Serum- and substratum-dependent modulation of neuritic growth

Explants of embryonic day 8 (E8) chicken dorsal root ganglia (DRG) have been cultured with medium containing serum or the serum-free supplement N1 on one of three substrata: collagen, polyornithine (PORN), or PORN exposed to a polyornithine-binding neurite-promoting factor (PNPF-PORN). Replicate cultures were maintained with or without nerve growth factor (NGF). NGF elicited its classical neuritic outgrowth on all three substrata in serum-containing or serum-free medium. In the absence of NGF, however, a gradation of increasing neurite growth was seen with: PNPF-PORN greater than PORN greater than collagen. This response occurred in both media. In addition, the neuritic halo in each instance was markedly more developed in the absence of serum, especially on PNPF-PORN. Nonneuronal behaviors reflected both serum and substratum influences: thus, nonneuronal outgrowth consisted mainly of flat cells with serum and collagen, was nonexistent with serum and PORN or PNPF-PORN, and involved mostly Schwann-like scattered cells in the absence of serum on any one substratum. The serum-dependent behaviors of ganglionic neurites were examined further with explants from chicken E11 sympathetic ganglia. A single substratum was used (PORN), without exogenous trophic factor. Neurite outgrowth was depressed by the presence of fetal calf serum, thus supporting the generality of this phenomenon. Lastly, PC12 cells, a clonal line of rat pheochromocytoma, will grow neurites in the presence of NGF after 48 hr in serum-free, but not serum-containing media. Addition of serum to serum-free cultures at this time results in the rapid and complete retraction of neurites.