Requisites for growth and myelination of urodele sensory neurons in tissue culture.

We describe a system for long-term culture of adult salamander dorsal root ganglia and present initial observations on the regulation of nonneuronal cell proliferation in this system. Observations of the region of axonal outgrowth in these cultures indicated that, on the one hand, fibroblasts proliferate equally well with neurons present or absent. Schwann cells, on the other hand, require not only the presence of neurons but also proximity to or contact with their neurites. These results indicate that neural tissue is not mitogenic for all cell types represented in the limb regeneration blastema. Further, we describe, for the first time, myelination of salamander axons in vitro. The critical factors found to be required for this high degree of differentiation were the use of long culture periods and addition to the culture medium of ascorbic acid, which is shown to promote extracellular matrix deposition. These observations correlate with extensive observations made on mammalian tissues in vitro, indicating a linkage between deposition of extracellular matrix and full expression of other Schwann cell functions. We anticipate this culture system will be useful in studies of limb blastema cell proliferation.