Journal of Neuroscience, Vol 9, 3796-3802, Copyright © 1989 by Society for Neuroscience
Axonal transport and distribution of endogenous calcitonin gene-related peptide in rat peripheral nerve
Y Kashihara, M Sakaguchi and M Kuno
National Institute for Physiological Sciences, Okazaki, Japan.
Calcitonin gene-related peptide (CGRP) has been found in both sensory and
motor neurons. It has been suggested that CGRP is transported from neuron
cell bodies to their terminals, where it may act as an anterograde trophic
factor. However, it is not known how fast CGRP is transported or whether
CGRP found in the innervated target organ indeed originated in neural
tissues. We have quantified endogenous CGRP in the rat peripheral nerve by
a newly developed enzyme immunoassay. The CGRP immunoreactive material
obtained from neural tissues coincided with synthetic rat CGRP in
fractional distributions separated by gel filtration. After ligation of the
sciatic nerve, tissue CGRP accumulated in the segment central to the
ligature. The rate of anterograde transport of CGRP was about 1 mm/hr in
both sensory and motor fibers. In the sciatic nerve, only a small fraction
of CGRP measured was found to originate from the motor nerve fibers. This
may be due in part to the disproportionately large number of sensory fibers
in the sciatic nerve and in part to the possible presence of CGRP in
sympathetic nerve fibers. The CGRP content in the dorsal root fibers was
significantly lower than that in the peripheral processes of the sensory
neurons. The CGRP content in the hind leg muscle was much higher than that
expected from the amount of CGRP per nerve fiber in the sciatic nerve. Most
CGRP in muscle disappeared following denervation. It is concluded that CGRP
highly concentrated in nerve terminals is supplied by axonal transport from
the neuron cell bodies.
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