We have studied the expression of
basic fibroblast growth factor 2 (FGF-2) and
FGF receptor 1 (FGFR1) in the hypoglossal motor system during degeneration and regeneration by using an
RNase protection assay, in situ hybridization, and Western blot analysis. The
FGF-2 transcript was found to be weakly expressed in the hypoglossal motoneurons of the adult rat. Both peripheral transection and
crush injury of the hypoglossal nerve resulted in a marked up-regulation of the
FGF-2 mRNA in motoneurons of the hypoglossal nucleus (with a peak
at 10 and 11 days postlesion) as well as in the proximal and distal nerve stumps. The FGFR1 transcript was strongly expressed by hypoglossal motoneurons of unlesioned rats. Neither
axotomy nor crush lesion of the hypoglossal nerve revealed any alteration of the expression level and cellular localization in the hypoglossal nucleus, but they did result in a significant increase of the FGFR1
mRNA level in the proximal and distal nerve stump. Western blot analysis of the hypoglossal nucleus revealed the presence of the 21 kD and 23 kD
isoforms and of a weak expression of the 18 kD
isoform.
Hypoglossal nerve transection resulted in a complete down-regulation of the
FGF-2 protein 3 days after lesion. After 14 days, however, the level of the three
isoforms was increased above the control level. The regulation of
FGF-2 in hypoglossal motoneurons after experimental nerve injury is in agreement with the idea of a lesion-related function of
FGF-2. Together with previously reported neurotrophic effects, these results suggest that
FGF-2 provides trophic support for lesioned motoneurons. At the injury site,
FGF-2 could be involved in the regulation of the myelination.