Avoidance of Skeletal Muscle Atrophy in Spontaneous and Facultative Hibernators

Clark J Cotton,Henry J Harlow

doi:10.1086/650471

Abstract

Smooth and skeletal muscle changes were compared from overwintering white-tailed prairie dogs, spontaneous hibernators that undergo regular, low-temperature torpor bouts, and black-tailed prairie dogs, facultative hibernators that use sporadic, moderate-temperature torpor bouts. The objectives were to assess the abilities of these two species with dramatically different torpor patterns (1) to conserve skeletal muscle morphology, protein, and strength and (2) to use labile protein in the small intestine and liver during the winter season of reduced activity and food intake. Mass and protein concentration of the extensor digitorum longus (EDL), soleus, liver, and small intestine, as well as skeletal muscle strength and fiber morphology for the EDL and soleus, were compared before and after hibernation in both species. Both species appeared to be similar to overwintering black bears and underwent very little strength and protein loss, as compared with euthermic models of immobility and long-term fasting. Although the two species used vastly different hibernation strategies, none of the changes in parameters related to muscle atrophy and labile-protein use during the hibernation season differed significantly between them. Therefore, it appears that regardless of the phenotypic expressions of hibernation, the outcome is the conservation of skeletal muscle.

Highlights

Hibernation benefits animals that must cope with cold environments and low food availability through a decreased body temperature and metabolic rate and concomitantly reduced energy needs (Geiser 1998)
The WTPD has retained the ancestral expression of spontaneous hibernation, the BTPD appears to have evolved into a facultative hibernator, with reduced expression of torpor
The extensor digitorum longus (EDL) for both species did lose strength/ cross-sectional area (CSA) over the winter (WTPDs: q p 3.337, P p 0.023; BTPDs: q p 3.767, P p 0.011; Fig. 2), there was no change in soleus strength for either species (Fig. 2)

Summary

Introduction

Hibernation benefits animals that must cope with cold environments and low food availability through a decreased body temperature and metabolic rate and concomitantly reduced energy needs (Geiser 1998). Despite the corresponding long periods of immobility and reduced food intake associated with torpor, hibernators are resilient to skeletal muscle atrophy, as the WTPD has retained the ancestral expression of spontaneous hibernation, the BTPD appears to have evolved into a facultative hibernator, with reduced expression of torpor. Food and water, total darkness, and 4ЊC ambient temperature, WTPDs will initiate regular, low–body temperature torpor bouts in early October (Harlow and Menkens 1986). BTPDs in the laboratory, engage in a more facultative torpor, with a moderate reduction in body temperature that can be induced only when animals are completely deprived of food and water at concomitant low ambient temperatures (Harlow and Menkens 1986). This study will establish the effectiveness of each hibernation strategy in attenuating skeletal muscle loss

Methods

Results

Discussion

Conclusion