Interactions between Schwann cell and axon during reinnervation to the motor endplate

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Age-related changes of the interactions between the axon, Schwann cell and extracellular material on reinnervation to the motor endplate were examined during the period of I-8 weeks after crush injury of the sciatic nerve with immunonuofluorescence histochemistry. Observations were done by confocal laser scanning microscopy. To define the distribution and co-localization of the structural components of the regenerating nerve fibers, some specific antibodies were used to label axons (neurofilament, PGP 9.5), Schwann cells (S 100), adhesion molecules [neural cell adhesion molecule. (N-CAM)] and the extracellular material (tenascin). In addition, the structural associations between regenerating nerves and acetylcholine receptors (AChR) were also examined. In the aged animal, the main abnormalities in the process of reinnervation consisted of occasional preterminal and terminal axons which either took a distorted course or were damaged. The most obvious changes was the consistency with degeneration of the terminal Schwann cells. In the motor endplate, loci of aneural or abandoned AChR were frequently found particularly late in the reinnervation process. The distribution and continuities of N-CAM-like immunoreactivity around the Schwann cells Were deranged, and the tenascin pathway through which regenerating axons pass was incompletely constructed. These results taken together indicate disturbance in the axonal guidance coupled with incomplete reformation of synapses with a decrease in the effective area of synaptic contact. This may be due to an age-related unsynchronous maturation among the Schwann cells, axon, and extracellular material during the nerve regeneration.