Journal of Neuroscience, Vol 8, 3951-3957, Copyright © 1988 by Society for Neuroscience
Calcitonin gene-related peptide prevents disuse-induced sprouting of rat motor nerve terminals
T Tsujimoto and M Kuno
Department of Physiology, Kyoto University Faculty of Medicine, Japan.
Calcitonin gene-related peptide (CGRP) coexists with acetylcholine (ACh) in
motor nerve terminals. Externally applied CGRP has been shown to increase
the synthesis of ACh receptors in cultured myotubes by a mechanism
independent of muscle activity. Thus, CGRP is suggested to be a
neurotrophic factor that may regulate the expression of several long- term
events occurring at the neuromuscular junction. We have examined the effect
of CGRP on the sprouting of motor nerve terminals induced by chronic block
of nerve-muscle activity in adult rats. Daily treatment with CGRP
suppressed the disuse-induced terminal sprouting in a dose- dependent
manner, whereas the morphology of motor nerve terminals in active muscles
was unaffected by CGRP. CGRP may be a possible candidate for an
antisprouting agent which has been postulated to exist in nerve terminals.
The disuse-induced outgrowth of terminal sprouts was accompanied by an
increase in the mean quantum content of end-plate potentials, as well as in
the frequency of spontaneous miniature end- plate potentials. This
increased transmitter release was still maintained at the junctions in
which disuse-induced terminal sprouting had been suppressed by CGRP. It is
suggested that the formation of terminal sprouts per se is not responsible
for the plastic change of transmitter release induced by prolonged disuse
of the neuromuscular junction.