Growth of ascending spinal axons in CNS scar tissue

The aim of the present study was to test the capacity of spinal cord scar tissue to assist and sustain axon regrowth. In adult rats and cats the dorsal funiculus (DF) was cut at mid-thoracic or lumbar level, and a superficial incision in the DF rostral to the lesion was made in order to extend the penetrating lesion. Axonal tracing in rats 50-100 days postinjury with anterogradely transported wheatgerm agglutinin-conjugated horseradish peroxidase or rhodamine-conjugated dextran demonstrated that nerve fibers had entered the scar tissue. Axon ingrowth in the scar was further indicated by axonal immunoreactivity to the growth-associated protein GAP-43. The scar tissue showed low-affinity neurotropin receptor-like immunoreactivity in association with blood vessels and in the interstitium. The integrity of the blood-brain barrier in the extended dorsal funiculus lesion was disrupted for at least 11 months postinjury, assessed by i.v. injections of free HRP or Evans blue. The present study shows that penetrating injury in the dorsal funiculus produces a CNS environment permissive for axonal sprouting and that PNS influence is not necessary for spinal tract regrowth. A possible relationship between the absence of an intact BBB and injury-induced axonal sprouting is discussed.