two approaches were used : ( 1 ) dynorphin-related peptides ( 0.02-20.4 mm ) were injected intracerebroventricularly 1 min before decapitating the animal , and ( 2 ) the action of endogenous opioid peptides was blocked by injecting subcutaneously or intracerebroventricularly either naloxone or a selective kappa receptor antagonist , mr 2266 or nor-binaltorphimine .
C0013355
dynorphin
C0205753
endogenous opioid peptides