Neuronal organization in long term cultures of the spinal cord of the fetal mouse

Explants of spinal cord from 14–16 day old fetal mice were cultured for 18–54 days in vitro. They were fixed and stained with cresyl violet or the Holmes method. In most explants a basic pattern of cell and fiber architectonics was recognizable. In many aspects the pattern seen in the explants resembles the structure of the spinal cord at the time of explantation, and some of the same cell groups are present in both. Most explants resmble a transverse section of spinal cord. A ventral commissure and dorsal and ventral roots are readily identified. In addition, two characteristic circular bands of fibers form around the periphery of the explants. Many axons in the ventral roots arise from large ventral horn cells and form terminal arborizations at some distance from the explants. These axons are comparable to in vivo ventral root fibers. The fibers in the dorsal roots, however, are generally fibers that deviate from the circular bands and return again, thus forming extensive loops. The circular bands may represent regenerated axons of long association pathways. The structure of these explants demonstrates that pieces of nervous tissue grown in complete isolation can maintain much of their internal organization. Their axons appear to follow relatively constant growth patterns which are characteristic for particular cell types and, to a certain extent, appropriate to the pattern that would be formed in vivo .