nAChRs	nicotine acetylcholine receptors
CPP	conditioned place preference
NRT	nicotine replacement therapy
MHb	medial habenula
IPN	interpeduncular nucleus
18-MC	18-methoxycoronidine
i.c.v.	intracerebroventricular injections
s.c.	subcutaneous injection
OFT	open field test
ELPM	elevated plus maze test
PCA	principal component analysis
OPLS-DA	orthogonal partial least-squares discriminant analysis
QC	quality control
VIP	variable important in projection
KEGG	kyoto encyclopedia of genes and genomes
NAcc	nucleus accumbens
NAD+	nicotinamide adenine dinucleotide
NADP+	nicotinamide adenine dinucleotide phosphate
TCA	tricarboxylic acid
WHO	World Health Organization
CNS	central nervous system