Axonal blockade induces the expression of vasoactive intestinal polypeptide and galanin in rat dorsal root ganglion neurons.

Nerve growth factor (NGF) undergoes retrograde transport from peripheral target organs, and has been recently reported to regulate the production of some neuropeptides in dorsal root ganglion (DRG) neurons. Therefore, to ascertain whether or not the expression of calcitonin gene-related peptide (CGRP), vasoactive intestinal polypeptide (VIP), and galanin was regulated by the retrograde transport of factors such as NGF, we carried out an immunocytochemical analysis using vinblastine as an axonal transport blocker and a monoclonal antibody to the NGF receptor (NGFR) as a marker of NGF-responsive neurons. The percentage of CGRP-containing DRG neurons (L5) was decreased by sciatic nerve transection or by the application of higher doses of vinblastine (0.3-0.6 mM) to the sciatic nerve. VIP and galanin were expressed in some DRG neurons after the application of a low dose of vinblastine (0.15 mM), which can block axonal flow without causing neuronal damage. The expression of these peptides was not affected by dorsal rhizotomy. About 70% of the CGRP-containing neurons also expressed NGFR, while most of the VIP-containing or galanin-containing neurons lacked NGFR. These findings indicate that the depletion of peripheral target-derived neurotrophic factor(s) other than NGF by axonal blockade may induce the gene expression of VIP and galanin.