Neurite outgrowth from embryonic chicken spinal neurons is promoted by media conditioned by muscle cells.

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Abstract
The effect of media conditioned by muscle cells on the development in vitro of chicken spinal neurons was studied. Neural tube cells of 4.5 day chicken embryos were dissociated after trypsinization and cultured in serum-free minumum essential medium conditioned for 4 days over cultures of fused chicken myotubes. After 20 h in conditioned medium (protein concentration, 10-50 .mu.g/ml), about 50% of surviving cells had extended neurites; in cultures in nonconditioned medium this value was about 10%. Active factor(s) in conditioned medium is macromolecular and its activity was completely destroyed by incubation with trypsin. Concentrated samples of conditioned medium were analyzed by gel filtration on columns of Sepharose CL-6B. Activity was recovered in peaks with apparent MW of 40,000 and 500,000 and at the exclusion volume of the column. Media conditioned by chicken liver and skin cells also contained neurite-promoting activity but at lower levels. No activity was detected in nerve growth factor, insulin, fetal calf serum, horse serum or in media conditioned by chicken lung, chicken heart or C6 glioma cells.