the level of opioid peptides : beta-endorphin and dynorphin , binding to the mu and kappa opioid receptors and the analgesic response of those endogenous opioid systems to stress were investigated in two strains of mice : c57bl/6 ( c57 ) and dba/2 ( dba ) .
C0205753
opioid peptides
C0013355
dynorphin