Molecular signalling during cross talk between gut brain axis regulation and progression of irritable bowel syndrome: A comprehensive review

Table 1 Types of regulation of serotonergic (5-Hydroxytryptamine) pathway by specific enteric microbiota in gastrointestinal tract

Microbiota spp.	5-HT pathway	Mechanisms of action and observations	Ref.
Akkermansia muciniphila (Amuc_1100)	Upregulation	Promote intestinal 5-HT biosynthesis and extracellular availability through TLR2 signalling	[129]
Akkermansia muciniphila (extracellular vesicles)	Upregulation	Increase expression of the Htr4 gene, and decreases expression of the Htr2B, Htr3B, and Htr7 genes	[129]
Bacteriodes thetaiotaomicron	Upregulation	Restore 5-HT+ EC cells and shape EC networks in the GI tract of GF mice by producing SCFAs	[130]
Bifidobacterium dentium	Upregulation	Increase intestinal 5-HT level; expressions of 5-HTra receptors 2a and 4, and SERT by producing acetate	[131]
Bifidobacterium longum and	Downregulation	Upregulate SERT expression	[132]
Lactobacillus acidophilus
Bifidobacterium pseudolongum	Downregulation	Diminish EC cells	[133]
Clostridium ramosum	Upregulation	Promote 5-HT synthesis in colonic EC cells and program differentiation of intestinal stem progenitors toward a secretory 5-HT-producing lineage	[134]
Corynebacterium spp., Enterococcus spp., Streptococcus spp.	Upregulation	Enable the direct production of 5-HT	[135]
Escherichia coli Nissle 1917	Upregulation	Enhance 5-HT bioavailability in ileal tissue through interaction with compounds secreted from host tissue	[136]
Indigenous spore-forming bacteria	Upregulation	Enhance colonic 5-HT pathway by upregulation of Htr4	[137]
Lactobacillus acidophilus	Down regulation	Upregulate SERT expression	[138]
Lactobacillus plantarum IS-10506	Upregulation	Increase gut 5-HT production along with brain 5-HTT, neurotrophin, and brain-derived neurotrophic factor	[139]
Lactobacillus plantarum PS128	Upregulation	Increase 5-HT+ cells in the gut and alter expression levels of Tph1, Chga, Slc6a4, and Htr4	[140]
Lactobacillus rhamnosus	Down regulation	Upregulate gene and protein level of SERT	[141]
SadA-expressing Staphylococci, Trichinella spiralis and Campylobacter jejuni (pathogens)	Upregulation	Promote converting 5-HTP into 5-HT; increase EC cell number and reduce SERT expression	[141]

5-HT: 5-Hydroxytryptamine; 5-HTP: 5-Hydroxytryptophan; EC: Enterochromaffin cell; SERT: Serotonin transporters.