Rat facial motoneurons express increased levels of calcitonin gene-related peptide mRNA in response to axotomy.

The expression and localization of the mRNA encoding the calcitonin gene-related peptide (CGRP) were analyzed in the rat facial nucleus after axotomy by Northern blot analysis and by in situ hybridization histochemistry (ISH) using a synthetic 32P-labeled oligonucleotide probe. Northern blot analysis revealed the presence of the 1.2 kb CGRP mRNA in RNA extracted from the facial nucleus. This mRNA species was strongly increased after axotomy of the facial nerve. By ISH increased levels of CGRP mRNA were observed as soon as 16 hr after axotomy compared with the unoperated nucleus. CGRP mRNA could be localized in more than 50% of the motoneurons. Three populations of motoneurons with no, moderate, or strong labeling for CGRP mRNA could be distinguished. Peak expression of CGRP mRNA during the first 48 hr was followed by a decline to moderate levels at day 4 after lesion, and to almost basal levels at days 7 and 9. These data demonstrate that axotomy of the facial nerve leads to an early and strong induction of CGRP gene expression in motoneurons of the facial nucleus.