Age-related changes in orolingual motor function in F344 vs F344/BN rats

Abstract

Normal aging is associated with both locomotor and orolingual motor deficits. Preclinical studies of motor function in normal aging, however, have focused primarily on locomotor activity. The purpose of this study was to measure age-related changes in orolingual motor function and compare these changes between two rat strains commonly used in aging studies: Fischer 344 (F344) and Fischer 344/Brown Norway hybrid (F344/BN) rats. Rats (6-, 12-, 18- and 24-months of age) were trained to lick water from an isometric force-sensing operandum so that the number of licks per session, licking rhythm (licks/second) and lick force could be measured. In both strains, the number of licks per session was greatest in the oldest group, while this measure was greater for F344/BN rats at all ages. Peak tongue force increased with age in F344/BN rats, did not change with age in the F344 rats, and was greater for the F344/BN rats at all ages. Both strains exhibited an age-related slowing of licking rhythm beginning with the 18-month-old group. These findings suggest that despite lifespan differences between these two rat strains, diminished tongue motility emerges at the same age.

Figure 1

Raw force-time waveforms depicting 10 s samples of licking. Waveforms are from representative sessions for 6- month (top row), 12-month (second row), 18-month (third row) and 24-month (bottom row) F344 (left column) and F344/BN (right column) rats.

Figure 2

Orolingual motor measures and body weights as a function of age and strain. (A) Rats exhibited an age-related increase in the number of licks/session (#p<0.05). At each age, the number of licks/session was greater for F344/BN rats (^*p<0.05). (B) Licking rhythm was significantly slower in both strains beginning with the 18-month group (#p<0.05). (C) Peak tongue force was significantly greater for F344/BN rats than for F344 rats at all ages (^*p<0.05). Neither the main effect for age nor the age X strain interaction reached significance. (D) Both F344 and F344/BN rats exhibited age-related increases in body weights. After reaching a maximum at 12 months, body weights decreased with age in F344 rats (they remained higher than the 6-month group at each age however). F344/BN rats exhibited progressive weight increases across the four age groups. Note: ^#denotes significant difference from 6-months group, ^*denotes significant strain difference at this age, ^Xdenotes significant strain by age interaction.