Decreases in body temperature and body mass constitute pre-hibernation remodelling in the Syrian golden hamster, a facultative mammalian hibernator

Abstract

Hibernation is an adaptive strategy for surviving during periods with little or no food availability, by profoundly reducing the metabolic rate and the core body temperature (Tb). Obligate hibernators (e.g. bears, ground squirrels, etc.) hibernate every winter under the strict regulation of endogenous circannual rhythms, and they are assumed to undergo adaptive remodelling in autumn, the pre-hibernation period, prior to hibernation. However, little is known about the nature of pre-hibernation remodelling. Syrian hamsters (Mesocricetus auratus) are facultative hibernators that can hibernate irrespective of seasons when exposed to prolonged short photoperiod and cold ambient temperature (SD-Cold) conditions. Their Tb set point reduced by the first deep torpor (DT) and then increased gradually after repeated cycles of DT and periodic arousal (PA), and finally recovered to the level observed before the prolonged SD-Cold in the post-hibernation period. We also found that, before the initiation of hibernation, the body mass of animals decreased below a threshold, indicating that hibernation in this species depends on body condition. These observations suggest that Syrian hamsters undergo pre-hibernation remodelling and that Tb and body mass can be useful physiological markers to monitor the remodelling process during the pre-hibernation period.

Huddling remodels gut microbiota to reduce energy requirements in a small mammal species during cold exposure

“…The shifts in caecal microbiota were associated with a reduction in T core during cold exposure and in huddling in Brandt’s voles. Hibernating mammals exhibit an annual temperature rhythm [ 78 , 79 ] and alter the diversity and composition of gut microbiota over the circannual hibernation cycle [ 20 , 80 ]. Most mammals such as mice, desert hamsters ( Phodopus roborovskii ), and even humans show daily body temperature rhythm [ 81 , 82 ] and the diurnal variation of gut microbiota has been reported in mice [ 83 , 84 ].…”

Neural Signaling Metabolites May Modulate Energy Use in Hibernation

“…In obligate hibernators season drives remodeling of mechanisms that preserve energy balance. Similar pre-hibernation mechanisms are conserved in facultative hibernators 16 . Less is known about fasting-induced torpor.…”

“…14 T b decreases by 1 to 2°C before animals hibernate and this gradual modification of thermogenesis and metabolism predicts onset of hibernation. 14–16 Remodeling of thermoregulation and metabolism is postulated to result from changes within the hypothalamus 44 as well as from altered sensitivity of A 1 AR. 14 Increased sleep drive and lower T b in winter ground squirrels that are not hibernating when compared to summer ground squirrels is consistent with increased sensitivity of A 1 AR.…”

“…11, 12 Field and laboratory studies suggest that pre-hibernation energy conservation begins with a gradual decrease in body temperature (T b ) 13–16 presumably via a decrease in thermogenesis. In the arctic ground squirrel the pre-hibernation decrease in T b begins prior to a decline in food intake 14 suggesting that decreased energy expenditure leads to a decrease in food intake.…”

Environmental temperature effects on adipose tissue growth in a hibernator

“…Hibernation is classified as either facultative, occurring only under environmental conditions that are particularly unfavourable, or obligate, occurring at approximately the same time each year regardless of environmental conditions (Strijkstra, 2009). Facultative hibernators include the Syrian hamster, which only hibernates after acclimation for approximately 74 days to cold T a (5°C) and short (8 h light:16 h dark) photoperiods (Chayama et al, 2016). In contrast, obligate hibernators, such the golden-mantled ground squirrel (Callospermophilus lateralis), are thought to show an endogenous circannual rhythm (Pengelley and Asmundson, 1969).…”