Date of Award

2014

Document Type

Scholarly Project

Degree Name

Doctor of Physical Therapy (DPT)

Department

Physical Therapy

First Advisor

Mark Romanick

Keywords

Aging -- physiology; Mice -- anatomy & histology; Muscle Weakness; Sarcopenia

Abstract

Background: Ames dwarf mice demonstrate delayed aging processes in multiple body systems. We compared muscle composition and area between dwarf and wild-type mice to determine if any significant differences exist.

Methods: We resected soleus, gastrocnemius/plantaris, tibialis anterior, and extensor digitorum longus muscles from both dwarf and wild-type mice, then froze, sliced, set on slides, and stained to isolate fast-twitch and slow-twitch fibers. Microscopy images were taken at 10x magnification and fiber composition and cross-sectional area were measured in soleus muscles.

Results: Wild-type mice had an average composition of 52.3% fast-twitch and 47.7% slow-twitch fibers while dwarf mice had 66.3% slow-twitch and 33.7% fast-twitch fibers. Differences between fast- and slow-twitch composition of dwarfs and fast-twitch and slow-twitch composition of 12-month-old wild-type versus dwarfs all yielded statistical significance. Dwarf mice had a smaller cross-sectional area than both 3-month and 12- month wild-type mice. Both comparisons were significant at p<0.0001.

Conclusion: Dwarfs demonstrated smaller muscle fiber area than wild-type mice, which was not surprising as dwarf mice have an innately slighter stature than wild-types. Wild-type mice, with a higher ratio of fast-twitch fibers, would exhibit higher rates of myosin ATPase hydrolysis and muscular strength, while dwarf mice, with more slow-twitch fibers, would display greater oxidative capacity and muscular endurance in the soleus muscle.

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