Hibernation Season Research Articles

Antioxidant system in Uromastyx philbyi during hibernation and activity periods

AbstractHibernation is an extreme physiological state characterized by profound decreases in oxidative metabolism and body temperature during bouts of prolonged torpor, interrupted by brief periods of arousal with sudden increases in oxidative metabolism, with alterations in antioxidant defenses. We monitored the activities of antioxidant enzymes and oxidative stress during hibernation and activity in Uromastyx philbyi. 20 animals were used, 10 of which were collected in the hibernation season (group I) and the other 10 collected during the active period (group II). Blood, liver, brown adipose tissue (BAT) and brain samples were used to determine free radical and antioxidant levels. The results indicated a significant decrease of free radicals and increase of vitamin C, especially in serum during hibernation. In contrast, during the active period free radicals, enzymatic antioxidants as glutathione peroxidase (GPX), glutathione reductase (GR), superoxide dismutase (SOD) and catalase (CAT) and non-enzymatic antioxidants as reduce glutathione (GSH) and vitamin E increased in all studied tissues. It can be concluded that Uromastyx philbyi has a strong antioxidant defense system that protects it from the injurious effects of free radicals either at the periods of arousal or during activity periods.

Temporal dynamics of the cecal gut microbiota of juvenile arctic ground squirrels: a strong litter effect across the first active season.

Arctic ground squirrels (Urocitellus parryii) are active for a scant 3 to 5 months of the year. During the active season, adult squirrels compete for mates, reproduce, and fatten in preparation for hibernation, while juvenile squirrels, weaned in early July, must grow and acquire sufficient fat to survive their first hibernation season. During hibernation, the gut microbial community is altered in diversity, abundance, and activity. To date, no studies have examined the gut microbiota of hibernators across the truncated active season. We characterized trends in diversity (454 pyrosequencing), density (flow cytometry), viability (flow cytometry), and metabolism (short-chain fatty acid analysis) of the gut microbial community of juvenile arctic ground squirrels across their first active season at weaning and at 4, 6, 8, and 10 weeks postweaning. At 8 weeks postweaning, the mean bacterial density was significantly higher than that at weaning, and the mean percentage of live bacteria was significantly higher than that at either weaning or 4 weeks postweaning. No significant differences in microbial diversity, total short-chain fatty acid concentrations, or molar proportions of individual short-chain fatty acids were observed among sample periods. The level of variability in gut microbial diversity among squirrels was high across the active season but was most similar among littermates, except at weaning, indicating strong maternal or genetic influences across development. Our results indicate that genetic or maternal influences exert profound effects on the gut microbial community of juvenile arctic ground squirrels. We did not find a correlation between host adiposity and gut microbial diversity during prehibernation fattening, likely due to a high level of variability among squirrels.

Transcriptomic analysis of brown adipose tissue across the physiological extremes of natural hibernation.

We used RNAseq to generate a comprehensive transcriptome of Brown Adipose Tissue (BAT) over the course of a year in the naturally hibernating thirteen-lined ground squirrel, Ictidomys tridecemlineatus. During hibernation ground squirrels do not feed and use fat stored in White Adipose Tissue (WAT) as their primary source of fuel. Stored lipid is consumed at high rates by BAT to generate heat at specific points during the hibernation season. The highest rate of BAT activity occurs during periodic arousals from hypothermic torpor bouts, referred to as Interbout Arousals (IBAs). IBAs are characterized by whole body re-warming (from 5 to 37 °C) in 2-3 hours, and provide a unique opportunity to determine the genes responsible for the highly efficient lipid oxidation and heat generation that drives the arousal process. Illumina HighSeq sequencing identified 14,573 distinct BAT mRNAs and quantified their levels at four points: active ground squirrels in April and October, and hibernating animals during both torpor and IBA. Based on significant changes in mRNA levels across the four collection points, 2,083 genes were shown to be differentially expressed. In addition to providing detail on the expression of nuclear genes encoding mitochondrial proteins, and genes involved in beta-adrenergic and lipolytic pathways, we identified differentially expressed genes encoding various transcription factors and other regulatory proteins which may play critical roles in high efficiency fat catabolism, non-shivering thermogenesis, and transitions into and out of the torpid state.

Body mass dependent use of hibernation: why not prolong the active season, if they can?

Summary Hibernation is the most effective means for energy conservation during winter in mammals. The drawbacks of deep and prolonged torpor include reduced immunocompetence, and consequently, hibernators should be selected to minimize torpor expression when climatic conditions or energy availability (e.g. food or fat stores) permit. Therefore, it seems surprising that some hibernators employ extraordinary long hibernation seasons, lasting well beyond periods with unfavourable conditions. Because of their extended use of torpor, edible dormice (Glis glis) provide an ideal model for scrutinizing interactions between energy reserves (i.e. body fat stores) and thermoregulatory patterns. We used a multimodel inference approach to analyse body temperature data (i.e. use of torpor) from 42 entire hibernation seasons over 4 years in females in relation to body mass. Body mass prior to hibernation did not affect the duration of the hibernation season, but animals hibernated for c. 8 months, that is, 2 months longer than required by environmental conditions. Fatter individuals aroused significantly more often, had a higher mean minimum body temperature during torpor and remained euthermic for longer periods than leaner animals. Surplus energy was therefore not used to shorten the hibernation season, but to rewarm more frequently, and to allow shallower torpor bouts. These adjustments apparently serve to avoid negative effects of torpor and, perhaps equally importantly, to minimize the time active above‐ground. We argue that maintaining a short active season, despite surplus energy reserves, may be explained by known beneficial effects of hibernation on survival rates (via predator avoidance). Our data provide quantitative evidence that hibernation is a flexible tool within life‐history strategies. We conclude that, apart from energetic necessities due to harsh environmental conditions, predator avoidance may be an important factor influencing patterns of hibernation and torpor in mammals. Thus, our study indicates that climatic conditions alone are not a good predictor of hibernation patterns or survival in hibernating species during global climate change.

Torpor in the Patagonian opossum (Lestodelphys halli): implications for the evolution of daily torpor and hibernation

Hibernation and daily torpor are two distinct forms of torpor, and although they are related, it is not known how and in which sequence they evolved. As the pattern of torpor expressed by the oldest marsupial order the opossums (Didelphimorphia) may provide insights into the evolution of torpor, we aimed to provide the first quantitative data on the thermal biology and torpor expression of the rare Patagonian opossum (Lestodelphys halli). It is the opossum with the southernmost distribution, has a propensity of autumnal fattening, and therefore, is likely to hibernate. We captured two male Lestodelphys, which while in captivity displayed strong daily fluctuations of body temperatures (Tb) measured with implanted miniature data loggers even when they remained normothermic. In autumn and early winter, torpor was expressed occasionally when food was available, but cold exposure and food withdrawal increased torpor use. The mean Tb throughout the study was 32.2 ± 1.4 °C, the minimum Tb measured in torpid Lestodelphys was 7.7 °C, average torpor bout duration was 10.3 h, and the maximum torpor bout duration was 42.5 h. Thus, the pattern of torpor expressed by Lestodelphys was intermediate between that of daily heterotherms and hibernators suggesting that it may represent an ancestral opportunistic torpor pattern from which the derived patterns of daily torpor and seasonal hibernation diverged.

Non-invasive genetics can help find rare species: a case study with Rhinolophus mehelyi and R. euryale (Rhinolophidae: Chiroptera) in Western Europe

AbstractThe reliability of species identification is of primary importance as much of biodiversity studies, ecology, legislation, and conservation are based on this taxonomic level. Species identification problems can obscure the conservation status, especially for rare and endangered species, which are of special concern for conservation. This problem is especially significant for some taxonomic groups such as chiropterans, as many monitoring programs are run during the hibernation season when animals should not be disturbed, hence not handled. In the present study, we used

The impact of cold acclimation and hibernation on antioxidant defenses in the ground squirrel (Spermophilus citellus): An update

Any alteration in oxidative metabolism is coupled with a corresponding response by an antioxidant defense (AD) in appropriate subcellular compartments. Seasonal hibernators pass through circannual metabolic adaptations that allow them to either maintain euthermy (cold acclimation) or enter winter torpor with body temperature falling to low values. The present study aimed to investigate the corresponding pattern of AD enzyme protein expressions associated with these strategies in the main tissues involved in whole animal energy homeostasis: brown and white adipose tissues (BAT and WAT, respectively), liver, and skeletal muscle. European ground squirrels (Spermophilus citellus) were exposed to low temperature (4 ± 1°C) and then divided into two groups: (1) animals fell into torpor (hibernating group) and (2) animals stayed active and euthermic for 1, 3, 7, 12, or 21 days (cold-exposed group). We examined the effects of cold acclimation and hibernation on the tissue-dependent protein expression of four enzymes which catalyze the two-step detoxification of superoxide to water: superoxide dismutase 1 and 2 (SOD 1 and 2), catalase (CAT), and glutathione peroxidase (GSH-Px). The results showed that hibernation induced an increase of AD enzyme protein expressions in BAT and skeletal muscle. However, AD enzyme contents in liver were largely unaffected during torpor. Under these conditions, different WAT depots responded by elevating the amounts of specific enzymes, as follows: SOD 1 in retroperitoneal WAT, GSH-Px in gonadal WAT, and CAT in subcutaneous WAT. Similar perturbations of AD enzymes contents were seen in all tissues during cold acclimation, often in a time-dependent manner. It can be concluded that BAT and muscle AD capacity undergo the most dramatic changes during both cold acclimation and hibernation, while liver is relatively unaffected by either condition. Additionally, this study provides a basis for further metabolic study that will illuminate the causes of these tissue-specific AD responses, particularly the novel finding of distinct responses by different WAT depots in hibernators.

Circannual Rhythm in Body Temperature, Torpor, and Sensitivity to A1 Adenosine Receptor Agonist in Arctic Ground Squirrels

A₁ adenosine receptor (A₁AR) activation within the central nervous system induces torpor, but in obligate hibernators such as the arctic ground squirrel (AGS; Urocitellus parryii), A₁AR stimulation induces torpor only during the hibernation season, suggesting a seasonal increase in sensitivity to A₁AR signaling. The purpose of this research was to investigate the relationship between body temperature (Tb) and sensitivity to an adenosine A1 receptor agonist in AGS. We tested the hypothesis that increased sensitivity in A₁AR signaling would lead to lower Tb in euthermic animals during the hibernation season when compared with the summer season. We further predicted that if a decrease in euthermic Tb reflects increased sensitivity to A₁AR activation, then it should likewise predict spontaneous torpor. We used subcutaneous IPTT-300 transponders to monitor Tb in AGS housed under constant ambient conditions (12:12 L:D, 18 °C) for up to 16 months. These animals displayed an obvious rhythm in euthermic Tb that cycled with a period of approximately 8 months. Synchrony in the Tb rhythm within the group was lost after several months of constant L:D conditions; however, individual rhythms in Tb continued to show clear sine wave-like waxing and waning. AGS displayed spontaneous torpor only during troughs in euthermic Tb. To assess sensitivity to A₁AR activation, AGS were administered the A₁AR agonist N(6)-cyclohexyladenosine (CHA, 0.1 mg/kg, ip), and subcutaneous Tb was monitored. AGS administered CHA during a seasonal minimum in euthermic Tb showed a greater drug-induced decrease in Tb (1.6 ± 0.3 °C) than did AGS administered CHA during a peak in euthermic Tb (0.4 ± 0.3 °C). These results provide evidence for a circannual rhythm in Tb that is associated with increased sensitivity to A₁AR signaling and correlates with the onset of torpor.

THE EFFECTS OF THE ANNUAL CYCLE ON UROMASTYXACANTHINURA (BELL, 1825)UTERUS STRUCTURE AND FUNCTIONS.

This study describes the effects of the annual cycle on the structure and functions of uterus of Uromastyx acanthinura (Bell, 1825) (hibernation and activity seasons). The results revealed that, histological sections in uterus of U. acanthinura during hibernation season showed considerable atrophy and degeneration of the glandular region, comparedto nearly normal structure and less atrophied glandular mucosa after hibernation. The expression of protein bands and their concentration markedly decreased during hibernation season and increased during activity season. Genomic DNA showed apparent separation during hibernation. Also, caspase3 and caspase7 activity reached high levels in the uterus tissue during hibernation compared to activity season.

Seasonal variation in telomere length of a hibernating rodent

Small hibernating rodents have greater maximum lifespans and hence appear to age more slowly than similar-sized non-hibernators. We tested for a direct effect of hibernation on somatic maintenance and ageing by measuring seasonal changes in relative telomere length (RTL) in the edible dormouse Glis glis. Average RTL in our population did not change significantly over the hibernation season, and a regression model explaining individual variation in post-hibernation RTL suggested a significant negative effect of the reduction in body mass over the inactive hibernation period (an index of time spent euthermic), supporting the idea that torpor slows ageing. Over the active season, RTL on average decreased in sub-adults but increased in adults, supporting previous findings of greater telomere shortening at younger ages. Telomere length increase might also have been associated with reproduction, which occurred only in adults. Our study reveals how seasonal changes in physiological state influence the progress of life-history traits, such as somatic maintenance and ageing, in a small hibernating rodent.

Differential Expression of Toll‐like Receptors in the Cecum of Hibernating Ground Squirrels

Mammalian hibernation is a response to periods of low temperature and limited food availability. The GI tract of hibernators undergoes significant physiological changes. Recent studies have found shifts in the microbial populations inhabiting the cecum during hibernation. We used immunoblotting to examine the expression of Toll‐like receptors (TLRs) in the cecum of summer, hibernating and spring ground squirrels. TLR4 expression decreased during the hibernation season with the lowest levels found in squirrels that had been hibernating at least 3 months (late‐season hibernators). TLR5 expression showed the opposite trend with increased expression in late‐season hibernators compared to summer. Levels of TLR5 in spring squirrels were similar to summer, but TLR4 was similar to late‐season hibernators. Expression of both TLRs did not differ between torpid and aroused hibernators at the same point in the season (early versus late). Together, these results suggest that hibernation induces changes in microbial sensing, perhaps as a result of increased permeability of the GI epithelium and shifts in the composition of the microbiota. Supported by UW‐Oshkosh Student‐Faculty Collaborative Grant Program.

Seasonal and Regional Differences in Gene Expression in the Brain of a Hibernating Mammal

Mammalian hibernation presents a unique opportunity to study naturally occurring neuroprotection. Hibernating ground squirrels undergo rapid and extreme physiological changes in body temperature, oxygen consumption, and heart rate without suffering neurological damage from ischemia and reperfusion injury. Different brain regions show markedly different activity during the torpor/arousal cycle: the cerebral cortex shows activity only during the periodic returns to normothermia, while the hypothalamus is active over the entire temperature range. Therefore, region-specific neuroprotective strategies must exist to permit this compartmentalized spectrum of activity. In this study, we use the Illumina HiSeq platform to compare the transcriptomes of these two brain regions at four collection points across the hibernation season: April Active, October Active, Torpor, and IBA. In the cerebral cortex, 1,085 genes were found to be differentially expressed across collection points, while 1,063 genes were differentially expressed in the hypothalamus. Comparison of these transcripts indicates that the cerebral cortex and hypothalamus implement very different strategies during hibernation, showing less than 20% of these differentially expressed genes in common. The cerebral cortex transcriptome shows evidence of remodeling and plasticity during hibernation, including transcripts for the presynaptic cytomatrix proteins bassoon and piccolo, and extracellular matrix components, including laminins and collagens. Conversely, the hypothalamic transcriptome displays upregulation of transcripts involved in damage response signaling and protein turnover during hibernation, including the DNA damage repair gene RAD50 and ubiquitin E3 ligases UBR1 and UBR5. Additionally, the hypothalamus transcriptome also provides evidence of potential mechanisms underlying the hibernation phenotype, including feeding and satiety signaling, seasonal timing mechanisms, and fuel utilization. This study provides insight into potential neuroprotective strategies and hibernation control mechanisms, and also specifically shows that the hibernator brain exhibits both seasonal and regional differences in mRNA expression.

Inhibition of NMDA‐type glutamate receptors induces arousal from torpor in hibernating arctic ground squirrels (Urocitellus parryii)

Hibernation is an adaptation to overcome periods of resource limitation often associated with extreme climatic conditions. The hibernation season consists of prolonged bouts of torpor that are interrupted by brief interbout arousals. Physiological mechanisms regulating spontaneous arousals are poorly understood, but may be related to a need for gluconeogenesis or elimination of metabolic wastes. Glutamate is derived from glutamine through the glutamate-glutamine cycle and from glucose via the pyruvate carboxylase pathway when nitrogen balance favors formation of glutamine. This study tests the hypothesis that activation of NMDA-type glutamate receptors (NMDAR) maintains torpor in arctic ground squirrel (arctic ground squirrel (AGS); Urocitellus parryii). Administration of NMDAR antagonists MK-801 (5 mg/kg, i.p.) that crosses the blood-brain barrier and AP5 (5 mg/kg, i.p.) that does not cross the blood-brain barrier induced arousal in AGS. Central administration of MK-801 (0.2, 2, 20 or 200 μg; icv) to hibernating AGS failed to induce arousal. Results suggest that activation of NMDAR at a peripheral or circumventricular site is necessary to maintain prolonged torpor and that a decrease in glutamate at these sites may contribute to spontaneous arousal in AGS.

Frequent Arousal from Hibernation Linked to Severity of Infection and Mortality in Bats with White-Nose Syndrome

White-nose syndrome (WNS), an emerging infectious disease that has killed over 5.5 million hibernating bats, is named for the causative agent, a white fungus (Geomyces destructans (Gd)) that invades the skin of torpid bats. During hibernation, arousals to warm (euthermic) body temperatures are normal but deplete fat stores. Temperature-sensitive dataloggers were attached to the backs of 504 free-ranging little brown bats (Myotis lucifugus) in hibernacula located throughout the northeastern USA. Dataloggers were retrieved at the end of the hibernation season and complete profiles of skin temperature data were available from 83 bats, which were categorized as: (1) unaffected, (2) WNS-affected but alive at time of datalogger removal, or (3) WNS-affected but found dead at time of datalogger removal. Histological confirmation of WNS severity (as indexed by degree of fungal infection) as well as confirmation of presence/absence of DNA from Gd by PCR was determined for 26 animals. We demonstrated that WNS-affected bats aroused to euthermic body temperatures more frequently than unaffected bats, likely contributing to subsequent mortality. Within the subset of WNS-affected bats that were found dead at the time of datalogger removal, the number of arousal bouts since datalogger attachment significantly predicted date of death. Additionally, the severity of cutaneous Gd infection correlated with the number of arousal episodes from torpor during hibernation. Thus, increased frequency of arousal from torpor likely contributes to WNS-associated mortality, but the question of how Gd infection induces increased arousals remains unanswered.

Neuroprotection supports signal processing in the hippocampus of Syrian hamsters, a facultative hibernator

Studies on several species of mammalian seasonal hibernators (those hibernating only in winter) show that their neurons are more tolerant to hypoxia than those in non-hibernating species. Such tolerance has not been studied in facultative hibernators [e.g., Syrian hamsters (Mesocricetus auratus)], which can hibernate at any time of year. We tested the hypotheses that, when exposed to hypoxia, hamster hippocampal pyramidal cells more effectively support signal processing than do rat hippocampal neurons and this protection is enhanced in slices from hibernating versus non-hibernating hamsters and as temperature decreases. Population spike amplitudes (PSAs) were recorded from CA1 pyramidal cells. Slices were perfused in oxygenated artificial cerebral spinal fluid (O2ACSF) to establish a baseline. Oxygen was then replaced by nitrogen (N2ACSF) for 15min, followed by a 30-min recovery period in O2ACSF. Three minutes after slices were returned to O2ACSF, PSAs recovered to 62.4±6.8% of baseline in 15 slices from 8 non-hibernating hamsters but only to 22.7±5.6% in 17 slices from 5 rats. Additionally, PSA recovery was greater in slices from hibernating than non-hibernating hamsters and recovery increased as temperature decreased. These significant differences (P≤0.05) suggest Syrian hamsters are a useful model for studying naturally occurring neuroprotective mechanisms.

Resistance to multi organ damage after hemorrhagic shock induced ischemia/reperfusion in arctic ground squirrels

During hemorrhagic shock (HS), the body undergoes global ischemia as blood pressure drops below the threshold at which tissues can be adequately perfused. Resistance to ischemia/reperfusion (I/R) injury is a characteristic of hibernating mammals. The present study sought to determine if arctic ground squirrels (AGS) are protected from HS induced I/R and if any protection is dependent upon their hibernation season. Rats, euthermic AGS, and interbout arousal AGS were subject to HS by withdrawing blood to a mean arterial blood pressure (MAP) of 35 mmHg. Low MAP was maintained for 20 min and then the animals were reperfused with Ringers. The animals’ temperature was maintained at 36.5–37.5 °C. After reperfusion, animals were monitored for 3 hrs then tissues and blood were collected for histopathology, clinical chemistries, and cytokine level analysis. In addition, a group rats and AGS were monitored for three days after HS to access survival and physiological impairment. AGS were able to survive three days beyond HS with no impairment noticeable after 12 hrs whereas rats did not survive to 12 hrs. Regardless of season, blood chemistries indicate no organ damage in the ground squirrel while the rat showed signs of liver damage. In addition, both winter and summer AGS had a lower cytokine response after HS than did rats. Funded by USAMRMC W81XWH009‐2‐0134.

Metabolism during winter in a subtropical hibernating bat, the Formosan leaf-nosed bat (Hipposideros terasensis)

The 60-g subtropical Formosan leaf-nosed bat, Hipposideros terasensis, hibernates in the wild at warm roost (and hence body) temperatures up to 23°C. For small hibernators, torpid metabolic rate is temperature dependent and thus hibernation in warm hibernacula is predicted to be energetically costly. This species, however, rarely feeds during the hibernation season to offset the expected high energetic costs. In this study we used a respirometry system to quantify physiological characteristics of euthermic and torpid H. terasensis in winter. We tested the hypothesis that H. terasensis exhibits metabolic inhibition during torpor. Our results showed that H. terasensis saved 94.6% energy by using torpor at air temperatures of 15°C, compared with its euthermic metabolic rate at that air temperature. Torpor metabolic rate declined with declining air temperature to around 14°C, but then increased at lower air temperatures of 10–14°C. Above 14°C, the slope of − 13.0°K ± 1.4°K between metabolic rates and body temperatures in an Arrhenius plot (or Q10 = 4.4) suggests that, in addition to direct temperature effects, H. terasensis exhibited metabolic inhibition during torpor. A model used to evaluate energy expenditure of H. terasensis showed that at 20°C and 23°C a 55-g bat needs 194 kJ (4.9 g fat) and 273.2 kJ (6.9 g fat), respectively, to survive a 70-day hibernation period.

Resistance to cerebral ischemia/reperfusion injury in the Arctic Ground Squirrel (Urocitellus parryii) does not depend on the hibernation season

Event Abstract Back to Event Resistance to cerebral ischemia/reperfusion injury in the Arctic Ground Squirrel (Urocitellus parryii) does not depend on the hibernation season Kelly L. Drew1* and Jeanette T. Moore1 1 University of Alaska Fairbanks, Alaska Basic Neuroscience Program, Institute of Arctic Biology, United States Each year, 15 million people suffer stroke worldwide. Of these, 5 million die and another 5 million are permanently disabled. The arctic ground squirrel (AGS; Urocitellus parryii) resists neuronal injury following cerebral ischemia/reperfusion (I/R) in vivo or following I/R modeled by oxygen glucose deprivation (OGD) in vitro. Resistance to cerebral I/R is evident at tissue temperatures of 35-37°C even when animals are not hibernating. Resistance to I/R injury in other organs and in other hibernating species have been shown to depend on the hibernation season. Resistance to cerebral I/R injury in summer AGS in vivo has suggested that the unique phenotype expressed during the hibernation season may not be necessary for cerebral I/R tolerance in AGS. Thus, we hypothesized that acute physiological events leading to cerebral I/R injury are attenuated by mechanisms independent of the hibernation season in AGS. A novel microperfusion device was used to investigate the role of the hibernation season to resistance to OGD-induced cell death in acute hippocampal slices from AGS. Hippocampus from adult AGS, was sampled during summer and winter animals. In winter, tissue from torpid animals was sampled during torpor (T0), or at 4h (T4) or 20h (T20) after inducing arousal by gentle handling and movement to an ambient temperature of 20°C. All groups were compared to Sprague Dawley rat as a positive control species vulnerable to cerebral I/R injury. Hippocampal slices (400μm) were placed into microchambers with perfusion solutions delivered at 7 μL/min and perfusate collected at 15 minute intervals. LDH in the perfusate was quantified and normalized to total LDH per slice as a measure of I/R injury. In response to 30 minutes OGD followed by reperfusion with normoxic artificial cerebral spinal fluid, acute slices from rats exhibited a 6 fold increase in LDH over baseline levels. By contrast, in AGS over all seasons, OGD-induced an increase in LDH release of only 2 times baseline levels. The smallest LDH response was observed in slices from both hibernating AGS (T0) and summer euthermic AGS. A slightly greater LDH response was observed in slices from AGS during induced, interbout arousal that was about 3 times baseline. Results suggest that resistance to cerebral ischemia does not depend on the hibernation season. Acknowledgements Support Provided: USAMRMC # 05178001, NS041069-06, P20GM103395 Disclosures: None Keywords: ground squirrels, hypoxia tolerance, ischemia reperfusion, torpor Conference: Tenth International Congress of Neuroethology, College Park. Maryland USA, United States, 5 Aug - 10 Aug, 2012. Presentation Type: Plenary Address (including special lectures) (Note, these individuals have already been invited) Topic: Cellular Properties Citation: Drew KL and Moore JT (2012). Resistance to cerebral ischemia/reperfusion injury in the Arctic Ground Squirrel (Urocitellus parryii) does not depend on the hibernation season. Conference Abstract: Tenth International Congress of Neuroethology. doi: 10.3389/conf.fnbeh.2012.27.00049 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 04 Jul 2012; Published Online: 07 Jul 2012. * Correspondence: Dr. Kelly L Drew, University of Alaska Fairbanks, Alaska Basic Neuroscience Program, Institute of Arctic Biology, Fairbanks, Alaska, 99775-7000, United States, kdrew@alaska.edu Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Kelly L Drew Jeanette T Moore Google Kelly L Drew Jeanette T Moore Google Scholar Kelly L Drew Jeanette T Moore PubMed Kelly L Drew Jeanette T Moore Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Season Primes the Brain in an Arctic Hibernator to Facilitate Entrance into Torpor Mediated by Adenosine A1 Receptors

Torpor in hibernating mammals defines the nadir in mammalian metabolic demand and body temperature that accommodates seasonal periods of reduced energy availability. The mechanism of metabolic suppression during torpor onset is unknown, although the CNS is a key regulator of torpor. Seasonal hibernators, such as the arctic ground squirrel (AGS), display torpor only during the winter, hibernation season. The seasonal character of hibernation thus provides a clue to its regulation. In the present study, we delivered adenosine receptor agonists and antagonists into the lateral ventricle of AGSs at different times of the year while monitoring the rate of O(2) consumption and core body temperature as indicators of torpor. The A(1) antagonist cyclopentyltheophylline reversed spontaneous entrance into torpor. The adenosine A(1) receptor agonist N(6)-cyclohexyladenosine (CHA) induced torpor in six of six AGSs tested during the mid-hibernation season, two of six AGSs tested early in the hibernation season, and none of the six AGSs tested during the summer, off-season. CHA-induced torpor within the hibernation season was specific to A(1)AR activation; the A(3)AR agonist 2-Cl-IB MECA failed to induce torpor, and the A(2a)R antagonist MSX-3 failed to reverse spontaneous onset of torpor. CHA-induced torpor was similar to spontaneous entrance into torpor. These results show that metabolic suppression during torpor onset is regulated within the CNS via A(1)AR activation and requires a seasonal switch in the sensitivity of purinergic signaling.

Cyclic structural changes of endoplasmic reticulum and Golgi complex in hippocampal neurons of ground squirrels during hibernation

Repetitive remodeling and renewal of the cytoplasmic structures realizing protein synthesis accompanies the cycling of the ground squirrels between torpor and arousal states during hibernation season. Previously, we have shown the partial loss of ribosomes and inactivation of the nucleolus in pyramidal neurons in the hippocampus CA3 area at each bout of torpor with their rapid and full recovery after warming up. In the present paper, we describe reversible structural changes of the endoplasmic reticulum (ER) and Golgi complex (GC) in these neurons. The transformation of the ER form from mainly granular stacks of flattened cisternae to smooth tubules occurs at every entrance in torpor, while the reverse change happens at arousal. The torpor state is also associated with GC fragmentation and loss of their flattened cisternae, i.e., dictiosomes. In neurons, the appearance of the autophagosomal vacuoles containing fragments of membrane structures and ribosomes in torpor state is a sign of the partial destruction of ER and GC. Granular ER restoration, perhaps through assembly from the multilamellar membrane structures, bags or whorls begins in the middle of the torpor bout, while GC dictiosomes reappear only during warming. The ER and GC completely restore their structure 2–3 h after the beginning of arousal. Thus, hibernation represents an example of the structural adaptation of the nerve cell to deep changes in functional and metabolic activity through both the active destruction and renewal of ribosomes, ER, and GC. Perhaps, namely the incomplete ER autophagosomal degradation in torpor provides its rapid renewal at arousal through the reassembly from the preserved fragments.