[Effect of age on the number and size of myelinated nerve fibers. A study after localized freezing on section-suture of the sciatic nerve in the pubescent rat].

The regeneration of the myelinated fibers has been studied after a localized congelation or a section followed by an immediate suture in the left sciatic nerve of rats aged of 1 1/2, 3, 6, 12, 18 and 24 months at the moment of the operation. The regenerated fibers has been observed in the left internal gastrocnemius nerve, the right nerve being considered as the sham. For each nerve, the number and the caliber of the myelinated nerves has been systematically registered at standard levels allowing to calculate the average diameter of the fibers, their repartition and to draw their histogram. The results seem to prove that the potential of regeneration is correlated to the age, the velocity and intensity of the axonal growth decreasing in the old age. This potential of regeneration remains during the whole life. The integrity of the schwannian membranes considerably facilitates the nervous fibers regeneration, their interruption is a major obstacle to the axonal regrowth.