scholarly journals The Chemistry of Cold: Mechanisms of Torpor Regulation in the Siberian Hamster

Physiology ◽  
2016 ◽  
Vol 31 (1) ◽  
pp. 51-59 ◽  
Author(s):  
Ceyda Cubuk ◽  
Jonathan H. H. Bank ◽  
Annika Herwig
Keyword(s):  
Physiological State ◽  
Daily Torpor ◽  
Brain Areas ◽  
Siberian Hamster ◽  
Siberian Hamsters ◽  
Save Energy

Siberian hamsters use spontaneous daily torpor, a state of hypometabolism and hypothermia, to save energy during winter. Multiple neuroendocrine signals set the scene for spontaneous torpor to occur, and several brain areas have been identified as potential sites for torpor regulation. Here, we summarize the known mechanisms of a fascinating physiological state in the Siberian hamster.

Control of torpor and body weight patterns by a seasonal timer in Siberian hamsters

1989 ◽  
Vol 257 (1) ◽  
pp. R142-R149 ◽  
Author(s):  
T. J. Bartness ◽  
J. A. Elliott ◽  
B. D. Goldman
Keyword(s):  
Body Weight ◽  
Food Intake ◽  
Implant Removal ◽  
Daily Torpor ◽  
Short Day ◽  
Siberian Hamsters ◽  
Long Day ◽  
Preparatory Phase ◽  
Pelage Color ◽  
Seasonal Responses

Two experiments were designed to assess whether the short-day-induced patterns of shallow daily torpor, body weight, and other seasonal responses (food intake and pelage pigmentation) exhibited by Siberian hamsters (Phodopus sungorus sungorus) are under the control of a "seasonal timekeeping mechanism" that is independent of reproductive status [testosterone, (T)]. We examined whether the patterning and expression of these seasonal responses were altered by decreases in serum T that accompany gonadal regression during the first 8 wk of short-day exposure (i.e., the "preparatory phase" of the torpor season) or by experimental increases in serum T after this phase. Short-day-housed, castrated hamsters bearing T implants had long-day levels of the hormone and did not exhibit torpor. Appropriate seasonal patterns and levels of torpor, body weight, pelage color stage, and food intake were exhibited after T implant removal although serum T was clamped to long-day levels during the preparatory phase. In animals that were gonad intact during the preparatory phase and were subsequently castrated and given T implants, torpor did not occur as long as the implants were in place. However, the patterns and levels of daily torpor, food intake, and body weight rapidly returned to appropriate seasonal values compared with the castrated, blank-implanted controls on T implant removal; these effects occurred whether the T implants were removed when torpor frequency was increasing, at its peak, or decreasing across the torpor season. T did not affect pelage color stage under any condition.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiac dynamics during daily torpor in the Djungarian hamster (Phodopus sungorus)

2008 ◽  
Vol 294 (2) ◽  
pp. R639-R650 ◽  
Author(s):  
Alexander Mertens ◽  
Oliver Stiedl ◽  
Stephan Steinlechner ◽  
Michael Meyer
Keyword(s):  
Conduction Block ◽  
Phodopus Sungorus ◽  
Control Mechanisms ◽  
Daily Torpor ◽  
Qrs Complex ◽  
Siberian Hamsters ◽  
Cardiac Dynamics ◽  
St Segment ◽  
Electrocardiogram Ecg ◽  
Ventricular Conduction

Djungarian or Siberian hamsters ( Phodopus sungorus) acclimated to short photoperiod display episodes of spontaneous daily torpor with metabolic rate depressed by ∼70% and body temperature (Tb) reduced by ∼20°C. To study the cardiovascular adjustment to daily torpor in Phodopus, electrocardiogram (ECG) and Tb were continuously recorded by telemetry during entrance into torpor, in deep torpor, and during arousal from torpor. Minimum Tb during torpor bouts was ∼21°C, and heart rate, ∼349 beats/min at euthermy, displayed marked sinus bradyarrhythmia at ∼70 beats/min. Arousal was typically completed within ∼40 min, followed by a sustained posttorpor inactivity tachycardia (∼540 beats/min). The absence of episodes of conduction block, tachyarrhythmia, or other forms of ectopy throughout the torpor cycle demonstrates a remarkable resistance to arrhythmogenesis. The ECG morphology lacks a distinct isoelectric interval following the QRS complex, and the ST segment resembles the ECG pattern in mice, with a prominent fast transient outward K+ current ( Ito,f) determining the early phase of ventricular repolarization. During low-temperature torpor, the amplitudes of the QRS complex substantially increased, suggesting that in the euthermic state the terminal portion of ventricular depolarization is fused with the beginning of repolarization, low Tb acting to decorrelate the superposition between depolarization and repolarization by delaying the repolarization onset. Atrioventricular and ventricular conduction times were prolonged as function of Tb. In contrast, the QT vs. Tb relationship showed marked hysteresis indicating the operation of nonlinear control mechanisms whereby the rapid QT shortening during arousal results from additional mechanisms (probably sympathetic stimulation) other than temperature alone.

scholarly journals Daily torpor is associated with telomere length change over winter in Djungarian hamsters

2011 ◽  
Vol 8 (2) ◽  
pp. 304-307 ◽  
Author(s):  
Christopher Turbill ◽  
Steve Smith ◽  
Caroline Deimel ◽  
Thomas Ruf
Keyword(s):  
Telomere Length ◽  
Energy Savings ◽  
Physiological State ◽  
Length Change ◽  
Phodopus Sungorus ◽  
Physiological Changes ◽  
Daily Torpor ◽  
Positive Effects ◽  
Relative Telomere Length ◽  
Air Temperatures

Ageing can progress at different rates according to an individual's physiological state. Natural hypothermia, including torpor and hibernation, is a common adaptation of small mammals to survive intermittent or seasonal declines in environmental conditions. In addition to allowing energy savings, hypothermia and torpor have been associated with retarded ageing and increased longevity. We tested the hypothesis that torpor use slows ageing by measuring changes in the relative telomere length (RTL) of Djungarian hamsters, Phodopus sungorus , a highly seasonal rodent using spontaneous daily torpor, over 180 days of exposure to a short-day photoperiod and warm (approx. 20°C) or cold (approx. 9°C) air temperatures. Multi-model inference showed that change in RTL within individuals was best explained by positive effects of frequency of torpor use, particularly at low body temperatures, as well as the change in body mass and initial RTL. Telomere dynamics have been linked to future survival and proposed as an index of rates of biological ageing. Our results therefore support the hypothesis that daily torpor is associated with physiological changes that increase somatic maintenance and slow the processes of ageing.

scholarly journals Daily torpor in mice: high foraging costs trigger energy-saving hypothermia

2009 ◽  
Vol 6 (1) ◽  
pp. 132-135 ◽  
Author(s):  
Kristin A. Schubert ◽  
Ate S. Boerema ◽  
Lobke M. Vaanholt ◽  
Sietse F. de Boer ◽  
Arjen M. Strijkstra ◽  
...  
Keyword(s):  
Body Temperature ◽  
Energy Saving ◽  
Active Phase ◽  
Daily Torpor ◽  
Cost Controls ◽  
Cost Treatment ◽  
Phase Temperature ◽  
Save Energy ◽  
The Relationship ◽  
Temperature Responses

Many animal species employ natural hypothermia in seasonal (hibernation) and daily (torpor) strategies to save energy. Facultative daily torpor is a typical response to fluctuations in food availability, but the relationship between environmental quality, foraging behaviour and torpor responses is poorly understood. We studied body temperature responses of outbred ICR (CD-1) mice exposed to different food reward schedules, simulating variation in habitat quality. Our main comparison was between female mice exposed to low foraging-cost environments and high-cost environments. As controls, we pair-fed a group of inactive animals (no-cost treatment) the same amount of pellets as high-cost animals. Mice faced with high foraging costs were more likely to employ torpor than mice exposed to low foraging costs, or no-cost controls (100% versus 40% and 33% of animals, respectively). While resting-phase temperature showed a non-significant decrease in high-cost animals, torpor was not associated with depressions in active-phase body temperature. These results demonstrate (i) that mice show daily torpor in response to poor foraging conditions; (ii) that torpor incidence is not attributable to food restriction alone; and (iii) that high levels of nocturnal activity do not preclude the use of daily torpor as an energy-saving strategy. The finding that daily torpor is not restricted to conditions of severe starvation puts torpor in mice in a more fundamental ecological context.

Daily torpor in the absence of the suprachiasmatic nucleus in Siberian hamsters

1992 ◽  
Vol 263 (2) ◽  
pp. R353-R362 ◽  
Author(s):  
N. F. Ruby ◽  
I. Zucker
Keyword(s):  
Suprachiasmatic Nucleus ◽  
Food Restriction ◽  
Temporal Organization ◽  
Daily Torpor ◽  
Short Day ◽  
Siberian Hamsters ◽  
Random Fashion ◽  
Before And After ◽  
Ad Libitum ◽  
Short Days

Siberian hamsters express torpor spontaneously after several weeks of exposure to short days. In long days, torpor is expressed only when food intake is restricted. Hamsters maintained in a long photoperiod (16 h light/day) at 15 degrees C expressed daily torpor during food restriction both before and after bilateral ablation of the suprachiasmatic nucleus (SCN). Hamsters housed in short days (8 h light/day, ambient temperature 15 degrees C) and fed ad libitum displayed torpor before, but not after, ablation of the SCN (SCNX). Torpor was reinstated in all short-day SCNX hamsters during postoperative food restriction and persisted in several animals even after ad libitum feeding was reinstated. Torpor was entrained to the light-dark cycle in both long- and short-day hamsters preoperatively but appeared to occur in a temporally random fashion in SCNX animals. SCNX hamsters, unlike control animals, displayed multiple torpor bouts per 24 h. The SCN is not essential for the expression of torpor but plays a crucial role in its temporal organization.

scholarly journals Somatostatin Agonist Pasireotide Promotes a Physiological State Resembling Short-Day Acclimation in the Photoperiodic Male Siberian Hamster (Phodopus sungorus)

2015 ◽  
Vol 27 (7) ◽  
pp. 588-599 ◽  
Author(s):  
R. A. Dumbell ◽  
F. Scherbarth ◽  
V. Diedrich ◽  
H. A. Schmid ◽  
S. Steinlechner ◽  
...  
Keyword(s):  
Physiological State ◽  
Phodopus Sungorus ◽  
Siberian Hamster ◽  
Short Day

Torpor shortens the period of Siberian hamster circadian rhythms

1993 ◽  
Vol 265 (4) ◽  
pp. R951-R956 ◽  
Author(s):  
E. M. Thomas ◽  
M. E. Jewett ◽  
I. Zucker
Keyword(s):  
Body Temperature ◽  
Circadian Rhythms ◽  
Body Mass ◽  
Short Term ◽  
Running Wheel ◽  
Siberian Hamster ◽  
Short Day ◽  
Siberian Hamsters ◽  
Wheel Activity

We investigated the influence of ambient and body temperature (Ta and Tb) on circadian rhythms of gonadectomized male Siberian hamsters. Animals that entered torpor (Tb < 30 degrees C) had significantly shorter circadian periods (tau s) than did nontorpid hamsters at a Ta of 13 degrees C (24.17 +/- 0.05 vs. 24.33 +/- 0.04 h). The tau s of homeothermic hamsters were not affected by Ta change. Short-term decreases in Tb, rather than changes in Ta, appear to affect tau. Access to activity wheels inhibited expression of torpor in short daylengths and was associated with significant increases in body mass. Running wheel activity can mask or block specific short-day responses.

Direct innervation of white fat and adrenal medullary catecholamines mediate photoperiodic changes in body fat

2001 ◽  
Vol 281 (5) ◽  
pp. R1499-R1505 ◽  
Author(s):  
Gregory E. Demas ◽  
Timothy J. Bartness
Keyword(s):  
Adipose Tissue ◽  
Body Fat ◽  
White Adipose Tissue ◽  
Sympathetic Innervation ◽  
Day Length ◽  
Sympathetic Denervation ◽  
Siberian Hamster ◽  
Siberian Hamsters ◽  
Length Changes ◽  
White Fat

Seasonal adjustments in Siberian hamster adiposity are triggered by day length changes [i.e., short “winter-like” days (SDs) elicit body fat decreases vs. long “summer-like” days (LDs)]. These and other white adipose tissue (WAT) mass decreases traditionally have been ascribed to lipolysis triggered by sympathetically mediated, adrenal medullary released epinephrine; however, recent evidence suggests that direct sympathetic innervation of WAT also is important. Therefore, the contributions of WAT sympathetic innervation and adrenal medullary catecholamines to SD-induced decreases in adiposity were tested. Siberian hamsters were surgically bilaterally adrenal demedullated (ADMEDx) or sham ADMEDx, and all had one inguinal WAT (IWAT) pad sympathectomized via locally injected guanethidine, with the contralateral pad serving as a within-animal innervated control. One-half of the hamsters remained in LDs; the remainder was transferred to SDs. Guanethidine and ADMEDx abolished IWAT norepinephrine and adrenal epinephrine contents, respectively. Although sympathetic denervation or ADMEDx alone did not block SD-induced decreases in IWAT mass, their combination did. These results suggest that both adrenal catecholamines and the sympathetic innervation of WAT interact to decrease SD-induced decreased adiposity.

scholarly journals Single caudate neurons encode temporally discounted value for formulating motivation for action

2020 ◽  
Author(s):  
Yukiko Hori ◽  
Koki Mimura ◽  
Yuji Nagai ◽  
Atsushi Fujimoto ◽  
Kei Oyama ◽  
...  
Keyword(s):  
Dorsolateral Prefrontal Cortex ◽  
Physiological State ◽  
Temporal Discounting ◽  
Brain Areas ◽  
Macaque Monkeys ◽  
Caudate Head ◽  
Delay Duration ◽  
Instrumental Task ◽  
Dorsolateral Prefrontal ◽  
Multidimensional Information

AbstractTemporal discounting captures both choice preferences and motivation for delayed rewards. While temporally discounted value for choice is represented in brain areas including the dorsolateral prefrontal cortex (DLPFC) and the striatum, the neural process of motivation for delayed rewards remains unidentified. Here we show that neuronal activity of the dorsal part of the primate caudate head (dCDh) — a striatal region receiving projection from the DLPFC — signals temporally discounted value essential for computing motivation for delayed rewards. Macaque monkeys performed an instrumental task, in which a visual cue indicated the forthcoming size and delay duration before reward. Single dCDh neurons represented the temporally discounted value without reflecting changes in the animal’s physiological state. Bilateral pharmacological or chemogenetic inactivation of dCDh specifically distorted a normal motivational performance based on the integration of reward size and delay. These results suggest a major contribution of dCDh to encoding a temporally discounted value, the integrated multidimensional information critical for formulating the motivation for action.

Melatonin Production Accompanies Arousal from Daily Torpor in Siberian Hamsters

2003 ◽  
Vol 76 (4) ◽  
pp. 577-585 ◽  
Author(s):  
Jennie E. Larkin ◽  
Steven M. Yellon ◽  
Irving Zucker
Keyword(s):  
Daily Torpor ◽  
Siberian Hamsters ◽  
Melatonin Production
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