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Gallbladder bile color varies by season and hibernation. A) Photograph of bile collected from golden-mantled ground squirrels (Spermophilus lateralis) as a function of state. Bile was collected from squirrels collected monthly (2–3 squirrels per month) from May (left) until September (right; summer active, SA), squirrels during winter that were torpid (T) when body temperature was ~5°C, squirrels during the euthermic period between bouts of torpor (interbout-aroused; IBA), and squirrels that were sampled in winter but had failed to hibernate (abnormal, AB). As an indication of approximate volumes, microcentrifuge tubes contain all of the collected bile for each animal except one AB animal (full tube on lower right; ~2.5 ml of bile was collected from that animal). B) Spectral characteristics of bile as a function of state. Each line represents one animal. Data are depicted for 3 animals of each state and only every 50th symbol is plotted for clarity.
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Golden-mantled ground squirrels (S. lateralis) are anorexic during the winter and survive by exploiting hibernation to reduce energetic demands. The liver normally plays a critical role in fueling and regulating metabolism and one might expect significant changes in hepatobiliary function with hibernation. We analyzed bile collected from animals in...
Citations
... However, the prevention of torpor use in ground squirrels to accommodate learning and memory studies is more problematic. Marked physiological differences are apparent in ground squirrels that are competent to enter torpor versus those that cannot enter torpor (Baker and van Breukelen 2009). Squirrels that cannot enter torpor typically become anorexic like squirrels that do use torpor. ...
Mammalian hibernation in ground squirrels is characterized by periods of torpor wherein body temperature approaches ambient temperature and metabolism is reduced to as low as 1/100th of active rates. It is unclear how hibernation affects long-term spatial memory, as tremendous remodeling of neurons is associated with torpor use. Given the suspected links between remodeling and memory formation and retention, we examined long-term spatial memory retention throughout a hibernation season. Animals were trained on a Barnes maze before entering torpor. Animals were tested for memory retention once a month throughout a hibernation season. Results indicate marked variation between individuals. Some squirrels retained memory across multiple torpor bouts, while other squirrels did not. No relationship was found between the number of torpor bouts, duration of bouts, or time spent torpid on long-term memory retention. However, that some squirrels successfully retain memory suggests that the profound remodeling of dendritic spines during torpor does not always lead to memory loss.
... Indeed, although a decrease was observed in pancreatic mass during hibernation (Bauman et al., 1987), this does not necessarily lead to decreased lipase content, as shown in three-day starved rats experiencing a similar decrease in pancreatic mass (Nagy et al., 1989). It is also important to note that pancreatic lipase mRNA in hibernating species has been shown to be continuously synthesized and translated into protein (Squire and Andrews, 2003), whereas bile composition does not vary compared to summer values (Baker and van Breukelen, 2009). ...
... On the other hand bilirubin, the end product of haemoglobin metabolism was also significantly increased during hibernation. Baker and Breukelen also found similar results in the hibernating golden mantled ground squirrel [6] . The reduced haemoglobin concentration and increased bilirubin concentration may have significant physiological consequence that could aid in survivorship of hibernation. ...
Amphibians are not tremble with winter wind but triumph over the winter with an amazing
behavioral adaptation – hibernation. Through winter environment is hostile to their nature and
behavior, they are capable to guard over the winter harshness. They emerge from the condition
and embark on a new task.
... Like the kidneys, the liver is largely metabolically inactive, but still functioning during hibernation (Baker and van Breukelen, 2009;Green et al., 1984). Indeed, ground squirrels experience no significant changes in bile constituents throughout the hibernation period (Baker and van Breukelen, 2009), indicating that the liver remains viable. ...
... Like the kidneys, the liver is largely metabolically inactive, but still functioning during hibernation (Baker and van Breukelen, 2009;Green et al., 1984). Indeed, ground squirrels experience no significant changes in bile constituents throughout the hibernation period (Baker and van Breukelen, 2009), indicating that the liver remains viable. Considering this and that ALP can be produced and is also cleared by the liver, we would expect that there would be no significant fluctuation of liver alkaline phosphatase. ...
Long periods of inactivity in most mammals lead to significant bone loss that may not be completely recovered during an individual’s lifetime regardless of future activity. Extended bouts of inactivity are the norm for hibernating mammals. It remains largely unknown, however, how these animals avoid adversely affecting bone, their quality, and ultimately survival given the challenges posed to their skeletons by inactivity and nutritional deprivation during hibernation. The primary goal of this project was to identify the physiological mechanisms regulating bone density, area and strength during extended periods of annual inactivity in hibernating woodchucks (Marmota monax). The overall hypothesis that bone integrity is unaffected by several months of inactivity during hibernation in woodchucks was tested across multiple levels of biological function. To gain a holistic assessment of seasonal bone integrity, the locomotor behavior and estimated stresses acting on woodchuck bones were investigated in conjunction with computed tomography scans and three-point bending tests to determine bone density, geometry, and mechanical properties of the long bones throughout the year. In addition, serum protein expression was examined to ascertain bone resorption and formation processes indicative of overall annual skeletal health. It was determined that woodchucks avoid significant changes in gait preference, but experience a decrease in bending stresses acting on distal limb bones following hibernation. Computed tomography scans indicated that bone mass, distribution, and trabecular structure are maintained in these animals throughout the year. Surprisingly, cortical density increased significantly posthibernation. Furthermore, three-point bending tests revealed that although less stiff, woodchuck femora were just as tough during the hibernation season, unlike brittle bones associated with osteoporosis. Finally, bone serum markers suggested a net maintenance of bone resorption and formation processes throughout the year. Taken together, these findings strongly suggest that woodchucks do not lose bone to the extent that would be expected from a non-hibernating animal during four months of inactivity. It is concluded that bone integrity is not adversely affected by hibernation in woodchucks. The results of this work have several broader implications toward skeletal biology research, the evolution of skeletal plasticity, and biomedical applications to osteoporosis prevention and treatment.
... to the contrary, bilirubin, the end product of haemoglobin metabolism, also significantly increased in the toads during hibernation. Baker & Breukelen (2009) also found similar results in the hibernating golden mantled ground squirrel. the recurring nature of metabolic rate depression as a survival strategy of animals suggests that the regulation of metabolic arrest has fundamental principles and mechanisms that are expressed not only in all cell types of an individual animal, but also, across phylogenetic lines. ...
Hibernation occurs with exposure to low temperatures and, under normal conditions,
during winter seasons when there are lengthy periods of low environmental temperatures. This
investigation reports the effect of hibernation on the blood-plasma and biochemical parameters -
plasma protein, plasma glucose, cholesterol, blood haemoglobin, bilirubin thyroid hormone and serum
ion in the Indian common toad (Duttaphrynus melanostictus). Metabolic rate and blood cell count was
also investigated to elucidate adjustments in hibernation. Adaptation during hibernation is crucial for
the toad’s winter survival.
... Previous work to measure metabolite changes in hibernators documents a number of alterations in liver (2,32,36), brain (21,40), brown adipose tissue (13), bile (4), and blood (1,9,24,31) that begin to assess the metabolites cycling in association with hibernation. These data suggest a two-switch model for the circannual rhythm of hibernation whereby the torporarousal cycle is temporally segregated from the summer-winter cycle such that torpor-arousal occurs only in winter (36). ...
Hibernation as manifested in ground squirrels is arguably the most plastic and extreme of physiological phenotypes in mammals. Homeostasis is challenged by prolonged fasting accompanied by heterothermy, yet must be facilitated for survival. We performed LC and GC-MS metabolomic profiling of plasma samples taken reproducibly during seven natural stages of the hibernator's year, three in summer and four in winter (each n ≥ 5), employing a nontargeted approach to define the metabolite shifts associated with the phenotype. We quantified 231 named metabolites; 106 of these altered significantly, demarcating a cycle within a cycle where torpor-arousal cycles recur during the winter portion of the seasonal cycle. A number of robust hibernation biomarkers that alter with season and winter stage are identified, including specific free fatty acids, antioxidants, and previously unpublished modified amino acids that are likely to be associated with the fasting state. The major pattern in metabolite levels is one of either depletion or accrual during torpor, followed by reversal to an apparent homeostatic level by interbout arousal. This finding provides new data that strongly support the predictions of a long-standing hypothesis that periodic arousals are necessary to restore metabolic homeostasis.
... Yet, a basal level of cholesterol synthesis must continue during the winter fast because biliary cholesterol concentrations are maintained (and even increase, likely due to biliary fluid reabsorption in intervals between gallbladder emptying). Biliary cholesterol levels also rise in hibernating bears [10], but are unchanged in hibernating golden-mantled ground squirrels [43]. Although some cholesterol secreted into bile in hibernators is excreted during interbout arousals, some may be reabsorbed via the intestinal epithelium via NPC1L1. ...
Previous work has suggested that central and peripheral opioid signaling are involved in regulating torpor behavior and tissue protection associated with the hibernation phenotype. We used quantitative real-time PCR (qRT-PCR) to measure mRNA levels of opioid peptide precursors and receptors in the brain and heart of summer ground squirrels (Ictidomys tridecemlineatus) and winter hibernating squirrels in the torpid or interbout arousal states. The use of appropriate reference genes for normalization of qRT-PCR gene expression data can have profound effects on the analysis and interpretation of results. This may be particularly important when experimental subjects, such as hibernating animals, undergo significant morphological and/or functional changes during the study. Therefore, an additional goal of this study was to identify stable reference genes for use in qRT-PCR studies of the 13-lined ground squirrel. Expression levels of 10 potential reference genes were measured in the small intestine, liver, brain, and heart, and the optimal combinations of the most stable reference genes were identified by the GeNorm Excel applet. Based on this analysis, we provide recommendations for reference genes to use in each tissue that would be suitable for comparative studies among different activity states. When appropriate normalization of mRNA levels was used, there were no changes in opioid-related genes in heart among the three activity states; in brain, DOR expression was highest during torpor, lowest in interbout arousal and intermediate in summer. The results support the idea that changes in DOR expression may regulate the level of neuronal activity in brain during the annual hibernation cycle and may contribute to hibernation-associated tissue protection.
The ultimate manifestations of life, birth, survival under various environmental pressures and death are based on bioenergetics. These manifestations of life were made possible by the remarkable "social" behaviour of biomolecules during billions of years of evolution: the evolution of life with oxygen. Oxygen was necessary for energy production and the evolutionary explosion of aerobic organisms. Nevertheless, reactive oxygen species, formed through oxidative metabolism, are dangerous - they can kill a cell and, on the other hand, play a plethora of fundamentally valuable roles. Therefore, the evolution of life depended on energy metabolism and redox-metabolic adaptations. The more extreme the conditions for survival are, the more sophisticated the adaptive responses of organisms become. Hibernation is a beautiful illustration of this principle. Hibernating animals use evolutionarily conserved molecular mechanisms to survive adverse environmental conditions, including reducing body temperature to ambient levels (often to near 0 °C) and severe metabolic depression. This long-built secret of life lies at the intersection of oxygen, metabolism, and bioenergetics, and hibernating organisms have learned to exploit all the underlying capacities of molecular pathways to survive. This is the story of integrated redox-metabolic orchestration in hibernation.
We demonstrated that the level of phospholipids in the liver mitochondrial fraction is increased by 60% during the winter hibernation season in the Yakut ground squirrel S. undulatus; the phospholipid composition in sleeping animals is characterized by an increase in phosphatidylethanolamine compared with summer animals. A sharp increase in the level of cholesterol, as well as fatty acid, monoglycerides, and diglycerides was found in the mitochondrial fraction of hibernating ground squirrels in relation to summer ground squirrels. Functional changes during hibernation concern the level of phosphatidylserine (the growth in sleeping animals compared with active animals). Seasonal modification of the lipid composition of the liver mitochondria (particularly, an increase in the level of cholesterol) can play a role in the resistance of mitochondria to the seasonal increase in the level of fatty acids in the liver. Lipids of the liver mitochondrial fraction are involved in the ground squirrel adaptation to the hibernation season.
Winter sleep of the ground squirrel Spermophilus undulatus was accompanied by a 20% decrease in phospholipid content (µg phospholipid per 1 mg protein) in microsomal fractions of the liver as compared with summer-active squirrels. The phosphatidylcholine level (mol %) in hibernating squirrels was lower than in summer-active squirrels, and the content of sphingomyelin (mol %) during the torpor bout was higher than in winter- and summer-active squirrels. The cholesterol, fatty acid, monoglyceride, and diglyceride levels in the microsomal fraction of the liver were elevated during hibernation. Pronounced seasonal changes in the lipid/protein ratio implicate the lipids of the liver microsomal fraction in adaptation of the ground squirrel to hibernation.
