations in the gut microbial species for diagnostic, prognostic, and therapeutic purposes for these diseases. Lastly, the implications of the microbiota-gut-brain axis for promoting longevity and healthy ageing are illustrated.