Figure 4.

NGF/Sema3A overexpression targeted regeneration of injured SP⁺ nociceptive axons to superficial dorsal horn. Sections were colabeled using SP and IB4 immunohistochemistry to identify two classes of nociceptive axons. SP-containing axons normally terminate at laminas I and II (left side in A, C, E, G) and disappeared after dorsal root injury (C). NGF/GFP overexpression induced extensive regeneration of SP axons into the dorsal horn (E), and NGF/Sema3A overexpression reduced axon growth into deeper laminas, shaping regenerating axons toward a normal distribution (G). IB4-binding nociceptive axons normally terminate at inner aspect of lamina II (left side in B, D, F, H), and NGF/GFP (F) or NGF/Sema3A (H) treatment has no effect on this class of axons after injury. Scale bar, 0.5 mm.