Figure 6. Axonal growth of CTB-labeled ascending sensory axons in response to regulated NT-3 expression 4 weeks post-injury.

(A) Numerous axons grow across the rostral host/graft border and extend into the spinal cord when NT-3 gene expression is turned on (−Dox). (B) In contrast, few CTB-labeled axons penetrate the graft and grow across the lesion/graft border if NT-3 gene expression is turned off (+Dox). (C, D) Axons are hardly observed beyond the rostral lesion border in animals that received GFP virus and were either (C) untreated or (D) treated with doxycycline. Dotted lines indicate the host/graft interface. Higher magnification of boxed areas in (A–D) are shown in (a₁–d₁) (rostral host/graft interface) and (a₂–d₂) (rostral to the lesion site). Scale bars: 200 μm in (A–D) and, 50 μm in (a₁–d₂).