Morphological Changes in Unmyelinated Nerve Fibres in the Sural Nerve With Age

Abstract

Quantitative changes in unmyelinated nerve fibres in sural nerves obtained at autopsy were evaluated in 28 normal adults. The following conclusions were reached. (1) The density of unmyelinated axons showed no significant correlation with age, but the densities of (2) Schwann cell subunits with axons, (3) Schwann cell subunits without axons, (4) single protrusions of Schwann cells and (5) collagen pockets, and (6) the mean number of Schwann cell profiles per axon, all showed positive correlations with age. Additionally, (7) the percentage of subunits containing unmyelinated axons and (8) the mean number of axons in single axon-containing Schwann cell subunits demonstrated negative correlations with age. The density of Schwann cell nuclei related to unmyelinated fibres did not show a significant change with age. The age-dependent changes in unmyelinated nerve fibres thus mainly consist of an increased production of processes by Schwann cells in the absence of cell multiplication. A decrease in unmyelinated nerve fibre density or a compensatory increase of small unmyelinated axons did not occur in these normal adults. In terms of relative sensitivity for the detection of the earliest changes in unmyelinated fibres, the indices (6) and (7) are considered to be useful and superior to the conventional assessment of unmyelinated axon density and diameter distribution. These two indices are not influenced by postmortem swelling of the axons and Schwann cells. Measurements of unmyelinated axon density and size distribution will continue to be useful in the assessment of more advanced pathological conditions.

The Structural and Functional Integrity of Peripheral Nerves Depends on the Glial-Derived Signal Desert Hedgehog

“…These include axonal loss that involves substantially greater reduction in the number of unmyelinated axons than myelinated ones, the presence of regenerating myelinated fibers, increased numbers of resident macrophages, widening of individual SLIs, increase in SLI number, and a shift toward fewer axons per nonmyelinating Schwann cell in Remak fibers (Kanda et al, 1991;Ceballos et al, 1999;Tabata et al, 2000).…”

Effect of Age, Sex and Gender on Pain Sensitivity: A Narrative Review

“…It has been documented that there is a decrease in the density of myelinated fibres with aging [43 -45]. In contrast, some studies have found a decrease in the density of unmyelinated fibres [43,46], whereas others did not report these changes [47,48]. It has been recognized that myelinated fibres tend to show more decline in density [43] and function [49] than unmyelinated fibres, as well as decreased nerve conduction velocity and structural modifications in the elderly [38,44].…”

A new combined Bodian-Luxol technique for staining unmyelinated axons in semithin, resin-embedded peripheral nerves: a comparison with electron microscopy

“…Ultrastructurally, control specimens did not show significant postmortem changes probably due to the short interval between death and sampling [8]. Axonal and Schwann cell membranes and organelles were well preserved (Fig.…”

“…Unmyelinated axons with diameters larger than 0.8 µm represented 65% (control 1) and 84% (control 2) of the population of UF [15]. Densities of empty Schwann cell bands of 2129/mm 2 (control 1) and 2429/mm 2 (control 2) were within the normal range for the patients' age [8]. Case 1 exhibited a severe loss of myelinated fibers of all caliber and a moderate loss of UF.…”

“…Fiber-size histograms as an indicator of regeneration, and quantitation of empty Schwann cell subunits as a gross approximation of axonal loss are mandatory. Ultrastructural morphometry remains the standard method for early detection and exhaustive study of changes in the UF population [2,8]. Our method of histochemical staining does not allow measurement of axonal diameter.…”