EXPRESSION OF INSULIN-LIKE GROWTH-FACTOR-I AND RELATED PEPTIDES DURING MOTONEURON REGENERATION

The regulation of insulin-like growth factor-I (IGF-I) and related pep tides during motoneuron regeneration was examined in the facial nerve following facial nerve transection. One to 39 days after axotomy, the mRNAs and peptides of IGF-I, type-I insulin-like growth factor recepto r (IGFR), insulin-like growth factor binding proteins 1-5 (IGFBP-1-5), and glial fibrillary acidic protein (GFAP) were assayed in brain stem sections by in situ hybridization and immunohistochemistry. Relative mRNA levels of IGF I, IGFR, IGFBP-2, and GFAP in the ipsilateral facia l nucleus were highest 4-7 days after transection and declined thereaf ter. Double immunostaining experiments showed that both IGF-I and IGFB P-2 were localized in GFAP-positive astrocytic processes, many of whic h were perineuronal. Peak staining intensity was found 4-7 days after transection and immunoreactivity still was present after 21-35 days. I GFR mRNA was found in some regenerating neurons; however, IGFR peptide was not detected in these neurons or in any other cells in the facial nucleus. Our findings suggest that astrocytic production of IGF-I and IGFBP-2 may accompany regeneration of neurons undergoing retrograde c hanges induced by axotomy.