ACTH	adrenocorticotropic hormone
AE	adverse event
cAMP	cyclic adenosine mono phosphate
CCI	chronic constriction injury
CeA	the central nucleus of amygdala
CRF	corticotropin-releasing factor
CREB	cAMP response element-binding protein
CGRP	calcitonin gene-related peptide
CPP	conditioned place preference
D1R	dopamine D1 receptor
DOP	δ-opioid peptide receptor
DRG	dorsal root ganglia
DRN	dorsal raphe nucleus
ECL	extracellular loop
EC50	half-maximal effective concentration
ED50	median effective dose
ERK	extracellular signal-regulated kinase
FAS	full analysis set
GABA	gamma-aminobutyric acid
GIRK	G-protein-gated inwardly rectifying potassium channels
GPCR	G-protein-coupled receptor
HPA	hypothalamic–pituitary–adrenal axis
ICL	intracellular loop
i.p.	intraperitoneal
i.v.	intravenous
JNK	c-Jun N-terminal kinase
KOP	κ-opioid peptide receptor
LTP	long-term potentiation
MAPK	mitogen-activated protein kinase
MOP	μ-opioid peptide receptor
N/OFQ	nociceptin/orphanin FQ
NAc	the nucleus accumbens
NMR	nociceptin/orphanin FQ and μ-opioid receptor (NOP/MOP)
NMDA	N-methyl-D-aspartate
NOP	nociceptin opioid peptide receptor
NRS	numeric rating scale
OIRD	opioid-induced respiratory depression
ORL1	opioid receptor-like 1
PAG	periaqueductal gray
PK	pharmacokinetic
PK-PD	pharmacokinetic–pharmacodynamic
PKA	protein kinase A
PNOC	prepronociceptin
PR	prolonged release
RVM	rostral ventromedial medulla
SAE	serious adverse event
SDH	spinal dorsal horn
TEAE	treatment-emergent adverse event
TH	tyrosine hydroxylase
TM	transmembrane
VAS	visual analog scale
VTA	ventral tegmental area