Long distance adult axon regeneration in degenerating spinal cord white matter. a, A confocal montage of scans from a single sagittally orientated 60 μm section showing the long distance growth (7.5 mm shown in this section) of numerous GFP-immunolabeled adult sensory axons that have extended caudally from a C1/C2 set 1 transplant (at 0 mm) within acutely lesioned dorsal column white matter at 8 d survival.b, A similarly constructed confocal montage showing the robust bidirectional regeneration of GFP+ donor axons from a set 1 transplant (Tp, arrowhead) injected into 2 week subchronically degenerated dorsal column white matter at 8 d survival after transplantation. Scale bar, 500 μm.c, A high-power confocal image of the transplant inb containing individual large and small neuronal cell bodies with their axons extending out into host white matter.Arrows indicate position of dorsal horn gray–cuneate white matter boundary. Scale bar, 200 μm. d, A double-channel confocal image of a coronally orientated 60 μm section immunostained for GFP (green channel) and GFAP (red channel) 2 mm rostral to an 8 d survival transplant at C1/C2. Numerous end on profiles of GFP+ regenerating axons can be seen throughout subchronically degenerating white matter of the cuneate (C,arrowhead) and gracile (G,arrowhead) fasciculi. M(arrowhead), Midline; Py, pyramidal tract; CC, central canal. Scale bar, 250 μm.e, A 1 μm semithin section cut in the coronal plane counterstained with toluidine blue of a representative C4/C5 lesion site. Note the complete transection of the cuneate fasciculus (C, arrowhead) and sparing of only a small portion of the most medial axons of the gracile tract (G, arrowhead). Scale bar, 200 μm.