Department of Physiology and Biomedical Engineering, Mayo Clinic, Rochester, MN 55905, USA.
Department of Physiology and Biomedical Engineering, Mayo Clinic, Rochester, MN 55905, USA.
Respir Physiol Neurobiol. 2024 Jan;319:104180. doi: 10.1016/j.resp.2023.104180. Epub 2023 Oct 18.
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.
舌头是一种肌肉液压系统，在呼吸、咀嚼、吞咽、发声、呕吐、咳嗽和梳理/性行为中都会发生舌部运动。在老年人中，舌部功能减退和虚弱会增加阻塞性睡眠呼吸暂停和吸入性肺炎的风险。在 Fischer 344（F344）大鼠中，舌咽运动神经元死亡是明显的，尽管没有关于舌力的信息。内在舌肌，包括上、下纵肌、横肌和垂直肌，存在相互交错的状态。最近，我们建立了一种测量单个内在舌肌比力的方法，考虑到不在单轴力方向上的组织体积。在 6 个月（n=10）、18 个月（n=9）和 24 个月（n=12）龄的雌性和雄性 F344 大鼠的舌纵肌中，我们评估了比力、疲劳性、纤维类型依赖性横截面积（CSA）和总 CSA。使用铂板模拟电极在体外用肌肉力和疲劳进行评估。舌肌在融化的异戊烷中冷冻，并在 10μm 处横切切片。根据肌球蛋白重链（MyHC）同工型抗体的免疫反应性对肌肉纤维类型进行分类。在 H&E 染色的肌肉中，评估 CSA 和单轴肌肉对总舌体体积的贡献。我们观察到纵向比力显著下降约 30%，总纵向肌肉纤维 CSA 减少，IIx/IIb 纤维特异性萎缩。研究舌下运动神经元死亡和舌肌无力的机制基础，最终为与年龄相关的舌功能障碍提供治疗方法非常重要。
