Date of Award

12-17-2022

Document Type

Dissertation

Abstract

Hibernating animals, such as the arctic ground squirrel (AGS), are subjected to a wide range of temperature variations. During hibernation, when they are predominantly physically inactive, body temperature can drop as low as -3°C, while in summer, body temperature can climb as high as 40°C. Torpor is a state of inactivity in an animal induced by a lack of food, which is followed by a fall in body temperature and metabolic rate. Torpor lasts around 21 days in AGS, and the progression of torpor begins with early torpor, followed by mid and late torpor, and culminates with interbout arousal lasting less than 24 hours. AGS exhibit reduced muscular atrophy and protein loss despite lengthy periods of immobility, hypometabolism, and severe hypothermic conditions during hibernation. Skeletal muscle plasticity, unique to mammalian hibernators, may explain why cardiac and respiratory skeletal muscle can function at hypothermic temperatures during and after hibernation. As a result, understanding the effects of ambient temperature on muscle physiology and contractile function is critical. The focus of this research was to investigate skeletal muscle contractile performance and fatigue resistance in ex vivo muscle tissues during hypothermic temperature stress. Ex vivo tissue organ bath functional assays were performed in hibernator and/or non-hibernator rodent models to determine changes in performance and fatigue resistance in the AGS diaphragm induced by polyunsaturated fatty acid dietary modification or ambient hypothermic stress. This study lends support to the idea that diet and hypothermic stress might modify certain functional aspects of skeletal muscle, most likely via membrane lipid composition, ambient temperature, and torpor interaction. Furthermore, summer active AGS has a higher fatigue resistance than mid torpor AGS during the hibernating season. Furthermore, skeletal muscle fatigue resistance was significantly lower in Sprague Dawley rats than in both summer active and hibernating AGS. Preliminary data also suggested that hypothermic stress, to some extent, enhanced fatigue resistance regardless of torpor status or species difference.

Handle

http://hdl.handle.net/11122/13123

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