“…The CNS, via PNS, is known to interact with the gut and plays a role in intestinal motility, secretion, absorption, immune function, and overall intestinal homeostasis ( Rhee et al, 2009 ; Carabotti et al, 2015 ). The sensory communication between the gut and the brain is mediated via the vagal and spinal sensory nerve afferents ( Carabotti et al, 2015 ; Yu et al, 2020 ), while the nervous system can, in turn, modulate the GI environment and function via motor nerves and direct hormonal effects ( Berthoud, 2008 ; Browning and Travagli, 2014 ; Carabotti et al, 2015 ; Fung et al, 2019 ; Menon et al, 2019 ). Bacteria can produce major neurotransmitters like serotonin ( Carabotti et al, 2015 ; Fung et al, 2019 ; Chen et al, 2021 ), modulate the production of host neurotransmitters ( Appleton, 2018 ) and neurotrophic factors ( Maqsood and Stone, 2016 ), in part via gut bacterial metabolites like SCFAs ( Vecsey et al, 2007 ; Ryan et al, 2016 ; Silva et al, 2020 ).…”