Long-term effects of deprivation of cell support in the distal stump on peripheral nerve regeneration.

The distal stump of an injured peripheral nerve supports regenerating axons by offering a favourable growth substratum and several cell-produced growth factors. Deprivation of cellular factors alone has been shown not to prevent fairly rapid axonal elongation after nerve injury if the growth substratum was preserved. The present study examined possible long-term untoward effects of cell support deprivation during an early phase of nerve regeneration. Rat sciatic nerve was crushed and a 25 mm long distal nerve segment was made acellular by freezing-thawing, while the integrity of the growth substratum for the regenerating axons was preserved. Toe-spreading reflex and skin sensitivity to pinch in the foot were monitored to follow recovery of motor and sensory function, respectively. The number of myelinated axons was determined in the sciatic nerve proximally to the lesion site, and distally in the predominantly sensory sural nerve as well as in the mixed motor nerve to the soleus muscle. Except for a short delay in the onset of recovery, explainable by the reduced elongation rate of axons growing through the acellular nerve segment, we found no deleterious effect of cell support deprivation on sensory or motor function recovery after nerve crush. Most of regenerating sensory neurons did not critically depend on the distal stump cell support. However, a 15% and 25% loss of myelinated axons both proximally to the lesion and distally in the sensory sural nerve, respectively, indicated that a corresponding minor loss of injured sensory neurons occurred when they were deprived of such cell support even if provided with a favourable growth substratum for successful regeneration.(ABSTRACT TRUNCATED AT 250 WORDS)