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2.
Nature ; 583(7814): 115-121, 2020 07.
Artigo em Inglês | MEDLINE | ID: mdl-32528180

RESUMO

The advent of endothermy, which is achieved through the continuous homeostatic regulation of body temperature and metabolism1,2, is a defining feature of mammalian and avian evolution. However, when challenged by food deprivation or harsh environmental conditions, many mammalian species initiate adaptive energy-conserving survival strategies-including torpor and hibernation-during which their body temperature decreases far below its homeostatic set-point3-5. How homeothermic mammals initiate and regulate these hypothermic states remains largely unknown. Here we show that entry into mouse torpor, a fasting-induced state with a greatly decreased metabolic rate and a body temperature as low as 20 °C6, is regulated by neurons in the medial and lateral preoptic area of the hypothalamus. We show that restimulation of neurons that were activated during a previous bout of torpor is sufficient to initiate the key features of torpor, even in mice that are not calorically restricted. Among these neurons we identify a population of glutamatergic Adcyap1-positive cells, the activity of which accurately determines when mice naturally initiate and exit torpor, and the inhibition of which disrupts the natural process of torpor entry, maintenance and arousal. Taken together, our results reveal a specific neuronal population in the mouse hypothalamus that serves as a core regulator of torpor. This work forms a basis for the future exploration of mechanisms and circuitry that regulate extreme hypothermic and hypometabolic states, and enables genetic access to monitor, initiate, manipulate and study these ancient adaptations of homeotherm biology.


Assuntos
Metabolismo Energético/fisiologia , Hipotálamo/citologia , Vias Neurais/fisiologia , Neurônios/fisiologia , Torpor/fisiologia , Animais , Jejum , Feminino , Privação de Alimentos , Glutamina/metabolismo , Hipotálamo/fisiologia , Masculino , Camundongos , Polipeptídeo Hipofisário Ativador de Adenilato Ciclase/metabolismo
3.
Oecologia ; 193(1): 67-75, 2020 May.
Artigo em Inglês | MEDLINE | ID: mdl-32306117

RESUMO

The extent to which migratory bats forage at stopover sites or while in migratory flight is poorly understood. Endogenous fat stores have lower δ13C values relative to the dietary substrates from which they were synthesized, and so, the fed versus fasted state of bats should be discernable by comparing their breath δ13C at capture to that after a known period of fasting. We captured silver-haired bats (Lasionycteris noctivagans) at a stopover site at Long Point, Ontario, Canada, during spring and fall migration. We collected breath samples at capture and after fasting in captivity for 12 h, providing a fasted-state δ13C value corresponding to metabolism of fat stores. We also collected and weighed fecal pellets produced while in captivity. Breath δ13C values at capture were positively correlated with mass of feces produced. During spring migration, δ13C values of breath CO2 at capture were low and similar to fasting values, but increased with date consistent with increased foraging at stopover and reliance on exogenous dietary nutrients as the season progressed. The opposite temporal pattern was found during fall migration. Our findings suggest that bats forage during migratory stopover when environmental conditions permit despite potential time trade-offs between feeding and travel, and the energy savings resulting from torpor during roosting. This study provides insight into the eco-physiology of bat migration and shows the importance of foraging habitat for migratory bats.


Assuntos
Quirópteros , Torpor , Migração Animal , Animais , Dióxido de Carbono , Ontário , Estações do Ano
4.
Biochim Biophys Acta Gene Regul Mech ; 1863(1): 194473, 2020 01.
Artigo em Inglês | MEDLINE | ID: mdl-31837470

RESUMO

When food scarcity is coupled with decreased temperatures, gray mouse lemurs (Microcebus murinus) depress their metabolic rates and retreat into bouts of either daily torpor or multi-day hibernation, without dramatically dropping body temperatures like other 'traditional hibernators'. Rapid and reversible mechanisms are required to coordinate the simultaneous suppression of energetically expensive processes and activation of pro-survival pathways critical for successful torpor-arousal cycling. MicroRNAs, a class of endogenous non-coding small RNAs, are effective post-transcriptional regulators that modulate all aspects of cellular function. The present study hypothesizes that miRNAs are intimately involved in facilitating the molecular reorganization events necessary for lemur skeletal muscle torpor. Small RNA-Sequencing was used to compare miRNA profiles from skeletal muscles of torpid and control primates. We characterized 234 conserved miRNAs, of which 20 were differentially expressed during torpor, relative to control. Examples included downregulation of key muscle-specific (myomiR) members, miR-1 and miR-133, suggesting a switch to muscle-specific energy-saving strategies. In silico target mapping and logistic regression-based gene set analysis indicated the inhibition of energy costly pathways such as oxidative phosphorylation and muscle proliferation. The suppression of these metabolic pathways was balanced with a lack of miRNA inhibition of various signaling pathways, such as MAPK, mTOR, focal adhesion, and ErbB. This study identifies unique miRNA signatures and 'biomarkers of torpor' that provide us with primate-specific insights on torpor at high body temperatures that can be exploited for human biomedical concerns.


Assuntos
Cheirogaleidae/genética , MicroRNAs/metabolismo , Músculo Esquelético/metabolismo , Torpor/genética , Animais , Cheirogaleidae/metabolismo , Análise por Conglomerados , Regulação para Baixo , Regulação da Expressão Gênica , RNA-Seq , Reação em Cadeia da Polimerase em Tempo Real
5.
PLoS One ; 14(10): e0222311, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31671100

RESUMO

Hibernation consists of extended durations of torpor interrupted by periodic arousals. The 'dehydration hypothesis' proposes that hibernating mammals arouse to replenish water lost through evaporation during torpor. Arousals are energetically expensive, and increased arousal frequency can alter survival throughout hibernation. Yet we lack a means to assess the effect of evaporative water loss (EWL), determined by animal physiology and hibernation microclimate, on torpor bout duration and subsequent survival. White-nose syndrome (WNS), a devastating disease impacting hibernating bats, causes increased frequency of arousals during hibernation and EWL has been hypothesized to contribute to this increased arousal frequency. WNS is caused by a fungus, which grows well in humid hibernaculum environments and damages wing tissue important for water conservation. Here, we integrated the effect of EWL on torpor expression in a hibernation energetics model, including the effects of fungal infection, to determine the link between EWL and survival. We collected field data for Myotis lucifugus, a species that experiences high mortality from WNS, to gather parameters for the model. In saturating conditions, we predicted healthy bats experience minimal mortality. Infected bats, however, suffer high fungal growth in highly saturated environments, leading to exhaustion of fat stores before spring. Our results suggest that host adaptation to humid environments leads to increased arousal frequency from infection, which drives mortality across hibernaculum conditions. Our modified hibernation model provides a tool to assess the interplay between host physiology, hibernaculum microclimate, and diseases such as WNS on winter survival.


Assuntos
Hibernação/fisiologia , Interações Hospedeiro-Patógeno/fisiologia , Torpor/fisiologia , Água/metabolismo , Animais , Nível de Alerta/fisiologia , Quirópteros/microbiologia , Quirópteros/fisiologia , Fungos/patogenicidade , Nariz/microbiologia , Nariz/fisiopatologia
6.
Biol Lett ; 15(10): 20190466, 2019 10 31.
Artigo em Inglês | MEDLINE | ID: mdl-31573426

RESUMO

We experimentally tested the costs of deep torpor at low temperatures by comparing telomere dynamics in two species of rodents hibernating at either 3 or 14°C. Our data show that hibernators kept at the warmer temperature had higher arousal frequencies, but maintained longer telomeres than individuals hibernating at the colder temperature. We suggest that the high-energy demand of frequent arousals is counteracted by a lower temperature differential between torpid and euthermic body temperature and that telomere length is restored during arousals when the body temperature is returned to normothermic values. Taken together, our study shows that hibernation at low body temperatures comes with costs on a cellular level and that hibernators need to actively counterbalance the shortening of telomeres.


Assuntos
Hibernação , Torpor , Animais , Temperatura Corporal , Temperatura Baixa , Telômero , Temperatura
7.
PLoS One ; 14(8): e0220839, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31393965

RESUMO

Few studies have described winter microclimate selection by bats in the southern United States. This is of particular importance as the cold-adapted fungus, Pseudogymnoascus destructans, which causes the fatal bat disease white-nose syndrome (WNS), continues to spread into southern United States. To better understand the suitability of winter bat habitats for the growth of P. destructans in this region, we collected roost temperature and vapor pressure deficit from 97 hibernacula in six ecoregions in Texas during winter 2016-17 and 2017-18. We also measured skin temperature of Rafinesque's big-eared bats (Corynorhinus townsendii), Townsend's big-eared bats (C. townsendii), big-brown bats (Eptesicus fuscus), southeastern myotis (Myotis austroriparius), cave myotis (M. velifer), tri-colored bats (Perimyotis subflavus), and Mexican free-tailed bats (Tadarida brasiliensis) during hibernation to study their use of torpor in these habitats. We found that temperatures within hibernacula were strongly correlated with external air temperatures and were often within the optimal range of temperatures for P. destructans growth. Hibernacula and skin temperatures differed among species, with Rafinesque's big-eared bats, southeastern myotis, and Mexican free-tailed bats occupying warmer microclimates and having higher torpid skin temperatures. For species that were broadly distributed throughout Texas, hibernacula and skin temperatures differed within species by ecoregion; Tri-colored bats and cave myotis in colder, northern regions occupied colder microclimates within hibernacula and exhibited colder skin temperatures, than individuals of the same species in warmer, southern regions. These data illustrate the variability in microclimates used as hibernacula by bats in Texas and suggest similar variation in susceptibility to WNS in the state. Thus, monitoring microclimates at winter roosts may help predict where WNS may develop, and where management efforts would be most effective.


Assuntos
Quirópteros/microbiologia , Ecossistema , Micoses/etiologia , Estações do Ano , Animais , Hibernação , Temperatura Cutânea , Especificidade da Espécie , Texas , Torpor
8.
Am Nat ; 194(2): 135-151, 2019 08.
Artigo em Inglês | MEDLINE | ID: mdl-31318286

RESUMO

Although metacommunity ecology has improved our understanding of how dispersal affects community structure and dynamics across spatial scales, it has yet to adequately account for dormancy. Dormancy is a reversible state of reduced metabolic activity that enables temporal dispersal within the metacommunity. Dormancy is also a metacommunity-level process because it can covary with spatial dispersal and affect diversity across spatial scales. We develop a framework to integrate dispersal and dormancy, focusing on the covariation they exhibit, to predict how dormancy modifies the importance of species interactions, dispersal, and historical contingencies in metacommunities. We used empirical and modeling approaches to demonstrate the utility of this framework. We examined case studies of microcrustaceans in ephemeral ponds, where dormancy underlies metacommunity dynamics, and identified constraints on the dispersal and dormancy strategies of bromeliad-dwelling invertebrates. Using simulations, we showed that dormancy can alter classic metacommunity patterns of diversity in ways that depend on dispersal-dormancy covariation and spatiotemporal environmental variability. We propose that dormancy may also facilitate evolution-mediated priority effects if locally adapted seed banks prevent colonization by more dispersal-limited species. Last, we present testable predictions for the implications of dormancy in metacommunities, some of which may fundamentally alter our understanding of metacommunity ecology.


Assuntos
Biota , Torpor , Distribuição Animal , Animais , Evolução Biológica , Ecossistema , Dispersão Vegetal , Dormência de Plantas , Plantas , Dinâmica Populacional , Sementes
9.
Biol Lett ; 15(6): 20190211, 2019 06 28.
Artigo em Inglês | MEDLINE | ID: mdl-31238856

RESUMO

Many passerine birds are small and require a high mass-specific rate of resting energy expenditure, especially in the cold. The energetics of thermoregulation is, therefore, an important aspect of their ecology, yet few studies have quantified thermoregulatory patterns in wild passerines. We used miniature telemetry to record the skin temperature ( Tskin) of free-living superb fairy-wrens ( Malurus cyaneus, 8.6 g; n = 6 birds over N = 7-22 days) and determine the importance of controlled reductions in body temperature during resting to their winter energy budgets. Fairy-wrens routinely exhibited large daily fluctuations in Tskin between maxima of 41.9 ± 0.6°C and minima of 30.4 ± 0.7°C, with overall individual minima of 27.4 ± 1.1°C (maximum daily range: 14.7 ± 0.9°C). These results provide strong evidence of nocturnal torpor in this small passerine, which we calculated to provide a 42% reduction in resting metabolic rate at a Ta of 5°C compared to active-phase Tskin. A capacity for energy-saving torpor has important consequences for understanding the behaviour and life-history ecology of superb fairy-wrens. Moreover, our novel field data suggest that torpor could be more widespread and important than previously thought within passerines, the most diverse order of birds.


Assuntos
Aves Canoras , Torpor , Animais , Temperatura Corporal , Regulação da Temperatura Corporal , Metabolismo Energético
10.
J Exp Zool A Ecol Integr Physiol ; 331(6): 319-325, 2019 07.
Artigo em Inglês | MEDLINE | ID: mdl-31074950

RESUMO

Cunner (Tautogolabrus adspersus) are a temperate labrid species that inhabit the Western Atlantic and experience temperatures ranging from 0°C to 25°C. During autumn, once temperatures drop below 10°C in Long Island Sound, cunner find shelter and enter a state of quiescence. Previous work has shown that acclimation to low temperatures limits the performance of locomotor musculature, which significantly lowers steady swimming capabilities. We aimed to understand how the escape response (C-start) might be impacted by temperatures experienced by cunner in Long Island Sound over the course of a year. Escape responses were recorded at 250 frames/s at 20°C, 15°C, 10°C, and 5°C. Average peak velocities and accelerations were faster in fish acclimated to 20°C than to 5°C and 10°C. Despite taking a similar turn angle to 10°C and 15°C fish, the 5°C treatment group took longer to complete the C-start, which might make them more susceptible to predation at this temperature. Based on these results it appears that the escape response is reduced at cold temperatures. Previous research has shown that locomotor musculature performance is significantly reduced at cold temperatures, which could explain the results seen here. The decrease in escape performance at cold temperatures could explain their state of extended torpor as the slowed C-start at these cold temperatures might make them more susceptible to predation.


Assuntos
Aclimatação/fisiologia , Temperatura Baixa , Reação de Fuga/fisiologia , Perciformes/fisiologia , Animais , Estações do Ano , Natação , Torpor/fisiologia
11.
Naturwissenschaften ; 106(5-6): 28, 2019 May 27.
Artigo em Inglês | MEDLINE | ID: mdl-31134403

RESUMO

Torpor in birds is considered to be far less common than in mammals. This is particularly true for passerine birds for which knowledge of torpor expression is scarce, although almost all are small, have high energy expenditure and could profit energetically from using torpor. To assess whether the extent and diversity of avian and especially passerine torpor expression and heterothermy may be currently underestimated because of limited long-term data on free-ranging birds, core body temperature fluctuations were quantified over ~ 4.3 months in a medium-sized honeyeater, the noisy miner (Manorina melanocephala, ~ 75 g), in an open woodland during the cold season in eastern Australia. Miners used shallow nocturnal torpor frequently (63% of days), torpor bouts lasted on average for 6.5 h (maximum 13.5 h) and, unlike during hypothermia, torpor was terminated by endogenous heat production for rewarming. Body temperatures (Tb) ranged from a maximum of 43.5 °C to a minimum of 33.0 °C, often fell by 7 °C at night, and the overall mean Tb was 38.7 ± 0.7 °C. The data show that yet another passerine bird, widely viewed to be homeothermic, expresses torpor in the wild for energy conservation. Considering the size of miners, it seems probable that many other, especially smaller birds, use a similar approach at least in winter to enhance the chance of survival in the face of high energy expenditure and low food availability.


Assuntos
Passeriformes/fisiologia , Torpor/fisiologia , Animais , Austrália , Temperatura Corporal , Regulação da Temperatura Corporal/fisiologia
12.
Am J Physiol Regul Integr Comp Physiol ; 317(2): R262-R269, 2019 08 01.
Artigo em Inglês | MEDLINE | ID: mdl-31067076

RESUMO

During hibernation, small mammals, including the 13-lined ground squirrel (Ictidomys tridecemlineatus), cycle between two distinct metabolic states: torpor, where metabolic rate is suppressed by >95% and body temperature falls to ~5°C, and interbout euthermia (IBE), where both metabolic rate and body temperature rapidly increase to euthermic levels. Suppression of whole animal metabolism during torpor is paralleled by rapid, reversible suppression of mitochondrial respiration. We hypothesized that these changes in mitochondrial metabolism are regulated by posttranslational modifications to mitochondrial proteins. Differential two-dimensional gel electrophoresis and two-dimensional blue-native PAGE revealed differences in the isoelectric point of several liver mitochondrial proteins between torpor and IBE. Quadrupole time-of-flight LC/MS and matrix-assisted laser desorption/ionization MS identified these as proteins involved in ß-oxidation, the tricarboxylic acid cycle, reactive oxygen species detoxification, and the electron transport system (ETS). Immunoblots revealed that subunit 1 of ETS complex IV was acetylated during torpor but not IBE. Phosphoprotein staining revealed significantly greater phosphorylation of succinyl-CoA ligase and the flavoprotein subunit of ETS complex II in IBE than torpor. In addition, the 75-kDa subunit of ETS complex I was 1.5-fold more phosphorylated in torpor. In vitro treatment with alkaline phosphatase increased the maximal activity of complex I from liver mitochondria isolated from torpid, but not IBE, animals. By contrast, phosphatase treatment decreased complex II activity in IBE but not torpor. These findings suggest that the rapid changes in mitochondrial metabolism in hibernators are mediated by posttranslational modifications of key metabolic enzymes, perhaps by intramitochondrial kinases and deacetylases.


Assuntos
Hibernação/fisiologia , Fígado/metabolismo , Mitocôndrias Hepáticas/metabolismo , Mitocôndrias/metabolismo , Animais , Proteínas Mitocondriais/metabolismo , Consumo de Oxigênio/fisiologia , Processamento de Proteína Pós-Traducional/fisiologia , Espécies Reativas de Oxigênio/metabolismo , Torpor/fisiologia
13.
J Therm Biol ; 82: 150-156, 2019 May.
Artigo em Inglês | MEDLINE | ID: mdl-31128642

RESUMO

Hibernating bats optimise the duration of torpor bouts and arousals in relation to hibernaculum microclimatic conditions and fat reserves. Clustering has significant physiological and ecological benefits, promoting successful hibernation of individuals. Such aggregations may help maintain optimal temperatures, allowing better energy utilisation than in solitarily bats. However, aroused bats in a cluster could conceivably disturb those still hibernating, starting an energy-demanding arousal process. Our study was conducted over two winters in two different hibernacula (cave and mine) in the Czech Republic, where Greater mouse-eared bats (Myotis myotis) have previously been diagnosed with white-nose syndrome. In 118 arousal episodes we recorded 193 individual arousals in which a warming phase was observed, 135 (69.9%) being cold arousals, where bats ceased increasing their body temperatures at ≤ 10 °C. The remaining arousals were standard normothermic arousals, where body (fur) surface temperatures reached > 20 °C. Cold arousals occurred during the mid- and late hibernation periods, suggesting they were a response to disturbance by a neighbour in the same cluster. Arousal cascades, where bats aroused in series, were rare (12.7%) and reached a maximum in mid-January. Our data suggest that Myotis bats prolong their torpor bouts using numerous cold arousals but few arousal cascades. Upon arrival of a bat, the clustered bats show tolerance to disturbing by conspecifics.


Assuntos
Quirópteros/fisiologia , Hibernação , Animais , Nível de Alerta , Comportamento Animal , Temperatura Corporal , Temperatura Baixa , Estações do Ano , Torpor
14.
J Exp Biol ; 222(Pt 6)2019 03 15.
Artigo em Inglês | MEDLINE | ID: mdl-30877147

RESUMO

Theoretical modelling predicts that the thermoregulatory strategies of endothermic animals range from those represented by thermal generalists to those characteristic for thermal specialists. While the generalists tolerate wide variations in body temperature (T b), the specialists maintain T b at a more constant level. The model has gained support from inter-specific comparisons relating to species and population levels. However, little is known about consistent among-individual variation within populations that could be shaped by natural selection. We studied the consistency of individual heterothermic responses to environmental challenges in a single population of yellow-necked mice (Apodemus flavicollis), by verifying the hypothesis that T b variation is a repeatable trait. To induce the heterothermic response, the same individuals were repeatedly food deprived for 24 h. We measured T b with implanted miniaturised data loggers. Before each fasting experiment, we measured basal metabolic rate (BMR). Thus, we also tested whether individual variation of heterothermy correlates with individual self-maintenance costs, and the potential benefits arising from heterothermic responses that should correlate with body size/mass. We found that some individuals clearly entered torpor while others kept T b stable, and that there were also individuals that showed intermediate thermoregulatory patterns. Heterothermy was found to correlate negatively with body mass and slightly positively with the BMR achieved 1-2 days before fasting. Nonetheless, heterothermy was shown to be highly repeatable, irrespective of whether we controlled for self-maintenance costs and body size. Our results indicate that specialist and generalist thermoregulatory phenotypes can co-exist in a single population, creating a heterothermy continuum.


Assuntos
Metabolismo Basal , Regulação da Temperatura Corporal , Privação de Alimentos , Murinae/fisiologia , Animais , Feminino , Masculino , Torpor
15.
Life Sci ; 219: 190-198, 2019 Feb 15.
Artigo em Inglês | MEDLINE | ID: mdl-30658098

RESUMO

AIMS: To initiate a state of artificial torpor we suggested a pharmacological multi-targeting strategy for simulation of the physiological pattern of natural hibernation including a significant reduction in heart rate, respiratory rate, body temperature and oxygen consumption as well as a decline in brain activity known as torpor. MATERIALS AND METHODS: We have developed a composition which initiates a pharmacologically induced torpor-like state (PITS-composition), made up of eight therapeutic agents, inert gas xenon and lipid emulsion served as a drug vehicle. KEY FINDINGS: After a single intravenous injection to rats, PITS-composition causes a rapid decline in heart rate followed by a steady decrease in body temperature from about 38.5 °C to 31.5 °C, at ambient temperature of 22 °C-23 °C. The hypothermic state may continue on average for 16-17 h with the subsequent spontaneous return of heart rate and body temperature to the initial values. In the open field test at torpor the motility, rearing and grooming were suppressed but 4-8 days later they were restored. SIGNIFICANCE: Suspended animation states, including natural hibernation or pharmacologically induced synthetic torpor are of special attention of medicine, since it may improve survival rate after cardiac arrest, brain hemorrhage and ischemia, and during long-term space traveling. The suggested here multi-targeting strategy made possible to develop the pharmacological composition able, after a single intravenous injection, to initiate long, stable and reversible hypothermia and torpor at room temperature. After the torpor, animals were able to spontaneously restore both physiological parameters, and behavioral reactions.


Assuntos
Hipotermia/induzido quimicamente , Torpor/efeitos dos fármacos , Animais , Temperatura Corporal/efeitos dos fármacos , Encéfalo/efeitos dos fármacos , Difenidramina/administração & dosagem , Difenidramina/farmacologia , Combinação de Medicamentos , Frequência Cardíaca/efeitos dos fármacos , Injeções Intravenosas , Ivabradina/administração & dosagem , Ivabradina/farmacologia , Sulfato de Magnésio/administração & dosagem , Sulfato de Magnésio/farmacologia , Masculino , Consumo de Oxigênio/efeitos dos fármacos , Fenotiazinas/administração & dosagem , Fenotiazinas/farmacologia , Fosfolipídeos/administração & dosagem , Fosfolipídeos/farmacologia , Propranolol/administração & dosagem , Propranolol/farmacologia , Propiltiouracila/administração & dosagem , Propiltiouracila/farmacologia , Ratos , Ratos Wistar , Reserpina/administração & dosagem , Reserpina/farmacologia , Taxa Respiratória/efeitos dos fármacos , Serotonina/administração & dosagem , Serotonina/farmacologia , Sorbitol/administração & dosagem , Sorbitol/farmacologia , Xenônio/administração & dosagem , Xenônio/farmacologia
16.
Pflugers Arch ; 471(6): 819-828, 2019 06.
Artigo em Inglês | MEDLINE | ID: mdl-30569200

RESUMO

For long-duration manned space missions to Mars and beyond, reduction of astronaut metabolism by torpor, the metabolic state during hibernation of animals, would be a game changer: Water and food intake could be reduced by up to 75% and thus reducing payload of the spacecraft. Metabolic rate reduction in natural torpor is linked to profound changes in biochemical processes, i.e., shift from glycolysis to lipolysis and ketone utilization, intensive but reversible alterations in organs like the brain and kidney, and in heart rate control via Ca2+. This state would prevent degenerative processes due to organ disuse and increase resistance against radiation defects. Neuro-endocrine factors have been identified as main targets to induce torpor although the exact mechanisms are not known yet. The widespread occurrence of torpor in mammals and examples of human hypometabolic states support the idea of human torpor and its beneficial applications in medicine and space exploration.


Assuntos
Metabolismo Basal , Mamíferos/metabolismo , Voo Espacial , Torpor/fisiologia , Animais , Humanos
17.
Artigo em Inglês | MEDLINE | ID: mdl-30343059

RESUMO

Hibernating mammals use strong metabolic rate depression and a reduction in body temperature to near-ambient to survive the cold winter months. During torpor, protein synthesis is suppressed but can resume during interbout arousals. The current study aimed to identify molecular targets responsible for the global suppression of protein synthesis during torpor as well as possible mechanisms that could allow for selective protein translation to continue over this time. Relative changes in protein expression and/or phosphorylation levels of key translation factors (ribosomal protein S6, eIF4E, eIF2α, eEF2) and their upstream regulators (mTOR, TSC2, p70 S6K, 4EBP) were analyzed in liver and kidney of 13-lined ground squirrels (Ictidomys tridecemlineatus) sampled from six points over the torpor-arousal cycle. The results indicate that both organs reduce protein synthesis during torpor by decreasing mTOR and TSC2 phosphorylation between 30 and 70% of control levels. Translation resumes during interbout arousal when p-p70 S6K, p-rpS6, and p-4EBP levels returned to control values or above. Only liver translation factors were activated or disinhibited during periods of torpor itself, with >3-fold increases in total eIF2α and eEF2 protein levels, and a decrease in p-eEF2 (T56) to as low as 16% of the euthermic control value. These data shed light on a possible molecular mechanism involving eIF2α that could enable the translation of key transcripts during times of cell stress.


Assuntos
Fator de Iniciação 2 em Eucariotos/metabolismo , Sciuridae/fisiologia , Torpor , Animais , Biossíntese de Proteínas , RNA Mensageiro/metabolismo , Sciuridae/metabolismo
18.
J Comp Physiol B ; 189(1): 167-177, 2019 02.
Artigo em Inglês | MEDLINE | ID: mdl-30317383

RESUMO

13-lined ground squirrels (Ictidomys tridecemlineatus) enter hibernation as a survival strategy during extreme environmental conditions. Typical ground squirrel hibernation is characterized by prolonged periods of torpor with significantly reduced heart rate, blood pressure, and blood flow, interrupted every few weeks by brief interbout arousals (IBA) during which blood flow fluctuates dramatically. These physiological conditions should increase the risk of stasis-induced blood clots and myocardial ischemia. However, ground squirrels have adapted to survive repeated bouts of torpor and IBA without forming lethal blood clots or sustaining lethal ischemic myocardial damage. The purpose of this study was to determine if ground squirrels are resistant to thrombosis and myocardial ischemia during hibernation. Blood markers of coagulation, fibrinolysis, thrombosis, and ischemia, as well as histological markers of myocardial ischemia were measured throughout the annual hibernation cycle. Hibernating ground squirrels were also treated with isoprenaline to induce myocardial ischemia. Thrombin-antithrombin complex levels were significantly reduced (p < 0.05) during hibernation, while D-dimer level remained unchanged throughout the annual cycle, both consistent with an antithrombotic state. During torpor, the ground squirrels were in a hyperfibrinolytic state with an elevated ratio of tissue plasminogen activator complexed with plasminogen activator inhibitor to total plasminogen activator inhibitor (p < 0.05). Histological markers of myocardial ischemia were reversibly elevated during hibernation with no increase in markers of myocardial cell death in the blood. These data suggest that ground squirrels do not form major blood clots during hibernation through suppression of coagulation and a hyperfibrinolytic state. These animals also demonstrate myocardial resistance to ischemia.


Assuntos
Coagulação Sanguínea/fisiologia , Sciuridae/sangue , Trombose , Torpor/fisiologia , Animais , Antitrombinas/metabolismo , Isquemia Miocárdica/patologia , Miocárdio/patologia , Inibidor 1 de Ativador de Plasminogênio/sangue , Inibidor 1 de Ativador de Plasminogênio/genética , Sciuridae/fisiologia , Trombina/metabolismo , Ativador de Plasminogênio Tecidual/sangue , Troponina T/sangue
19.
Oecologia ; 189(1): 47-53, 2019 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-30460539

RESUMO

Compared to mammals, there are relatively few studies examining heterothermy in birds. In 13 bird families known to contain heterothermic species, the common poorwill (Phalaenoptilus nuttallii) is the only species that ostensibly hibernates. We used temperature-sensitive radio-transmitters to collect roost and skin temperature (Tskin) data, and winter roost preferences for free-ranging poorwills in southern Arizona. Further, to determine the effect of passive rewarming on torpor bout duration and active rewarming (i.e., the use of metabolic heat to increase Tskin), we experimentally shaded seven birds during winter to prevent them from passively rewarming via solar radiation. Poorwills selected winter roosts that were open to the south or southwest, facilitating passive solar warming in the late afternoon. Shaded birds actively rewarmed following at least 3 days of continuous torpor. Average torpor bout duration by shaded birds was 122 h and ranged from 91 to 164 h. Active rewarming by shaded birds occurred on significantly warmer days than those when poorwills remained torpid. One shaded bird remained inactive for 45 days, during which it spontaneously rewarmed actively on eight occasions. Our findings show that during winter poorwills exhibit physiological patterns and active rewarming similar to hibernating mammals.


Assuntos
Hibernação , Torpor , Animais , Arizona , Regulação da Temperatura Corporal , Estações do Ano , Temperatura Cutânea
20.
J Therm Biol ; 78: 352-355, 2018 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-30509657

RESUMO

In the Neotropics, captive vespertilionid bats substantially reduce their metabolic rate at low ambient temperatures, similar to their temperate counterparts, whereas the ability of phyllostomids to lower metabolic rate seems to be more limited, even in mountain species. Nevertheless, field data on the thermal behaviour of syntopic individuals from these two families is lacking. Consequently, we aimed to test whether torpor was more common and deeper in vesper bats compared to leaf-nosed bats by studying skin temperature (Tsk) variation in individuals experiencing the same environmental conditions at a mountain area. Bats experienced ambient temperatures below 15 °C. Average Tsk was 10 °C in Myotis oxyotus gardneri (Vespertilionidae) during the day, while Sturnira burtonlimi (Phyllostomidae) regulated diurnal Tsk above 30 °C. Constant food availability may explain why diurnal Sturnira burtonlimi pay the high energetic cost required to remain normothermic and to defend a wide Ta-Tsk gap but further studies are needed to elucidate additional strategies that may be employed by these bats to reduce the energetic demands of normothermy. Our study shows that the contrasting thermal strategies and torpor use adopted by vespertilionid insectivores and phyllostomid frugivores in captive settings also occur in free-ranging conditions, thus providing a basis to develop further studies with predictions more accurately rooted in field data.


Assuntos
Altitude , Quirópteros/fisiologia , Temperatura Cutânea , Torpor , Aclimatação , Animais , Metabolismo Energético , Comportamento Alimentar , Fotoperíodo
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