C - Michigan Technological University

experience periodic arousals in which they experience bursts of high metabolism thatraise their body temperatures back to near-normal levels [115, 121, 122]. Because ofthese intermittent arousals, small hibernators reload their bones periodically throughoutwinter; though this reloading probably remains minimal since these animals are confinedto small burrows during hibernation. Small hibernators also periodically excrete wastessuch as urine [122-124], which could result in net excretion of calcium throughout thewinter. Thus, calcium mobilized by resorption of bone during hibernation in small animalsmay not be available for incorporation into newly forming bone as it would be in the bear.These differences in metabolism and calcium excretion could explain why small animalsmay lose bone during hibernation, whereas bears do not.1.7.2 Bone response to hibernation—small hibernatorsEarly studies in the bone of small hibernators—including the little brown bat(Myotis lucifugus), golden hamster (Mesocricetus auratus), and 13-lined ground squirrel(Ictidomys tridecemlineatus)—suggest that these animals undergo disuse-induced boneloss during hibernation [104-109, 125, 126]. Between fall and spring, bone porosityincreases due to enlarged osteocyte lacunae [104, 105, 108, 109, 126]. Hibernating batsand hamsters reduce cortical bone thickness [104, 105, 108, 126]. Bone mineral contentdecreases in the hibernating bat [125]. Although these studies all suggest that smallhibernators lose bone during hibernation, most of them are based on qualitativeobservations (for review see: [103]). Some quantitative data have been collected morerecently in the golden-mantled ground squirrel (Callospermophilus lateralis) [110]. Thisstudy found that femoral and tibial bone strength is not affected by 8 months ofhibernation. The Donahue lab has collected some preliminary quantitative data on thefemurs of 13-lined ground squirrels, finding that during the hibernation season bone islost on the microstructural scale due to increased lacunar size; however, despite thesemicrostructural changes, the bone geometrical properties and mineral content were notdifferent before, during, and after hibernation [103]. Therefore, more comprehensivestudies need to be completed before interpreting the effects of hibernation on bone ofsmall animals.11