Endogenous sensory axon regeneration across GDA-transplanted dorsal column injuries at 8 days after lesion and transplantation. (a) A montaged, low-magnification confocal image scanned from a single 25-μm thick sagittal section, showing BDA-labeled ascending dorsal column axons (green) that have entered, grown within and exited a hPAP+ (red) GDA-transplanted dorsal column lesion. LC, lesion center. (b) A high-magnification image of a rostral graft/host interface showing BDA+ axons exiting the GDA graft and entering host white matter. A few axons were observed to have turned away from the interface and grown back towards the lesion center (arrowhead). (c) In control lesions, the vast majority of BDA+ axons have formed dystrophic endings and failed to leave the caudal margins of the lesion, marked by hypertrophic GFAP+ astrocytes (red). (d) A high-magnification image showing numerous BDA+ axons that have successfully crossed the host/graft interface at the caudal lesion margin. A few cut axons (arrowheads) have, however, failed to leave the caudal lesion interface and can be seen to have turned and/or formed dystrophic endings, particularly in regions containing few hPAP+ GDAs (red). (e) BDA+ axons located near the pial surface and ventral regions of cuneate white matter at 1.5 mm rostral to a GDA-bridged lesion site. (f) BDA+ axon growth cones in white matter 1.5 mm rostral to the lesion site often display streamlined growth cones indicative of rapid growth. Scale bars: (a,c) 100 μm; (b-e) 50 μm; (f) 5 μm (top) and 10 μm (bottom).