Survival of Schwann cells in chronically denervated skeletal muscles

It is well established that over time Schwann cells disappear from the endoneurial space of the distal stump of a chronically transected sciatic nerve trunk. Nevertheless, the status of the Schwann cells within terminal branches of the transected sciatic nerve remains poorly understood. To elucidate this issue we examined the endoneurial space of the intramuscular nerves in rat hindlimb skeletal muscles, which had been denervated for a 25-month period. Based on specific ultrastructural characteristics, we identified a small population of viable Schwann cells within the intramuscular nerve trunks. The surviving Schwann cells continued to be immunopositive for both S-100 protein and neural cell adhesion molecule. In addition, reverse transcription-polymerase chain reaction and/or Western blot analyses have shown that at least two molecules, brain-derived neurotrophic factor and a non-catalytic truncated form of tyrosine protein kinase receptor B, which could potentially participate in the process of nerve repair, were detectable in chronically denervated skeletal muscle. Our results demonstrate that Schwann cells can survive inside the intramuscular nerve trunks of denervated skeletal muscle for a 25-month period without axonal contact.