Fig. 3

The sprouted intact corticospinal tract axons re-form synaptic structures and are myelinated at the C5-7 segments in the chronic phase of severe TBI. a, b Representative images show the new synapse formation of the sprouted intact corticospinal tract in the denervated side of cervical spinal cord. The boxed area in the low power image of panel a is enlarged in panel b. c Representative orthogonal view of the newly formed synapses co-expressing BDA, PSD-95 and synaptophysin. Enlarged image of the boxed area shown in panel b. The boxed area in panel c is enlarged and shown in panels d–g. d–g The separated confocal images show a newly formed synapse co-expressing BDA, PSD-95 and synaptophysin (indicated by the arrows). h A schematic diagram indicates the imaging area (blue boxed area in the transverse spinal cord) showing the myelin formation in the sprouted corticospinal tract axon projecting from the contralesional cortex to the denervated side of the cervical spinal cord. i–k The separated confocal images show a sprouted corticospinal tract axon (BDA⁺) that is wrapped by an MBP positive sheath-like structure (indicated by the arrows), indicating that the sprouted corticospinal tract axon is myelinated