Spinal cord atrophy and reorganization of motoneuron connections followinglong-standing limb loss in primates

Primates with long-standing therapeutic amputations of a limb at a young ag e were used to investigate the possibility that deefferented motor nerves s prout to new muscle targets. Injections of anatomical tracers into the musc les proximal to the amputated stump labeled a larger extent of motoneurons than matched injections on the intact side or in normal animals, including motoneurons that would normally supply only the missing limb muscles. Altho ugh the total numbers of distal limb motoneurons remained normal, some dist al limb motoneurons on the amputated side were smaller in size and simpler in form. These results suggest that deprived motoneurons survive and retain function by reinnervating new muscle targets. The sprouted motor efferents may account for some of the reorganization of primary motor cortex that fo llows long-standing amputation.