Functional gastrointestinal disorders and gut-brain axis: What does the future hold?

Table 1 Different factors that influence the brain - Gut interaction in functional gastrointestinal disorders

Nature of link	Evidence	Comments
Dysbiosis	Kassinen et al[82]; Tojo et al[83]; Chassard et al[84]; Cryan et al[85]	Disturbance in the complex community of microbiota seems to influence gut-brain axis by modulating neuroendocrine, neuroimmunal and visceral sensory system.
Altered mucosal secretions	Mazmanian et al[86]; Xue et al[87]	Secretion is modulated by complex interaction of intrinsic and extrinsic factors acting on gut mucosa. Dysregulation of the epithelial cells due to autonomic reactivity may lead to 5-HT release contributing to altered secretion
Disturbance in motility	Randich et al[13]; Dass et al[88]; Barbara et al[89]	Products of metabolism of gut bacteria, such as short-chain fatty acids modulate enteric system and influence the rate of gut transit
Visceral hypersensitivity	O'Mahony et al[22]; Akbar et al [34]	Patients with IBS have been found to have an increased concentration of pain-sensing receptors such as TPRV1 compared to the controls.
Altered processing of visceral signals	Lemann et al[90]; Mertz et al[91]	There is increased activation of certain cerebral areas in IBS patients compared to the controls. Altered processing of the visceral pain in the central nervous system has been a recurring theme in many studies.
Immune dysfunction	Chadwick et al[92]; Dinan et al[24]; Keely et al[93]	Patients with prolonged Infectious diarrhea are much more prone to developing IBS. Also, biopsies of patients with IBS have shown increased immune cells in the mucosa[92].
Psychological disturbances	Creed et al[17]; Gwee et al[94]; Drossman et al[95]; Monnikes et al[2,12]	Patients with FGIDs have co-existing psychosocial symptoms such as stress, anxiety and depression and thus a biopsychosocial model has been proposed for FGIDs
Early life stress	O'Mahony et al[22]; Bailey et al[96]	Early life-stress can alter the composition of gut microbiota

5-HT: 5-hydroxytryptamine; FGID: Functional Gastrointestinal diseases; IBS: Inflammatory bowel disease; TRPV1: Transient receptor potential vallinoid 1.