Journal of Neuroscience, Vol 7, 1698-1704, Copyright © 1987 by Society for Neuroscience
Effect of endogenous opioid peptides on acetylcholine release from the cat superior cervical ganglion: selective effect of a heptapeptide
DM Araujo and B Collier
The present experiments show the presence of both metenkephalin-like and
met-enkephalin-Arg6-Phe7-like immunoreactivity in the superior cervical
ganglion of the cat; this was determined by radioimmunoassay after
high-pressure liquid chromatography separation of tissue extracts. There
was measurable efflux of both peptides, as determined by radioimmunoassay
of ganglionic perfusates; this measure was increased by thiorphan, an
enkephalinase inhibitor. The effect of the 2 peptides on ACh release was
determined: The stable analog of methionine- enkephalin,
D-Ala2-methionine-enkephalinamide, did not affect ACh release from the
ganglion; in contrast, methionine-enkephalin-Arg6-Phe7 significantly
depressed evoked ACh release. The effect of met- enkephalin-Arg6-Phe7 to
decrease ACh release was antagonized, although only partially, by the
opioid antagonist naloxone. Thus, it appears that
methionine-enkephalin-Arg6-Phe7 alters ACh release from the superior
cervical ganglion by acting, at least in part, on a presynaptic opioid
receptor. The results suggest that in the cat superior cervical ganglion,
the heptapeptide enkephalin might have a significant role in the regulation
of synaptic transmission, which is unrelated to its potential function as a
precursor for methionine- enkephalin.