Alterations of intrinsic tongue muscle properties with aging

Abstract

Introduction Age-related decline in the intrinsic lingual musculature could contribute to swallowing disorders, yet the effects of age on these muscles is unknown. We hypothesized reduced muscle fiber size and shifts to slower MyHC fiber types with age. Methods Intrinsic lingual muscles were sampled from 8 young-adult (9 months) and 8 old (32 months) Fischer 344/Brown Norway rats. Fiber size and MyHC were determined by fluorescent immunohistochemistry. Results Age was associated with a reduced abundance of rapidly-contracting muscle fibers, and more slowly-contracting fibers. Decreased fiber size was found only in the transverse and verticalis muscles. Discussion Shifts in muscle composition from faster to slower MyHC fiber types may contribute to age-related changes in swallowing duration. Decreasing muscle fiber size in the protrusive transverse and verticalis muscles may contribute to reductions in maximum isometric tongue pressure found with age. Differences among regions and muscles may be associated with different functional demands.

Differential impact of tongue exercise on intrinsic lingual muscles

“…As previously reported with age, there was a significant multivariate interaction between age and region (V = 0.738, F (6,23) = 10.81, P < .001). Old animals had significantly less MyHC IIb fibers and more fibers positive for MyHC IIx in all regions, as well as significantly more IIa‐positive fibers in the middle and posterior regions (Table ).…”

“…) and sectioned at 10 μm on a cryostat (Leica, Wetzlar, Germany). A detailed description of intrinsic tongue muscle sampling and staining for MyHC types has been published previously …”

“…Each section was imaged at 20× (Nikon N‐STORM, Andor iXon 897 EMCCD camera; Nikon Corp., Tokyo, Japan) with three randomly sampled fields of view, for 18 total images per muscle (2 sections × 3 regions × 3 images). A detailed description of intrinsic tongue muscle sampling and staining for MyHC types has been published previously . Image analysis was performed in the MATLAB application SMASH (MathWorks, Natick, MA) .…”

“…With health challenges, an exacerbation of these factors can compromise swallowing . Age‐related changes in the intrinsic tongue muscles may contribute to manifestations of altered swallowing. These muscles have an active role in swallowing, particularly bolus containment and propulsion .…”

“…A prior study found that with age, the intrinsic tongue muscles had increased percentages of slowly contracting fatigue‐resistant fibers. Additionally, in the protrusive transverse and verticalis muscles, muscle fiber sizes were reduced . Electromyographic (EMG) activity in the intrinsic tongue has been shown to increase with protrusive tongue force generation, indicating that these muscles are likely targeted by tongue exercise.…”