CNS	central nervous system
SCFA	short-chain fatty acids
AAM	amino acid metabolites
ASD	autism spectrum disorder
MS	multiple sclerosis
PD	Parkinson’s disease
AD	Alzheimer’s disease
GIT	gastrointestinal tract
GBA	gut–brain axis
BBB	blood–brain barrier
BA	butyric acid
PA	propionic acid
AA	acetic acid
VA	valeric acid
TMAO	trimethylamine N-oxide
IS	indoxyl sulphate
4EPS	4-ethylphenylsulfate
IAA	indole acetic acid
IPA	indole propionic acid
IBS	irritable bowel syndrome
GF	germ free
WT	wild type
HDACI	histone deacetylase inhibition/inhibitor
NT	neurotypical
FMT	faecal microbiome transplants
HC	healthy controls
DBH	dopamine beta-hydroxylase
MDD	major depressive disorder
HAB	high anxiety-like behaviour
NaB	sodium butyrate
αSyn	alpha-synuclein protein
AAA	aromatic amino acids
Tyr	tyrosine
Phe	phenylalanine
Trp	tryptophan
5-HT	serotonin
ATD	acute tryptophan depletion
DA	dopamine
AHR	aryl hydrogen receptor