Abstract
Neurite formation in culture was examined as a model for nerve regeneration. Dorsal root ganglion cells were isolated from newborn rats and cultured with fresh Eagle's minimum essential medium (MEM) or conditioned medium (CM) obtained from a culture of C6 glioma cells. Their fine structures were examined by electron microscopy. Microspikes were developed rapidly on the cell surface and extended into the substratum. In fresh MEM a rim was formed around the cell body. The rim was widened further and then the neuron was degenerated. In CM, veils were formed between some neighboring microspikes, became enlarged and protruded; thereafter growth cones were formed. As the neurites became extended, microspikes and veils were concentrated on growth cones but disappeared from the cell surface. Microspikes, rims and veils from the cell body were filled with bundles and networks of microfilaments. Growth cones contained agranular reticula, microtubules, mitochondria, vacuoles and microfilaments. Neurons kept in fresh MEM had a large number of neurofilaments but few microtubules in the cell body. Neurofilaments formed large bundles in the degenerating neurons. The neurons in CM had many microtubules but bundles of neurofilaments were not formed. It was suggested that microtubules are essential for initiation and elongation of the neurites and also for nerve regeneration.
