Age-related changes in maturation of regenerated motor innervation.

The dependence of spontaneous transmitter release by regenerated nerve endings on age was studied in rat extensor digitorum longus muscle after sciatic nerve crush during the first year of life. Intracellular recordings were carried out at different times after denervation in muscles of 1.5-, 3- or 12-month-old animals. The frequency of miniature endplate potentials was detected. In order to determine the percentage of multiple innervation, nerve-evoked endplate potentials were recorded. The time course of the percentage of polyinnervated muscle cells was similar in the three groups of animals, but mepp frequency increased more slowly with increasing age. Moreover, by extrapolating the intercept of linear regression for mepp frequency vs days from denervation, a conventional initial time of reinnervation may be computed: the results are consistent with a decrease in the nerve regeneration rate during the first year of life.