injection of theo ( 20 , 40 mg kg-1 ) or caffeine ( 40 mg kg-1 ) reversed or blocked the inhibitory effects of leu-enkephalin ( 50 micrograms i.c.v . ) and a systemically active enkephalin fk 33,824 ( 0.5 mg kg-1 ) on the release of acetylcholine ( ach ) from the rat cortex in vivo .
C0014294
leu-enkephalin
C0014298
enkephalin