EXPRESSION OF FIBROBLAST GROWTH FACTOR-II IN HYPOGLOSSAL MOTONEURONS IS STIMULATED BY PERIPHERAL-NERVE INJURY

We have studied the expression of basic fibroblast growth factor 2 (FG F-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 wa s found to be weakly expressed in the hypoglossal motoneurons of the a dult rat. Both peripheral transection and crush injury of the hypoglos sal nerve resulted in a marked up-regulation of the FGF-2 mRNA in moto neurons of the hypoglossal nucleus (with a peak at 10 and II days post lesion) as well as in the proximal and distal nerve stumps. The FGFR1 transcript was strongly expressed by hypoglossal motoneurons of unlesi oned rats. Neither axotomy nor crush lesion of the hypoglossal nerve r evealed any alteration of the expression level and cellular localizati on in the hypoglossal nucleus, but they did result in a significant in crease of the FGFR1 mRNA level in the proximal and distal nerve stump. Western blot analysis of the hypoglossal nucleus revealed the presenc e of the 21 kD and 23 kD isoforms and of a weak expression of the 18 k D isoform. Hypoglossal nerve transection resulted in a complete down-r egulation of the FGF-2 protein 3 days after lesion. After 14 days, how ever, the level of the three isoforms was increased above the control level. The regulation of FGF-2 in hypoglossal motoneurons after experi mental nerve injury is in agreement with the idea of a lesion-related function of FGF-2. Together with previously reported neurotrophic effe cts, these results suggest that FGF-2 provides trophic support for les ioned motoneurons. At the injury site, FGF-2 could be involved in the regulation of the myelination. (C) 1997 Wiley-Liss, Inc.