Morphometry of axon cytoskeleton at internodal regions of rat sciatic nerve during aging

Ugo Caselli, Carlo Bertoni-Freddari, Roberta Paoloni, Patrizia Fattoretti, Tiziana Casoli, William Meier-Ruge

Research output: Contribution to journalArticlepeer-review

Abstract

Background: Nerve endings undergo a lifespan morpho-functional modulation which is reported to be markedly impaired with aging. Neurone structural remodelling is in charge of processes occurring in the nerve cell soma, however the axonal transportation of organelles and molecules by cytoskeletal elements plays a very important role in the morphological rearrangements taking place at peripheral compartments. Objective: To assess the involvement of axonal ultrastructure in the reported age-related decline of slow axoplasm flow mechanisms, we carried out a morphometric study of axon cytoskeleton in aging. Methods: Female Wistar rats (3, 12 and 30 months of age) were anesthetized and perfused with saline followed by a fixation solution (glutaraldehyde 5% + formalin 2% in 0.1 cacodylate buffer pH 7.4). The excised sciatic nerves were processed according to conventional electron microsopic procedures. Axons sectioned perpendicularly to their longitudinal axis at the internodal region (mean axoplasm area: 18.25-26.5 μm2) were sampled by a systematic random procedure. The overall number of neurofilaments (No.Nfs) and microtubules (No.Mts) per total axoplasm area analysed, the numeric density (number/μm2 of axoplasm area) of neurofilaments (NaNfs) and microtubules (NaMts), the myelin thickness, the number of myelin lamellae and the R proportion [No.Nfs/(No.Nfs + No.Mts)l were the parameters measured by computer-assisted semiautomatic methods. Results: No.Nfs, NaNfs, myelin thickness and the number of myelin lamellae did not change between 12 and 30 months of age, while a significant increase of these parameters was found in a comparison with younger rats. No.Mts and NaMts were significantly increased at 12 vs. 3 as well as at 30 vs. 12 months of age, respectively. R proportion did not show any difference due to age. Conclusions: The present findings support that the dynamic condition of the axonal cytoskeleton appears to be preserved at a high extent in aging. Thus, the intra axonal defective spacing of cytoskeletal elements (e.g. neurofilaments), rather than their number, is proposed to contribute to the decline of the slow axonal transport of organelles and molecules reported in aging.

Original languageEnglish
Pages (from-to)307-311
Number of pages5
JournalGerontology
Volume45
Issue number6
DOIs
Publication statusPublished - 1999

Keywords

  • Axonal cytoskeleton
  • Axonal transport and aging
  • Axoplasm aging
  • Computer-assisted morphometry
  • Microtubules
  • Neurofilaments
  • Sciatic nerve

ASJC Scopus subject areas

  • Ageing

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