Bile constituents in hibernating golden-mantled ground squirrels (Spermophilus lateralis)

Hibernation is an adaptation for energy conservation, which probably evolved as an extension of non-rapid-eye-movement sleep mechanisms. Yet, during periodic arousals from bouts of deep hibernation, ground squirrels (Spermophilus lateralis) spend most of their time asleep. Spectral analysis of the electroencephalogram revealed that cortical slow-wave intensity during sleep is high at the beginning of a euthermic period and declines thereafter. Sleep slow-wave intensity is greater after longer bouts of hibernation than after shorter bouts. We hypothesize that low body temperatures during hibernation are incompatible with the restorative function of sleep as reflected in cortical slow-wave activity. Animals must incur the energetic costs of periodic arousals from hibernation to receive the restorative benefits of euthermic slow-wave sleep. The timing of arousals from hibernation may be a function of accumulated sleep debt.

Download Full-text

Circannual and Seasonal Variations in Plasma Luteinizing Hormone Levels of Ovariectomized Ground Squirrels (Spermophilus lateralis)

Biology of Reproduction ◽

10.1095/biolreprod28.1.178 ◽

1983 ◽

Vol 28 (1) ◽

pp. 178-185 ◽

Cited By ~ 10

Author(s):

Irving Zucker ◽

Paul Licht

Keyword(s):

Luteinizing Hormone ◽

Seasonal Variations ◽

Ground Squirrels ◽

Hormone Levels ◽

Spermophilus Lateralis

Download Full-text

Liver energy metabolism during hibernation in the golden-mantled ground squirrel, Spermophilus lateralis

Canadian Journal of Zoology ◽

10.1139/z97-127 ◽

1997 ◽

Vol 75 (7) ◽

pp. 1059-1065 ◽

Cited By ~ 11

Author(s):

James F. Staples ◽

Peter W. Hochachka

Keyword(s):

Ground Squirrels ◽

Atp Production ◽

Spermophilus Lateralis ◽

Energy Demands ◽

Hormone Status ◽

Consumption Rates ◽

Lower Temperature ◽

Production Capacities ◽

Deep Hibernation ◽

Normothermic Condition

Large changes in ATP production capacities and rates have been reported in mammalian hibernators throughout the different stages of the hibernation cycle. In this study we showed that total extractable liver [ATP], [ADP], and [ATP]/[ADP] do not differ among summer normothermic, hibernating, and aroused golden-mantled ground squirrels, Spermophilus lateralis, indicating that metabolism remains well balanced throughout the hibernation cycle. This implies that rates of ATP consumption must be down-regulated during deep hibernation in order to maintain this balance. Despite this, basal oxygen-consumption rates [Formula: see text] of hepatocytes isolated from hibernating, aroused, and summer cold-acclimated ground squirrels were 22.4–35.1% higher than those from ground squirrels in the summer normothermic condition when measured at 37 °C. The relatively high hepatocyte [Formula: see text] may help to minimize interbout arousal times, reducing energy demands during the hibernation season. At 7 °C, hepatocyte [Formula: see text] values do not differ among the four groups; however, the Q10 for hepatocyte [Formula: see text] is significantly lower for the summer group, suggesting lower temperature sensitivity. Despite the seasonal changes in thyroid hormone status known to occur in scuirid hibernators, the proportion of hepatocyte [Formula: see text] attributed to Na+,K+-ATPase, estimated by inhibition with 1 mM ouabain, is only around 15% and does not differ among hibernation/seasonal conditions.

Download Full-text

Increased heat loss affects hibernation in golden-mantled ground squirrels

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.00670.2003 ◽

2004 ◽

Vol 287 (1) ◽

pp. R167-R173 ◽

Cited By ~ 10

Author(s):

Alexander S. Kauffman ◽

Matthew J. Paul ◽

Irving Zucker

Keyword(s):

Food Intake ◽

Heat Loss ◽

Body Mass ◽

Complete Removal ◽

Ground Squirrels ◽

Control Procedure ◽

Ambient Temperatures ◽

Spermophilus Lateralis ◽

Maintain Body Temperature ◽

Body Heat

During hibernation at ambient temperatures (Ta) above 0°C, rodents typically maintain body temperature (Tb) ∼1°C above Ta, reduce metabolic rate, and suspend or substantially reduce many physiological functions. We tested the extent to which the presence of an insulative pelage affects hibernation. Tb was recorded telemetrically in golden-mantled ground squirrels ( Spermophilus lateralis) housed at a Ta of 5°C; food intake and body mass were measured at regular intervals throughout the hibernation season and after the terminal arousal. Animals were subjected to complete removal of the dorsal fur or a control procedure after they had been in hibernation for 3–4 wk. Shaved squirrels continued to hibernate with little or no change in minimum Tb, bout duration, duration of periodic normothermic bouts, and food intake during normothermia. Rates of rewarming from torpor were, however, significantly slower in shaved squirrels, and rates of body mass loss were significantly higher, indicating increased depletion of white adipose energy stores. An insulative pelage evidently conserves energy over the course of the hibernation season by decreasing body heat loss and reducing energy expenditure during periodic arousals from torpor and subsequent intervals of normothermia. This prolongs the hibernation season by several weeks, thereby eliminating the debilitating consequences associated with premature emergence from hibernation.

Download Full-text

Growth and its relationship to the initial annual cycle of the golden-mantled ground squirrel, Spermophilus lateralis

Canadian Journal of Zoology ◽

10.1139/z81-124 ◽

1981 ◽

Vol 59 (6) ◽

pp. 865-871 ◽

Cited By ~ 13

Author(s):

John A. Phillips

Keyword(s):

Litter Size ◽

Annual Cycle ◽

Ground Squirrel ◽

Growth And Development ◽

Reproductive Effort ◽

Ground Squirrels ◽

Active Season ◽

Spermophilus Lateralis ◽

Significant Difference ◽

Two Populations

Thirty-eight litters of golden-mantled ground squirrels (Spermophilus lateralis), from two populations that experienced different lengths of active season, were born and raised in the laboratory. Growth and development in young were inversely related to litter size. Offspring from smaller litters were both able to attain their prehibernation peak of body mass sooner and hibernate after fewer days of homeothermy than squirrels from larger litters. Young that remained homeothermic throughout the initial overwintering period were always from large litters and among the slowest growing littermates. Fecundity was lower in females from the temporally compressed environment. There was no significant difference between populations in the nutrition provided by mothers to their litters. The results suggest that reproductive effort is more conservative in populations of ground squirrels that experience short seasons of activity, yet this conservatism allows the offspring of those populations to reach independence and attain the prehibernation state of preparedness at an earlier age than their counterparts from populations of more moderate climates.

Download Full-text

Myosin Isoform Expression and MAFbx mRNA Levels in Hibernating Golden‐Mantled Ground Squirrels (Spermophilus lateralis)

Physiological and Biochemical Zoology ◽

10.1086/421753 ◽

2004 ◽

Vol 77 (4) ◽

pp. 582-593 ◽

Cited By ~ 41

Author(s):

Bryan C. Rourke ◽

Yuichi Yokoyama ◽

William K. Milsom ◽

Vincent J. Caiozzo

Keyword(s):

Ground Squirrels ◽

Mrna Levels ◽

Spermophilus Lateralis ◽

Isoform Expression

Download Full-text

Estradiol phase shifts circannual body mass rhythms of male ground squirrels

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.1998.274.3.r754 ◽

1998 ◽

Vol 274 (3) ◽

pp. R754-R759

Author(s):

Sara M. Hiebert ◽

Theresa M. Lee ◽

Paul Licht ◽

Irving Zucker

Keyword(s):

Mass Loss ◽

Body Mass ◽

Sexual Differentiation ◽

Statistical Significance ◽

Mass Gain ◽

Hormone Treatment ◽

Estradiol Benzoate ◽

Ground Squirrels ◽

Circannual Rhythm ◽

Spermophilus Lateralis

Gonadectomized male golden-mantled ground squirrels ( Spermophilus lateralis) were implanted with estradiol benzoate (EB)-filled or empty capsules. Body mass was monitored before, during, and for at least 1 yr after hormone treatment. EB treatment during the mass-gain phase of the annual cycle significantly decelerated increases in body mass; the period of the circannual rhythm (CAR) of body mass was 54 days longer in EB- than blank-treated squirrels. Hormone treatment during the mass-loss phase accelerated mass loss; although this effect only approached statistical significance, some phase markers of the CAR were significantly advanced in subsequent cycles. We conclude that, as in females, estradiol affects the waveform of the CAR of males differently at different phases of the circannual cycle. Sexual differentiation does not eliminate responsiveness of CARs of squirrels to estradiol; sex differences, if any, are subtle rather than absolute and, in this respect, differ from circadian rhythms.

Download Full-text