Gastrointestinal neuromuscular apparatus: An underestimated target of gut microbiota

Table 1 Direct effect of bacterial fermentation products on gastrointestinal motility

Fermentation product	Effect on GI motility	Mechanism	Ref.
Short-chain fatty acids	Increase of ileal tone and propulsive contractions	Activation of G-protein coupled free fatty acid receptors (FFAR2, FFAR3, OLFR78, GPR109A)	[48-55]
	Smooth muscle and myenteric neurons activation	Release of 5-HT from EC cells
		Release of prostaglandins
Deconjugated bile salts	Relaxation of gallbladder smooth muscle cells	Activation of transmembrane G-protein coupled receptor	[58-61]
	Inhibition of gallbladder contractility	Reduction in cholecystokinin receptor binding
		Increase of inflammatory mediators and oxidative stress
Tryptamine	Stimulation of ileum motility	Synthesis of neurotransmitters	[63-65]
Gases	Decrease of small intestinal transit time	Methane (CH4) production	[66,67]
	Augmented ileal circular muscle contractile activity
	Shortening of colonic transit times	Hydrogen (H2) production	[68]
	Inhibition of intestinal contractile activity	Hydrogen sulfide (H2S) production	[66]

GI: Gastrointestinal.