Effect of aging on tongue protrusion forces in rats

Abstract

The purpose of this study was to ascertain the effect of aging on muscle contractile properties associated with tongue protrusion in a rat model. Fischer 344/Brown Norway hybrid rats, ten young (9 months old) and ten old (32 months old), were used to measure protrusive contractile properties. Results showed a significant reduction in tetanic forces in the old animals. The following measures of muscle contraction were not different between age groups: mean twitch contraction force, twitch contraction time, twitch contraction half-decay time, and a calculated measure of fatigability. In conclusion, aging influenced protrusive tongue muscle contractions in a rat model such that tetanic forces were reduced. The reduction of tetanus force may parallel findings in human subjects relative to isometric tongue force generation and may be associated with age-related disorders of swallowing.

Fig. 1

A Representative twitch contractions (g) from one old and one young animal. Contraction time (CT, ms) was measured as the duration between the onset of stimulation and the point of 50% peak force. Half-decay time (HDT, ms) was the duration between the onset of stimulation and the point of 50% decay from peak force. B Comparison of mean twitch forces (g) between old and young animals. C Comparison of mean contraction times (ms) between old and young animals. D Comparison of mean HDT (ms) between old and young animals. All error bars reflect standard deviations. There was no significant difference between age groups on any of the comparisons (p < 0.05)

Fig. 2

A Representative tetanic contractions (g) from one old and one young animal. Fusion of tetanic contraction was established at either 80 or 100 Hz. B Differences in mean tetanic force production between old and young animals was found such that old animals had significantly reduced tetanic force levels when compared with young rats (p < 0.002). Error bars = standard deviations

Fig. 3

A Representative tetanic force signals used in the calculation of fatigue index in one old and one young rat. The larger force wave is the initial force signal, which degraded over 2 min of contraction and is represented by the smaller force signal in each figure. B Mean fatigue index was not significantly different between old and young animals (p < 0.05). Error bars = standard deviations

Fig. 4

Schematic representation of the method used for stimulating the hypoglossal nerve, and placement of suture on the tongue connected to a transducer. The transducer assembly was oriented below the animal to maximize the force vector during evoked protrusive tongue actions