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<div>Although traditionally reserved for "deep" hibernators such as rodents, the term has been redefined to include animals such as bears[1] and is now applied based on active metabolic suppression rather than any absolute decline in body temperature. Many experts believe that the processes of daily torpor and hibernation form a continuum and utilise similar mechanisms.[2][3] The equivalent during the summer months is aestivation.</div><div></div><div></div><div></div><div></div><div></div><div>hibernator apk</div><div></div><div>N+AN+ADownload Zip: https://t.co/r4YXjGbZZL N+AN+A</div><div></div><div></div><div>Obligate hibernators are animals that spontaneously, and annually, enter hibernation regardless of ambient temperature and access to food. Obligate hibernators include many species of ground squirrels, other rodents, mouse lemurs, European hedgehogs and other insectivores, monotremes, and marsupials.[citation needed] These species undergo what has been traditionally called "hibernation": a physiological state wherein the body temperature drops to near ambient temperature, and heart and respiration rates slow drastically.</div><div></div><div></div><div>The typical winter season for obligate hibernators is characterized by periods of torpor interrupted by periodic, euthermic arousals, during which body temperatures and heart rates are restored to more typical levels. The cause and purpose of these arousals is still not clear; the question of why hibernators may return periodically to normal body temperatures has plagued researchers for decades, and while there is still no clear-cut explanation, there are multiple hypotheses on the topic. One favored hypothesis is that hibernators build a "sleep debt" during hibernation, and so must occasionally warm up to sleep. This has been supported by evidence in the Arctic ground squirrel.[11] Other theories postulate that brief periods of high body temperature during hibernation allow the animal to restore its available energy sources[12] or to initiate an immune response.[13]</div><div></div><div></div><div>Facultative hibernators enter hibernation only when either cold-stressed, food-deprived, or both, unlike obligate hibernators, who enter hibernation based on seasonal timing cues rather than as a response to stressors from the environment.</div><div></div><div></div><div>A good example of the differences between these two types of hibernation can be seen in prairie dogs. The white-tailed prairie dog is an obligate hibernator, while the closely related black-tailed prairie dog is a facultative hibernator.[15]</div><div></div><div></div><div>Hibernating bears are able to recycle their proteins and urine, allowing them to stop urinating for months and to avoid muscle atrophy.[21][22][23][24] They stay hydrated with the metabolic fat that is produced in sufficient quantities to satisfy the water needs of the bear. They also do not eat or drink while hibernating, but live off their stored fat.[25] Despite long-term inactivity and lack of food intake, hibernating bears are believed to maintain their bone mass and do not suffer from osteoporosis.[26][27] They also increase the availability of certain essential amino acids in the muscle, as well as regulate the transcription of a suite of genes that limit muscle wasting.[28]A study by G. Edgar Folk, Jill M. Hunt and Mary A. Folk compared EKG of typical hibernators to three different bear species with respect to season, activity and dormancy, and found that the reduced relaxation (QT) interval of small hibernators was the same for the three bear species. They also found the QT interval changed for both typical hibernators and the bears from summer to winter. This 1977 study was one of the first evidences used to show that bears are hibernators.[29]</div><div></div><div></div><div>Abstract:Mitochondrial failure is recognized to play an important role in a variety of diseases. We previously showed hibernating species to have cell-autonomous protective mechanisms to resist cellular stress and sustain mitochondrial function. Here, we set out to detail these mitochondrial features of hibernators. We compared two hibernator-derived cell lines (HaK and DDT1MF2) with two non-hibernating cell lines (HEK293 and NRK) during hypothermia (4 C) and rewarming (37 C). Although all cell lines showed a strong decrease in oxygen consumption upon cooling, hibernator cells maintained functional mitochondria during hypothermia, without mitochondrial permeability transition pore (mPTP) opening, mitochondrial membrane potential decline or decreased adenosine triphosphate (ATP) levels, which were all observed in both non-hibernator cell lines. In addition, hibernator cells survived hypothermia in the absence of extracellular energy sources, suggesting their use of an endogenous substrate to maintain ATP levels. Moreover, hibernator-derived cells did not accumulate reactive oxygen species (ROS) damage and showed normal cell viability even after 48 h of cold-exposure. In contrast, non-hibernator cells accumulated ROS and showed extensive cell death through ferroptosis. Understanding the mechanisms that hibernators use to sustain mitochondrial activity and counteract damage in hypothermic circumstances may help to define novel preservation techniques with relevance to a variety of fields, such as organ transplantation and cardiac arrest.Keywords: hibernation; mitochondria; ischemia-reperfusion; hypothermia; reactive oxygen species; ferroptosis</div><div></div><div></div><div>Alpine marmots belong to the fat-storing hibernators that cease to forage prior to hibernation in fall (Dark 2005). This is true for a majority of species, while fewer hibernators continue to take up food over winter. During hibernation, marmots live on body energy stores alone, i.e., for more than half a year. However, some hibernators rely on body energy reserves for a full year or even somewhat longer (Geiser 2007; Hoelzl et al. 2015).</div><div></div><div></div><div>However, a seasonal switch in food uptake seems particularly important as it creates a potential conflict. On one hand, hibernators must gain large body fat reserves to sustain maintenance for several months. This requires a digestive system that is large and efficient enough to acquire a surplus of energy. On the other hand, large alimentary organs may create an elevated BMR, which counteracts possible energy savings, at least in normothermic animals. In the present study, we investigate if and how much alimentary and other organs contribute to energy expenditure in alpine marmots. We hypothesized that marmots would sustain large digestive organs only in summer and fall, when they gain energy reserves. This temporal limitation should result in large changes of the size and mass of the alimentary tract, and result in corresponding changes of BMR.</div><div></div><div></div><div></div><div></div><div></div><div></div><div>Due to these constraints, one could argue that hibernators should only incorporate just sufficient energy to survive a future shortage. However, large fat stores are also used for an early hibernation onset and to minimize the time spent a very low body temperature during hibernation (Bieber et al. 2014; Hoelzl et al. 2015; Zervanos et al. 2014). Hence, it has been suggested that hibernation has not only advantages but also risks and drawbacks (Humphries et al. 2003). However, the cost of having large body fat reserves and an initially high body mass is still much smaller than the benefits of hibernation in terms of energy savings.</div><div></div><div></div><div>The yearly cycle of fat gain and loss is typical for hibernators relying on body energy stores and particularly for sciurids, such as the alpine marmot (Dark 2005). Marmots and ground squirrels typically emerge from hibernation with substantial body fat reserves that are used up during reproduction, which seems common in large hibernators (Huang and Morton 1976; Morton 1975). The later the marmots were trapped in April, the lower were their fat reserves (Fig. 1). However, WAT increased again in the second half of the year, and adults in the present study increased body mass from spring to fall by 68%, which is quite typical (Dark 2005).</div><div></div><div></div><div>Fattening in hibernators usually involves hyperphagia, and the orexigenic hormone ghrelin reaches peak values during the fattening period in fall (Florant and Healy 2011). Besides ghrelin, changes in circulating leptin and insulin, as well as in nutrients (glucose, and free fatty acids), and cellular enzymes such as AMP-activated protein kinase (AMPK) determine the activity of neurons involved in the food intake pathway. Importantly, during the fattening phase, hibernators become temporarily insensitive towards leptin, the hormone that normally signals white fat content and limits lipid uptake and deposition. In hibernators, leptin can be temporarily disassociated from adiposity (review in Jastroch et al. 2016). As outlined in Dark (2005), this seasonal change in lipid content is programmed and part of the circannual cycle. For example, ground squirrels quickly recover from the surgical excision of a substantial amount of WAT (Dark et al. 1984), and temporary food restriction does not prevent projected increases in body mass (Barnes and Mrosovsky 1974). It seems unlikely that the yearly cycle in fattening and fat loss is governed by photoperiod. As outlined by Davis (1976), various lengths of photoperiod or changes of photoperiod throughout the year have failed to cause animals to enter torpor or to undergo the seasonal changes typical for hibernators. There are only a few exceptions of hibernators in which photoperiod seems to play a role (e.g., Darrow et al. 1986). Many hibernators kept in constant conditions showed a cycle of about 11 months (Pengelley and Fisher 1961). Thus, the consumption of food apparently follows an annual rhythm (Davis 1976). This circannual rhythm may involve the expression of deiodinase (DIO2) in the tanycytes adjacent to the third ventricle of the brain. As reviewed by Jastroch et al. (2016), there is evidence to suggest that tanycytes mediate seasonal responses in food intake and body weight. These cells are able to receive metabolic information from the cerebrospinal fluid and the blood, and have been identified as major players in the seasonal control of energetic states in mammal and apparently have an important role in seasonal anorexia (Junkins et al. 2022; Bolborea and Langlet 2021).</div><div></div><div> dca57bae1f</div>
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