Figure 1. Bidirectional communication between the gut microbiota and the central nervous system (CNS). The composition of gut microbiota could modulate the function of CNS through various communication means including neural (vagus nerve activation), hormonal (enteroendocrine cells and bacterial neuropeptides), humeral (bacterial metabolites) and immunological (activation of mucosal immune system). The Brain-to-Gut microbiota axis is mediated via stress factors, alteration in intestinal permeability and motility and through release of neurotransmitters and mucus.