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PubMedDate not supplied

Effects of arousal from hibernation and plasma androgen levels on mating behavior in the male big brown bat, Eptesicus fuscus.

The effects of arousal from hibernation and presence of plasma androgen on the expression of mating behavior in male big brown bats (Eptesicus fuscus) were tested in a captive population exposed to seminatural conditions in central Alabama. In the mild winter of 1994-1995, flight cage temperatures never fell below 10 degrees C. Bats were never observed to enter sustained (over 2 d) torpor. They were also never observed to mate. Unmanipulated, sham-operated, and gonadectomized males and unmanipulated females were exposed to 6 d of 4 degrees C. All individuals appeared torpid, and body temperatures of monitored bats fell at least 15 degrees-20 degrees C. Plasma androgen levels of torpid unmanipulated, sham-operated, and gonadectomized males averaged 25.4 +/- 9.2, 19.7 +/- 9.1, and 1.5 +/- 0.25 ng/mL, respectively, and did not differ significantly from levels for the same groups 1 mo previous to induced torpor. When animals were returned to 23 degrees C, 57% of unmanipulated, 40% of the sham-operated, and 33% of gonadectomized males displayed mating behavior upon arousal. Almost all matings occurred within 48 h of arousal, the majority in the first 3 h. Males not exposed to low temperatures were not observed to mate. Although individuals from all three treatments mated, gonadectomized males averaged fewer mounts and copulations per individual. Androgen levels declined significantly from torpor levels in all groups 48 h after arousal. Thus, an extended period of low body temperature and arousal appeared to be a short-term activator of sexual behavior in the big brown bat; unmanipulated males were more strongly affected by this stimulus than gonadectomized males.

Androgens↗
PubMed1997

The response to calorie restriction in mammals shows features also common to hibernation: a cross-adaptation hypothesis.

The marked elevation in hepatic carbamyl phosphate synthetase I (CPSI) in calorie-restricted mice, and the changes in erythrocyte 2,3-diphosphoglycerate (2,3-DPG) and in hemoglobin oxygen affinity in calorie-restricted and hypoxic humans living in Biosphere 2 suggest similarities between physiologic events in calorie restriction and hibernation. Other data from the literature strengthen this comparison. Accordingly, we hypothesize that the response to the calorie restriction regime as studied by gerontologists, rather than being a laboratory artifact, is part of a spectrum of responses to food deprivation which have adaptive value in the wild, and whose triggering mechanism may primarily involve the neuroendocrine system.

Adaptation, Physiological↗
PubMed1983

Seasonal variations in drug response and staircase phenomena in atrial muscle from a hibernating rodent (Spermophilus richardsonii).

1 Electrically driven atrial muscle from a hibernating rodent (Spermophilus richardsonii) showed marked seasonal variations in inotropic responsiveness to both the cardiac glycoside actodigin and to raised extracellular calcium concentration. In contrast, glycoside toxicity was apparent and comparable in all tissues. 2 These variations were accompanied by changes in force-frequency ('staircase') characteristics of the tissues. 3 In contrast, no seasonal variation was observed in either positive inotropic responses to rubidium (a non-glycoside inhibitor of Na+ + K+ ATP-ase) or negative inotropic responses to methacholine. 4 In summer atria the calcium antagonist, verapamil (6 x 10(-7) M) abolished the positive staircase phenomenon but did not modify the positive inotropic actions of actodigin. 5 These data do not support the hypothesis that 'staircase' and glycoside-induced inotropism are mediated through a common mechanism.

Animals↗
PubMed1987

Electrophysiological effects of Ca antagonists, tetrodotoxin, [Ca]o and [Na]o on myocardium of hibernating chipmunks: possible involvement of Na-Ca exchange mechanism.

The electrophysiological performance of myocardium of hibernating chipmunks was investigated in the presence of Ca antagonists and tetrodotoxin, and the effects of high [Ca]o and low [Na]o were examined. The action potential of the preparations was characterized by the low amplitude of the plateau phase (APp). Ca antagonists, nifedipine (10(-6) M) and nitrendipine (2 X 10(-6) M), did not significantly inhibit this APp or the contraction. These nifedipine-insensitive electromechanical responses were completely abolished by an internal Ca release inhibitor, ryanodine. Both increasing [Ca]o and lowering [Na]o, by replacing Na by lithium or choline, also inhibited APp. Tetrodotoxin (10(-5) M) which markedly inhibited the initial rapid phase of the action potential slightly affected APp. These results suggest that the plateau potential of the present preparations is controlled by a process linked to Ca release from internal stores, most likely the Na-Ca exchange mechanism.

Action Potentials↗
PubMed1973

Memory and hibernation in Citellus lateralis.

Squirrels learned to escape from a water bath by making a visual discrimination. Twenty-four hours after reaching criterion for learned behavior, the animals were exposed to the first of two 11-day cold exposures. The animals that hibernated had better retention of the learned behavior.

Animals↗
PubMed1987

Post hibernational anorexia in captive Mediterranean tortoises (Testudo graeca and Thermanni).

Post hibernational anorexia in captive Mediterranean tortoises is an increasingly recognised condition. It is associated with increased blood urea and low blood glucose concentrations and dehydration. A theory to explain its underlying physiology is presented, based on studies of the seasonal and cyclic variations in the tortoises' blood composition. Measurements useful for predicting the condition are identified and a logical approach to therapy is proposed.

Animals↗
PubMed1981

Regulation of enzyme activity in the hibernator. A kinetic and spectroscopic study of muscle pyruvate kinase from the Arctic ground squirrel.

Pyruvate kinase skeletal muscle of the Arctic ground squirrel was purified to homogeneity. The purified enzyme variants from the summer-active and winter hibernating squirrel appear to be identical with a near-neutral pI of 6.9 and a molecular weight of 234,000 as determined by gel filtration chromatography on Bio-Gel A-0.5m. Evidence for subunit interaction during inhibition by L-phenylalanine is demonstrated with ultraviolet derivative spectroscopy. A model for this interaction and its importance for a regulatory role are discussed. The absence of a temperature break in the Arrhenius plot for the pyruvate kinase reaction, the kinetic and physical data, and the near-neutral pI, suggest an amino acid composition that conserves the overall geometry and resultant kinetic behavior which render regulation of the enzyme insensitive to temperature.

Animals↗
PubMedDate not supplied

Hypometabolic and hypothermic factors from small intestine of hibernating ground squirrels (Citellus undulatus).

Low molecular mass components of the acetic acid extract from the small intestine of hibernating ground squirrels (Citellus undulatus) produced a decrease in oxygen consumption and body temperature of white mice and a dose-dependent delay in embryonic development of sea urchin (Strongylocentrotus intermedius). Equivalent doses of low molecular mass components obtained by the same method from active (summer) animals did not have such an effect.

Animals↗
PubMed1976

Thyroid function in a hibernator, Spermophilus tridecemlineatus.

Thyroid hormone secretion (assessed as thyroid 125I release rate) was monitored in Spermophilus tridecemlineatus from summer to winter (July-December) in 1973. The average release rate in July was 2.3% per day, but in August this rate decreased significantly and remained at an average 0.52% per day until December. This low rate (being similar to that of hypophysectomized rats), and the absence of any change in oxygen consumption following thyroidectomy, suggested hormone secretion was "turned off" during this period. During the period August-December, four S. tridecemlineatus showed normal thermoregulatory responses to anterior hypothalamic cooling but no thyroidal response whether restrained, unrestrained, or anesthetized. Thyroid 125I uptake (and presumably hormone manufacture) continued during the period August-December and 24-h uptake averaged 27.0% in December. Possible reasons for "turning off" thyroid hormone secretion are discussed, and it is concluded this is to allow the membrane fatty acids to revert to a less-saturated condition in preparation for low body temperatures during hibernation.

Animals↗
PubMed1984

Preferential utilization of brown adipose tissue lipids during arousal from hibernation in hamsters.

The participation of brown adipose tissue in the arousal process of golden hamsters was studied. The utilization of lipids in different depots of brown adipose tissue was followed gravimetrically. From both the interscapular and the cervical brown adipose tissue depots, 28 mg of lipid were lost during arousal; there was no measurable loss of lipid from the white adipose tissue depots. The total weight of eight identified depots of brown adipose tissue in nonhibernating, cold-acclimated hamsters was estimated to be 1,700 mg, of which 475 g were lipid. It is calculated that a total of 255 mg lipid disappeared from brown adipose tissue during arousal; this lipid is theoretically capable of giving rise to 2.4 kcal (9.9 kJ) of heat. It is concluded that the heat produced by the combustion of the lipid that disappeared from the brown adipose tissue during the arousal process could be the major source of the heat needed to rewarm the hamster from hibernating to euthermic body temperatures.

Adipose Tissue↗
PubMed1987

Protection against fat cell hyperplasia in a hibernator, Glis glis.

Dormice, Glis glis, were fed a high-fat diet for 11 mo in one experiment: in another experiment they were fed a high-fat diet for 5 mo, either at room temperature (21.5 degrees C) or in a warm room (27 degrees C). Only in the latter group did adipocyte hyperplasia occur; this was significant in all the fat depots studied (inguinal, retroperitoneal, and gonadal). In the other groups there was no evidence of fat cell hyperplasia, despite weight gains from approximately 160 g (peaks on chow diet) to approximately 250 g (maximums on high-fat diet). Instead, fat cell size, assessed from biopsies of the inguinal area, became considerably enlarged. Taken together with earlier data from other species, the results suggest that hibernators are protected against fat cell hyperplasia. In dormice this protection appears to be present at all phases of their seasonal weight cycles. For species that experience several cycles of weight gain and loss in their lives, it may be adaptive to avoid increases in adipocyte number.

Adipose Tissue↗
PubMed1994

Hyperosmolality and sperm storage in hibernating bats: prolongation of sperm life by dehydration.

Osmolalities of epididymal fluids obtained by micropuncture from hibernating species of bats (Myotis lucifugus) rise during sperm storage periods to as high as 1,523 mmol/kgH2O (approximately 5 times that of plasma). In vitro studies establish that hyperosmolality can preserve viability and prevent initiation of progressive motility in bat epididymal spermatozoa as well as induce their quiescence by reducing respiration. Reduction of osmolality (to 500-600 mmol/kgH2O) induces swelling of sperm and allows the initiation of motility and increased metabolic rate; further reduction of osmolality to < 300 mmol/kgH2O compromises permeability barriers and causes loss of motility. We hypothesize that seasonal establishment of hyperosmotic conditions driven by those cells that constitute the limits of the epididymal lumen dehydrates the compliant spermatozoa and thereby minimizes their metabolic needs. A novel form of cell storage dependent on unique adaptations of the epididymal epithelium for solute and water transport is implicated. To date, the operative osmolyte or osmolytes responsible for elevating osmolality in this system remain elusive.

Animals↗
PubMed1998

Dissimilarity of slow-wave activity enhancement by torpor and sleep deprivation in a hibernator.

Sleep regulation processes have been hypothesized to be involved in function and timing of arousal episodes in hibernating ground squirrels. We investigated the importance of sleep regulation during arousal episodes by sleep deprivation experiments. After sleep deprivation of 4, 12, and 24 h, starting 4 h after onset of euthermy, a duration-dependent enhancement of slow-wave activity (SWA) of the cortical electroencephalogram during non-rapid eye movement sleep was found, as expected for normal sleep regulation. When sleep deprivation was applied during the initial phase of the arousal episode, in which effects of prior torpor were present in undisturbed recordings, no subsequent recurrence of SWA was found. In addition, prior torpor induced a reduction in the spectral activity of the sigma frequency range (7-14 Hz), which was not observed after sleep deprivation. The effects of torpor and sleep deprivation on subsequent SWA appear qualitatively different. This indicates that effects of deep torpor on sleep are dissimilar to normal sleep regulation.

Animals↗
PubMed2003

Pancreatic triacylglycerol lipase in a hibernating mammal. I. Novel genomic organization.

Pancreatic triacylglycerol lipase (PTL) is expressed in novel locations during hibernation in the thirteen-lined ground squirrel (Spermophilus tridecemlineatus). PTL cDNAs isolated from two of these locations, heart and white adipose tissue (WAT), contain divergent 5'-untranslated regions (5'-UTRs) suggesting alternative promoter usage or the possibility of multiple PTL genes in the ground squirrel genome. In addition, cDNAs isolated from WAT contain tracts of retroviral sequence in their 5'-UTRs. Our examination of PTL genomic clones isolated from a thirteen-lined ground squirrel genomic DNA library, coupled with genomic Southern blot analysis, enabled us to conclude that PTL mRNAs expressed in heart and WAT are the products of the same single-copy gene. The 5' portion of this gene spans 9.2 kb, is composed of 6 exons, and contains a full-length endogenous retroviral genome with conserved long terminal repeats (LTRs). Alignment of the ground squirrel PTL gene with the mouse, rat, and human PTL genes indicates that this retrovirus inserted into the ground squirrel genome approximately 200 bases upstream of the original PTL transcriptional start site. The insertion is a relatively recent event based on largely intact open-reading frames containing minimal frame-shift and nonsense mutations. The high-percentage identity (99.2%) shared between the 5'- and 3'-LTRs of this endogenous retrovirus suggests that the insertion occurred as recently as 300,000 years ago.

Adipose Tissue↗
PubMed1990

Myocardial hibernation in the ischemic neonatal heart.

We explored the effects of sustained low-flow ischemia on function and metabolism in isolated neonatal hearts. The hearts were extracted from 21 piglets (1-12 days old) and set up as modified Langendorff preparations beating isometrically. They were perfused with red blood cell-enhanced buffer at controlled rates of coronary flow. Mechanical measurements, O2 usage, and substrate oxidation were determined simultaneously at 30-minute intervals for 2 hours. In control hearts, coronary flow was maintained at 1.8 ml/min/g. There was no significant change in mechanical function, diastolic compliance, or O2 or substrate metabolism after 2 hours. In the ischemia group, coronary flow was reduced to 0.2 ml/min/g and sustained for 2 hours. With the onset of ischemia, mechanical function promptly fell to 20% of control. Although O2 delivery was reduced to 11%, O2 extraction doubled so that myocardial O2 consumption was 22% of control, matching mechanical function. Glucose oxidation fell from 37 to 12 nmol/min/g, and lactate release appeared. These measures and ventricular compliance remained constant for the full 2 hours. Concentrations of glycogen and creatine phosphate did not differ from the control group; ATP was 76% of controls. These studies indicate that when myocardial O2 supply is limited, mechanical function rapidly diminishes, largely preserving critical energy stores and preventing irreversible myocellular injury. Although the signal remains to be determined, the strategy is similar to that employed by hibernating species to survive extended periods of O2 deprivation.

Adenosine Triphosphate↗
PubMed1992

Recruitment of an inotropic reserve in moderately ischemic myocardium at the expense of metabolic recovery. A model of short-term hibernation.

The regional, functional as well as metabolic consequences of inotropic stimulation on myocardium subjected to prolonged moderate ischemia were investigated. In 35 enflurane-anesthetized swine the left anterior descending coronary artery was cannulated and perfused at constant flow. The vein paralleling the left anterior descending coronary artery was cannulated for measurement of lactate and oxygen content. Transmural biopsies from the anterior myocardium were taken for the measurement of ATP, creatine phosphate, and glycogen. After control measurements, flow was adjusted to reduce regional contractile function (expressed as a work index, determined by sonomicrometry) by approximately 50%. After either 5, 25, 40, or 85 minutes of moderate ischemia, dobutamine was infused for 5 minutes into the ischemic region. In a separate group of five swine also subjected to 85 minutes of ischemia followed by infusion of dobutamine and 2 hours of reperfusion, triphenyltetrazolium chloride staining and light microscopy were used to identify infarcted tissue. Moderate ischemia (regional myocardial blood flow, 0.21 +/- 0.07 ml.min-1.g-1, determined by radiolabeled microspheres) was associated with a reduction of creatine phosphate after 5 minutes (from 9.35 +/- 2.54 to 6.43 +/- 1.06 mumol/g wet wt, p less than 0.05) and a further reduction after 25 minutes (3.18 +/- 0.69 mumol/g wet wt, p less than 0.05). Thereafter, creatine phosphate recovered despite continued ischemia (after 40 minutes, 4.95 +/- 1.37 mumol/g wet wt; after 85 minutes, 5.78 +/- 2.27 mumol/g wet wt). Lactate consumption during control conditions was reversed to production after 5 minutes of ischemia, which moderated during more prolonged ischemia. Without changing regional myocardial blood flow, infusion of dobutamine increased the work index significantly at any time point but also caused worsening of metabolic markers of ischemia. Nevertheless, even after 85 minutes of ischemia followed by the infusion of dobutamine and 2 hours of reperfusion, there was no evidence of necrosis. This experimental model provides a means of characterizing the mechanisms of short-term hibernation.

Animals↗
PubMed1991

Cold entrainment of the annual cycle of ovarian activity in the lizard Lacerta vivipara: thermoperiodic rhythm versus hibernation.

A constant warm thermoperiod maintains ovarian quiescence in the lizard Lacerta vivipara, whereas a 4-month artificial hibernation rapidly induces synchronized vitellogenesis after transfer to warmth. The present study examined the possibility of a thermoperiodic regulation of the ovarian cycle and the formal properties of an internal temporal program. These questions were addressed using 24-hr thermoperiodic conditions that combined a long or a short thermophase (6 or 2 hr of basking) with a warm (19-21 degrees C), a cool (5-15 degrees C), or a cold (3-7 degrees C) cryophase. Lizards were exposed to the natural photocycle or to LD 12:12. Occurrence and timing of vitellogenesis completion were monitored using immunodetection of plasma vitellogenin and laparotomies. Cold remained stimulatory when given intermittently with a 24-hr periodicity. However, under long-thermophase conditions, lizards responded poorly to cool cryophases but fully to cold ones (72.7-100% vitellogenesis). Thus a certain amount of cold must be provided during each 24-hr cycle in order to be effective through the succession of thermocycles. Reduction of the daily heat input from 6 to 2 hr modulated the stimulating effects of cold cryophases: The median date for the beginning of vitellogenesis occurred 1 month earlier, but the number of responding females decreased from 100% to 40%. The thermoperiodic regulation of the ovarian cycle also relies upon a precise heat-cold balance per nycthemeral unit. This ensures the entrainment of an internal rhythm, since the timing of reproductive responses varies with the date of transfer from the inhibitory warm thermoperiod to the inducing thermoperiod (long thermophase, cold cryophase). At least half the females started vitellogenesis within 1-2 months after a late transfer (winter solstice) instead of 6 months after an early one (autumn equinox), and the median date for onset differed by 1 month between the two groups. However, autumn transfer was the only one to induce a group response in close agreement with the natural timing.

Animals↗