Spinal cord and ganglia regeneration in larval Xenopus laevis following unilateral ablation.

The experiments were carried out on larvae of Xenopus laevis at stage 48 (acc. to Nieuwkoop and Faber, 1956). Two different kinds of experiments were performed. Experiment I: Unilateral ablation of either a brachial or lumbar segment of the spinal cord and simultaneous removal of the related ganglia. Experiment II: Simple unilateral removal of either brachial or lumbar spinal ganglia. The results obtained in Experiment I show that not only an extensive restitution of the ablated spinal cord does take place, but the regeneration of spinal ganglia may also occur following migration of neural elements from the regenerating spinal cord. The medullary neuroblasts leave the spinal cord along two paths: i) through projections of the gray matter, probably due to the lack of an effective glia limitans; ii) through the motor fibers leaving the spinal cord to form the ventral roots. The first path is followed occasionally while the second is the one usually used when the ventral roots are present. Data based on animals injected with 5-bromodeoxyuridine and sacrificed at fixed intervals, suggest that ganglion precursors, as well as the medullary neurons and glia, originate in the ependyma. This conclusion is supported by the results of Experiment II which demonstrate that when the spinal cord is left intact no discrete groups of ganglion cells and/or glial cells are formed.