Deep Hibernation Research Articles

ECR Spotlight – Fredrik Markussen

ECR Spotlight is a series of interviews with early-career authors from a selection of papers published in Journal of Experimental Biology and aims to promote not only the diversity of early-career researchers (ECRs) working in experimental biology but also the huge variety of animals and physiological systems that are essential for the ‘comparative’ approach. Fredrik Markussen is an author on ‘ c-fos induction in the choroid plexus, tanycytes and pars tuberalis is an early indicator of spontaneous arousal from torpor in a deep hibernator’, published in JEB. Fredrik is a PhD student in the lab of Shona Wood at UiT – Arctic University of Norway, investigating hibernation timer mechanisms in golden hamsters.

C-fos induction in the choroid plexus, tanycytes and pars tuberalis is an early indicator of spontaneous arousal from torpor in a deep hibernator.

Hibernation is an extreme state of seasonal energy conservation, reducing metabolic rate to as little as 1% of the active state. During the hibernation season, many species of hibernating mammals cycle repeatedly between the active (aroused) and hibernating (torpid) states (T-A cycling), using brown adipose tissue (BAT) to drive cyclical rewarming. The regulatory mechanisms controlling this process remain undefined but are presumed to involve thermoregulatory centres in the hypothalamus. Here, we used the golden hamster (Mesocricetus auratus), and high-resolution monitoring of BAT, core body temperature and ventilation rate, to sample at precisely defined phases of the T-A cycle. Using c-fos as a marker of cellular activity, we show that although the dorsomedial hypothalamus is active during torpor entry, neither it nor the pre-optic area shows any significant changes during the earliest stages of spontaneous arousal. Contrastingly, in three non-neuronal sites previously linked to control of metabolic physiology over seasonal and daily time scales - the choroid plexus, pars tuberalis and third ventricle tanycytes - peak c-fos expression is seen at arousal initiation. We suggest that through their sensitivity to factors in the blood or cerebrospinal fluid, these sites may mediate metabolic feedback-based initiation of the spontaneous arousal process.

Automating Polysomnography in an Under-Explored Animal Model: Preliminary Results from Hibernating Bears

Animal hibernation is a hypometabolic state that may inform translational research to improve clinical outcomes for hypoxic patients whose oxygen supply does not match their demand. Bears are an excellent animal model, as they decrease their body temperature to only 30-35°C during hibernation and suppress their metabolism down to 25% of normal resting levels while having a more comparable physiology to humans than deep hibernators such as small rodents. As little is known about their sleep patterns during hibernation, we continuously monitored for more than 3500 days via biotelemetry a variety of physiological parameters from 16 captive American black bears in and out of hibernation. We recorded EEG, EOG and EMG signals that are commonly used to determine wake, REM sleep and NREM sleep vigilance states in conventional animal models (polysomnography). Such a data set is too large to fully annotate manually, so we compared two automated approaches. We first manually annotated two one-day recordings at body temperature extremes from each of 6 bears during hibernation when body temperatures were oscillating widely in multiday cycles with intermittent bouts of shivering (Tøien et al. 2011). We also manually scored a one-day, non-hibernating recording at normal (summer) body temperature from these bears. Based on this reference data set, we evaluated two automated scoring applications based on different machine learning classifiers: open source Somnotate (author Paul Brodersen), which is trained on multiple files, and proprietary Somnivore (author Giancarlo Allocca), which is trained on a subset of epochs from each individual recording. Somnotate gave best results during hold-one-out testing when using separate models for hibernating and non-hibernating data, and then performed comparably for both conditions. Somnivore was by design trained on a small subset (100 epochs of each kind) of each file to be tested. Both applications provided typical F-measures against manual reference scores in the 0.90-0.97 range. Outliers in the lower 0.72-0.88 range were highly correlated between the two applications, indicating that specific files are more challenging to annotate — either manually, automatically, or both. We conclude that both applications have accuracies on par with manual scorers when trained on high quality data. Supported by NIH COBRE under grant number [P20GM130443]. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Sulfide catabolism in hibernation and neuroprotection

The mammalian brain is exquisitely vulnerable to lack of oxygen. However, the mechanism underlying the brain's sensitivity to hypoxia is incompletely understood. In this narrative review, we present a case for sulfide catabolism as a key defense mechanism of the brain against acute oxygen shortage. We will examine literature on the role of sulfide in hypoxia/ischemia, deep hibernation, and leigh syndrome patients, and present our recent data that support the neuroprotective effects of sulfide catabolism and persulfide production. When oxygen levels become low, hydrogen sulfide (H2S) accumulates in brain cells and impairs the ability of these cells to use the remaining, available oxygen to produce energy. In recent studies, we found that hibernating ground squirrels, which can withstand very low levels of oxygen, have high levels of sulfide:quinone oxidoreductase (SQOR) and the capacity to catabolize hydrogen sulfide in the brain. Silencing SQOR increased the sensitivity of the brain of squirrels and mice to hypoxia, whereas neuron-specific SQOR expression prevented hypoxia-induced sulfide accumulation, bioenergetic failure, and ischemic brain injury in mice. Excluding SQOR from mitochondria increased sensitivity to hypoxia not only in the brain but also in heart and liver. Pharmacological agents that scavenge sulfide and/or increase persulfide maintained mitochondrial respiration in hypoxic neurons and made mice resistant to ischemic injury to the brain or spinal cord. Drugs that oxidize hydrogen sulfide and/or increase persulfide may prove to be an effective approach to the treatment of patients experiencing brain injury caused by oxygen deprivation or mitochondrial dysfunction.

An evaluation of the macro anatomy of the Hazel Dormouse’s (Muscardinus avellanarius Linnaeus, 1758) (Rodentia: Mammalia) skeletal system in Türkiye

Muscardinus avellanarius, one of the thirty species of the Gliridae family, is found in areas covered with deciduous forests, with a range stretching from Bursa (Uludağ) to Trabzon in Türkiye. Hazel Dormouse, classified as an endangered species and characterized by their deep hibernation patterns, possess significant value as bioindicators of environmental change. In this study, a macro-anatomical evaluation of the skeletal structure of forty-six specimens collected from the Eastern and Western Black Sea Regions between 1979 and 1983 were conducted. The evaluation revealed that the whole skeleton of Muscardinus avellanarius consisted of 225 bones. The morphometric variances and variations between the Eastern Black Sea and Western Black Sea specimens were detected by defining the skull and baculum bones that hold taxonomic value.

Induction of Hibernation and Changes in Physiological and Metabolic Indices in Pelodiscus sinensis.

Pelodiscus sinensis (P. sinensis) is a commonly cultivated turtle species with a habit of hibernation. To study the changes in histone expression and methylation of P. sinensis during hibernation induction, a model was established by artificial induction. Physiological and metabolic indices were measured, and the expression and localization of histone (H1, H2A, H2B, H3, and H4) and methylation-related genes (ASH2L, KMT2A, KMT2E, KDM1A, KDM1B, and KDM5A) were measured by quantitative PCR, immunohistochemistry, and Western blot analysis. The results indicated that the metabolism, antioxidation index, and relative expression of histone methyltransferase were significantly decreased (p < 0.05), whereas the activity and expression of histone demethyltransferase were significantly increased (p < 0.05). Although our results showed significant changes in physiological and gene expression after hibernation induction, we could not confirm that P. sinensis entered deep hibernation. Therefore, for the state after cooling-induced hibernation, cold torpor might be a more accurate description. The results indicate that the P. sinensis can enter cold torpor through artificial induction, and the expression of histones may promote gene transcription. Unlike histones expressed under normal conditions, histone methylation may activate gene transcription during hibernation induction. Western blot analysis revealed that the ASH2L and KDM5A proteins were differentially expressed in the testis at different months (p < 0.05), which may perform a role in regulating gene transcription. The immunohistochemical localization of ASH2L and KDM5A in spermatogonia and spermatozoa suggests that ASH2L and KDM5A may perform a role in mitosis and meiosis. In conclusion, this study is the first to report changes in histone-related genes in reptiles, which provides insight for further studies on the physiological metabolism and histone methylation regulation of P. sinensis during the hibernation induction and hibernation period.

Exodus

What makes a "religious" holiday? Does the combination of ritual, culture, and family custom all merge together to create "religion?" Does it even matter if the historical basis for religious stories are false? In this work of philosophical short story fiction, the spaceship computer AI wakes up a family in deep space hibernation to give them time to prepare for, and celebrate, Passover. There are many situations unique to being in space that must be overcome; determining the right time period when taking into consideration time dilation, not to mention missing ingredients for traditional foods. Also, they are short two people of the requisite ten and ask the computer AI to "convert" and serve the role of two additional Jewish people. Awkwardly, the computer reminds them that some of their traditional stories are not supported by archeological evidence. This all begs important questions about the complicated weaving of history, faith, culture, and family custom in religious ceremony.

17th Century Dialogue between Art and Science: The effect of the Scientific Contributions of Galileo on Late Renaissance and Baroque Art

After a deep scientific and cultural hibernation throughout the Middle Ages, during which politicized religious domination suppressed the creative freedom of humankind in all areas of life, the European Renaissance in the fifteenth century brought scientific and human prospects and discoveries that played a vital role in enriching culture and art and modernizing their structure and philosophy. This would not have been possible without the help of humanistic scientists and other thinkers who emerged during the Renaissance and the later Baroque era and developed new perspectives including a scientific approach to addressing life’s challenges, exploring them in a spirit that reconciled the holy with the secular. One of the most prominent of those scientists was Galileo Galilei, who is today considered the father of modern science. Galileo was also an artist, and his art incorporated the scientific ideas developed during this time. Among these ideas was the spirit of observation and experimentation, which was incorporated into the studies of nature, the world and the universe. This in turn was reflected in the visions of Renaissance and Baroque artists, whose work was characterized by the desire to simulate reality and to depict it in a simultaneously scientific and human spirit, and of subsequent artistic schools. This study will examine examples of the important works that illustrate the most prominent features of Galileo's influence on visual art - particularly representational art - and the aesthetic value of that influence. Keywords: Galileo, Art, Science, Astronomy , Space .

Regulatory metabolism over the hibernation‐activity cycle changes contribute to the adaptive enhancement of leech ( Whitmania pigra )

Whitmania pigra is an economically important medicinal and aquaculture species in China, but weight greatly reducing during hibernation seriously affects the production efficiency of aquaculture systems. We studied the levels of metabolites, metabolic enzymes in leech intestine in five hibernation-activity states. 1099 and 1766 metabolites were identified. 232 metabolites were up-regulated, and 123 metabolites were down-regulated during deep hibernation, 43 of them decreased and 30 of them increased in active after hibernation. Comprehensive analysis shows that metabolism was repressed globally in hibernation, including glycolysis, TCA, mitochondrial respiratory, which resulted in ATP synthesis decreased. Meanwhile, decreased glycolysis, increased beta-oxidation showed a shift of fuel use from carbohydrates to lipids. During hibernation, beta-oxidation elevated but MDA level remained stable along with glutathione antioxidant system inclined, other adaptive cytoprotection like PUFA elevated and membrane phospholipids remodelled. During arousal, oxidative stress increased, manifested by an increase in glutathione antioxidant system and MDA, which may be due to excessive production of reactive oxygen that accompany metabolism recovery during arousal. By the metabolism analysis in this study, we come closer to fully uncovering the mechanism of leech hibernation that may be applied to prevent pathological stress responses or metabolic dysregulation when interrupting or shortening leech hibernation.

Гистобиохимические признаки апоптоза в тканях сусликов при пробуждении после спячки

Histological preparations of ground squirrel liver, heart and brain tissues were studied in the middle of the hibernation bout (body temperature of 1–4 °C), at self-heating (body temperature of 6–29 °C) and upon complete awakening (body temperature of 37–38 °C). In the state of deep hibernation, no signs of apoptosis were identified in ground squirrel tissues. We observed microcirculatory dysfunction manifested in abnormal blood rheology: acute hyperaemia of brain and myocardial capillaries, central veins and sinusoids of the liver, as well as mild tissue oedema and aggregations of red blood cells (rouleaux) in microvasculature. At self-heating, signs of the initial stage of apoptosis were detected: mild granularity in cardiomyocyte cytoplasm as a sign of protein dystrophy, and mild cytoplasmic vacuolization in hepatocytes. Morphological signs of these processes were revealed upon the animal’s complete awakening. Shrinkage of individual hepatocytes was observed; cells with pyknotic nuclei appeared, which can be explained by the condensation of chromatin and intracellular organelles; cell fragments with karyorrhectic phenomena resembling apoptotic bodies were identified. Thus, no signs of apoptosis were found in ground squirrel tissues during deep hibernation. At self-heating, signs of the initial stage of apoptosis were detected, and only in the state of complete awakening were single hepatocytes and neurons similar to apoptotic bodies identified. In addition, the absence of an inflammatory reaction in the tissues under study allows us to suggest that we are observing the stages of apoptosis. Noteworthy, ground squirrel awakening was accompanied by a significant increase in the activity of lysosomal membrane markers cathepsin D and acid phosphatase.

Torpor expression is associated with differential spermatogenesis in hibernating eastern chipmunks.

Hibernators suppress physiological processes when expressing torpor, yet little is known about the effects of torpor on male reproductive physiology. Studies of hibernating mammals suggest that deep torpor negatively impacts spermatogenesis and that transitions between torpor and euthermic arousals increase cellular oxidative stress, with potentially damaging effects on sperm. Here, we hypothesize that variation in torpor expression affects the reproductive readiness of hibernators by impacting their sperm production. To test this, we examined the relationship between torpor expression and spermatogenesis in captive eastern chipmunks (Tamias striatus). We determined torpor depth with temperature data loggers and assessed its relationship with spermatogenesis by examining spermatogenic progression, cell division, sperm counts, sperm maturity, and DNA damage. We show that deep hibernators (high levels of torpor) largely halted spermatogenesis in late hibernation in comparison with shallow hibernators (low levels of torpor), where ongoing spermatogenesis was observed. Despite these differences in spermatogenic state during hibernation, spermatogenic progression, sperm numbers, and maturity did not differ in spring, potentially reflecting similar degrees of reproductive readiness. Interestingly, shallow hibernators exhibited higher rates of DNA damage in spermatogenic cells during hibernation, with this trend reversing in spring. Our results thus indicate that once heterothermy is terminated, deep hibernators resume spermatogenesis but are characterized by higher rates of DNA damage in spermatogenic cells at the seasonal stage when spring mating commences. Therefore, our study confirmed posthibernation recovery of sperm production but also a potential impact of deep torpor expression during winter on DNA damage in spring.

Proteome and phosphoproteome profiling reveals the regulation mechanism of hibernation in a freshwater leech (Whitmania pigra)

Hibernation is an energy-saving and adaptive strategy adopted by leech, an important medicinal resource in Asia, to survive low temperature. Reversible protein phosphorylation (RPP) plays a key role in the regulation of mammalian hibernation processes but has never been documented in freshwater invertebrate such as leech. In this study, we detected the effects of hibernation on the proteome and phosphoproteome of the leech Whitmania pigra. A total of 2184 proteins and 2598 sites were quantified. Deep-hibernation resulted in 85 up-regulated and 107 down-regulated proteins and 318 up-regulated and 204 down-regulated phosphosites using a 1.5-fold threshold (P<0.05). Proteins involved in protein digestion and absorption, amino acid metabolism and N-glycan biosynthesis were significantly down-regulated during deep-hibernation. However, proteins involved in maintaining cell structure stability in hibernating animals were up-regulated. Differentially phosphorylated proteins provided the first global picture of a shift in energy metabolism, protein synthesis, cytoprotection and signaling during deep hibernation. Furthermore, AMP-activated protein kinase and protein kinase C play major roles in the regulation of these functional processes. These data significantly improve our understanding of the regulatory mechanisms of leech hibernation processes and provides substantial candidate phosphorylated proteins that could be important for functionally adapt in freshwater animals. SignificanceThe leech Whitmania pigra as an important medicinal resource in Asia is an excellent model freshwater invertebrate for studies of environmentally-induced hibernation. The present study provides the first quantitative proteomics and phosphoproteomic analysis of leech hibernation using isobaric tag based TMT labeling and high-resolution mass spectrometry. These data significantly improve our understanding of the regulatory mechanisms when ectotherm animals face environmental stress and provides substantial candidate phosphorylated proteins that could be important for functionally adapt in freshwater animals.

A unified theory of cataclysmic variable evolution from feedback-dominated numerical simulations

The envelopes accreted by white dwarf stars from their hydrogen-rich companions1 experience thermonuclear-powered runaways2,3 observed as classical nova eruptions4,5 peaking at 105–106 solar luminosities6–9. Virtually all nova progenitors—‘nova-like variables’—exhibit high mass transfer rates to their white dwarfs before and after an eruption10. Surprisingly, 10–1,000 times lower mass transfer rate11 binaries, exhibiting accretion-powered ‘dwarf nova’ outbursts12, exist at identical orbital periods. Nova shells surrounding dwarf novae13–16 demonstrate that at least some novae metamorphize into dwarf novae17,18, though the mechanisms and timescales governing mass transfer rate variations are poorly understood. Here, we report simulations of the multi-Gyr evolution of novae modelling every eruption’s thermonuclear runaway, mass and angular momentum losses, feedback due to irradiation and variable mass transfer rate, and orbital size and period changes. These feedback-dominated simulations reproduce the observed range of mass transfer rates at a given orbital period, with large and cyclic kyr–Myr timescale changes. They also demonstrate Myr-long deep hibernation (complete stoppage of mass transfer), but only in short-period binaries; that initially different binaries converge to become nearly identical systems; low-mass-transfer-rate dwarf novae occasionally generate novae; and that the masses of white dwarfs decrease monotonically, but only slightly while their red dwarf companions are consumed. Cataclysmic variables—a binary pairing of a white dwarf and a hydrogen-rich donor star—experience mass transfer and other complex interactions. This numerical simulation by Hillman et al. models in particular the feedback between the stellar pair, and succeeds in reproducing many of the observed characteristics of cataclysmic variables.

Medullary Respiratory Circuit Is Reorganized by a Seasonally-Induced Program in Preparation for Hibernation.

Deep hibernators go through several cycles of profound drops in body temperature during the winter season, with core temperatures sometimes reaching near freezing. Yet unlike non-hibernating mammals, they can sustain breathing rhythms. The physiological processes that make this possible are still not understood. In this study, we focused on the medullary Ventral Respiratory Column of a facultative hibernator, the Syrian hamster. Using shortened day-lengths, we induced a “winter-adapted” physiological state, which is a prerequisite for hibernation. When recording electrophysiological signals from acute slices in the winter-adapted pre-Bötzinger complex (preBötC), spike trains showed higher spike rates, amplitudes, complexity, as well as higher temperature sensitivity, suggesting an increase in connectivity and/or synaptic strength during the winter season. We further examined action potential waveforms and found that the depolarization integral, as measured by the area under the curve, is selectively enhanced in winter-adapted animals. This suggests that a shift in the ion handling kinetics is also being induced by the winter-adaptation program. RNA sequencing of respiratory pre-motor neurons, followed by gene set enrichment analysis, revealed differential regulation and splicing in structural, synaptic, and ion handling genes. Splice junction analysis suggested that differential exon usage is occurring in a select subset of ion handling subunits (ATP1A3, KCNC3, SCN1B), and synaptic structure genes (SNCB, SNCG, RAB3A). Our findings show that the hamster respiratory center undergoes a seasonally-cued alteration in electrophysiological properties, likely protecting against respiratory failure at low temperatures.

A Hibernation-Like State for Transplantable Organs: Is Hydrogen Sulfide Therapy the Future of Organ Preservation?

Renal transplantation is the treatment of choice for end-stage renal disease, during which renal grafts from deceased donors are routinely cold stored to suppress metabolic demand and thereby limit ischemic injury. However, prolonged cold storage, followed by reperfusion, induces extensive tissue damage termed cold ischemia/reperfusion injury (IRI) and puts the graft at risk of both early and late rejection. Recent Advances: Deep hibernators constitute a natural model of coping with cold IRI as they regularly alternate between 4°C and 37°C. Recently, endogenous hydrogen sulfide (H2S), a gas with a characteristic rotten egg smell, has been implicated in organ protection in hibernation. In renal transplantation, H2S also seems to confer cytoprotection by lowering metabolism, thereby creating a hibernation-like environment, and increasing preservation time while allowing cellular processes of preservation of homeostasis and tissue remodeling to take place, thus increasing renal graft survival. Although the underlying cellular and molecular mechanisms of organ protection during hibernation have not been fully explored, mammalian hibernation may offer a great clinical promise to safely cold store and reperfuse donor organs. In this review, we first discuss mammalian hibernation as a natural model of cold organ preservation with reference to the kidney and highlight the involvement of H2S during hibernation. Next, we present recent developments on the protective effects and mechanisms of exogenous and endogenous H2S in preclinical models of transplant IRI and evaluate the potential of H2S therapy in organ preservation as great promise for renal transplant recipients in the future. Antioxid. Redox Signal. 28, 1503-1515.

The impact of hibernation and arousal on energy metabolism and antioxidant defenses in leech (Whitmania pigra)

Whitmania pigra is an important medicinal resource that is widely farmed in aquaculture in Asia, and a decrease in body weight occurring during hibernation and hibernation lasting long time has serious impacts on production efficiency in aquaculture system. We examined energy metabolic and antioxidant enzymes of intestine from a hibernator (W. pigra) over cycles of hibernation-arousal. Results of the study demonstrated that hibernation in W. pigra was characterized by a profound decrease in energy metabolic during deep hibernation that was interrupted by rewarming arousal. And energy metabolic increased significantly during the rewarming arousal. Regulated suppression of energy metabolism probably contributes to energy savings. Oxidative stress decreased during deep hibernation along with a reduction in oxidative metabolism, but increased during entrance into hibernation and arousal from hibernation. This up-regulation of antioxidant defense (AD) during arousal was interpreted as protection of the intestine against oxidative damage to come with the enormous increase in metabolic activity during arousal from hibernation, and the up-regulation of AD during entrance into hibernation was interpreted that leech are exposed to significant stresses (cold acclimation) that must be dealt with appropriately to avoid irreversible tissue damage. It can be concluded that W. pigra has a strong AD system that protects it from the injurious effects of free radicals either during periods of entrance into hibernation and arousal. These results indicate the adaptive mechanism of hibernation that may be applied to increase production efficiency of leech by interrupting or shortening hibernation.

Suspended animation: The Wan Brothers and the (In)animate Mainland-Hong Kong Encounter, 1947–1956

ABSTRACTThe Wan Brothers produced Princess Iron Fan (1941), the first animated feature film in Asia in wartime Shanghai. In order to produce their second animated feature film, The World of Insects, the Wan Brothers went to Hong Kong in the late 1940s and did not go back to Shanghai until the mid-1950s. The Wan Brothers’ encounter with Hong Kong was noneventful and non-spectacular, because the production of The World of Insects was suspended due to the lack of funds and artistic talents in postwar Hong Kong. The Wan Brothers’ sojourn in Hong Kong can be concluded as a period of suspended animation, a state of deep hibernation in history of Chinese animation. If we locate the Wan Brothers’ encounter with Hong Kong in the longue durée, however, we can see that it was still a necessary and important springboard for their later integration into the animation industry in socialist Shanghai and also for the belated emergence of the local animation industry in Hong Kong. The Wan Brothers’ inanimate encounter with Hong Kong would soon be reanimated and would even explode with outbursts of repressed artistic creativities and energies on both sides of the border, despite being belated.

Effects of low temperature on breathing pattern and ventilatory responses during hibernation in the golden-mantled ground squirrel.

During entrance into hibernation in golden-mantled ground squirrels (Callospermophilus lateralis), ventilation decreases as metabolic rate and body temperature fall. Two patterns of respiration occur during deep hibernation. At 7 °C body temperature (T b ), a breathing pattern characterized by episodes of multiple breaths (20.6 ± 1.9 breaths/episode) separated by long apneas or nonventilatory periods (T nvp ) (mean = 11.1 ± 1.2min) occurs, while at 4 °C T b , a pattern in which breaths are evenly distributed and separated by a relatively short T nvp (0.5 ± 0.05min) occurs. Squirrels exhibiting each pattern have similar metabolic rates and levels of total ventilation (0.2 and 0.23ml O2/hr/kg and 0.11 and 0.16ml air/min/kg, respectively). Squirrels at 7 °C T b exhibit a significant hypoxic ventilatory response, while squirrels at 4 °C T b do not respond to hypoxia at any level of O2 tested. Squirrels at both temperatures exhibit a significant hypercapnic ventilatory response, but the response is significantly reduced in the 4 °C T b squirrels. Carotid body denervation has little effect on the breathing patterns or on the hypercapnic ventilatory responses. It does reduce the magnitude and threshold for the hypoxic ventilatory response. Taken together the data suggest that (1) the fundamental rhythm generator remains functional at low temperatures; (2) the hypercapnic ventilatory response arises from central chemoreceptors that remain functional at very low temperatures; (3) the hypoxic ventilatory response arises from both carotid body and aortic chemoreceptors that are silenced at lower temperatures; and (4) there is a strong correlation between breathing pattern and chemosensitivity.

The influence of sex and diet on the characteristics of hibernation in Syrian hamsters

Research on deep hibernators almost exclusively uses species captured from the wild or from local breeding. An exception is Syrian hamster (Mesocricetus auratus), the only standard laboratory animal showing deep hibernation. In deep hibernators, several factors influence hibernation quality, including body mass, sex and diet. We examined hibernation quality in commercially obtained Syrian hamsters in relation to body mass, sex and a diet enriched in polyunsaturated fatty acids. Animals (M/F:30/30, 12 weeks of age) were obtained from Harlan (IN, USA) and individually housed at 21 °C and L:D 14:10 until 20 weeks of age, followed by L:D 8:16 until 27 weeks. Then conditions were changed to 5 °C and L:D 0:24 for 9 weeks to induce hibernation. Movement was continuously monitored with passive infrared detectors. Hamsters were randomized to control diet or a diet 3× enriched in linoleic acid from 16 weeks of age. Hamsters showed a high rate of premature death (n = 24, 40%), both in animals that did and did not initiate torpor, which was unrelated to body weight, sex and diet. Time to death (31.7 ± 3.1 days, n = 12) or time to first torpor bout (36.6 ± 1.6 days, n = 12) was similar in prematurely deceased hamsters. Timing of induction of hibernation and duration of torpor and arousal was unaffected by body weight, sex or diet. Thus, commercially obtained Syrian hamsters subjected to winter conditions showed poor survival, irrespective of body weight, sex and diet. These factors also did not affect hibernation parameters. Possibly, long-term commercial breeding from a confined genetic background has selected against the hibernation trait.

Heart rate dynamics in a marsupial hibernator.

The eastern pygmy possum (Cercartetus nanus) is a small marsupial that can express spontaneous short bouts of torpor, as well as multi-day bouts of deep hibernation. To examine heart rate (fH) control at various stages of torpor in a marsupial hibernator, and to see whether fH variability differs from that of deep placental hibernators, we used radiotelemetry to measure ECG and body temperature (Tb) while measuring the rate of O2 consumption and ventilation. fH and O2 consumption rate during euthermia were at a minimum (321±34 beats min-1, 0.705±0.048 ml O2 g-1 h-1) at an ambient temperature (Ta) of 31°C. fH had an inverse linear relationship with Ta to a maximum of 630±19 beats min-1 at a Ta of 20°C. During entry into torpor at a Ta of 20°C, fH slowed primarily as a result of episodic periods of cardiac activity where electrical activity of the heart occurred in groups of 3 or 4 heart beats. When Tb was stable at 24°C in these torpor bouts, the episodic nature of fH had disappeared (i.e. no asystoles) with a rate of 34±3 beats min-1 For multi-day bouts of deep torpor, Ta was lowered to 6.6±0.8°C. During these deep bouts of torpor, Tb reached a minimum of 8.0±1.0°C, with a minimum fH of 8 beats min-1 and a minimum O2 consumption rate of 0.029±0.07 ml O2g-1h-1 Shivering bouts occurred in deep torpor about every 8 min, during which ventilation occurred, and fH was elevated to 40 beats min-1 The duration of the QRS complex increased from 12 ms during euthermia to 69 ms at a Tb of 8°C. These findings demonstrate the dynamic functioning range of fH to be about 600 beats min-1 (∼80-fold), one of the largest known ranges in mammals. Our study shows that despite a separation of ∼160 million years, the control and function of the cardiac system seems indistinguishable in marsupial and placental hibernating mammals.