Electron Microscopic Observations of the Mechanisms of Terminal Club Formation in Transected Spinal Cord Axons

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Abstract
Following transection of spinal cords, axoplasmic flow occurred in the axons both proximal and distal to the transection. In the proximal axonal stump, the direction of flow was proximo-distal whereas in the distal axonal stump the direction of flow was disto-proximal. Thus the flows in transected axons were all directed toward the point of transection. Electron microscopic observation of the spinal cord tissue bordering at the cut ends of spinal cord stumps showed various structural changes in the axons and myelin sheaths of the transected fibers near the cut ends which interfered with the axoplasmic flow leading to the formation of the terminal clubs. Five prototypes of changes in axons and myelin sheaths near the cut ends of fibers are described and the mechanism of terminal club formation is discussed. It seemed that the terminal clubs within the transected spinal cord stumps resulted from two opposing forces acting simultaneously: (1) pressure of the axoplasmic flow toward the cut ends of the fibers, and (2) interference by structural changes which developed within individual fibers consequent to spinal cord injury.