To investigate the mutual dependence of calcitonin gene-related peptide (CGRP) and acetylcholine release, we examined the effect of a cholinesterase inhibitor neostigmine on the release of CGRP-like immunoreactivity in rat phrenic nerve-hemidiaphragm muscle preparation, and conversely, the effect of CGRP on [3H]acetylcholine release from motor nerve terminals loaded with [3H]choline in the same preparations of mice. Release of CGRP-like immunoreactivity was increased by electrical nerve stimulation (train of 40 pulses of 200 micros pulse duration and frequency of 50 Hz applied every 10 s) in the whole preparation but not in the segmental preparation containing the endplate region. Neostigmine (0.1-0.3 microM) enhanced the resting release of CGRP-like immunoreactivity in a concentration-dependent manner, whereas it depressed the nerve-evoked release of CGRP-like immunoreactivity. CGRP (1 microM) added to perfusate decreased nerve-evoked [3H]acetylcholine release. These results suggest that CGRP, which is released by electrical nerve stimulation or a cholinesterase inhibitor in intact skeletal muscles, negatively modulates nerve-evoked acetylcholine release.
Acetylcholine Animals