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PubMed2001

Temporal organisation of hibernation in wild-type and tau mutant Syrian hamsters.

The temporal pattern of hibernation was studied in three genotypes of Syrian hamsters with different circadian periodicity to assess a potential circadian control of alternating torpor and euthermy. We recorded the pattern of hibernation by measuring activity in continuous dim light and constant environmental temperature (6 +/- 1 degrees C). In spite of differences in the endogenous circadian period of three genotypes (tau +/+: approximately equals 24 h, tau +/-: approximately equals 22 h, and tau -/-: approximately equals 20 h) torpor bout duration was statistically indistinguishable (tau +/+: 86.9+/-5.3 h; tau +/-: 94.2+/-3.3 h; tau -/-: 88.8+/-6.2 h). The time between two consecutive arousals from torpor showed unimodal distributions not significantly different between genotypes. The first entry into torpor occurred within the active phase of the circadian cycle in all genotypes whereas the first arousal from torpor appeared to be timed randomly with respect to the prior circadian cycle. The amplitude of the activity rhythm was lower after hibernation compared with the amplitude before hibernation. The results suggest that in the Syrian hamster the circadian system does not control periodicity of torpor and arousal onsets in prolonged hibernation at 6 degrees C.

Animals↗
PubMed1997

The somatostatin system of the brain and hibernation in the European hamster (Cricetus cricetus).

The depression of physiological processes characteristic of mammalian hibernation is precisely regulated by the central nervous system, especially by the neuropeptidergic apparatus of the hypothalamus. Because of inhibitory influences on neuronal circuits within the brain and suppressive effects on the metabolism via the endocrine axis, somatostatin has been implicated in the regulation of hibernation. The somatostatin system of the brain was investigated with immunocytochemistry, in situ hybridization, and radioimmunoassays in euthermic summer, euthermic winter, and hibernating European hamsters (Cricetus cricetus). Numerous somatostatin-immunoreactive perikarya were observed in the periventricular hypothalamic nucleus. The striatum, amygdala, and cortex contained only scattered immunoreactive perikarya. These entities also contained immunoreactive fiber profiles, although the highest density of immunoreactive fibers was found in the median eminence. Immunocytochemistry and radioimmunoassays showed that the number of somatostatin-immunoreactive perikarya and fibers and the content of somatostatin in the hypothalamus and the median eminence was conspicuously lower in euthermic winter animals than in euthermic summer animals. This decrease was more pronounced in hibernating specimens. In situ hybridization also demonstrated a decrease in the expression and synthesis rate of somatostatin in euthermic winter animals; again, this was even more dramatic in hibernating hamsters. These changes were less pronounced or non-significant in the extrahypothalamic somatostatin-immunoreactive perikarya and fiber systems, as shown by immunocytochemistry and radioimmunoassay, respectively.

Animals↗
PubMed1998

Ultrastructural, morphometrical and immunocytochemical analyses of the exocrine pancreas in a hibernating dormouse.

Pancreatic acinar cells of euthermic, hibernating and arousing individuals of the hazel dormouse Muscardinus avellanarius (Gliridae) have been observed at the electron-microscopic level and analysed by means of ultrastructural morphometry and immunocytochemistry in order to investigate possible fine structural changes of cellular components during periods of strikingly different degrees of metabolic activity. During hibernation, the cisternae of the rough endoplasmic reticulum (RER) flatten assuming a parallel pattern, the Golgi apparatus is extremely reduced and the mitochondria contain many electron-dense particles. The cell nuclei appear irregularly shaped, with deep indentations containing small zymogen granules. They also contain abundant coiled bodies and unusual constituents, such as amorphous bodies and dense granular bodies. Large numbers of zymogen granules occur in all animals. However, the acinar lumina are open and filled with zymogen only in euthermic animals, whereas, in hibernating and arousing individuals, they appear to be closed. Morphometrical analyses indicate that, in pancreatic acinar cells, nuclei and zymogen granules significantly decrease in size from euthermia to hibernation, probably reflecting a drastic decrease of metabolic activities, mainly protein synthesis and processing. In all the studied animals, immunocytochemistry with specific antibodies has revealed an increasing gradient in alpha-amylase content along the RER-Golgi-zymogen granule pathway, reflecting the protein concentration along the secretory pathway. Moreover, during deep hibernation, significantly larger amounts of alpha-amylase accumulate in RER and zymogen granules in comparison to the other seasonal phases analysed. Upon arousal, all cytoplasmic and nuclear constituents restore their euthermic aspect and all morphometrical and immunocytochemical parameters exhibit the euthermic values, thereby indicating a rapid resumption of metabolic activities.

Amylases↗
PubMed2005

Cloning and expression of PPAR-gamma and PGC-1alpha from the hibernating ground squirrel, Spermophilus tridecemlineatus.

The peroxisome proliferator-activated receptor (PPAR) family of transcription factors play a key role in lipid metabolism and have been implicated in a number of disease states, most notably of which is obesity. Controlled regulation of lipid metabolism is a key ingredient for successful hibernation. Partial cDNA sequences for one of the PPAR proteins, PPARgamma and the PPARgamma co-activator (PGC-1alpha) have been cloned from the hibernating ground squirrel, Spermophilus tridecemlineatus and show differential regulation during hibernation at the mRNA level using relative RT-PCR and at the protein level via immunoblotting in brown adipose tissue (BAT), heart, skeletal muscle and white adipose tissue (WAT). The cDNA sequence for PGC-1alpha revealed a number of amino acid substitutions and two were worthy of note, one resulting in the loss of a potential protein kinase C (PKC) site, while another resulted in the creation of a PKC site, suggesting that PKC may be important in regulating PGC-1alpha. RT-PCR revealed a near 2-fold up-regulation of PPARgamma in BAT and to a lesser extent (<1.5-fold) in heart and WAT, while PGC-1alpha displayed significantly higher levels of expression in skeletal muscle during hibernation (3.1-fold, p < 0.005). The protein levels of PPARy were significantly increased in BAT and WAT (1.5 and 1.8-fold, respectively) while PGC-1alpha displayed significant changes in expression in heart (3.5-fold) and skeletal muscle (1.8-fold). Our current findings indicate a role for increased expression of PPARy and PGC-1alpha in hibernating animals.

Amino Acid Sequence↗
PubMed1975

Spin label evidence for the role of lysoglycerophosphatides in cellular membranes of hibernating mammals.

The phospholipid composition of ground squirrel heart muscle changes during hibernation: more lysoglycerophosphatides are found in the hibernating state than in the active state. Phase transitions inferred from spin label motion occur in the usual manner typical of mammalian mitochondria for the mitochondria and mitochondrial lipids from active squirrels. However, a conspicuous absence of a spin label-detectable phase transition is observed in equivalent preparations from hibernating animals. The addition of lysolecithin to preparations from active squirrels removes the break and induces a straight line in the Arrhenius plot. The lack of a spin label-detectable phase transition in hibernating animals, therefore, is attributed to an increased content of lysoglycerophosphatides present in the phospholipids during hibernation.

Adaptation, Physiological↗
PubMed1985

In vivo analysis of dopamine and its metabolites in the caudate nucleus during euthermia and hibernation.

Golden-mantled ground squirrels (Citellus lateralis) were chronically implanted with a unilateral push-pull cannula in the caudate nucleus. Perfusates obtained in these unanesthetized, unrestrained animals during the euthermic (non-hibernating) and hibernating states were analyzed for dopamine (DA) and its metabolites (homovanillic acid (HVA), 3,4-dihydroxyphenylacetic acid (DOPAC), and 3-methoxy-4-hydroxyphenethanol (MOPET) using high performance liquid chromatography with electrochemical detection. The data revealed clear differences in the performance of the caudate DA system in the two states. During the euthermic state, DA metabolism was indicative of a constant and high turnover rate. Free DA was not detectable in the majority of samples, HVA was detected at consistently high levels, and DOPAC and conjugated DA were present at low levels. By contrast, DA metabolism was sharply altered during hibernation. Free DA was present at high concentrations and HVA concentrations were low. DOPAC was not detected in any sample whereas MOPET was present in all samples. Conjugated DA was present at high concentrations during the second half of the hibernation bout. The shift in the post-release disposition of DA could enhance the stability of DA receptors (i.e. prevent supersensitivity) during the prolonged periods of reduced neural activity typical of hibernation.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1989

Action potential duration increases as body temperature decreases during hibernation.

The effect of temperature on the duration of both population spikes and action potentials of single neurons has been investigated in a variety of in vitro preparations. A few studies have examined the influence of temperature on spike potentials from spinal motoneurons of intact, anesthetized mammals. In all cases, the duration of the action potential or population spike increased as temperature decreased. A similar increase in the duration of action potentials accompanied hibernation in the ground squirrel (Spermophilus lateralis). Oscilloscope traces of 2 brainstem reticular formations, and 8 posterior thalamic single units were photographed at a body temperature (Tb) of 34-36 degrees C during euthermia prior to entrance into hibernation and at Tb's ranging from 10 to 27 degrees C during hibernation. There was a significant increase in the duration of the second component of the diphasic action potential at the lower Tb (P less than 0.01). This temperature effect was reversible, i.e. action potential durations returned to preentrance euthermic values following arousal from hibernation (Tb = 34-36 degrees C). This study is the first to use behaving animals to demonstrate that changes in biophysical characteristics of central nervous system neurons occur at low Tb. These changes in membrane characteristics probably result in alterations in neuronal functioning and information processing during hibernation.

Action Potentials↗
PubMed1984

Comparative physiological and biochemical aspects of hypothermia as a model for hibernation.

It is obvious that research is far from the last chapter in developing a model for natural hibernation. The relationships and comparative mechanisms for thermogenesis and survival in hibernation and experimental hypothermia are still unclear. Yet, two primary areas appear to be most promising, namely, the control of thermogenesis via the glucocorticoids and the specific role of the central nervous system (CNS) in survival of hypothermic subjects and arousal of hibernating subjects. Although there have been several approaches to understanding the role of the CNS in terms of circulation, integrity of the blood-brain barrier (BBB) system, and CNS sites of activity, it may appear that more questions have been raised than have been answered. However, a more optimistic view can also be taken. The development of a laboratory model, using experimental hypothermia for natural hibernation, is progressing. This view is justified in terms of results from the use of glucocorticoids in metabolic regulation of available carbohydrates, i.e., available glucose in hypothermia, and the continued promising parallel studies of physiological and biochemical integrity of areas of the CNS in hypothermic and hibernating subjects.

Adaptation, Physiological↗
PubMed1991

Seasonal variations in the rate and capacity of cardiac SR calcium accumulation in a hibernating species.

The rate of calcium uptake and the level of calcium accumulation was measured in cardiac muscle SR from hibernating and nonhibernating Richardson's ground squirrels. In whole heart homogenates, the rate of calcium uptake was higher (P less than 0.05) in hibernating animals than it was in active animals. Further purification of homogenates into sacroplasmic reticulum (SR) preparations showed that the hibernating animals had the highest rate of calcium uptake and the greatest level of calcium accumulation. These results could not be explained by variations in non-SR membrane contaminants nor by changes in the maximal activity or total amount of a SR marker enzyme, the Ca(2+)-ATPase. The addition of ryanodine to the calcium uptake medium increased the level of calcium accumulation in all groups by a similar amount. It is concluded that the high rate of calcium uptake by isolated cardiac SR vesicles from hibernating ground squirrels reflects the activity of the organelle in vivo, and that the ability of the ryanodine-insensitive population of SR vesicles to accumulate calcium is affected by hibernation.

Animals↗
PubMed1983

Persistence of a circadian rhythmicity for thyroid hormones in plasma and thyroid of hibernating male Rana ridibunda.

The presence and circadian rhythmicity of thyroid hormones was studied in plasma and the thyroid gland of male Rana ridibunda before and during hibernation. Hibernating January frogs do have a lower T3 and T4 content of their thyroid gland whereas plasma levels of T3 are maintained and of T4 increased compared to fed September or October frogs. It seems likely that the increased photoperiod in January will be responsible for this increased T4 secretion, since controlled laboratory experiments performed in December did not reveal any influence of low temperature on circulating T3 or T4 levels. Also feeding does not influence circulating levels and thyroid content of thyroid hormones in frogs kept at room temperature during the month of January. A circadian rhythmicity of T3 and T4 in the thyroid gland is present in fed October frogs and in non fed December frogs acclimated at 5 degrees C for 12 days with an acrophase for T3 at approximately 1500 h and for T4 at around 1900 h, whereas in plasma only T3 does have circadian variations (acrophase about midnight) but not T4. When December frogs are acclimated to room temperature for 12 days, frogs are active again, but do not eat and have a lower body weight than frogs hibernating at 5 degrees C. Their T3 content of the thyroid gland has disappeared, but T4 thyroid content and plasma levels of T3 and T4 are maintained. As in hibernating frogs, no circadian variations in T4 plasma concentrations are present whereas the circadian thyroid T4 rhythm disappears. At the same time a dampening in rhythmicity for plasma T3 as judged by the significantly lower amplitude occurs. It is concluded that the persistence of circulating levels of thyroid hormones and of a circadian cyclicity for T3 in plasma in non feeding hibernating frogs may reflect the special metabolic state e.g. availability of food reserves in these animals.

Animals↗
PubMed1987

Annual cycles in plasma testosterone and thyroxine in the male aspic viper Vipera aspis L., (Reptilia, Viperidae), in relation to the sexual cycle and hibernation.

Blood samples were taken monthly from males of Vipera aspis kept in outdoor terraria. Plasma testosterone was estimated by radioimmunoassay and plasma thyroxine by the technique of isotopic competition, between October 1979 and September 1985. Plasma testosterone showed an annual bimodal profile. The highest peak was observed from February 15 to the end of March. 2 to 5 weeks after the first emergence from hibernation. Values then decreased greatly, to reach a minimum level when the vernal spermiogenesis was at its maximum. The secondary peak of plasma testosterone was lower and less well marked. It occurred at the end of summer, during the strongest spermiogenesis, and preceded the autumnal facultative mating period. Plasma thyroxine was at a maximum concentration from February to March after which levels decreased markedly. The seasonal profile of plasma thyroxine was clearly marked during the period of hibernation. From September to October, 2 months before the beginning of hibernation, thyroxine levels began to decrease, and they reached a minimum in November-December. Endocrine reactivation of the thyroid appeared at the end of hibernation. However, in contrast to the plasma testosterone, endocrine activity of the thyroid began 2 to 3 weeks before the end of hibernation. Mechanisms of reactivation for testicular and thyroidal endocrine structures are discussed.

Animals↗
PubMed1992

Changes of LH level in the pituitary gland and plasma in hibernating frogs, Rana temporaria.

Pituitary and plasma luteinizing hormone (LH) levels were measured in female frogs, Rana temporaria, during and immediately after hibernation (0-4 degrees in darkness; 22-25 weeks) to study regulation of gonadotropin leading to posthibernation ovulation. Pituitary LH content began to rise progressively during the last third of hibernation (e.g., from starting levels of 5.3 +/- 0.09 micrograms/gland, 1.5 micrograms/mg between 8 and 11 weeks, to 18.6 +/- 9.7 micrograms/gland, 5.0 +/- 2.7 micrograms/mg at 19-22 weeks). Plasma LH increased in parallel, but with some delay (from 10 +/- 8 to 25 +/- 24 ng/ml). Frogs kept in light at low temperatures showed similar responses. Release of LH (rise in plasma levels with a drop in pituitary content) was observed during 32 hr immediately after termination of hibernation in association with the onset of ovulation. These data indicate the existence of regulatory mechanisms operating during hibernation under conditions of constant cold. Altogether, these and our previous results obtained after surgical deafferentiation of median eminence support the hypothesis of a progressive reduction of a CNS inhibition that results in the release of GnRH during hibernation in this frog.

Analysis of Variance↗
PubMed1984

Biosynthesis of dolichyl pyrophosphate N-acetylglucosaminyl intermediates in liver microsomes from hibernating ground squirrels (Citellus citellus L.).

Dolichyl pyrophosphate N-acetyl[14C]glucosamine was synthesized after incubation of liver microsomes from hibernating ground squirrels with UDP-N-acetyl[14C )glucosamine. The radioactivity of glycolipid formed by liver microsomes from hibernating ground squirrels was about 2-fold greater than by liver microsomes from active animals. Addition of exogenous dolichyl phosphate to the incubation mixture increased the formation of dolichyl pyrophosphate N-acetyl[14C]glucosamine by microsomes from both active and hibernating ground squirrels about 6 times. Liver microsomes from hibernating ground squirrels converted dolichyl pyrophosphate N-acetyl[14C]glucosamine into dolichyl pyrophosphate N,N'-diacetyl[14C]chitobiose in the presence of unlabelled UDP-N-acetylglucosamine. This conversion was maximal at 1.0 M concentration of unlabelled UDP-N-acetylglucosamine. The level of dolichyl phosphate assessed by the level of dolichyl pyrophosphate N-acetylglucosamine formation was nearly 2 times greater in liver microsomes from hibernating ground squirrels than from active animals.

Animals↗
PubMed1995

Tissue and plasma peptidase activity is altered during hypothermic hibernation in the 13 lined ground squirrel (Spermophilus tridecemlineatus).

Adult 13 lined ground squirrels were monitored for entry into a state of hypothermic hibernation or arousal in a cold room on a photoperiod LD 2:22. Once animals developed predictable hibernation patterns, animals were killed at the mid point of hypothermic hibernation or arousal for determination of plasma and tissue angiotensin-1-converting enzyme (Kininase II) activity. Enzyme was extracted from plasma, lung, kidney, liver, forebrain and brainstem and assayed in vitro. During hypothermic hibernation enzyme activity is significantly decreased in all tissues examined. These data suggest that the activity of tissue and plasma peptidases are altered during the cyclic torporous periods characteristics of hibernation in this species.

Animals↗
PubMed1995

An analysis of factors that induce hibernation in Syrian hamsters.

Factors that induce hibernation of Syrian hamsters were analyzed in young adults and older adults under two photoperiodic conditions (i.e., a long photoperiod and a natural photoperiod). The experiment was performed from September 1st, 1992 to March 24th, 1993. The older hamsters entered earlier into and spent longer in hibernation than the young ones. Water deprivation caused more torpor than free access to water in the older hamsters as well as in the young ones. As the ambient temperature dropped, not only the number of animals entering hibernation but also the number of days in hibernation increased. Long photoperiod in the cold environment tended to induce torpor in the older animals but not in the young ones. An examination of testicular weight at the end of the experiment revealed that the regressed testes were well correlated with the induction and maintenance of hibernation regardless of age and photoperiod.

Aging↗
PubMed1995

Pulmonary mechanics of hibernating squirrels (Spermophilus lateralis).

In this study we examined the effects of hibernation on several aspects of pulmonary mechanics in golden mantled ground squirrels. Measurements were made on anesthetized animals that were active in late fall (FA, n = 7), maintained at 23 degrees C and normal photoperiod in mid-winter (WA, n = 0) and hibernating at 5 degrees C in mid-winter (H, n = 8). Compared with FA animals, WA animals showed an increase in inspiratory reserve volume (IRV) and in inspiratory, vital and total lung capacities (IC, VC, and TLC). Hibernating animals exhibited further increases in IRV, IC, VC and TLC, an elevated residual volume, and virtual elimination of the expiratory reserve volume. There was also a decrease in specific lung compliance and a sharp knee in the lower portion of the quasi-static volume-pressure curve. There was a significant increase in the elastic work required to ventilate the hibernating animals compared with FA animals. The data suggest that, despite an increase in compliance at TLC, there is decreased compliance at low volumes, gas trapping at functional residual capacity, and an increase in the work required to breathe in hibernating animals.

Animals↗
PubMed1986

Brain opioid receptors in the hibernating bat, Myotis lucifugus: modification by low temperature and comparison with rat, mouse and hamster.

Several studies have provided evidence that brain opioid peptides may be involved in the control of the hibernation cycle. We have now examined the influence of hibernation on central opioid receptors. We have characterized the receptor binding properties of [3H]-naloxone in slices of the cerebral cortex and hypothalamus of the bat Myotis lucifugus. These receptors possess those characteristics expected of an opioid site namely high affinity, stereospecificity and saturability. Under normal incubation conditions (30 degrees C) we observed no effect of hibernation on [3H]-naloxone binding. However, when binding assays were performed at temperatures corresponding to the appropriate body temperature (e.g., 4 degrees C for hibernation) we detected a significant low temperature-induced increase in hypothalamic binding. Similar experiments in rat, mouse and hamster revealed that [3H]-naloxone binding was also increased at 4 degrees C when compared to 30 degrees C. This was true in hypothalamus and cortex. Additional studies in the rat demonstrated that the opioid receptor is of higher affinity at low temperatures. The behavioural and neurochemical consequences of this change in the opioid receptor, and whether this might be involved in the regulation of hibernation, remain to be studied.

Animals↗
PubMed1987

Seasonal difference in thermoregulatory responses to opiates in a mammalian hibernator.

Accumulated evidence suggests that increased endogenous opioid activities may facilitate the onset of hibernation. The present study investigated the change in thermoregulatory responses following ICV infusion of morphine or [D-Ala2]-Met enkephalinamide (EK) in unanesthetized, unrestrained Columbian ground squirrels (Spermophilus columbianus) during its annual hibernation cycle. In the nonhibernating phase, low doses of either morphine (less than 160 micrograms) or EK (less than 400 micrograms) elicited a dose-related hyperthermia and an increase in heat production, whereas a higher dose of opiates caused hypothermia and a decrease in metabolic rate. Naloxone (5 mg/kg, SC) pretreatment reduced or reversed both the hyper- and hypothermic responses to opiates. Lower ambient temperature (5 degrees C) enhanced the hypothermic response and attenuated the hyperthermic response. In the hibernating phase, euthermic ground squirrels exhibited a reduced responsiveness to exogenous opiates: the hyperthermic response to low dose of morphine (10 micrograms) was significantly reduced and hyperthermia, rather than hypothermia was observed at the highest dose of morphine (160 micrograms). The reduced responsiveness to opiates observed during the hibernating phase seems to suggest a reduction in opiate receptor efficacy which is in agreement with the contention that an increase in endogenous opioid activities may be incumbent with the commencement of hibernation.

Animals↗