Fate of GAP-43 in ascending spinal axons of DRG neurons after peripheral nerve injury: delayed accumulation and correlation with regenerative potential

Proteins characteristic of growing axons often fail to be induced or transported along axons that have been interrupted far from their cell bodies in the adult mammalian CNS. Here, we inquire whether long axons in the mammalian CNS can support efficient axonal transport and deposition of one such protein, GAP-43, when the protein is induced in neuron cell bodies. We have used immunocytochemistry to follow the fate of GAP-43 in dorsal column axons ascending the rat spinal cord from dorsal column axons ascending the rat spinal cord from dorsal root ganglion (DRG) neurons, after synthesis of the protein is induced in these cells by peripheral nerve injury. Sciatic nerve lesions do lead to an accumulation of GAP-43 in dorsal column axons derived from the lumbar DRG. However, in distal segments of these CNS axons, accumulation of GAP-43 is apparent only after a delay of 1-2 weeks, in contrast to its rapid accumulation in axon segments within the PNS environment, suggesting that deposition and stabilization of GAP-43 can be limited by local, posttranslational regulation. GAP-43 immunoreactivity subsides to control levels within 8 weeks after crush lesions that permit peripheral axon regeneration, but remains robust 8 weeks after resection lesions that prevent peripheral regeneration. Accumulation of GAP-43 in cervical dorsal column axons after peripheral nerve injury is closely correlated with the ability of these axons to respond to local cues capable of eliciting axon growth (Richardson and Verge, 1986).