Sarcopenia of the longitudinal tongue muscles in rats

• Published in: Respiratory physiology & neurobiology 2024-01, Vol.319, p.104180-104180, Article 104180
• Main Authors: Sieck, Gary C., Hernandez-Vizcarrondo, Genesis A., Brown, Alyssa D., Fogarty, Matthew J.
• Format: Article
• Language: English
• Subjects: Aged; Aging; Aging - physiology; Animals; Female; Humans; Infant; Male; Muscle fiber type; Muscle Fibers, Skeletal - pathology; Muscle specific force; Rats; Rats, Inbred F344; Sarcopenia - pathology; Tongue - physiology
• ISSN: 1569-9048; 1878-1519
• DOI: 10.1016/j.resp.2023.104180

The tongue is a muscular hydrostat, with lingual movements occurring during breathing, chewing, swallowing, vocalization, vomiting, coughing and grooming/sexual activities. In the elderly, reduced lingual dysfunction and weakness contribute to increased risks of obstructive sleep apnea and aspiration pneumonia. In Fischer 344 (F344) rats, a validated model of aging, hypoglossal motor neuron death is apparent, although there is no information regarding tongue strength. The intrinsic tongue muscles, the superior and inferior longitudinal, transversalis and verticalis exist in an interdigitated state. Recently, we established a method to measure the specific force of individual intrinsic tongue muscle, accounting for the tissue bulk that is not in the direction of uniaxial force. In the longitudinal muscles of 6- (n = 10), 18- (n = 9) and 24-month-old (n = 12) female and male F344 rats, we assessed specific force, fatigability, fiber type dependent cross-sectional area (CSA) and overall CSA. Muscle force and fatigue was assessed ex vivo using platinum plate simulation electrodes. Tongue muscles were frozen in melting isopentane, and transverse sections cut at 10 µm. Muscle fiber type was classified based on immunoreactivity to myosin heavy chain (MyHC) isoform antibodies. In H&E stained muscle, CSA and uniaxial muscle contributions to total tongue bulk was assessed. We observed a robust ∼30% loss of longitudinal specific force, with reductions in overall longitudinal muscle fiber CSA and specific atrophy of type IIx/IIb fibers. It will be important to investigate the mechanistic underpinnings of hypoglossal motor neuron death and tongue muscle weakness to eventually provide therapies for age-associated lingual dysfunctions. •Tongue dysfunction and weakness is implicated in the increased age-associated risks of OSA and aspiration pneumonia.•We assessed uniaxial specific force, fatigability and muscle fiber CSA of the superior and inferior longitudinal muscles.•In old age reduced specific force and muscle fiber atrophy is evident, which may underpin age-related lingual dysfunctions.