Fibroblast growth factor treatment produces differential effects on survival and neurite outgrowth from identified bulbospinal neurons in vitro

The in vivo application of appropriate trophic factors may enhance regenera tion of bulbospinal projections after spinal cord injury. Currently, little is known about the sensitivities of specific bulbospinal neuron population s to the many identified trophic factors. We devised novel in vitro assays to study trophic effects on the survival and neurite outgrowth of identifie d bulbospinal neurons. Carbocyanine dye crystals implanted into the cervica l spinal cord of embryonic day (E)5 chick embryos retrogradely labeled deve loping bulbospinal neurons. On E8, dissociated cultures containing labeled bulbospinal neurons were prepared. Fibroblast growth factor (FGF)-2 (but no t FGF-1) promoted the survival of bulbospinal neurons. FGF receptor express ion was widespread in the E8 brainstem, but not detected in young bulbospin al neurons, suggesting that nonneuronal cells mediated the FGF-stimulated s urvival response. Astrocytes synthesize a variety of trophic factors, and a strocyte-conditioned medium (ACM) also promoted the survival of bulbospinal neurons. As might be expected, FGF-2 function blocking antibodies did not suppress ACM-promoted survival, nor did an ELISA detect FGF-2 in ACM. This suggests that nonneuronal cells synthesize other factors in response to exo genous FGF-2 which promote the survival of bulbospinal neurons. Focusing on vestibulospinal neurons, dissociated (survival assay) or explant (neurite outgrowth assay) cultures were prepared. FGF-2 promoted both survival and n eurite outgrowth of identified vestibulospinal neurons. interestingly, FGF- 1 promoted neurite outgrowth but not survival; the converse was true of FGF -9. Thus, differential effects of specific growth factors on survival or ne urite outgrowth of bulbospinal neurons were distinguished. (C) 2000 Academi c Press.