Transection of the Spinal Cord in Developing Xenopus Laevis Available to Purchase

The spinal cord of X. laevis larvae at stage 56 of development was completely transected between the fifth and sixth neural arch. Observations were made on 33 larvae which survived the operation and a suitable group of normal control animals. They were fixed at intervals up to 6 months after the operation. Sections were prepared and either stained with cresyl violet or silvered by Bodian’s protargol method.

Normal larvae exhibited movements associated with locomotion, posture, and respiration. A knock on the side of their bowl evoked an avoiding reaction in which they darted through the water.

During the first 15 days after the operation the locomotory movement was performed only by the region of the experimental animals cranial to the lesion and the postural movement was performed only by the region caudal to the lesion. On the sixteenth postoperative day functional co-ordination across the lesion had returned in all the experimental animals. The response to a knock on the side of their container never returned to the region of these animals caudal to the site of transection.

The first axons to regenerate across the lesion were found on the seventh postoperative day—8 days before the return of functional co-ordination. The only change at the site of transection after this was an increase in the number of axons. The Mauthner axons and the large axons of primary motor neurones did not regenerate.

Perikarya of primary motor neurones showing chromatolytic changes were found for two segments cranial and half a segment caudal to the site of transection in the operated animals.

It was concluded that the movements associated with locomotion are mediated by a different central system to that mediating the postural movements of these animals.

It is suggested that the Mauthner axons of these animals are the central motor pathway for the avoiding response stimulated by a knock on the side of their container.

The evidence is consistent with the hypothesis that regeneration of axons after transection of the spinal cord is not limited by local changes consequent to the lesion.