Application of Vital Dyes to the Study of Sheath Cell Origin

That the spinal ganglion cells and sheath cells of Schwann have a common origin in the neural crest, his been accepted generally since Harrison's original experiments in 1904. When the dorsal portion of spinal cords of anuran embryos were removed (elimination of the ganglionic crest), the larvae lacked spinal ganglia and sensory nerves, and the motor nerves present were devoid of sheath cells. Recently Raven employing a different experimental approach assigns a cord origin to the sheath cells and claims that Harrison's conclusions were not justified, since in eliminating the neural crest he also destroyed the dorsal part of the spinal cord, thus not only removing such presumptive sheath cells as may originate there, but obstructing by deformation of the cord the dorsal migration of these elements which are supposed to lie in the ventral portion of this structure. Raven also concludes from his experimental results that sympathetic elements arise from both neural crest cells and from the ventral portion of the spinal cord. His findings do not support those of Müller and Ingvar and Van Campenhoutwho claim a neural crest origin exclusively for sympathetic ganglion cells, but they do support in part those of Kuntz and Batson, and Kuntz, and Jones, who assign a neural tube origin for the sympathetic elements. Raven interchanged trunk neural crest and also median part of medullary plate (future ventral portion of spinal cord) between embryos of Anzblystoma mexicanum (axolotl) and Triton tuaniatus (xenoplastic grafts). Axolotl (donor) cells in Triton embryos could be recognized by their larger nuclear sizes. Employing variation curves for nuclear size difference in both donor and host cells, Raven employed statistical methods in the analysis of his results. Although he obtained evidence for a dual origin of sympathetic ganglion cells, he says that the sheath cells of Schwann are derived exclusively from the tube.