(A and B) Corticospinal axons robustly regenerate into the rostral half of a GFP-expressing neural progenitor cell graft (green). Horizontal section; rostral to left and caudal to right. Corticospinal axons were labeled with red fluorescent protein (RFP). (A) Neural progenitor cell (NPC) and (B) NPC and rehabilitation groups. (C and D) Higher-magnification images of images in A and B, and (E and F) single RFP channel of corticospinal axons. (G and H) Host corticospinal axons (labeled for RFP) regenerating into grafts form bouton-like structures that contain vesicular glutamate transporter 1 (vGlut1, blue) in close apposition to grafted (GFP-expressing, green) cell processes, suggesting synapse formation. (I and J) In host gray matter located 3 spinal cord segments below the lesion, GFP-labeled graft axons also form bouton-like structures that colocalize with the presynaptic marker synaptophysin (Syn, red). (K) Quantification of total corticospinal axon regeneration into NPC grafts normalized to intensity of corticospinal axon labeling in the dorsal columns at C3. There is significantly greater corticospinal regeneration into NPC graft among animals that underwent rehabilitation (P < 0.05, Student’s 1-tailed t test). NPC graft n = 8; NPC and rehabilitation groups, n = 9. Scale bars: 1 mm (A and B); 250 μm (C–F); 30 μm (G); 2 μm (H); 20 μm (I); 4.5 μm (J).