Growth cone formation in cultures of sensory neurons.

Three experimental situations have been found in which cultured sensory neurons from embryonic chicken will form growth cones from positions along the length of the neurite. If the neurons are dissected with a remaining short axonal stump and plated into serum-free medium, they can form a morphologically normal growth cone from the stump within 15 min, even in the presence of cycloheximide or puromycin. When neurites growing in culture media with low levels of serum are cut at any point with microneedles, growth cones are produced quickly from the amputated stump, usually within 20 min. Treatment of growing neurons with low concentrations of colchicine, Colcemid, or podophyllotoxin results in the progressive appearance of lateral filopodia and regions of flattened cytoplasm that closely resemble growth cones except for their preterminal positions. These observations show that the potential to form growth cones is distributed throughout the neuron and suggest that this normally repressed in some way by the neuronal microtubules.