LIGHT AND ELECTRON MICROSCOPICAL OBSERVATIONS OF VENTRAL HORN AND VENTRAL ROOT IN LONG TERM CULTURES OF SPINAL CORD OF FETAL MOUSE

Segments of spinal cord from 14 to 16 day old fetal mice, grown in vitro for three weeks or longer, show some of the cytoarchitectonic subdivisions of adults cord and several characterstic fiber bundles. In the ventral horns the largest cells have thick axons which leave the explants in well defined ventral roots. These axons run a long course through the outgrowth zone and branch repeatedly there. They have no branches that ramify in the explants nor do they return to the explants. Smaller cells in the ventral horns from a distinct class of cells. Their axons ramify entirely within the explants, mainly within the homo‐ or contralateral ventral horn. Axons of dorsal horn cells also ramify within the ventral horns. Some of their branches pass into a fiber band that surrounds the explant while others enter the outgrowth zone. These last generally return to the explant and form terminal ramifications there. The development of fiber bundles and the appearance of cell groups can be followed in unstained explants, and it appears that each of the characteristic axon patterns develops in vitro. Dendrites of ventral horn cells enter the outgrowth zone and in the ventral roots they are closely related to many passing axons. At some distance from the original explant these processes from a tissue that resembles the central nervous system. New synaptic junctions are formed and the neuronal elements lie embedded amongst glial cells and their processes. The glial cells also from a more or less continuous epithelium separating the feeding solution from the neuronal elements. Copyright © 1968 The Wistar Institute Press