Maintenance of the pectoralis muscle during hibernation in the big brown bat,Eptesicus fuscus

Abstract

Summary.The relationship between pectoralis muscle mass and body mass is examined throughout the annual body mass cycle in Eptesicusfuscus in order to evaluate muscle maintenance during hibernation. E. fuscus undergoes large fluctuations in body mass during the year due to pregnancy, parturition, prehibernation fattening, and hibernation (Table 1). Parallel changes occur in pectoralis muscle mass and total pectoralis protein mass (Table 2). The strong correlation between log pectoralis mass and log body mass ( Fig. 3) and the lack of correlation between pectoralis mass and forearm length ( Fig. 1, 2) suggest that the seasonal variation in pectoralis muscle mass represents a compensatory response to changing body mass. In active bats this relationship closely resembles the compensatory response predicted by flight theory.Both pectoralis muscle mass and body mass decrease significantly during four months of hibernation (Tables 1, 2). Although pectoralis mass and body mass are not significantly correlated after four months of hibernation the values fall within the range of observations in active summer bats (Fig. 3), indicating an approximate maintenance of the pectoralis mass/body mass relationship. The lack of correlation in hibernating bats may result from differences in the function of pectoralis muscle during activity (powering flight) and hibernation (thermogenesis and supply of gluconeogenic precursors). The significant elevation of pectoralis muscle protein concentration during prehibernation fattening and its progressive decrease during hibernation (Fig. 4) support the idea that the pectoralis muscle serves as an important source of gluconeogenic precursors during hibernation.

Skeletal muscle atrophy occurs slowly and selectively during prolonged aestivation inCyclorana alboguttata(Günther 1867)

“…The sartorius muscle from six-month aestivators maintained CSA at control levels and then significantly decreased by 22% after nine months of aestivation (Fig.3B). These reductions in whole muscle CSA and mass are significant and they are not dissimilar to previous findings on hibernating mammals, which range from 14% to 63% (Steffen et al, 1991;Yacoe, 1983;Wickler et al, 1987;Reid et al, 1995;Wickler et al, 1991). The cruralis muscle, the largest of the four muscles examined and a powerful jumping muscle, did not exhibit any change in CSA during aestivation (Fig.3D).…”

“…Few studies have explored the effect of dormancy on muscle disuse atrophy in skeletal muscle (for reviews, see Carey et al, 2003;Shavlakadze and Grounds, 2006). In general, hibernators exhibit some level of muscle atrophy, although to a lesser extent than would be observed in humans under the same conditions (Yacoe, 1983;Wickler et al, 1987;Steffen et al, 1991;Wickler et al, 1991). There appear to be no published studies that examine the relationship between muscle fibre composition and biomechanical function and how this relationship might influence muscle disuse atrophy.…”

Skeletal muscle mass and composition during mammalian hibernation

“…The majority of studies conducted on hamsters (Deveci and Egginton, 2002b;James et al, 2011), ground squirrels (Cotton and Harlow, 2010;Gao et al, 2012;James et al, 2013;Nowell et al, 2011;Steffen et al, 1991;Yang et al, 2014) and bats (Kim et al, 2000;Lee et al, 2008;Yacoe, 1983a) have shown relatively minor changes in muscle mass and protein content during hibernation, with most reporting 5-30% decreases in mass and 5-15% decreases in protein (Table 1). There is, however, some variation depending on species, specific muscles and sampling period.…”

“…Collectively, these studies indicate that losses of muscle mass, protein and fiber size are typically small during hibernation. Furthermore, the ratio of skeletal muscle mass to body mass is maintained (James et al, 2013;Van Dyke et al, 2007;Yacoe, 1983a) or even improved (Hindle et al, 2014;Yang et al, 2014) following hibernation. Interestingly, animals may emerge from hibernation with greater functional capacity in regards to locomotor performance due to the much greater loss of adipose tissue in relation to skeletal muscle changes.…”

Getting the jump on skeletal muscle disuse atrophy: preservation of contractile performance in aestivatingCyclorana alboguttata(Günther 1867)

“…During dormancy the animal is primarily reliant upon stored lipids, with protein meeting additional energy demands (Harlow et al, 2001;Pakay et al, 2002;Pedler et al, 1996;Seymour, 1973;Tinker et al, 1998;van Beurden, 1980). Muscle comprises the largest protein store in the body, therefore catabolism of muscle tissue as an energy substrate during hibernation and aestivation may contribute to muscle disuse atrophy (Steffen et al, 1991;Wickler et al, 1987;Wickler et al, 1991b;Yacoe, 1983). Additionally, it has been demonstrated that protein synthesis is downregulated during dormancy, which may further compound the atrophic effects of dormancy on skeletal muscle (Frerichs et al, 1998;Fuery et al, 1998;Pakay et al, 2002).…”