Purpose-Age-related changes in tongue function may contribute to dysphagia in elderly people. Our purpose was to investigate whether aged rats that have undergone tongue exercise would manifest increased protrusive tongue forces and increased genioglossus (GG) muscle fiber cross sectional areas.Method-Forty-eight young adult, middle-aged and old Fischer 344/Brown Norway rats received 8 weeks of tongue exercise. Protrusive tongue forces were measured before and after exercise. GG muscle fiber cross sectional area was measured in exercised rats and compared with cross sectional areas in a no-exercise control group.Results-A significant increase in maximum tongue force was found following exercise in all age groups. In addition, a trend for increased GG muscle fiber cross sectional area, and a significant increase in variability of GG muscle fiber cross sectional area were identified post-exercise. Conclusion-The findings of this study have implications for treatment of elderly persons with dysphagia using tongue exercise programs. Specifically, increases in tongue force that occur following 8 weeks of progressive resistance tongue exercise may be accompanied by alterations in tongue muscle fiber morphology. These changes may provide greater strength and endurance for goal-oriented actions associated with the oropharyngeal swallow and should be investigated in future research.

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The tongue plays a vital role in swallowing actions. However, tongue muscles have been understudied, and it is unclear if tongue muscles are homogeneous with respect to muscle fiber-type distribution. We examined myosin heavy chain (MHC) composition of anterior, medial, and posterior sections of the genioglossus muscle (GG) using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) in ten adult (9 months old) male Fischer 344/Brown Norway hybrid rats. We found that Type IIx MHC predominated in the anterior, medial, and posterior regions of the GG muscle (p=0.002), followed by IIa, then IIb. The anterior GG contained a significantly greater (p=0.004) proportion of Type IIa than did the medial or posterior regions, while the posterior GG contained a significantly greater (p=0.002) proportion of Type IIb MHC than did the medial or anterior GG. Accordingly, we found variable expression of MHC isoforms across anterior, medial, and posterior portions of the GG muscle, with more fast-contracting isoforms found posteriorly. Because motor control of the tongue requires precise and rapid movements for bolus manipulation and airway protection, variable expression of MHC isoforms along the anteroposterior axis of the GG muscle may be required to efficiently achieve deglutition and maintenance of airway patency.

We serendipitously found a distal Disabled-1 (Dab1)-immunoreactive cell in retina of the C57BL/6J black mouse. The somata of these cells are located in the outermost part of the inner nuclear layer (INL). Their processes extend toward the outer plexiform layer (OPL), receiving synaptic inputs from horizontal and interplexiform cells. In the current study, we name this cell the "distal Dab1-immunoreactive cell." Double-labeling experiments demonstrate that the distal Dab1-immunoreactive cell is not a horizontal cell. Rather, the distal Dab1 cell appears to be a misplaced AII cell, by being glycine transporter-1-immunoreactive and by resembling the latter cell in an electron microscopic analysis. A distal Dab1 cell had been reported in the FVB/N mouse retina, a model of retinitis pigmentosa (Park et al. [2004] Cell Tissue Res 315:407-412). However, here, we found this distal Dab1-immunoreactive cell in the adult and normal developing mouse retinas. Hence, we show that such cells do not require the loss of photoreceptors as suggested previously (Park et al. [2004] Cell Tissue Res 315:407-412). Instead, two other pieces of data suggest an alternative explanation sources for distal Dab1 cells. First, we find a correlation between the number of these cells in the left and right eyes Second, developmental analysis shows that the distal Dab1-immunoreactive cell is first observed shortly after birth. At the same time, AII cells emerge, extending their neurites into the inner retina. These data suggest that distal Dab1-immunoreactive cells are misplaced AII amacrine cells, resulting from genetically modulated anomalies owing to migration errors.