A RE-EVALUATION OF THE QUESTION OF ASCENDING FIBERS IN THE PYRAMIDAL TRACT

A study in the cat with the Glees method demonstrated the occurrence of degenerating fibers in the pyramidal tract rostral to transections of the tract in the spinal cord. These fibers were interpreted as spinocortical fibers, which are also described in man. The existence of such fibers is disputed. Multiple injections of horseradish peroxidase (free and lectin-labeled) were made in the sensorimotor cortex of 4 cats. No retrogradely labeled cells were found in the spinal cord in these cases. Present and previously reported findings are discussed in the light of other studies of pathological changes in fiber tracts within the CNS. Although the present experiments were negative, the degenerating axons previously observed in Ag sections from the pyramid, pons and internal capsule after lesions of the pyramidal tract in the spinal cord cannot be satisfactorily explained as evidence of retrograde, indirect Wallerian degeneration of corticospinal fibers.