Age-related morphological regression of myelinated fibers and capillary architecture of distal peripheral nerves in rats.

Masahiro Sakita,Hidemi Fujino,Shinichiro Murakami

doi:10.1186/s12868-016-0277-4

Masahiro Sakita, Hidemi Fujino + Show 1 more

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https://doi.org/10.1186/s12868-016-0277-4

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Abstract

BackgroundRegression of myelinated peripheral nerve fibers in the lower extremities contributes to sarcopenia and balance dysfunction in normal aging. This subclinical regression of myelinated fibers (MFs) is heavily influenced by alterations in microvasculature, though the mechanism underlying these age-related degenerative phenomena remains unclear. The aim of the present study was to examine age-related regressions in myelinated distal peripheral nerve fibers as well as capillary architecture in rats using both morphological and histochemical methods.ResultsMFs were categorized into tertiles of ‘large’, ‘medium’, and ‘small’ sizes based on the distribution of MF diameters. A two-way ANOVA was used to assess effects of fiber size (large/medium/small) and group (young/elderly) on myelin thickness, axon diameter, myelin perimeter, axon perimeter, and G-ratio (axon diameter/fiber diameter). Significant main effects were observed for both MF size and group with respect to all dimensions except for G-ratio. Values for fiber diameter (P < 0.01), myelin thickness (P < 0.01), axon diameter (P < 0.01), myelin perimeter (P < 0.01), and axon perimeter (P < 0.01) were significantly lower than those in the young group. Additionally, mean capillary diameter and number of microvascular branch points were significantly lower in the elderly group than in the young group.ConclusionsThe present study demonstrated that spontaneous age-related regression predominantly occurs for all fiber sizes in the distal peripheral nerves and the capillary architecture. The results of the present study further suggest that both the distal MFs and capillaries in the peripheral nerve may simultaneously regress with aging.

Highlights

Regression of myelinated peripheral nerve fibers in the lower extremities contributes to sarcopenia and balance dysfunction in normal aging
Sarcopenia refers to the degenerative loss of skeletal muscle mass, muscle fibers, and strength associated with normal aging and is the main risk factor for falls in the elderly [1,2,3,4]
The rats were acquired at 10 weeks of age and maintained until 20 weeks of age, with a subset of 3 randomly selected rats maintained until 90 weeks of age

Summary

Introduction

Regression of myelinated peripheral nerve fibers in the lower extremities contributes to sarcopenia and balance dysfunction in normal aging. This subclinical regression of myelinated fibers (MFs) is heavily influenced by alterations in microvasculature, though the mechanism underlying these age-related degenerative phenomena remains unclear. A recent animal study found that atrophy of the peripheral nerve occurs prior to age-related sarcopenia [10]. It may be dysfunction of the peripheral nerve rather than sarcopenia itself that contributes to falls experienced by elderly people. VEGF activity promotes the formation and maintenance of the endothelial cells that form the inner lining of capillaries and has been associated with the pathogenesis of chronic

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