ACTH	adrenocorticotropic hormone
BBB	Blood–brain barrier
CNS	Central nervous system
CRP	C-reactive protein
GABA	Gamma-aminobutyric acid
HDAC	Histone deacetylase
HPA	Hypothalamic–pituitary–adrenal
HRV	Heart rate variability
IDO	Indoleamine 2,3-dioxygenase
IL-6	Interleukin-6
IL-1β	Interleukin-1β
LPS	Lipopolysaccharides
MDD	Major depressive disorder
SCFAs	Short-chain fatty acids
TLR4	Toll-like receptor 4 TLR4
TNF-α	Tumour necrosis factor-α