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PubMed1988

Organ distribution of interferon after intravenous injection into active and hibernating spotted susliks.

Spotted suslik fibroblast interferon (SuIFN-beta) was given intravenously to animals active in summer and hibernating in winter. In both groups, most IFN was detectable in the serum 1 min after injection; in hibernating susliks, in spite of their arousal from hibernation, IFN remained detectable for a longer period in the serum. IFN was also detected in lungs, liver, spleen, and kidneys and in peritoneal washings. IFN levels in the organs were lower in hibernating susliks than in active ones, but, particularly in the spleen and kidneys, IFN remained detectable for longer in hibernating animals than in active susliks.

Animals↗

PubMed1982

Lipofuscin accumulation and hibernation in the Turkish hamster, Mesocricetus brandti.

This report is based on previous data that showed that Turkish hamsters that hibernated lived longer than nonhibernating controls. Fluorescent microscopy was used to measure the lipofuscin content of brain and heart of hamsters that hibernated for various fractions of their lives. According to regression data the 13 animals that hibernated 11 to 37% of their lives had a slower accumulation of lipofuscin than 11 animals that hibernated 0 to 7% of their lives. It was calculated that the total amount of pigment accumulated during a life span was the same in both groups, in spite of the longer life of the hibernators.

Animals↗

PubMed1986

The influence of hibernation on testis growth and spermatogenesis in the golden-mantled ground squirrel, Spermophilus lateralis.

Testis size and spermatogenesis were monitored serially in individual golden-mantled ground squirrels before, during, and after the hibernation season. During hibernation, animals spent 81% of days in torpor at body temperatures of 3-4 degrees C. Torpor bouts of 6 days duration were interspersed with brief arousals from torpor during which animals were normothermic. In the 5 mo between December (when animals entered hibernation) and April (when torpor was spontaneously terminated), the estimated mass of testes increased gradually from 500 to 1100 mg, but spermatogenesis did not advance beyond pachytene spermatocytes, which were present before hibernation began. In contrast, during the month after torpor was terminated, testes increased rapidly to 3500 mg and after 31 days, spermatozoa were found in the epididymides. We suggest that the limited testis growth that occurred during the hibernation season was restricted to intervals during which squirrels were aroused from torpor. The major portion of gonadal growth and spermatogenesis in the laboratory, and presumably in the field, occurs after ground squirrels have regained the normothermic state. Since males are reproductively mature when first trapped in spring, these findings suggest that males are normothermic for several weeks before they emerge from their hibernacula in the spring.

Aging↗

PubMed1997

The use of hibernation induction triggers for cardiac transplant preservation.

Cardiac transplant is hindered by donor shortage and preservation time. Extended extracorporeal preservation could increase the number and distribution of hearts for transplantation. Interestingly, mammalian hibernation biology closely parallels the altered cardiac cellular physiology noted with hypothermic organ storage. The present study undertook to test whether treatment with hibernation induction triggers could improve myocardial functional recovery following prolonged ischemic storage in a nonhibernating mammalian model. To study this hypothesis, isolated rabbit hearts had baseline functional and metabolic parameters recorded and then received either hypothermic storage only or standard cardioplegia, or cardioplegia containing 1 mg/kg D-Ala2-Leu5-enkaphalin (DADLE), which mimics natural hibernation, or preperfusion with DADLE, administered for 15 min at 2 mmol, 25 min prior to cardioplegic ischemia. Hearts were then subjected to 18 hr of global ischemic storage at 4 degrees C. Isovolumic developed pressure, coronary flows, and myocardial oxygen consumption were significantly improved with DADLE pretreatment vs. all groups after storage and reflow. Furthermore, DADLE hearts demonstrated better histological ultrastructure preservation following prolonged storage ischemia. This study demonstrates that hibernation protection with DADLE is beneficial for prolonged cardiac storage. The use of hibernation induction triggers is promising for organ preservation and deserve further mechanistic study.

Analysis of Variance↗

PubMed1990

Mammalian hibernation.

In mammalian hibernation, the body temperature approaches that of the surroundings, allowing large savings in energy costs of basal metabolism and eliminating the need for heat production to compensate for heat loss. During entry into hibernation, heat production ceases while the body temperature set-point gradually decreases during slow-wave sleep. In the hibernating phase, the animal copes with problems concerning the maintenance of ion gradients, possible membrane phase transitions and the risk of ventricular fibrillation. In the arousal phase, the main part of the heat and practically all the necessary substrate comes from brown adipose tissue. The hibernation season is preceded by a preparatory phase. It may be concluded that hibernation is a practical, and perhaps even enviable, solution to a mammalian problem.

Animals↗

PubMedDate not supplied

Effect of cold exposure on testicular delta 5-3 beta and 17 beta hydroxysteroid dehydrogenase activities and plasma levels of testosterone in toad (Bufo melanostictus) in breeding and hibernating season: duration-dependent response.

The purpose of this study was to show the effect of cold exposure on testicular activities in breeding and hibernating seasons in the toad. Adult male toads were placed in a cold chamber in both breeding and hibernating seasons for periods of 7, 14 and 21 days. At the time of sacrifice on the 15th and 22nd days, cold-exposed animals showed a decrease in testicular weight, testicular delta 5-3 beta and 17 beta-hydroxysteroid dehydrogenase activities and low levels of plasma testosterone both in breeding and hibernating seasons. There was no significant alteration in the above mentioned steroidogenic enzymes and plasma levels of testosterone after 7 days of cold exposure, both in breeding and hibernating seasons in respect to the control animals. The results of our present experiment suggest that environmental cold is an important modulator of breeding activities in the male toad. It also indicates that the breeding and hibernating cycle in the toad (seasonal breeders) may be asynchronous to each other.

17-Hydroxysteroid Dehydrogenases↗

PubMed1983

Synaptosomal and brain mitochondrial lipids in hibernating and cold-acclimated golden hamsters.

Synaptosomes and mitochondria were isolated from the brains of warm-adapted, hibernating, and cold-acclimated golden hamsters (Mesocricetus auratus). Lipid extracts of these subcellular fractions were prepared and assayed for plasmenylethanolamine (ethanolamine plasmalogen) and cholesterol levels. The ganglioside composition of synaptosomes was also determined. Samples from the hibernating animals showed characteristic changes in lipid composition. These changes include decreases in plasmenylethanolamine levels and a shift in the ganglioside composition toward a higher percentage of the more polar gangliosides. Those animals which were exposed to cold and did not hibernate (cold-acclimated) showed no such changes. Fatty acid analyses of synaptosomal and mitochondrial ethanolamine glycerophospholipids demonstrated a similar trend. Samples from hibernators showed decreases in 16:0, 18:0, and 22:6 (n-3), and increases in 16:1, 18:1, and 20:4 (n-6) fatty acids. No changes were detectable in samples from cold-acclimated animals, indicating that hibernating and cold-acclimated hamsters represent chemically distinct populations.

Acclimatization↗

PubMed1984

Calcium source for excitation-contraction coupling in myocardium of nonhibernating and hibernating chipmunks.

The amplitude of the early plateau phase of the action potential and the slow action potential of cardiac muscle were much lower in hibernating chipmunks than in nonhibernating chipmunks. The frequency-dependent contraction was decreased in hibernating animals but increased in nonhibernating animals. Caffeine caused a negative inotropic effect in hibernating animals but a positive inotropic effect in nonhibernating animals. Ryanodine caused greater inhibition in hibernating animals than in nonhibernating animals. These results suggest that the respective roles of the sources of calcium for cardiac excitation-contraction coupling are changed during hibernation.

Action Potentials↗

PubMed1990

Smooth muscle contractility and calcium channel density in hibernating and nonhibernating animals.

Hibernating animals consistently survive prolonged periods of cold with body temperatures near the freezing point. Previous studies have suggested that regulation of calcium influx may be a fundamental cellular mechanism for cold tolerance in hibernating species. The present study was undertaken to compare (i) the calcium dependence of contractility and (ii) [3H]nitrendipine binding in homogenates of ileal longitudinal smooth muscle from the nonhibernating guinea pig (Cavia porcellus) and a hibernator, the ground squirrel (Spermophilus richardsonii). The contractility studies indicate that both the activation threshold for calcium and the concentration-response curve were shifted to the right in ground squirrel when compared with guinea pig. The binding site density in ground squirrel muscle was about an order of magnitude less than in guinea pig (Bmax = 10 +/- 2 (n = 12) and 86 +/- 6 fmol/mg protein (n = 5), respectively). These results indicate that ground squirrel tissues are less sensitive to external calcium and clearly have fewer calcium channels than the smooth muscle of the non-hibernator. The results continue to support the hypothesis that cold tolerance in hibernating species involves calcium homeostatic control mechanisms.

Animals↗

PubMed1975

Cold resistance of the brain during hibernation. III. Evidence of a lipid adaptation.

The composition of membrane-bound lipids of brain from both warm-adapted and hibernating hamsters were different in the complex lipid fraction as well as their fatty acyl chains. During hibernation the content of cholesterol was less, but there were greater amounts of both the phosphatidylcholines and phosphatidylethanolamines. There were small but significant increases in monounsaturated fatty acids as well as arachidonic acid in all the glycerophosphatides of the hibernating hamster, whereas a decrease in isomyristic acid was o0served in the sphingomyelins. The most significant changes observed occurred in the fatty aldehyde composition of ethanolamine plasmalogen. A dramatic increase in oleyaldehyde was observed during hibernation. These changes in membrane-bound lipids may account for the cold-resistant properties of the brain during hibernation by retaining the fluid nature of the cell membrane.

Acclimatization↗

PubMed2005

Sympathetic alpha-adrenergic regulation of blood flow and volume in hamsters arousing from hibernation.

Mammals arousing from hibernation display pronounced regional heterothermy, where the thoracic and head regions warm faster than the abdominal and hindlimb regions. We used laser-Doppler flowmetry to measure peripheral hind foot blood flow during hibernation and arousal and gamma imaging of technetium-labeled albumin to measure whole blood volume distribution in hamsters arousing from hibernation. It was discovered that the hibernating hamster responds to physical but not to sound or hypercapnic stimulation with rapid, 73% reduction of hind foot blood flow. Hind foot blood flow vasoconstriction was maintained from the onset of arousal until late in arousal when rectal temperature was rapidly increased. alpha-Adrenergic blockade early in arousal increased hind foot blood flow by 700%, suggesting that vasoconstriction was mediated by activation of sympathetic tone. Gamma imaging revealed that, by the early phase of arousal from hibernation, the blood volume of the body below the liver is greatly reduced, whereas blood volumes of the thorax and head are much greater than corresponding volumes in anesthetized hamsters. As arousal progresses and cardiac activity increases and regional heterothermy develops, this regional blood volume distribution is largely maintained; however, blood volume slowly decreases in the thoracic region and slowly increases in the shoulder and head regions. The rapid increase in rectal temperature, characteristic of mid- to late- arousal phases, is probably mediated, in part, by reduction of adrenergic tone on abdominal and hindlimb vasculature. Warm blood then moves into the hind body, produces an increase in temperature, blood flow, and blood volume in the hind body and compensatory reductions of blood volume in the neck, head, and thoracic regions.

Animals↗

PubMed1981

Coronary circulation in hearts from hibernating, normothermic, and cold-acclimated hamsters.

We have investigated the influence of temperature, acute global ischemia, adenosine administration, and alterations in perfusion pressure on the coronary circulation of isolated, perfused spontaneously beating hearts from hibernating, normothermic, and cold-acclimated (nonhibernating) hamsters. No differences in heart rates were observed among groups at either 9 or 38 degrees C. Hearts from hibernating hamsters showed some differences in autoregulatory capacity at both the low and normal temperatures. All hearts exhibited similar responses to 30 s of global ischemia at both temperatures, with a marked reduction in the response at 9 degrees C. Similarly, the magnitude of the vasculature response to adenosine (250 micrograms) at 38 and 9 degrees C was equal in both normothermic and hibernating hearts perfused at 38 degrees C. Responses were abolished in all groups at 9 degrees C. We conclude that the altered ability of hibernating hearts to autoregulate is possibly due to intrinsic differences initiated by hibernation, while the responses to adenosine, and global ischemia are largely temperature-dependent effects.

Acclimatization↗

PubMed1984

Plasma melatonin concentrations in hibernating marmots: absence of a plasma melatonin rhythm.

Plasma melatonin concentrations were measured throughout bouts of hibernation in marmots maintained in a short photoperiod (light-dark 8:16) and ambient temperature of 5 or 15 degrees C. Melatonin concentration was also measured in two animals maintained in constant darkness. As an animal entered hibernation, plasma melatonin concentrations dropped to basal levels when body temperature reached 25 degrees C, and they remained low until arousal. During deep hibernation plasma melatonin values did not vary significantly (P greater than 0.05) with respect to time of day or different ambient temperatures. With nocturnal arousal plasma melatonin levels were similar to euthermic night values. Lack of a plasma melatonin rhythm during hibernation suggests that the pineal gland is not temperature compensated during hibernation, and due to the low tissue temperature of the pineal the circadian pacemaker driving melatonin secretion is incapable of stimulating a rhythm.

Animals↗

PubMed1986

Vascular smooth muscle responsiveness in a hibernator: effects of season and temperature.

To determine the effects of season, acclimation state, and hibernation on the reactivity of vascular smooth muscle from a hibernant species, strips of thoracic aorta, renal and femoral arteries, and portal vein obtained from adult woodchucks, Marmota monax, were suspended for isometric tension measurements in physiological salt solution. These blood vessels exhibited no seasonal variation in resting tension, connective tissue content, or maximum tension developed to norepinephrine. However, the concentration-response curves to norepinephrine in both aortic and portal vein strips from animals tested in May and June were shifted to the left of those from animals tested in either August or November through February. This increased sensitivity to the catecholamine was seen also in renal vessels from hibernating compared with nonhibernating animals. Decreasing organ bath temperature from 37 to 28 degrees C increased tension developed in response to norepinephrine in aortic and renal strips, whereas that of the femoral artery was unchanged. With further cooling to 17 degrees C, the responses to norepinephrine in aortic and renal strips were similar to the responses at 37 degrees C. The contraction developed to 40 mM KCl was diminished in all tissues at 28 degrees C. Blockade of beta-adrenergic receptors did not augment the response to norepinephrine at 37 degrees C. Contractions of the woodchuck aorta in calcium-free medium were sustained longer than comparable tissue obtained from a rabbit. These data suggest that receptor-mediated processes are modulated in hibernating animals. This modulation varies among vascular beds and may act to maintain or divert perfusion of the tissue through entry, during, and arousal from hibernation.

Acclimatization↗

PubMed1988

Neuronal activity during sleep and complete bouts of hibernation.

Changes in arousal state in a euthermic mammal exert powerful influences on major neural regulatory systems. Changes in behavioral state occur at body temperature (Tb) greater than 25 degrees C during hibernation. However, no information exists regarding alterations in arousal states during deep torpor. In this study we used a combination of electroencephalographic, electromyographic, and posterior thalamic neuronal activity in ground squirrels (Spermophilus lateralis) to evaluate arousal states during deep hibernation. No state homologous to rapid-eye-movement sleep was observed below Tb = 21 degrees C during hibernation. However, the animals did continue to cycle through states homologous to electrophysiologically defined wakefulness (AW) and non-rapid-eye-movement (NREM) sleep at all temperatures examined (Tb = 14-36 degrees C). These results extend previous observations that hibernation is not a homogeneous state. Instead, deep torpor consists primarily of a state similar to NREM sleep, interrupted periodically by short intervals of a form of AW. These periodic alterations in state should be accompanied by changes in the properties of many regulatory systems and must be accounted for in any theory of the neural control of hibernation.

Acclimatization↗

PubMed1989

Rare fatty acids in brown fat are substrates for thermogenesis during arousal from hibernation.

Because brown adipose tissue lipids are the preferred substrate for thermogenesis during arousal from hibernation, the fatty acid composition of brown fat lipids was followed during cold acclimation and during a hibernation bout. In control golden hamsters (living at 22 degrees C), the fatty acid composition of the white adipose tissue closely resembled that of the food, but brown adipose tissue contained more animal-derived fatty acids. As an effect of acclimation to cold, the fatty acid composition of brown adipose tissue changed to resemble that of the food, and no marked differences between white and brown adipose tissue were then evident. During a hibernation bout, a major part of the fatty acids accumulated in brown fat during entry into hibernation consisted of "rare" acids, such as homo-gamma-linoleic acid. Homo-gamma-linoleic, together with eicosadienoic acid and lignoceric acid, was preferentially utilized during the early phase of arousal. During this phase, "bulk" fatty acids, such as linoleic acid, were spared, whereas in late arousal, linoleic acid was the preferred substrate. It was concluded that rare fatty acids are of quantitative significance in brown adipose tissue during hibernation and arousal.

Adipose Tissue↗

PubMed1989

Brown fat thermogenesis during hibernation and arousal in Richardson's ground squirrel.

The thermogenic activity [mitochondrial guanosine 5'-diphosphate (GDP) binding] and capacity (uncoupling protein concentration, cytochrome oxidase activity) of brown adipose tissue have been investigated at different phases of the seasonally linked hibernation cycle in Richardson's ground squirrel. The amount of axillary brown adipose tissue and the total mitochondrial content of the tissue were substantially greater in hibernating squirrels than in squirrels caught posthibernation in April or May; cold acclimation induced qualitatively similar differences. The specific mitochondrial concentration of uncoupling protein was high under all conditions (compared with other species), differing little between hibernating, posthibernating, and cold-acclimated squirrels. The thermogenic capacity of brown adipose tissue in Richardson's ground squirrels is therefore modulated almost exclusively by changes in the mitochondrial content of the tissue. Mitochondrial GDP binding was increased on cold acclimation, but similar binding levels were observed in hibernating and posthibernation (May) animals. GDP binding and the GDP-sensitive component of acetate-induced mitochondrial swelling were increased during the early stages of arousal from hibernation. These changes, which indicate an activation of the thermogenic proton conductance pathway in arousal, occurred without an alteration in the specific mitochondrial concentration of uncoupling protein. Increased GDP binding during arousal is clearly due to the unmasking of binding sites, reflecting an acute activation of preexisting uncoupling protein.

Acetates↗

PubMed1993

The effect of a low essential fatty acid diet on hibernation in marmots.

We investigated the effect of an essential fatty acid (EFA)-deficient diet on hibernation patterns in yellow-bellied marmots (Marmota flaviventris). Fatty acid (FA) analysis of white adipose tissue (WAT) from animals maintained for 2 mo on the EFA-deficient diet suggested that little or no EFAs were present in the gonadal or omental fat depots. Hibernation about lengths of the EFA-deficient animals were significantly shorter (P < 0.01) than control animals. Stated another way, these animals aroused twice as frequently compared with control animals and used more energy to survive winter. Analysis of WAT composition and blood samples revealed that animals were highly lipolytic during winter. Furthermore, the release of FAs was not random: linoleate (cis-9,cis-12-octadecadienoic acid; 18:2, a diene EFA) was significantly (P < 0.05) under-represented in venous outflow from the gonadal WAT pad based on the percentage of this species in WAT. The concentration of saturated FAs was higher than that predicted from the WAT-FA composition. We conclude that linoleate is preferentially retained within WAT and that concentrations of this EFA may influence hibernation behavior. Thus EFAs may have a thermoregulatory role in hibernation in addition to their role as essential precursors for physiologically important lipids after hibernation is over.

Adipose Tissue↗