Age‐Related Changes in Muscle Fiber Types in the Human Thyroarytenoid Muscle: An Immunohistochemical and Stereological Study Using Confocal Laser Scanning Microscopy

Abstract

A decline in motor performance contributes to laryngeal dysfunction in the elderly, but the pathogenetic mechanisms are unknown. Quantitative 3-dimensional, age-related changes in the muscle fiber content of the human thyroarytenoid muscle were estimated from geometric probability (stereology) by use of a technique that provided a statistically unbiased sample of all possible section orientations and locations in the entire muscle volume. There was a preferential 27% age-related loss in the length density (L(V type, muscle)) of type 1 (slow) fibers in contrast to the selective type 2 (fast) fiber loss typical of aging limb muscles. In type 2 fibers there was no significant loss in the L(V), but there was an age-related decrease (P < 0.05) in the surface density (S(V type, muscle)) and an increase (P < 0.05) in the atrophy factor, an index of the content of very small, atrophic fibers. There was also an age-related increase in the length fraction (L(L type, all fibers)) of muscle fibers that coexpress both fast and slow myosin heavy-chain isoforms (P < 0.05). These findings demonstrate a type-specific fiber loss and atrophy that differs from that in aging limb muscles and an age-related increase in motor unit remodeling.

Posterior Cricoarytenoid Bellies: Relationship Between Their Function and Histology

“…The findings of the present study demonstrate that there are regional differences in both parts of the PCA (Figures 6 and 7), which is in accordance with Wu et al 17 Secondly, as suggested by many ''fiber-type grouping'' observed, these phenotypic changes, as in other skeletal muscles, occur by denervation and subsequent reinnervation and/or aging. 21 Histochemical studies of human PCA in elderly patients have already shown the presence of the ''fiber-type grouping,'' which is a result of a degenerative-aging process. 11,12 Generally in this condition, dendritic sprouts from a single motor neuron reinnervate a group of denervated muscle fibers.…”

Muscle Fiber Type Composition and Effects of Vocal Fold Immobilization on the Two Compartments of the Human Posterior Cricoarytenoid: A Case Study of Four Patients

“…9 Subsequent studies have identified neonatal myosin heavy chain (MyHC) isoform presence with immunohistochemical staining as indicative of muscle regeneration after reinnervation has been established. 10 Normally neonatal MyHC is expressed in adult muscle only in regenerating fibers, 11 as a response to denervation (especially in type IIA fibers), 12 or as a transient response from stretch-induced hypertrophy of muscle.…”

Unloaded Shortening Velocity and Myosin Heavy Chain Variations in Human Laryngeal Muscle Fibers

“…29,30 A recent histochemical report confirms these earlier results on human TA muscle. 31 Immunohistochemical identification of myosin isoforms has only recently been investigated, and shows that antibodies reactive for type I MHC, general fast type II MHCs, 32 tonic MHCs, 21 and neonatal MHC do react with fibers in human TA muscles. The neonatal MHC is thought to be expressed in regenerating fibers associated with age-related muscle changes, 33 rather than as part of normal protein expression.…”