INSULIN-LIKE GROWTH FACTOR-I COUNTERACTS BFGF-INDUCED SURVIVAL OF NITRIC-OXIDE SYNTHASE (NOS)-POSITIVE SPINAL-CORD NEURONS AFTER TARGET-LESION INVIVO

We have used nitric oxide synthase (NOS) histochemistry as a perikaryal viability marker to trace the retrograde reaction of spinal cord intermediolateral (IML) sympathoadrenal projection (SAP)-neurons to target-removal, i.e., selective adrenomedullectomy and local administration of either insulin-like growth factor-I (IGF-I), basic fibroblast growth factor (bFGF) or a combination of both. Counting of NOS-positive preganglionic spinal cord neurons 4 weeks post surgery indicated that more than 80% of stained neurons were lost from the IML-cell column. This percentage loss corresponds to the numerical loss of NOS-stained SAP-neurons labeled retrogradely with Fast-blue prior to adrenomedullectomy. Basic FGF-supplementation at the site of lesion resulted in maintenance of the majority of NOS-positive IML-neurons, a finding confirmed by the survival rate of Fast-blue prelabeled SAP-neurons. Thus, besides maintenance of the structural integrity of SAP-neurons, bFGF prevents loss of intracellular NOS-activity which may reflect unaltered cell metabolism (and function) of these neurons following target-removal in vivo. By contrast, IGF-I failed to alter the rate of disappearance of NOS-staining and labeling index of neurons within the IML-cell column postlesion, suggesting that IGF-I is not neurotrophic for SAP-neurons by itself. Combined treatment with both factors resulted in a more widespread loss of NOS-stained and Fast-blue-prelabeled SAP-neurons than registered after bFGF-only treatment. No co-trophic effect of bFGF and IGF-I was evident; rather, the pronounced bFGF-induced rescuing effect was significantly suppressed by exogenous IGF-I in vivo, supporting the idea that this or another molecule induced by the treatment enhances rather than prevents retrograde degeneration and neuronal death within the adult lesioned IML-adrenal pathway.