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PubMed1982

Large intestine bacterial flora of nonhibernating and hibernating leopard frogs (Rana pipiens).

The bacteria in the large intestines of 10 northern leopard frogs (Rana pipiens) were enumerated and partially characterized. Four nonhibernating frogs were collected in the summer, four hibernating frogs were collected in the winter, and two frogs just emerged from hibernation were collected in the spring. All frogs had about 10(10) bacteria per g (wet weight) of intestinal contents and about 10(9) bacteria per g (wet weight) of mucosal scraping, although the counts from the winter frogs were slightly less than those from the other two groups of frogs. Another group of 14 summer frogs, after treatment to induce hibernation, showed a drop in bacterial counts accompanied by a change in the composition of the flora. In most frogs, Bacteroides was the dominant organism. Other bacteria repeatedly isolated at high dilutions were strict anaerobes, including butyrigenic and acetogenic helically coiled bacteria; fusobacteria; and acetogenic, small, gram-positive bacilli. These data indicate that the intestinal flora of frogs is similar to that of mammals and birds and that this flora can be maintained at temperatures close to freezing.

Anaerobiosis↗
PubMed1988

Possible mechanisms responsible for the reduced intestinal flora in hibernating leopard frogs (Rana pipiens).

Mechanisms and factors that normally control the large intestinal flora were investigated to determine whether changes in these parameters could account for the decreased bacterial concentration and facultative nature of the flora found in hibernating frogs. It appeared that low temperatures and limited nutrients were the main factors responsible for the decrease in the bacterial concentration and may also have been responsible for the increase in the proportions of facultative organisms, since no change in the redox potential was seen. The hibernating frogs were extremely sluggish in the removal of India ink particles from the circulatory system by the Kupffer cells of the liver compared with nonhibernating frogs. They were unable to mount an antibody response to bovine serum albumin, but their serum did exhibit killing of Pseudomonas paucimobilis, suggesting opsonization by preformed antibody and complement. The role of these host factors in protecting the hibernating frog against this indigenous flora is discussed.

Animals↗
PubMed1998

Comparisons of the effects of temperature on the liver fatty acid binding proteins from hibernator and nonhibernator mammals.

Hibernating mammals rely heavily on lipid metabolism to supply energy during hibernation. We wondered if the fatty acid binding protein from a hibernator responded to temperature differently than that from a nonhibernator. We found that the Kd for oleate of the liver fatty acid binding protein (1.5 microM) isolated from ground squirrel (Spermophilus richardsonii) was temperature insensitive over 5-37 degrees C, while the rat liver fatty acid binding protein was affected with the Kd at 37 degrees C being about half (0.8 microM) that found at lower temperatures. This same trend was observed when comparing the specificity of various fatty acids of differing chain length and degree of unsaturation for the two proteins at 5 and 37 degrees C. At the lower temperature, ground squirrel protein bound long-chain unsaturated fatty acids, particularly linoleate and linolenate, at least as well as at the higher temperature and matched requirements for these fatty acids in the diet. The most common long-chain fatty acid, palmitate, was a more effective ligand for ground squirrel liver fatty acid binding protein at 5 degrees C than at 37 degrees C, with the opposite occurring in the eutherm. Rat protein was clearly not adapted to function optimally at temperatures lower than the animal's body temperature.

Animals↗
PubMed2004

Metabolic rate and body temperature reduction during hibernation and daily torpor.

Although it is well established that during periods of torpor heterothermic mammals and birds can reduce metabolic rates (MR) substantially, the mechanisms causing the reduction of MR remain a controversial subject. The comparative analysis provided here suggests that MR reduction depends on patterns of torpor used, the state of torpor, and body mass. Daily heterotherms, which are species that enter daily torpor exclusively, appear to rely mostly on the fall of body temperature (Tb) for MR reduction, perhaps with the exception of very small species and at high torpor Tb, where some metabolic inhibition may be used. In contrast, hibernators (species capable of prolonged torpor bouts) rely extensively on metabolic inhibition, in addition to Tb effects, to reduce MR to a fraction of that observed in daily heterotherms. In small hibernators, metabolic inhibition and the large fall of Tb are employed to maximize energy conservation, whereas in large hibernators, metabolic inhibition appears to be employed to facilitate MR and Tb reduction at torpor onset. Over the ambient temperature (Ta) range where torpid heterotherms are thermo-conforming, the Tb-Ta differential is more or less constant despite a decline of MR with Ta; however, in thermo-regulating torpid individuals, the Tb-Ta differential is maintained by a proportional increase of MR as during normothermia, albeit at a lower Tb. Thermal conductance in most torpid thermo-regulating individuals is similar to that in normothermic individuals despite the substantially lower MR in the former. However, conductance is low when deeply torpid animals are thermo-conforming probably because of peripheral vasoconstriction.

Animals↗
PubMed1991

Effect of hibernation and jejunal bypass on mucosal structure and function.

Intestinal mucosal structure and function may be regulated by systemic factors associated with oral feeding, as well as local responses initiated by contact of the mucosa with food. This study compared the relative effects of these factors in an animal model that undergoes seasonal long-term fasting. Jejunal bypass operations or sham surgeries were performed on active fed ground squirrels or on squirrels that subsequently ceased feeding and hibernated. Mucosal wet weight, protein content, villus height, and surface area were reduced in jejunal segments that had minimal exposure to luminal contents (bypassed segments of active squirrels and all segments of hibernators) compared with segments exposed to the luminal stream (incontinuity and sham segments of active squirrels). When normalized to mucosal weight, transepithelial absorption of 3-O-methylglucose and alanine-dependent sodium flux were greater in jejunal segments with minimal exposure to luminal nutrients. Altered structure in bypassed segments of active and hibernating squirrels paralleled changes in functional parameters despite the presence of different systemic factors in the two groups. Thus, in this animal model, contact of the mucosa with food, and not systemic factors associated with oral feeding, is the primary factor maintaining mucosal mass. The absence of mucosal contact with nutrients enhances specific absorptive function by mechanisms that have yet to be determined.

3-O-Methylglucose↗
PubMed1975

Responses to preoptic temperature manipulation in the awake and hibernating marmot.

Responses of normothermic and hibernating marmots to manipulations of the preoptic-hypothalamic temperature (TPO) were studied. Independent variables included alteration of TPO and, during normothermia, room temperature. Hibernation occurred at an ambient of 6 degrees C. Dependent variables include brain, subdermal, and surface temperatures, heart rate, and behavioral, electromyographic cortical, and hippocampal responses. Although normothermic autumn marmots displayed most of the usual mammalian responses to alterations of the TPO, evidence of effective dermal vasomotion was not obtained. Single episodes of water drinking accompanied prolonged raising of the TPO; sleep was not elicited. During hibernation, effective central thermoregulation was not apparent until 3 or 4 days had elapsed. After this, thermoregulation was readily demonstrable in response to both raising and lowering the TPO. The apparent open-loop gains (OLG) for rise in body temperature after lowering of the TPO showed an exponential increase in value at lower prestimulus body temperatures. It was postulated that this could be explained on the basis of the recruitment of cold-sensitive neurones, which in turn would provide an explanation for the hypothesized "alarm temperature."

Animals↗
PubMed1975

Responses to cold in the midbrain sonar center of hibernating and tropical bats.

The central gray matter of the bat midbrain, when electrically stimulated, causes the animal to produce a string of species-specific biosonar cries. Changes in this response with progressive cooling were studied in tropical homeothermic bats and in temperate hibernating bats. The species of hibernators chosen often move between hibernacula in the winter, flying and echolocating at low body temperatures (Tb). It was found that the midbrain "sonar center" exhibits a differential response to cooling that depends on the thermal propensities of the animal and its natural environment. Tropical bats followed a Q10 similar to that reported for other nonhibernating mammals and ceased responding at Tb 14-15 degrees C. Temperate zone-hibernating bat brains showed a relative insensitivity to temperature change and still responded at Tb 4-5 degrees C. Individual sonar cries within a string showed that duration was correlated with temperature but amplitude was unaffected. The study provides data for the functional separation of some parameters of biosonar and gives further evidence for differential nervous function in eurythermal versus stenothermal animals.

Adaptation, Physiological↗
PubMed1976

Effects of temperature on cardiac transmembrane potentials in hibernation.

Resting and action potential parameters were measured from papillary muscle isolated from hibernating and control hamsters and from rats. The temperature range of the study was 12-38 degrees C. The decrease in resting membrane potential (Em) with decreasing temperature was significantly less in the hibernation preparations (HH), down to 20 degrees C, than in either the control hamsters or rats. Below 20 degrees C the declines in Em of all preparations were indistinguishable. Action potential magnitude was adequately maintained in HH to 12 degrees C while both control hamster and rat action potentials declined markedly as temperatures were reduced. Both types of hamster preparations showed greatly prolonged action potentials with reduced temperatures as contrasted to a limited prolongation of rat action potentials. The data are suggestive of a membrane modication in hibernation.

Action Potentials↗
PubMed1976

Inhibition of the CNA trigger process for arousal from hibernation.

Ground squirrels (Citellus lateralis) produced three distinct types of thermogenic response during hibernation. These responses were evoked spontaneously as well as after stimulation produced by brief handling, or after microinjection of acetylcholine into the midbrain reticular formation. Type I responses were characterized by small magnitude and a slow (mean rate, 0.03 degrees C/min), variable rising phase. Type II responses were characterized by a smooth, rapid rising phase with a mean rate of increase of 0.11 degrees C/min and by an abrupt reversal of the rising phase within a restricted ceiling temperature band with a mean value of 9.4 degrees C. The third type of response, full arousal, was characterized by a return of body temperature to euthermic (nonhibernating) levels and by an early rising phase that was indistinguishable from the rising phase of type II responses. This indicates that the rising phase of type II responses and the duplicate portion of full arousals are produced by a common neuronal mechanism that functions as the trigger for arousal from hibernation, and that this mechanism can be spontaneously inhibited when increasing internal temperature reaches a hibernation ceiling level.

Acetylcholine↗
PubMed2002

Loss of circadian organization of sleep and wakefulness during hibernation.

We investigated circadian and homeostatic regulation of nonrapid eye movement (NREM) sleep in golden-mantled ground squirrels during euthermic intervals between torpor bouts. Slow-wave activity (SWA; 1-4 Hz) and sigma activity (10-15 Hz) represent the two dominant electroencephalographic (EEG) frequency components of NREM sleep. EEG sigma activity has a strong circadian component in addition to a sleep homeostatic component, whereas SWA mainly reflects sleep homeostasis [Dijk DJ and Czeisler CA. J Neurosci 15: 3526-3538, 1995; Dijk DJ, Shanahan TL, Duffy JF, Ronda JM, and Czeisler CA. J Physiol (Lond) 505: 851-858, 1997]. Animals maintained under constant conditions continued to display circadian rhythms in both sigma activity and brain temperature throughout euthermic intervals, whereas sleep and wakefulness showed no circadian organization. Instead, sleep and wakefulness were distributed according to a 6-h ultradian rhythm. SWA, NREM sleep bout length, and sigma activity responded homeostatically to the ultradian sleep-wake pattern. We suggest that the loss of sleep-wake consolidation in ground squirrels during the hibernation season may be related to the greatly decreased locomotor activity during the hibernation season and may be necessary for maintenance of multiday torpor bouts characteristic of hibernating species.

Animals↗
PubMed1977

Regulation of arousal from hibernation by temperature in three species of Citellus.

The frequency of arousal from periods of hibernation of Citellus lateralis, C. tridecemlineatus, and C. columbianus was demonstrated to be regulated by environmental (and therefore body) temperature over the range of 2-12 degrees C in a log-linear relationship. The slopes of the lines of regression for all three species were not significantly different from one another. Durations of the periods of hibernation for the considerably larger C. columbianus, however, were significantly longer at all levels of temperature than those for the similar-sized C. lateralis and C. tridecemlineatus. The mechanism(s) regulating the duration of the period of hibernation was considered to be concerned with some aspect of metabolism and probably the same for all three species.

Animals↗
PubMed2005

Seasonally hibernating phenotype assessed through transcript screening.

Hibernation is a seasonally entrained and profound phenotypic transition to conserve energy in winter. It involves significant biochemical reprogramming, although our understanding of the underpinning molecular events is fragmentary and selective. We have conducted a large-scale gene expression screen of the golden-mantled ground squirrel, Spermophilus lateralis, to identify transcriptional responses associated specifically with the summer-winter transition and the torpid-arousal transition in winter. We used 112 cDNA microarrays comprising 12,288 probes that cover at least 5,109 genes. In liver, the profiles of torpid and active states in the winter were almost identical, although we identified 102 cDNAs that were differentially expressed between winter and summer, 90% of which were downregulated in the winter states. By contrast, in cardiac tissue, 59 and 115 cDNAs were elevated in interbout arousal and torpor, respectively, relative to the summer active condition, but only 7 were common to both winter states, and during arousal none was downregulated. In brain, 78 cDNAs were found to change in winter, 44 of which were upregulated. Thus transcriptional changes associated with hibernation are qualitatively modest and, since these changes are generally less than twofold, also quantitatively modest. Unbiased Gene Ontology profiling of the transcripts suggests a winter switch to beta-oxidation of lipids in liver and heart, a reduction in metabolism of toxic compounds and the urea cycle in liver, and downregulated electron transport in the brain. We identified just one strongly winter-induced transcript common to all tissues, namely an RNA-binding protein, RBM3. This analysis clearly differentiates responses of the principal tissues, identifies a large number of new genes undergoing regulation, and broadens our understanding of affected cellular processes that, in part, account for the winter-adaptive hibernating phenotype.

Animals↗
PubMed2005

Cryoprotection by urea in a terrestrially hibernating frog.

The role of urea as a balancing osmolyte in osmotic adaptation is well known, but this 'waste product' also has myriad other functions in diverse taxa. We report that urea plays an important, previously undocumented role in freezing tolerance of the wood frog (Rana sylvatica), a northern woodland species that hibernates terrestrially in sites where dehydration and freezing may occur. Wood frogs inhabiting an outdoor enclosure accumulated urea to 65 mmol l-1 in autumn and early winter, when soil moisture was scarce, but subsequently urea levels fell to approximately 2 mmol l-1 as the availability of environmental water increased. Laboratory experiments showed that hibernating R. sylvatica can accumulate at least 90 mmol l-1 urea under relatively dry, warm conditions. During experimental freezing, frogs synthesized glucose but did not accumulate additional urea. Nevertheless, the concentrations of urea and glucose in some tissues were similar. We tested urea's efficacy as a cryoprotectant by measuring lysis and lactate dehydrogenase (LDH) leakage in samples of R. sylvatica erythrocytes frozen/thawed in the presence of physiological levels of urea or other osmolytes. In conferring protection against freeze/thaw damage, urea was comparable to glycerol and as good as or better than glucose, cryoprotectants found in freeze-tolerant frogs and other animals. Urea treatment also improved the viability of intact tissues frozen in vitro, as demonstrated by post-thaw measures of metabolic activity and LDH leakage. Collectively, our findings suggest that urea functions both as an osmoprotectant and a cryoprotectant in terrestrially hibernating amphibians.

Adaptation, Physiological↗
PubMed2000

The effect of metabolic depression on proton leak rate in mitochondria from hibernating frogs.

Futile cycling of protons across the mitochondrial inner membrane accounts for 20 % or more of the total standard metabolic rate of a rat. Approximately 15 % of this total is due to proton leakage inside the skeletal muscle alone. This study examined whether the rate of proton leak is down-regulated as a part of a coordinated response to energy conservation during metabolic depression in cold-submerged frogs. We compared the proton leak rate of skeletal muscle mitochondria isolated from frogs at different stages of hibernation (control, 1 month and 4 months of submergence in normoxia and hypoxia). The kinetics of mitochondrial proton leak rate was unaltered throughout normoxic and hypoxic submergence. The state 4 respiration rates did not differ between control animals and frogs hibernating in normoxia. In contrast, the state 4 respiration rates obtained from frogs submerged in hypoxic water for 4 months were half those of control animals. This 50 % reduction in respiration rate in hypoxic hibernation was due to a reduction in electron transport chain activity and consequent decrease in mitochondrial membrane potential. We conclude that proton leak rate is reduced during metabolic depression as a secondary result of a decrease in electron transport chain activity, but that the proton conductance is unchanged. In addition, we show that the rate of proton leakage and the activity of the electron transport chain are lower in frogs than in rats, strengthening the observation that mitochondria from ectotherms have a lower proton conductance than mitochondria from endotherms.

Animals↗
PubMed2006

Seasonal abundance and mortality of Oebalus poecilus (Dallas) (Hemiptera: Pentatomidae) in a hibernation refuge.

Oebalus poecilus (Dallas) is an important pest affecting irrigated rice in Rio Grande do Sul, Brazil. It hibernates during the coldest months of the year in refuges such as bamboo litter. This study examined O. poecilus hibernation to determine the causes of mortality during this period. The study was conducted in a 140 m(2) bamboo plantation located in a rice-growing area in Eldorado do Sul County (30 degrees 02 S and 51 degrees 23 W), RS. During June 2000 to April 2002, 63 samples of litter were taken in weekly or fortnightly intervals, and the number of bugs recorded in the laboratory. The arrival at the hibernation site (bamboo litter) began in the first fortnight of March, and was completed in the beginning of May. O. poecilus left this refuge from middle October to the end of December. Parasitism by tachinid flies and Beauveria bassiana (Bals.) Vuill. fungus were the most important mortality factors.

Animals↗
PubMed1977

Changes in enzyme levels in the testis and liver of the 13-lined ground squirrel (spermophilus tridecemlineatus) at the time of arousal from hibernation.

Male 13-lined ground squirrels induced to emerge from hibernation resumed feeding and gained weight. The weight gain was supported by increases in the levels of glucose 6-phosphate dehydrogenase, L-alanine aminotransferase and carnitine acetyltransferase in the liver. Maturation of the testis occurred in a period of about 16 days spanning the time of induced arousal. The testes of hibernating males were characterized by higher levels of L-alanine aminotransferase, glucose 6-phosphate dehydrogenase and 3-hydroxyacyl-CoA dehydrogenase than the testes of aroused males. Hexokinase, carnitine acetyltransferase and citrate synthase levels were similar in the testes of hibernating and aroused males. 3-Hydroxyacyl-CoA dehydrogenase was more active and L-alanine aminotransferase less active in ground squirrel sperm than in rat sperm.

Adaptation, Physiological↗
PubMed1975

Erythrocyte 2,3-diphosphoglycerate concentrations in hibernating, hypothermic, and rewarming hamsters (38589).

Hematocrit, hemoglobin and erythrocyte 2,3-DPG concentrations were examined in normothermic control, hibernating, and helium-cold hypothermic hamsters. Hematocrit was not signigicantly different (P greater than 0.05) between groups, but did reflect alterations reported for hemoglobin. Hemoglobin concentration did not change from control values during 12 hr at Tre 7 degrees; however, approximately a 20% decrease occurred in hibernators (48 hrs) and animals hypothermic (24 hr). 2,3-DPG concentrations declined 39.1 and 33.9% from control values in the hibernating and 24 hr hypothermic groups, respectively. No change was observed in animals hypothermic for 12 hr. Both parameters were studied in the aroused animal. Hemoglobin returns to control values immediately after the animals reached a stable Tre approximately equal to 37 degrees. Although 2,3-DPG levels increased during arousal, they were still 10% lower than control values in both metabolically depressed groups. 2,3-DPG remained approximately 10% less than controls in rewarmed hypothermic animals studied 2 hr after reaching stable Tre approximately equal to 37 degrees. The data are discussed in terms of cold depression of erythrocyte glycolysis.

Animals↗
PubMed2005

Atypical hematological response to combined calorie restriction and chronic hypoxia in Biosphere 2 crew: a possible link to latent features of hibernation capacity.

Eight humans were isolated for 2 years in Biosphere 2, a sealed airtight habitat with recycled air, food, water, and wastes. A combination of conditions led to selective decline of oxygen (O2) in the internal atmosphere from 21% to 14%, inducing symptoms of high-altitude sickness but with little or no compensatory increase in red cell production. All crew members exhibited significant decreases in both erythrocyte 2,3-bisphosphoglycerate (2,3-BPG) concentrations and P50 [partial pressure of O2 for 50% hemoglobin (Hb) saturation] values, changes opposite those expected in adaptation to high-altitude hypoxia. Lower P50 with increased Hb-O2 affinity induced by low 2,3-BPG is a characteristic of hibernating species and could be advantageous in O2-impoverished environments. The mechanisms underlying these changes in the Biosphere 2 crew remain obscure but could be related to low-calorie diet (1750-2100 kcal/day). Because the combination of hypoxia and limited caloric intake is also characteristic of hibernation, this unusual response may represent a cross-adaptation phenomenon in which certain features of hibernation capability are expressed in humans.

2,3-Diphosphoglycerate↗