POMC is a polypeptide precursor protein with 241 amino acid residues. Ten different peptides can be derived from POMC through tissue-specific posttranslational processing, including adrenocorticotropin (ACTH) and beta-endorphin, which are principal components of the HPA axis. Studies in rodents have shown that stressors elevate POMC mRNA levels in the pituitary. POMC-derived peptides actively regulate drug-related behaviors (Kiefer et al. 2002; O'Malley et al. 2002). Beta-endorphin is a 31-amino acid peptide that is the major endogenous ligand of the mu opioid receptor and is found mainly in neurons of the hypothalamus and the pituitary gland (Dores and Baron et al. 2011).
