Axoplasmic transport of calcitonin gene-related peptide in rat peripheral nerve as a function of age

Calcitonin gene-related peptide (CGRP) has been implicated in the trophic regulation of acetyl-choline receptors and G4 acetylcholinesterase at the rat neuromuscular junction. Since these latter molecules exhibit significant changes with advancing age, we examined the possibility that certain aspects of CGRP transport are also influenced by aging. Double nerve ligations and CGRP radio-immunoassay of 3-mm nerve segments permitted the assessment of the peptide's apparent transport rates in sciatic nerves from 3-, 12-, and 24-month-old Fischer 344 rats. Results confirm that CGRP is conveyed by anterograde axoplasmic transport; more importantly, they suggest that CGRP is also transported retrogradely, but in smaller amounts and at slower rates. In addition, our findings indicate that the apparent rates of CGRP transport in both directions significantly decline with advancing age. These data are consistent with the notion that changes in CGRP delivery may contribute to age-related changes in junctional acetylcholine receptors and acetylcholinesterase.