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PubMed1996

Decreased calcium accumulation in isolated nerve endings during hibernation in ground squirrels.

Resting and depolarization-induced 45CaCl2 accumulation was compared for synaptosomes isolated from hibernating and nonhibernating ground squirrels. Channel subtype antagonists were used to identify the active voltage-sensitive calcium channel subtypes in these preparations. There was significantly less 45Ca2+ accumulation in synaptosomes isolated from hibernating as compared to cold-adapted nonhibernating ground squirrels in both basal (p < 0.005) and depolarizing (p < 0.03) media over a 30 sec to 5 min incubation period. The elevation in 45Ca2+ accumulation triggered by K+ depolarization was blocked by 50 microM CdCl2, 1 microM omega-conotoxin MVIIC or 1 microM omega-agatoxin IVA. Inhibition was not observed with 1 microM nifedipine or with 1 microM omega-conotoxin GVIA. These results suggest that hibernation is associated with reduced presynaptic 45Ca2+ conductance via voltage-sensitive channels with a pharmacological sensitivity that is different from the established L-, N-, and P-types in other systems but share features of the recently described Q-type calcium channel. This decrease may reflect a cellular adaptation that helps confer tolerance to the near total cerebral ischemia associated with hibernation.

Acetylcholinesterase↗
PubMed2005

Proteolysis is depressed during torpor in hibernators at the level of the 20S core protease.

Protein synthesis is depressed during mammalian hibernation in concordance with metabolic demands. In the absence of significant protein synthesis, continued proteolysis would rapidly deplete protein pools. Since ubiquitin-dependent proteolysis is implicated in the turnover of most regulatory proteins, we examined the fate of this system during hibernation. Ubiquitin-dependent proteolysis consists of two major steps: (1) the tagging of a protein substrate by ubiquitin and (2) the protein substrate's subsequent degradation by the 26S proteasome. An earlier study revealed a two to threefold elevation of ubiquitin conjugate concentrations during hibernation: an unexpected result that seemingly would suggest increased proteolytic activity. A more likely explanation for these data would be that proteolysis per se was depressed and that the increased levels of ubiquitylated proteins reflect an inability to degrade tagged proteins. We employed an assay based on the cleavage of fluorogenic substrates to address the well characterized proteolytic activities of the proteasome. All activities show little to no activity at temperatures associated with deep torpor. Coordinated depression of proteolytic activities by low temperature supports the hypothesis that the increased levels of ubiquitylated proteins during hibernation is explained by a net accumulation due to an inability to degrade the tagged proteins.

Adaptation, Physiological↗
PubMed2005

Effects of hibernation on multicatalytic proteinase complex in thirteen-lined ground squirrels, Spermophilus tridecemlineatus.

Multicatalytic proteinase complex (MCP) was studied in skeletal muscle of the hibernating ground squirrel, Spermophilus tridecemlineatus. MCP was partially purified using a S-400 gel filtration column and Centricon concentrating devices and assayed fluorometrically using three AMC-labeled substrates. K(m) and V(max) values were determined for each substrate with no significant differences between the enzyme from euthermic versus hibernating animals when assayed at 23 degrees C. However, properties of MCP from euthermic and hibernating ground squirrels were differentially affected by low assay temperature (8-10 degrees C) and also differed from the mouse enzyme, the data indicating that ground squirrel MCP is better suited for low temperature function. MCP preferentially degrades oxidatively-damaged proteins and quantification of protein carbonyl content showed that the level of oxidatively-damaged protein in skeletal muscle decreased by > 75% during hibernation suggesting a continuing role for the MCP in the torpid state.

Animals↗
PubMed1996

Extended lung preservation with the use of hibernation trigger factors.

BACKGROUND: The complications of preserving lungs for transplantation are well known, with successful transplantation only being assured by preservation times of 5 to 6 hours or less. If a new method of consistent lung preservation could be identified, lung transplantation could be extended to many patients. We have previously reported lung preservation times averaging 14.8 hours using a multiorgan autoperfusion block infused with physiologic saline solution as a model. When plasma from deeply hibernating woodchucks (Marmota monax) or the delta opioid DADLE was infused into the multi-organ block, lung preservation times increased threefold to 45 hours. METHODS: In this study, we examined the effect of infusing plasma containing the hibernation induction trigger molecule on lung preservation for transplantation using a multiorgan autoperfusion block. RESULTS: This study demonstrated that successful orthotopic transplantation of single canine lungs is possible after 24 to 33 hours of preservation when the lung has been maintained with plasma containing the hibernation induction trigger molecule. CONCLUSIONS: Theoretically, hibernation induction trigger could be administered to donors before lung harvest in an effort to extend lung preservation times.

Animals↗
PubMed1976

Cultured cells from renal cortex of hibernators and nonhibernators. Regulation of cell K+ at low temperature.

Cells were grown as primary monolayer cultures from kidney cortex of guinea pigs (nonhibernators), hamsters and ground squirrels (both hibernating species). When plates of cells were placed at 5 degrees C, cells of guinea pigs lost 37% of their K+ in 2 h and those of the hibernator lost about 10%. Uptake of 42K into the cells exhibited a simple, single exponential time course at both temperatures. Unidirectional efflux of K+ was equal to K+ influx in all cultures at 37 degrees C and, within limits of error, in hibernator cells at 5 degrees C. Efflux was 3-to 5-fold greater than influx in guinea pig cells at 5 degrees C. After 2 h in the cold the ouabain sensitive K+ influx remaining (7-15% of that at 37 degrees C) was about the same in the cells of the 3 species. Cells from active hamsters and from hibernating ground squirrels, however, exhibited significantly greater pump activity after 45 min in the cold (19 and 14%, respectively). The stimulation of K+ influx by increasing [K+] did not show an increase in Km+ at 5 degrees C in cells of guinea pigs and ground squirrels. Lowering [K+]c and/or raising [Na+]c by treatment in low- and high-K+ media caused only slight stimulation of K+ influx, except in cells of ground squirrels at 5 degrees C in which the stimulation was at least 11-times greater than at 37 degrees C or in cells of guinea pigs at either temperature. This altered kinetic response of K+ transport to cytoplasmic ion stimulation with cooling accounted for about one-third of the improved regulation of K+ at 5 degrees C in ground squirrel cells; the other two-thirds was attributable to a greater decrease in K+ leak with cooling. The inhibition of active transport by cold in all 3 species was much less severe than that previously seen in any (Na++K+)-ATPase of mammalian cells.

Animals↗
PubMed1985

Antagonism of brain opioid peptide action reduces hibernation bout duration.

The effect of continuous intracerebroventricular (i.c.v.) administration of naloxone on the duration of individual bouts of hibernation was investigated in the golden-mantled ground squirrel (Citellus lateralis). Following entrance into hibernation, naloxone was continuously administered by an osmotic minipump at a rate of 1 microliter/h through a chronically implanted unilateral i.c.v. cannula guide. Naloxone (1, 5 and 7.5 micrograms/microliter) produced a dose-dependent reduction in hibernation bout duration ranging from 1 to 4 days (13.9-62.3% of expected bout duration). These data suggest that selected endogenous opioid system neurons may contribute to the CNS maintenance of the hibernating state and, consequently, to the overall conservation of energy in this species.

Animals↗
PubMed1989

Metabolism in the hamster brain during hibernation and arousal.

Hibernation was induced in hamsters by placing them in a cold room for an extended period of time, after which the hibernating state was confirmed by marked reductions in heart rate, body temperature, and the respiratory rate. The animals were either frozen intact in liquid nitrogen, or aroused and then frozen when body temperature reached 8, 12, 16, 20, 24 or 32 degrees C. A metabolite profile, including glucose-related metabolites, high-energy phosphates, gamma-aminobutyric acid (GABA) and cyclic nucleotides, was determined for both the cerebral cortex and cerebellum. In general, the metabolite changes in the two regions elicited by hypothermia were alike, although some differences were evident. The brains of hibernators were biochemically characterized by (1) a high concentration of energy reserves including glycogen, glucose, adenosine triphosphate, and P-creatine, (2) significantly elevated levels of lactate and GABA, and (3) near depletion of cyclic guanosine monophosphate with only a moderate depression of cyclic adenosine monophosphate. During arousal, the metabolites were restored to near normal values and there was little or no indication that the brain energy metabolism was compromised by the arousal process. The study provides certain insights into the metabolic adaptation of the brain to prolonged periods of profound hypothermia in a hibernating species.

Adenosine Triphosphate↗
PubMed1983

Ventricular fibrillation in hibernators and nonhibernators.

Previous studies have shown that there are differences between hibernators and nonhibernators in the susceptibility to ventricular fibrillation. In an attempt to clarify these differences ventricular fibrillation was induced in isolated hearts of the hibernator, the woodchuck, Marmota monax by cooling, warming, puncture, and by norepinephrine administration. It was shown that the hearts of the winter animals were completely resistant toward the ventricular fibrillation inducing agents, which was not the case for the hearts from summer, active animals. Further, the hearts of another hibernator, the hedgehog, Erinaceus europaeus, and guinea pig, Cavia porcellus, were studied electrophysiologically in anesthetized animals with open chests and with bipolar electrodes attached to the epicardium. During pacing it was shown that the hedgehog had a higher stimulus threshold and a lower maximal following frequency than the guinea pig. The summer hedgehogs showed resistance toward both ventricular premature beats and ventricular fibrillation. Sixty percent of the summer hedgehogs and 100 percent of the winter hedgehogs and guinea pigs developed ventricular fibrillation. The threshold for ventricular fibrillation was highest for summer hedgehogs. The effective refractory period of papillary muscle of summer hedgehogs was shorter than that of guinea pigs. The force frequency relationship of the isolated papillary muscle showed a greater degree of independence in the hedgehog than in the guinea pig. Consequently, the results show that the heart of the hibernator is more arrhythmia resistant than the heart of the nonhibernator, although there are seasonal differences.

Animals↗
PubMed1986

Ultrastructure of the proximal convoluted tubule in the hibernating garden dormouse (Eliomys quercinus L.).

We have carried out an ultrastructural study of the proximal convoluted kidney tubule in hibernating and nonhibernating garden dormice. Deep hibernation produced the following changes: the nuclei had an irregular shape; saccular cavities appeared near the nucleus and there was an increase in the components of the lysosomal system; hibernation seems to have no influence on the number of mitochondria; hypertrophic mitochondria occur in controls, whereas none were ever seen in hibernating dormice.

Animals↗
PubMed1992

Hibernation alters the frog's immune system.

The lymphomyeloid organs and blood leukocyte populations of the leopard frog, Rana pipiens, undergo conspicuous changes during hibernation at 4 degrees C. Within the blood, spleen, thymus, jugular bodies, and bone marrow there was a progressive loss of hemopoietic populations resulting in a marked lymphocyte depletion. Termination of the 135-day hibernation period resulted in the restoration of all hemopoietic elements in the blood and lymphomyeloid organs within 30 days. Frogs subjected to experimental hibernation and immunized showed weakened immune responses when brought from the hibernaculum. Plaque-forming cells (PFC) were lower in spleen, jugular bodies, and bone marrow, and serum antibody titers were also lower. Although the kinetics of the primary responses were essentially the same, the secondary responses differed suggesting major rearrangements with respect to the numbers of cells and their function in secreting antibody. The apparent lymphocyte aplasia may contribute to the absence of immunological responsiveness during periods of hibernation.

Animals↗
PubMed1990

Carboxyatractylate-sensitive uncoupling in liver mitochondria from ground squirrels during hibernation and arousal.

Energy coupling parameters of liver mitochondria from hibernating and arousing ground squirrels have been studied. In the oligomycin-treated mitochondria, carboxyatractylate, an inhibitor of the ATP/ADP-antiporter, is shown to decrease the respiration rate, to increase the membrane potential and to lower the rate of the membrane-potential discharge after the addition of cyanide to liver mitochondria from hibernating and arousing animals. BSA effectively substitutes for carboxyactactylate so that carboxyactactylate, added after BSA, has no effect. In mitochondria from hibernating animals, the maximal respiration rate in the presence of DNP and the rate of the membrane potential discharge in its absence are much lower than in those from arousing animals. It has been concluded that upon arousal of the animals from hibernation, the uncoupling of oxidative phosphorylation, mediated by free fatty acids and ATP/ADP-antiporter, parallels the respiratory chain activation.

2,4-Dinitrophenol↗
PubMed1986

Annual cycles of gonadotropins and androgens in the hibernating golden-mantled ground squirrel.

Ground squirrels, captured in the field, were housed at ambient temperatures of 23 degrees (photoperiod = 10L:14D) for 13 months. Plasma was sampled at 3 to 4-week intervals and measured for gonadotropin and androgen levels. Testis size was examined monthly by laparotomy. Male ground squirrels showed clear circannual cycles in body mass, testis size, and levels of follicle-stimulating hormone (FSH), luteinizing hormone (LH), testosterone (T), and dihydrotestosterone (DHT). During summer and fall, FSH, LH and androgen levels were low, testes were undeveloped, and body mass was increasing. Testes began to rapidly enlarge in January and reached maximum size in February. A rise in FSH preceded gonadal growth but LH remained low until near the time of testis mass peak. LH remained elevated during spring while FSH levels fell and testes regressed. Plasma T and DHT levels generally paralleled LH concentrations; DHT levels were approximately one-fifth those of T levels. During winter animals lost weight but were only occasionally found in a slightly hypothermic condition. Females had elevated plasma LH levels (greater than 1 ng/ml) predominantly in the spring but displayed no cycle in plasma FSH levels. A second group of males held at 4 degrees for 8 months (photoperiod = stimulated natural for 47 degrees N) were regularly torpid during a hibernation season that lasted between November and May. Most (15/21) of these males did not show gonadal development by spring; these non-reproductive males had had restricted body mass gains the previous fall. Plasma FSH was low in both reproductive and non-reproductive males during fall and winter but increased in March while animals were still hibernating. FSH levels continued to increase in April only in reproductive males and reached maximal levels after hibernation was spontaneously terminated. LH titers were elevated in individual males in winter during torpor and were greater in reproductive than in non-reproductive males in May. Androgen levels were undetectable in torpid squirrels, elevated in animals sampled during periodic arousals, and elevated in most males within 3 weeks after terminating hibernation.

Androgens↗
PubMed1987

[Relations between hibernation and the resumption of endocrine, testicular and thyroid activities, in Vipera aspis L. (Reptilia, Viperidae)].

The relationships between the end of hibernation and testicular and thyroid endocrine recrudescence were tested in Vipera aspis by subjecting hibernating vipers to experimental climatic conditions. Vipers kept under artificially warmed conditions (for 3.5 hr during the day to a thermal gradient from 11 to 27 degrees) 1 month before emergence showed an increase in plasma testosterone before vipers exposed to natural conditions (outdoor enclosures) did. The use of different photoperiodic conditions, long, LD 12:12, and short, LD 8:16, shows that photoperiod length has no effect on this increase. For vipers kept under prolonged hibernation (under a uniform temperature of 5 degrees or exposed to natural conditions at the northern limit of the species' distribution), testicular endocrine recrudescence was observed as soon as the first emergence only for the vipers placed at the northern range limit. Whatever the conditions, experimental or natural, the emergence of vipers always corresponds to a weight loss correlated with the increase of plasma thyroxine level. The relationship between the end of hibernation and testicular and thyroid endocrine recrudescence is discussed.

Animals↗
PubMed1988

Thyroid hormone resistance in hibernating ground squirrels, Spermophilus richardsoni. II. Reduction of hepatic nuclear receptors.

Hepatic nuclear triiodo-L-thyronine (T3) receptors were studied to investigate the mechanism of thyroid hormone resistance in Richardson's ground squirrels, Spermophilus richardsoni, during the hibernation phase of the annual cycle. The cycle is divided into an active phase and a hibernation phase, the latter composed of alternating dormancy and arousal bouts. In addition to animals in these three states, a group of cold-exposed animals was also examined (those animals held at 6 degrees which showed no indications of entering hibernation). Binding of T3, to squirrel hepatic nuclei from all groups, was characterized as high affinity, Kd ranging from 111 to 267 pM, and low capacity, 50 to 314 fmol T3/mg DNA. Based on these data, other criteria examined, and models established in the literature for other species, this binding site has been tentatively identified as a T3 receptor. Receptor concentrations in nuclei from dormant and aroused squirrels were only 15-20% of the concentration in active animals. There were no differences in the affinity of the T3 receptor over the annual cycle estimated by the in vitro assay at 24-26 degrees. The reduction in nuclear T3 receptors, together with the previously reported increase in serum binding of thyroid hormone, provides an explanation for thyroid hormone resistance during the hibernation phase in S. richardsoni.

Animals↗
PubMed1985

Pulmonary design in a microchiropteran bat (Pipistrellus subflavus) during hibernation.

The Eastern pipistrelle (Pipistrellus subflavus) is typical of exceptionally small bats capable of a 30-fold range in aerobic metabolism as they arouse from hypothermia and sustain foraging flight. This report describes their basic lung structure and the extent to which this organ is protected from protein depletion during hibernation. Bats were collected at the beginning (Fall), middle (Winter), and end (Spring) of hibernation from a permanent overwintering cave, and analyzed within several days of capture. Regardless of whether bats were examined in the Fall (average body weight = 6.22 g) or in the Spring (4.58 g) no significant differences existed for total lung volume (237 microliter), alveolar surface area (338 cm2), harmonic mean septal thickness, tau ht (0.221 micron), or membrane diffusing capacity (4.13 microliter O2/sec/mbar). These parameters exceed predictions based on body weights for either season, and resemble published data for another highly active mammalian group, the insectivorous shrews. Both tau ht and the minimal septal thickness of 0.083 micron approach the anatomical limits for thinning of alveolar septa without loss of epithelial continuity. Although both the heart and lungs lost 13% of their fresh weights during hibernation, compared to 25% for the liver, the lung contents of DNA (0.14 mg) and blood-free protein (7.38 mg) were not altered significantly. These small bats possess lungs which are well suited for the high aerobic cost of flight. Those lungs are resistant to hibernation-induced proteolysis, and also resistant to the deterioration of alveolar membranes which occurs in nonhibernators subjected to starvation-induced weight losses of similar magnitude.

Animals↗
PubMed1987

Nuclear changes and morphology of the epidermis in the hibernating frog.

Cytochemical changes of chromatin and DNA in frog epidermal cells were correlated with some morphological features to investigate the skin physiology during hibernation in comparison with the active period. The epidermal cells of hibernating frogs showed less condensed chromatin in all the layers; a greater loss of DNA was found during the transition from the middle to the superficial layer. In the germinative layer, a lesser frequency of hyperdiploid cells and a remarkably low amount of mitoses were detected; this is accompanied by the increase of epidermal thickness and the presence of two layers of cornified cells. The slowing of tissue differentiation and cell renewal kinetics during hibernation can be related to lowered activity of the frog skin. Further, the smaller intercellular spaces as well as the scarcity of puffed ER and vacuoles may be indicative of a lower ion transport in epidermal cells during hibernation.

Animals↗
PubMed1981

Brain serotonin metabolism in hibernation.

It has been shown that notwithstanding 2-fold decreased monoamine oxidase (MAO) activity in brain of hibernating ground squirrels (Citellus erythrogenys major, Brandt), serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) levels in most of the brain areas studied were not significantly different from the ones in active ground squirrels. However, marked changes were revealed in 5-HT and 5-HIAA brain level in entering hibernation (body temperature 11-9 degrees C) and arousing (body temperature 22 degrees C) animals. In entry into hibernation an increase in brain 5-HT, decrease in 5-HIAA level and lowered MAO activity was found. In arousal from hibernation 5-HT was decreased, 5-HIAA was increased and MAO activity was found to be increased to the level of the active ground squirrels.

Animals↗
PubMed1982

Hibernation "trigger": opioid-like inhibitory action on brain function of the monkey.

A hibernation "trigger" factor derived from the blood of the hibernating woodchuck acts to suppress vital physiological processes in the primate. When infused into the cerebral ventricle of the conscious monkey, the factor induced hypothermia, behavioral depression, bradycardia and aphagia. The opiate antagonists, naloxone and naltrexone, either reverse or retard these behavioral and physiological signs. We hypothesize that the "trigger" molecule is an endogenous opioid-like peptide which may be unique to the hibernator. Moreover, the non-hibernating primate apparently possesses receptor sites in the brain that are capable of responding to this potent molecule.

Animals↗