Daily torpor reduces mass and changes stress and power output of soleus and EDL muscles in the Djungarian hamster, <i>Phodopus sungorus</i>

Hibernation is characterized by prolonged periods of inactivity with concomitantly low nutrient intake, conditions that would typically result in muscle atrophy combined with a loss of oxidative fibers. Yet, hibernators consistently emerge from winter with very little atrophy, frequently accompanied by a slight shift in fiber ratios to more oxidative fiber types. Preservation of muscle morphology is combined with downregulation of glycolytic pathways and increased reliance on lipid metabolism instead. Furthermore, while rates of protein synthesis are reduced during hibernation, balance is maintained by correspondingly low rates of protein degradation. Proposed mechanisms include a number of signaling pathways and transcription factors that lead to increased oxidative fiber expression, enhanced protein synthesis and reduced protein degradation, ultimately resulting in minimal loss of skeletal muscle protein and oxidative capacity. The functional significance of these outcomes is maintenance of skeletal muscle strength and fatigue resistance, which enables hibernating animals to resume active behaviors such as predator avoidance, foraging and mating immediately following terminal arousal in the spring.

Section: Skeletal Muscle Contractile Performance During Hibernationmentioning

confidence: 83%

Section: Morphological Changes During Hibernationmentioning

confidence: 99%

Section: Skeletal Muscle Contractile Performance During Hibernationmentioning

confidence: 99%

See 1 more Smart Citation

Skeletal muscle mass and composition during mammalian hibernation

Cotton

2016

“…This applies to many species, such as bears, squirrels, woodchucks, bats, hamsters, prairie dogs and marmots (Cotton, 2016;Cotton and Harlow, 2010;Doherty et al, 2012;James et al, 2011;McGee-Lawrence et al, 2015Utz et al, 2009;Wojda et al, 2012). However, some small hibernators, such as the 13-lined ground squirrel (Ictidomys tridecemlineatus) have been reported to exhibit microstructural bone loss (osteocytic osteolysis) during hibernation bouts, which has not been observed in larger hibernating animals (McGeeLawrence et al, 2011).…”

Section: Maintenance Of Musculoskeletal Properties In Hibernators Andmentioning

confidence: 99%

Prevention of muscle wasting and osteoporosis: the value of examining novel animal models

Reilly

Franklin

2016

Bone mass and skeletal muscle mass are controlled by factors such as genetics, diet and nutrition, growth factors and mechanical stimuli. Whereas increased mechanical loading of the musculoskeletal system stimulates an increase in the mass and strength of skeletal muscle and bone, reduced mechanical loading and disuse rapidly promote a decrease in musculoskeletal mass, strength and ultimately performance (i.e. muscle atrophy and osteoporosis). In stark contrast to artificially immobilised laboratory mammals, animals that experience natural, prolonged bouts of disuse and reduced mechanical loading, such as hibernating mammals and aestivating frogs, consistently exhibit limited or no change in musculoskeletal performance. What factors modulate skeletal muscle and bone mass, and what physiological and molecular mechanisms protect against losses of muscle and bone during dormancy and following arousal? Understanding the events that occur in different organisms that undergo natural periods of prolonged disuse and suffer negligible musculoskeletal deterioration could not only reveal novel regulatory factors but also might lead to new therapeutic options. Here, we review recent work from a diverse array of species that has revealed novel information regarding physiological and molecular mechanisms that dormant animals may use to conserve musculoskeletal mass despite prolonged inactivity. By highlighting some of the differences and similarities in musculoskeletal biology between vertebrates that experience disparate modes of dormancy, it is hoped that this Review will stimulate new insights and ideas for future studies regarding the regulation of atrophy and osteoporosis in both natural and clinical models of muscle and bone disuse.

“…James and co-workers demonstrated that daily torpor in the Djungarian hamster actually increased isometric force and work loop power output in soleus muscle but had no effect on either soleus or extensor digitorum longus (EDL) work loop fatigue resistance (James et al, 2011). However, the Djungarian hamster spends only a few hours each day in torpor, while most hibernators undergo much longer torpor bouts that could cause more significant changes in contractile performance that might not have been detected via the use of isometric methods in all other previous studies on hibernators.…”

Section: Introductionmentioning

confidence: 99%

The effects of hibernation on the contractile and biochemical properties of skeletal muscles in the thirteen-lined ground squirrel, Ictidomys tridecemlineatus

James

Staples

Brown

et al. 2013

Self Cite

SUMMARYHibernation is a crucial strategy of winter survival used by many mammals. During hibernation, thirteen-lined ground squirrels, Ictidomys tridecemlineatus, cycle through a series of torpor bouts, each lasting more than a week, during which the animals are largely immobile. Previous hibernation studies have demonstrated that such natural models of skeletal muscle disuse cause limited or no change in either skeletal muscle size or contractile performance. However, work loop analysis of skeletal muscle, which provides a realistic assessment of in vivo power output, has not previously been undertaken in mammals that undergo prolonged torpor during hibernation. In the present study, our aim was to assess the effects of 3months of hibernation on contractile performance (using the work loop technique) and several biochemical properties that may affect performance. There was no significant difference in soleus muscle power output-cycle frequency curves between winter (torpid) and summer (active) animals. Total antioxidant capacity of gastrocnemius muscle was 156% higher in torpid than in summer animals, suggesting one potential mechanism for maintenance of acute muscle performance. Soleus muscle fatigue resistance was significantly lower in torpid than in summer animals. Gastrocnemius muscle glycogen content was unchanged. However, state 3 and state 4 mitochondrial respiration rates were significantly suppressed, by 59% and 44%, respectively, in mixed hindlimb skeletal muscle from torpid animals compared with summer controls. These findings in hindlimb skeletal muscles suggest that, although maximal contractile power output is maintained in torpor, there is both suppression of ATP production capacity and reduced fatigue resistance.