REGENERATING AXONS ENHANCE DIFFERENTIATION OF PERINEURIAL-LIKE CELLS INVOLVED IN MINIFASCICLE FORMATION IN THE INJURED PERIPHERAL-NERVE

The role of regenerating axons in the restructuring of the endoneurium into minifascicles after peripheral nerve injury was investigated. En doneurial changes were studied in the control distal stumps of crushed rat sciatic nerves and in the distal nerve stumps in which, in additi on to other cellular elements, the original perineurium had also been destroyed by freezing and thawing. Injured nerves in which axonal rege neration had been prevented were examined for comparison. The changes were observed at light microscopic and ultrastructural levels. Two wee ks after nerve injury, incipient endoneurial restructuring by prolifer ating endoneurial fibroblast-like cells was observed in the distal ner ve stumps in all groups of animals. By 4 weeks, the endoneurial change s in control regenerating nerves (crush only) displayed no progress. O n the contrary, extensive minifascicular reorganization of the endoneu rium was observed in the distal nerve stumps in which the original per ineurial barrier had been eliminated. The cells that encircled the min ifascicles in the nerves with regenerating axons looked like different iated perineurial cells, whereas in the absence of regenerating axons, the endoneurial cells that encircled the neurilemmal tubes mostly lac ked typical features of the perineurial cells. Therefore, persistent p erineurial damage is necessary to induce complete endoneurial compartm entalization. In this case, the regenerating axons enhance differentia tion of the endoneurial fibroblast-like cells into the perineurial cel ls.