Date of Award

2011

Document Type

Scholarly Project

Degree Name

Doctor of Physical Therapy (DPT)

Department

Physical Therapy

First Advisor

Mark Romanick

Abstract

Introduction: Normal muscle wasting due to aging, known as sarcopenia, has many implications in society, especially with a growing population of elderly people. In this study, muscle fiber size and count, nuclei count, and ratio of fast- to slow-twitch fibers was studied between Ames dwarf mice (df), an established model of aging, and wild-type mice (WT) to learn more about the mechanisms of aging, specifically related to skeletal muscle.

Methods: Four hind limb muscles were harvested from two Ames dwarf mice and two wildtype mice, sliced cross-sectionally and mounted on slides. After mounting, the slides were stained three different ways to reveal fast-twitch fibers, slow-twitch fibers and nuclei.

Results: Data regarding size and number were collected from images of the stained slices. Statistically significant differences between the two species included mean cross-sectional area of the individual soleus muscle fibers (1973.9 μm WT, 770.3 μm df) —P<0.001; nuclear count of the soleus muscle (2.8x higher in WT); ratio of fast- to slow- twitch fibers (df 1:2, WT 1:1); entire soleus cross-sectional area (WT 5x > df); and total number of fibers per soleus muscle (833 WT, 219 df.)

Conclusion: The differences seen between dwarf and wild-type skeletal muscle found in this study are attributed to the genetic mutation of the Ames dwarf mouse, specifically the lack of GH action, causing a decreased cross-sectional area of muscle fibers and decreased number of fibers resulting in decreased cross-sectional area of the whole muscle, as well as decreased nuclear count, and decreased number of fast-twitch fibers to each slow-twitch fiber. The same characteristics of skeletal muscle will need to be studied in older mice (multiple age groups) for both mouse lines in future studies to make this study’s results conclusively applicable to GH effect on sarcopenia.

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