Wheel running affects seasonal acclimatization of physiological and morphological traits in the Djungarian hamster (<i>Phodopus sungorus</i>)

Scherbarth, Frank; Rozman, Jan; Klingenspor, Martin; Brabant, Georg; Steinlechner, Stephan

doi:10.1152/ajpregu.00106.2007

Cited by 12 publications

(17 citation statements)

References 44 publications

(53 reference statements)

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“…This assumption is in accordance with the fact that not only body fat but also lean mass decreases during SP acclimation (16), which is accompanied by increased gene expression of myostatin, resulting in suppressed muscle growth (5). Interestingly, regular running exercise not only prevents the normal SP-induced reduction in body weight but also daily torpor (24,25,29). Since our studies also provide evidence that exercise stimulates somatic growth, a role for the hypothalamic pituitary growth axis in the control of seasonal torpor is conceivable.…”

supporting

confidence: 67%

Somatostatin receptor activation is involved in the control of daily torpor in a seasonal mammal

Scherbarth¹,

Diedrich²,

Dumbell³

et al. 2015

American Journal of Physiology-Regulatory, Integrative and Comp

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Scherbarth F, Diedrich V, Dumbell RA, Schmid HA, Steinlechner S, Barrett P. Somatostatin receptor activation is involved in the control of daily torpor in a seasonal mammal. Am J Physiol Regul Integr Comp Physiol 309: R668 -R674, 2015. First published July 8, 2015 doi:10.1152/ajpregu.00191.2015 show spontaneous daily torpor only after ϳ2 mo in winter-like short photoperiods (SP). Although some SP-induced hormonal changes have been demonstrated to be necessary for the occurrence of seasonal torpor, the whole set of preconditions is still unknown. Recent findings provide evidence that the hypothalamic pituitary growth axis is involved in endocrine responses to SP exposure in the photoperiodic hamsters. To examine whether suppression of growth hormone (GH) and insulin-like growth factor-1 (IGF-1) secretion affects the incidence of daily torpor, we used two somatostatin receptor agonists, pasireotide (SOM230) and octreotide, with different affinity profiles for receptor subtypes. Pasireotide strikingly increased the torpor frequency in male hamsters compared with sham-treated controls, and torpor duration was often increased, which in some cases exceeded 12 h. In contrast, administration of octreotide reduced the body weight of SP hamsters but had only a marginal effect on torpor frequency in males and no effect in females. Together with measured concentrations of circulating IGF-1, the present results strongly suggest that reduced activity of the GH/IGF-1 axis is not critical for stimulation of torpor expression but activation of specific somatostatin receptors is critical. This putative role for certain somatostatin receptor subtypes in torpor induction provides a promising new approach to unravel the endocrine mechanisms of torpor regulation.GH/IGF-1 axis; somatostatin receptors; torpor; seasonality; pasireotide (SOM230); octreotide SPONTANEOUS DAILY TORPOR REPRESENTS one trait of the substantial acclimation to winter-like short photoperiods (SP) in Siberian hamsters (Phodopus sungorus; a.k.a. Djungarian hamster; for review, see Ref. 26). Together with a considerably reduced body weight and improved insulative properties of the white winter fur, daily torpor contributes significantly to reduce energy demands (12). Unlike fasting-induced torpor, spontaneous daily torpor is not necessarily linked to food scarcity. Instead, Siberian hamsters show this energy-saving behavior after ϳ10 wk of SP exposure despite food abundance. Interestingly, the frequency of torpor varies largely between individuals, ranging from animals that show torpor almost every day to individuals that never enter torpor (23). Thus these hamsters exhibit an individual propensity to use this state of reduced metabolism and body temperature (T b ). Despite several decades of study, the underlying metabolic and/or hormonal factors that tip the balance in support of, or against, entry into torpor at the beginning of the (diurnal) resting phase are still unknown.SP-mediated loss of body weight appears to be a prerequisite for the occurrence of torpo...

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confidence: 67%

Somatostatin receptor activation is involved in the control of daily torpor in a seasonal mammal

Scherbarth¹,

Diedrich²,

Dumbell³

et al. 2015

American Journal of Physiology-Regulatory, Integrative and Comp

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“…It is also reported that access to a running wheel induces growth demonstrated by the femora length and increase in organ sizes [30], [31]. We would therefore suggest that the Siberian hamster represents a model of disrupted or reversible growth.…”

Section: Introductionmentioning

confidence: 70%

“…When this analysis is applied to sedentary and running wheel hamsters it becomes evident that there is no reduction in lean and fat mass at either 8 or 16 weeks of exposure to SD in hamsters with a running wheel whereas this was evident in SD sedentary hamsters. Whilst these experiments were performed on hamsters given access to a running wheel at the beginning of the experimental photoperiod exposure, body weight can also increase following a photoperiod induced decrease in body weight [30]. This finding would suggest that the underlying drive to seasonal body weight physiology is overridden.…”

Section: Discussionmentioning

confidence: 99%

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Effect of Exercise on Photoperiod-Regulated Hypothalamic Gene Expression and Peripheral Hormones in the Seasonal Dwarf Hamster Phodopus sungorus

et al. 2014

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The Siberian hamster (Phodopus sungorus) is a seasonal mammal responding to the annual cycle in photoperiod with anticipatory physiological adaptations. This includes a reduction in food intake and body weight during the autumn in anticipation of seasonally reduced food availability. In the laboratory, short-day induction of body weight loss can be reversed or prevented by voluntary exercise undertaken when a running wheel is introduced into the home cage. The mechanism by which exercise prevents or reverses body weight reduction is unknown, but one hypothesis is a reversal of short-day photoperiod induced gene expression changes in the hypothalamus that underpin body weight regulation. Alternatively, we postulate an exercise-related anabolic effect involving the growth hormone axis. To test these hypotheses we established photoperiod-running wheel experiments of 8 to 16 weeks duration assessing body weight, food intake, organ mass, lean and fat mass by magnetic resonance, circulating hormones FGF21 and insulin and hypothalamic gene expression. In response to running wheel activity, short-day housed hamsters increased body weight. Compared to short-day housed sedentary hamsters the body weight increase was accompanied by higher food intake, maintenance of tissue mass of key organs such as the liver, maintenance of lean and fat mass and hormonal profiles indicative of long day housed hamsters but there was no overall reversal of hypothalamic gene expression regulated by photoperiod. Therefore the mechanism by which activity induces body weight gain is likely to act largely independently of photoperiod regulated gene expression in the hypothalamus.

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“…The breeding pairs for our laboratory colony were kindly provided by N. Y. Vasileva (Institute of Animals Evolutionary Morphology and Ecology, Moscow, Russia), S. Steinlechner (School of Veterinary Medicine, Hannover, Germany), and K. Rudloff (Tierpark, Berlin, Germany) (Weinert & Schöttner, 2007). All these breeders have reported seasonal changes in the hamsters they provided and Steinlechner's group, in particular, has investigated these changes for many years in great detail (Scherbarth et al, 2007Steinlechner et al, 1995). However, the hamsters in those studies were kept under natural lighting conditions, whereas our animals were kept in a consistent light-dark cycle (14L/10D) since 2000, when the colony was established.…”

Section: Discussionmentioning

confidence: 99%

Short-Day Response in Djungarian Hamsters of Different Circadian Phenotypes

Schöttner

Schmidt

Hering

et al. 2012

Chronobiology International

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In Djungarian hamsters (Phodopus sungorus) bred at the authors' institute, a certain number of animals show activity patterns incompatible with proper entrainment of their endogenous circadian pacemaker to the environmental light-dark (LD) cycle. Even though the activity-offset in these animals is stably coupled to "light-on," activity-onset is increasingly delayed, leading to a compression of the activity time (α). If α falls below a critical value, the circadian rhythm in these so called delayed activity-onset (DAO) hamsters starts to free-run and finally breaks down. Animals then show an arrhythmic activity pattern (AR hamsters). Previous studies revealed the mechanisms of photic entrainment have deteriorated (DAO) or the suprachiasmatic nucleus (SCN) does not generate a rhythmic signal (AR). The aim of the present study was to investigate the consequences that these deteriorations have upon photoperiodic time measurement. Animals were bred and kept under standardized housing conditions with food and water ad libitum and a 14L/10D (long day, LD) regimen. Locomotor activity was recorded continuously using passive infrared motion detectors. Body mass, testes size, and fur coloration were measured weekly or biweekly to further quantify the photoperiodic reaction. In a first experiment, adult male wild-type (WT), DAO, and AR hamsters were transferred initially to a 16L/8D cycle. After 3-4 wks, the light period was shortened symmetrically by 8 h. After 14 wks, none of the DAO and AR hamsters, and only 1 of 8 WT hamsters showed short-day (SD) traits. Therefore, in a second experiment, hamsters were transferred to SD conditions (8L/16D cycle) for 8 wks directly from standard LD conditions. In 6 of 7 WT hamsters, activity time expanded, body mass and testes size decreased, and fur coloration changed from summer to winter pelage. In contrast, none of the DAO and AR hamsters displayed an SD response. In a third experiment, DAO and AR hamsters were kept in constant darkness (DD) for 8 and 14 wks. After 8 wks, DAO hamsters showed a similar photoperiodic reaction to WT hamsters that had been kept for 8 wks under SD conditions. However, the level of adaptation was still less compared to WT hamsters, but this difference was not apparent after 14 wks. In contrast, AR animals did not display any photoperiodic reaction, even after 14 wks in DD. Type VI phase response curves (PRCs) were constructed to better understand the mechanism behind the SD response. In WT hamsters, the photosensitive phase, where light pulses induce phase shifts, was lengthened in SD condition. In DAO hamsters, in contrast, the PRCs were similar under LD and SD conditions with a compressed photosensitive phase corresponding to α. Also, "light-on" induced only weak phase advances of activity-onset, insufficient to compensate for the long endogenous period. The results show that physiological mechanisms necessary for seasonal adaptation are working in DAO hamsters and that it is the inadequate interaction of the LD cycle with the SCN that prevents the photo...

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Wheel running affects seasonal acclimatization of physiological and morphological traits in the Djungarian hamster (Phodopus sungorus)

Cited by 12 publications

References 44 publications

Somatostatin receptor activation is involved in the control of daily torpor in a seasonal mammal

Somatostatin receptor activation is involved in the control of daily torpor in a seasonal mammal

Effect of Exercise on Photoperiod-Regulated Hypothalamic Gene Expression and Peripheral Hormones in the Seasonal Dwarf Hamster Phodopus sungorus

Short-Day Response in Djungarian Hamsters of Different Circadian Phenotypes

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