Nerve growth factor stimulates synthesis of calcitonin gene-related peptide in dorsal root ganglion cells during sensory regeneration in capsaicin-treated rats.

Abstract

Administration of human recombinant nerve growth factor (rhNGF) into one hindpaw of capsaicin-treated rats can locally facilitate the regeneration of calcitonin gene-related peptide (CGRP)-containing primary sensory neurons (Schicho, R., Skofitsch, G., Donnerer, J., 1999. Brain Res. 815, 60-69). In this study we used in situ hybridization histochemistry (ISH) to determine synthesis of CGRP mRNA in lumbar L4 dorsal root ganglion (DRG) cells during NGF-induced regeneration. Whereas 8 days after the capsaicin treatment alone (50 mg/kg s.c.) CGRP mRNA expression in DRG cells was reduced to 40-60% of control levels, the additional intraplantar injections of rhNGF (5 x 4 microg) during this time period were able to raise CGRP mRNA expression again. The increase in CGRP expression was seen ipsi- and contralaterally and it was more pronounced in small- and medium-sized (about 110% of control levels), than in large-sized CGRP-producing cells (70% of controls). The percentage of the CGRP-expressing neurons in capsaicinized and in capsaicin + NGF-treated animals stayed unaltered. In conclusion, the present results demonstrate that NGF-induced regeneration of capsaicin-lesioned sensory afferents is accompanied by an elevated production of CGRPmRNA mainly in small- and medium-sized DRG cells.