Conditioned medium promotes neurite growth from both central and peripheral neurons.

Explants or dissociated neurons of spinal cord and other parts from chick embryos and rat fetuses were cultured for 1-4 days. Extensive outgrowth of neurites from the spinal cord was observed in the medium which had been conditioned by skeletal and heart muscle cells. In the fresh medium, the neurites were short and accompanied by the migrating non-neuronal cells. The conditioned medium promoted also the neurite outgrowth from retina, optic tectum, ciliary ganglion, superior cervical ganglion and dorsal root ganglion.