5-HT	5-hydroxytryptamine
AD	Alzheimer’s disease
Aβ42	amyloid β42
ASD	autism spectrum disorder
BBB	blood–brain barrier
CNS	central nervous system
CSF	cerebrospinal fluid
EECs	enteroendocrine cells
GF	germ-free
GIT	gastrointestinal tract
GABA	gamma-aminobutyric acid
IBD	inflammatory bowel disease
IFNγ	interferon γ
LPS	lipopolysaccharides
MAMP	microbe-associated molecular pattern
MGBA	microbiota–gut–brain Axis
SCFAs	short chain fatty acids
TNF	tumor necrosis factor