Seasonal control of energy requirements for thermoregulation in the djungarian hamster (Phodopus sungorus), living in natural photoperiod

Summary Djungarian dwarf hamsters,Phodopus s. sungorus, were kept in natural photoperiodic conditions throughout the year, either inside at a constantT _a of 23°C or outside subjected to seasonally varyingT _a. Comparisons were made between hamsters from both conditions to evaluate the significance of seasonal changes in photoperiod and/orT _a as environmental cues for seasonal acclimatization inPhodopus. Basal metabolic rate was lowest in July (1.68 ml/g·h) and highest in January (2.06 ml/g·h inPhodopus living outside), combined with a decrease inT _1c from 26°C in July to 20°C in January. This was parallelled by seasonal changes in body weight (summer 42 g, winter 25g), fur colouration, fur depth and the occurrence of short daily torpor.AtT _a below thermoneutrality total energy requirements for thermoregulation in winter acclimatizedPhodopus were found 36% lower than summer values (e.g. at O°CT _a in summer 1,160 mW, in winter 760 mW), which were effected by a combined strategy of reducing body weight (19%) together with improvements of thermal insulation of the body surface (17%). All seasonal changes were similar inPhodopus living inside or outside, suggesting that seasonal changes in photoperiod and not seasonal changes inT _a is the overriding controller for the environmental cueing of seasonality in energy requirements for thermoregulation.This research was supported by the Deutsche Forschungsgemeinschaft (He 990)     

Effects of high fat diets on hibernation and adipose tissue in Turkish hamsters

Summary The effects of dietary fat saturation and fat content on hibernation and several properties of white and brown adipose tissue (WAT and BAT, respectively) were investigated in Turkish hamsters (Mesocricetus brandti). Male hamsters were housed in a long photoperiod (LD 16:8) at 23°C and fed one of three diets: (1) chow (6.5% fat per weight), (2) chow+13.5% vegetable oil (OIL, 20% fat per weight [largely unsaturated fat]) and (3) chow+13.5% vegetable shortening [SHORTENING, 20% fat per weight (largely saturated fat)]. Five weeks later body weights had stabilized and the animals were transferred to a short photoperiod (LD 8:16) at 3°C. At the peak of the hibernation season (17 weeks) the animals were sacrificed within 24 h of arousal. Chow-fed hamsters had the greatest percentage of animals hibernating and days found torpid compared with the two fat-fed groups, with no differences found between the latter two groups for these measures. There were no differences between hibernating (HIB) and nonhibernating (NON-HIB) hamsters across or within the diet groups for any of the BAT measures [uncoupling protein content, mitochondrial mass, lipoprotein lipase (LPL) activity, and in vivo lipogenesis], nor were there significant effects of the diet on these measures. CHOW-and OIL-fed HIB hamsters showed decreases in body weight. All HIB groups had decreases in each carcass component, several fat pad weights, testes weight, and food intake. No consistent differences in WAT LPL activity or in vivo lipogenesis were found between HIB and NON-HIB hamsters. Feeding saturated high fat diets inhibits hibernation in some species; however, in the present experiment, feeding of both saturated and unsaturated fat-laden diets inhibited hibernation to a similar degree.Abbreviations BAT brown adipose tissue - COA cytochrome-c oxidase - DS dorsal subcutaneus - DSWAT dorsal subcutaneous white adipose tissue - E epididymal - EWAT epididymal white adipose tissue - FFDM fat-free dry mass - HIB hibernating - I interscapular - IBAT intercapsular brown adipose tissue - IS inguinal subeutaneus - ISWAT inguinal subcutaneous white adipose tissue - LPL lipoprotein lipase - NON-HIB non-hibernating - R retroperitoneal - RWAT retroperitoneal white adipose tissue - SDS sodium dodecyl sul - UCP uncoupling protein - WAT white adipose tissue     

Sources of heat during nonshivering thermogenesis in Djungarian hamsters: a dominant role of brown adipose tissue during cold adaptation

Summary To assess the thermogenic importance of BAT in Djungarian hamsters we removed about 40% of their BAT and compared their thermogenic abilities before and after the operation. BAT was weighed and assayed for its respiratory properties (Cox, mitochondria). Following removal of BAT we observed considerable reductions of NST. The comparison of NST with BAT weight and with respiratory properties of BAT following partial removal of BAT revealed that at least three different pathways for heat production were involved in NST. In cold-adapted hamsters (values for warm-adapted hamsters in parentheses) we estimated that 66.2% (37.0%) of all NST was produced by mitochondrial respiration in BAT; 16.3% (38.4%) was produced in other organ sites but required the presence of BAT, i.e. there was a mediatory action of BAT on thermogenesis in other organ sites. A further 11.5% (23%) of NST occurred outside of and independent of BAT. Mitochondrial respiration in BAT was the only compartment of NST which increased its contribution during cold adaptation (238 mW to 1,062 mW), whereas the other sources of heat remained largely unchanged.Abbreviations BAT brown adipose tissue - BATex partial removal of brown adipose tissue - BMR basal metabolic rate at thermoneutrality - Cox cytochrome c oxidase - NA noradrenaline - NST nonshivering thermogenesis     

Seasonal changes in daily metabolic patterns of Lacerta viridis

Summary Lacerta viridis maintained under natural photoperiodic conditions show daily and seasonal changes in metabolic rates and body temperature (T _b) as well as seasonal differences in sensitivity to temperature change. At all times of the year lizards have a daily fluctuation in oxygen consumption, with higher metabolic rates during the light phase of the day when tested at a constant ambient temperature (T _a) of 30°C. Rhythmicity of metabolic rate persists under constant darkness, but there is a decrease in the amplitude of the rhythm.Oxygen consumption measured at various T_as shows significant seasonal differences at T _as above 20°C. Expressed as the Arrhenius activation energy, metabolic sensitivity of Lacerta viridis shows temperature dependence in autumn, which changes to metabolic temperature independence in spring at T _as above 20°C. The results indicate a synergic relationship between changing photoperiod and body temperature selection, resulting in seasonal metabolic adjustment and seasonal adaptation.Abbreviations ANOVA analysis of variance - LD long day (16 h light) - SD short day (8 h light) - T _a ambient temperature - T _b body temperature     

The impact of dietary fats,photoperiod, temperature and season on morphological variables,torpor patterns,and brown adipose tissue fatty acid composition of hamsters,Phodopus sungorus

We investigated how dietary fats and oils of different fatty acid composition influence the seasonal change of body mass, fur colour, testes size and torpor in Djungarian hamsters, Phodopus sungorus, maintained from autumn to winter under different photoperiods and temperature regimes. Dietary fatty acids influenced the occurrence of spontaneous torpor (food and water ad libitum) in P. sungorus maintained at 18°C under natural and artificial short photoperiods. Torpor was most pronounced in individuals on a diet containing 10% safflower oil (rich in polyunsaturated fatty acids), intermediate in individuals on a diet containing 10% olive oil (rich in monounsaturated fatty acids) and least pronounced in individuals on a diet containing 10% coconut fat (rich in saturated fatty acids). Torpor in P. sungorus on chow containing no added fat or oil was intermediate between those on coconut fat and olive oil. Dietary fatty acids had little effect on torpor in animals maintained at 23°C. Body mass, fur colour and testes size were also little affected by dietary fatty acids. The fatty acid composition of brown fat from hamsters maintained at 18°C and under natural photoperiod strongly reflected that of the dietary fatty acids. Our study suggests that the seasonal change of body mass, fur colour and testes size are not significantly affected by dietary fatty acids. However, dietary fats influence the occurrence of torpor in individuals maintained at low temperatures and that have been photoperiodically primed for the display of torpor.Abbreviations BAT brown adipose tissue - bm body mass - FA fatty acid(s) - MR metabolic rate - MUFA monounsaturated fatty acid(s) - PUFA polyunsaturated fatty acid(s) - SFA saturated fatty acid(s) - T _a air temperature - T _b body temperature - T_s body surface temperature(s) - TNZ thermoneutral zone - UFA unsaturated fatty acid(s)     

Seasonal effects on metabolism and thermoregulation abilities of the Red-winged Starling (Onychognathus morio)

Basal metabolic rate (BMR) of birds is beginning to be viewed as a highly flexible physiological trait influenced by environmental fluctuations, and in particular changes in ambient temperatures (T_a). Southern Africa is characterized by an unpredictable environment with daily and seasonal variation. This study sought to evaluate the effects of seasonal changes in T_a on mass-specific resting metabolic rate (RMR), BMR and body temperature (T_b) of Red-winged Starlings (Onychognathus morio). They have a broad distribution, from Ethiopia to the Cape in South Africa and are medium-sized frugivorous birds. Metabolic rate (VO₂) and T_b were measured in wild caught Red-winged Starlings after a period of summer and winter acclimatization in outdoor aviaries. RMR and BMR were significantly higher in winter than summer. Body mass of Starlings was significantly higher in winter compared with summer. The increased RMR and BMR in winter indicate improved ability to cope with cold and maintenance of a high T_b. These results show that the metabolism of Red-winged Starlings are not constant, but exhibit a pronounced seasonal phenotypic flexibility with maintenance of a high T_b.     

Seasonal and photoperiodic effects on lipid droplet size and lipid peroxidation in the brown adipose tissue of bank voles (<Emphasis Type="Italic">Myodes glareolus</Emphasis>)

Seasonal changes in lipid droplet size and lipid peroxidation in the brown adipose tissue (BAT) of wild bank voles were examined. In addition, a role of photoperiod in these changes was studied; bank voles were held from the birth under long photoperiod (LP) for 12 weeks, and then half of them was transferred to short photoperiod (SP) for 6 weeks and another one remained under LP. In the wild bank voles the absolute BAT weight was seasonally constant, while the significant differences in the lipid droplet size were observed. The smallest lipid droplets (mean, 11 μm²) were seen in winter; they increased by 30 % in spring and reached the highest size (24 μm²) in summer. Lipid peroxidation in the BAT did not differ significantly between the seasons, although high intraseason variation of this process was noted. The laboratory experiment revealed that the size of lipid droplets was determined by photoperiod; SP induced 13-fold decrease, and continuous exposure to LP brought about a further 2.5-fold increase in the size of lipid droplets. Conversely, a significant decrease in lipid peroxidation was seen in LP bank voles in comparison with the SP animals. The data indicate that short photoperiod is responsible for the small size of lipid droplets in the BAT of bank voles during winter, which may be a necessary requirement for high thermogenic capacity of the tissue. Photoperiod appears also to affect lipid peroxidation in the BAT of these animals.     

Cold-induced changes in brown adipose tissue thermogenic capacity of immunocompetent and immunodeficient hairless mice

Mild cold acclimation (22°C, 3 weeks) of hairless mice was shown to increase 5-fold the brown adipose tissue uncoupling protein content in immunodeficient BALB/c nu/nu mice, but by only 2.3-fold in immunocompetent BFU mice. The difference in activation of brown adipose tissue thermogenic capacity was due to a 2-fold increase in the content of brown adipose tissue in nu/nu mice only, which was paralleled by an increase in brown adipose tissue protein but not DNA content. Likewise, only in nu/nu mice the cold acclimation increased the reaction of natural killer cells in blood and peritoneal exudate with a shift from spleen to lymph nodes and increased the phagocytic index. The results indicate that the immune system may influence the defence against cold at the level of brown adipose tissue thermogenesis.Abbreviations AU arbitrary unit(s) - bw body weight - HEMA 2-hydromethyl-metacrylate copolymer - BAT brown adipose tissue - UCP uncoupling protein - ATPase mitochondrial F_oF₁-ATPsynthase - IL-1 interleukin 1 - TNF tumour necrosis factor - NK cells natural killer cells - T _a ambient temperature     

Thyroid hormone status affects expression of daily torpor and gene transcription in Djungarian hamsters (Phodopus sungorus)

Thyroid hormones (TH) play a key role in regulation of seasonal as well as acute changes in metabolism. Djungarian hamsters (Phodopus sungorus) adapt to winter by multiple changes in behaviour and physiology including spontaneous daily torpor, a state of hypometabolism and hypothermia. We investigated effects of systemic TH administration and ablation on the torpor behaviour in Djungarian hamsters adapted to short photoperiod. Hyperthyroidism was induced by giving T4 or T3 and hypothyroidism by giving methimazole (MMI) and sodium perchlorate via drinking water. T3 treatment increased water, food intake and body mass, whereas MMI had the opposite effect. Continuous recording of body temperature revealed that low T3 serum concentrations increased torpor incidence, lowered T_b and duration, whereas high T3 serum concentrations inhibited torpor expression. Gene expression of deiodinases (dio) and uncoupling proteins (ucp) were analysed by qPCR in hypothalamus, brown adipose tissue (BAT) and skeletal muscle. Expression of dio2, the enzyme generating T3 by deiodination of T4, and ucps, involved in thermoregulation, indicated a tissue specific response to treatment. Torpor per se decreased dio2 expression irrespective of treatment or tissue, suggesting low intracellular T3 concentrations during torpor. Down regulation of ucp1 and ucp3 during torpor might be a factor for the inhibition of BAT thermogenesis. Hypothalamic gene expression of neuropeptide Y, propopiomelanocortin and somatostatin, involved in feeding behaviour and energy balance, were not affected by treatment. Taken together our data indicate a strong effect of thyroid hormones on torpor, suggesting that lowered intracellular T3 concentrations in peripheral tissues promote torpor.     

Are the short-photoperiod-induced decreases in serum prolactin responsible for the seasonal changes in energy balance in Syrian and Siberian hamsters?

Serum prolactin (PRL) decreases in Syrian (Mesocricetus auratus) and Siberian (Phodopus sungorus sungorus) hamsters following short-photoperiod exposure. Both species also exhibit short-photoperiod-induced changes in body and lipid mass, but in opposite directions; Syrian hamsters increase and Siberian hamsters decrease their body weight, changes reflected nearly exclusively in their carcass lipid content. The purpose of these experiments was to determine whether the photoperiod-induced changes in PRL were responsible for the seasonal changes in energy balance in Syrian and Siberian hamsters by using the strategy of experimentally producing serum PRL levels opposite to those normally associated with the photoperiod in which the animals were housed. In long photoperiods serum PRL was reduced to short-day levels by subcutaneous (s.c.) CB-154 (bromoergocryptine, a dopamine agonist) injections. In short photoperiods, serum PRL was elevated to long-day levels in Syrian hamsters by ectopic pituitary explants, and in Siberian hamsters, serum PRL was elevated by chronic s.c. infusions of ovine PRL (oPRL). In both species, manipulations of serum PRL did not affect food intake, carcass composition, or the wet weight of various white and brown adipose tissue pads (WAT and BAT, respectively). Body weight increased in CB-154-treated Syrian hamsters and decreased in Siberian hamsters, an effect partially reversed by coadministration of oPRL in Syrian, but not Siberian, hamsters. Thus, lowering serum PRL to short-day levels in long-day-housed hamsters of both species mimicked the directional change in body weight appropriate for each species when they are exposed to short days. This effect of CB-154 on body weight may be a result of some as yet unidentified effect of dopaminergic stimulation on overall growth since 1) these changes in body weight were not reflected as changes in lipid mass, as occurs naturally following short-day exposure for each species, and 2) neither species exhibited a reciprocal change in body weight when serum PRL was experimentally elevated in short days. Alternatively, it may be that once the energetic responses to short-day exposure have been fully expressed, the ability of PRL to stimulate the target sites of action for PRL for these responses may be decreased. BAT protein content, cytochrome oxidase activity (measures of metabolic growth of this tissue), and retroperitoneal total and specific lipoprotein lipase (LPL) activities were increased by CB-154 treatment in Syrian hamsters.(ABSTRACT TRUNCATED AT 400 WORDS)     

Seasonal acclimation of bank voles and wood mice: nonshivering thermogenesis and thermogenic properties of brown adipose tissue mitochondria

Summary Seasonal acclimation of nonshivering thermogenesis and brown adipose tissue was studied in wild bank voles (Clethrionomys glareolus), yellow necked field mice and wood mice (Apodemus flavicollis, A. sylvaticus). Both, voles and mice increased their capacity for nonshivering thermogenesis during winter. Thermogenic properties of brown fat (cytochrome c oxidase activity, mitochondrial protein content, GDP-binding of brown fat mitochondria) showed similar changes during seasonal acclimation;Clethrionomys andApodemus spp. both showed lowest thermogenic properties in the summer during August, a rapid increase during fall, and highest levels of thermogenic activity in the winter months. With regard to changes in body weight and brown fat mass these species show different strategies for seasonal acclimation. InClethrionomys a reduction of body mass in the winter was found, both in the wild population as well as in individual animals housed in the laboratory.A. flavicollis showed a reduction of body weight during fall, whereasA. sylvaticus maintained a constant body mass throughout the year. Brown fat mass and cellularity increased in theApodemus spp. during winter, in parallel with the thermogenic properties of brown fat, whereas inClethrionomys brown fat mass and cellularity remained seasonally constant. These species live in the same habitat and were trapped in the same area. It is concluded that seasonal improvements of in vivo and in vitro thermogenesis are very similar in these species, although the physiological basis for this improvement is different inClethrionomys andApodemus.Abbreviations BAT brown adipose tissue - BMR basal metabolic rate (resting metabolic rate at thermoneutrality) - BW body weight - COX cytochrome c oxidase - GDP guanosine diphosphate - MP mitochondrial protein - NA noradrenaline - NST nonshivering thermogenesis - NSTcap NST capacity (NST maximum minus BMR) - T _a ambient temperature     

The effect of photoperiod on temperature selection in the European green lizard,Lacerta viridis

Summary Voluntary body temperature selection of unrestrained Lacerta viridis revealed consistant photoperiod entrained diel patterns. Each daily cycle was characterized by an elevation in body temperature (T _b) to a high level plateau which declined at the onset of scotophase to a low level; both of which were maintained within narrow ranges.Under natural photoperiod in fall, lizards responded to shorter days by sinking low level T _b's and expanding the duration of these low levels until no rhythmicity was shown. Subsequent exposure to long day, LD 16:8, induced self-arousal and a slightly altered diel T _b selection with significantly higher T _b's being chosen at both the elevated and lower daily levels. Changes in the relations of diel T _b selection due to shift in photoperiod, suggest that photoperiod acts as a seasonal indicator for thermal adaptation.This research was carried out in partial fulfillment of a diploma degree at the J.W.G. University, Frankfurt/Main     

Summer acclimatization in the short-tailed field vole,Microtus agrestis

We investigated the changes that occurred in basal and noradrenaline-induced metabolic rate, body temperature and body mass in short-tailed field voles,Microtus agrestis, during exposure to naturally increasing photoperiod and ambient temperature. These parameters were first measured in winter-acclimatized voles (n=8) and then in the same voles which had been allowed to seasonally acclimatize to photoperiod and ambient temperature (6 months later). Noradrenaline induced metabolic rate, basal metabolic rate and nonshivering thermogenesis were significantly higher in winter-acclimatized compared to summer-acclimatized voles. There was a significant positive relationship between basal metabolic rate and noradrenaline-induced metabolic rate. Body mass was significantly higher in summer-acclimatized compared to winter-acclimatized voles. There was a significant positive relationship between body mass and noradrenaline-induced metabolic rate in both winter-acclimalized and summer-acclimatized voles; however, there was no relationship between basal metabolic rate and body mass in either seasonal group of voles. Body temperature after measurements of basal metabolic rate was not significantly different in the seasonal cohorts of voles. However, body temperature was significantly higher in winter-acclimatized compared to summer-acclimatized voles after injection of noradrenaline. Previously we have found that a long photoperiod was not a sufficient stimulus to reduce thermogenic capacity in winter-acclimatized voles during cold exposure, since basal metabolic rate increased to compensate for a reduction in regulatory nonshivering thermogenesis. Here we found that a combination of increased ambient temperature and photoperiod did significantly reduce thermogenic capacity in winter-acclimatized voles. This provided evidence that the two aspects of non-shivering thermogenesis, obligatory and regulatory, are stimulated by different exogenous cues. Summer acclimatization in the shorttailed field vole is manifest as a significant decrease in both basal and noradrenaline-induced metabolic rate, combined with a significant increase in body mass.Abbreviations ANCOV A analysis of covariance - BAT brown adipose tissue - BM body mass - BMR basal metabolic rate - NST non-shivering thermogenesis - NA noradrenaline - V the maximum V recorded following mass specific injection of noradrenaline - V the maximum V recorded following mass specific injection of saline - T _a ambient temperature - T _b rectal body temperature - T _1c lower critical temperature - UCP uncoupling protein - V oxygen consumption     

Effect of unilateral surgical denervation of brown adipose tissue on uncoupling protein mRNA level and cytochrom-c-oxidase activity in the Djungarian hamster

The bilateral lobe of interscapular brown adipose tissue of the Djungarian hamster was unilaterally denervated in order to study the role of the sympathetic innervation for maintenance and cold-induced increase of non-shivering thermogenesis. Denervation decreased the noradrenaline content of brown adipose tissue to less than 9% of the intact contralateral pad. This low noradrenaline level was maintained for 1–14 days after denervation. First, to study the role of the sympathetic innervation of brown adipose tissue in the maintenance of the high thermogenic capacity characteristic of the cold acclimated state, brown adipose tissue was denervated in hamsters either kept at thermoneutrality or acclimated to 5°C ambient temperature for 4 weeks. Cold-acclimated hamsters had elevated levels of uncoupling protein messenger ribonucleic acid (8.1-fold) and cytochrom-c oxidase-activity (3-fold). Denervation of brown adipose tissue decreased uncoupling protein-messenger ribonucleic acid level and cytochrom-c-oxidase-activity as compared to the intact pad in thermoneutral and in cold-acclimated hamsters. However, in cold-acclimated hamsters uncoupling protein-messenger ribonucleic acid level and cytochrom-c-oxidase-activity in denervated brown adipose tissue both were maintained on an elevated 6-fold higher levels as compared to thermoneutral controls. Second, to study the role of the sympathetic innervation of brown adipose tissue in the cold-induced increase in thermogenic capacity, hamsters were denervated prior to cold acclimation and responses were measured after 3 and 14 days of cold exposure. Uncoupling protein-messenger ribonucleic acid level and cytochrom-c-oxidase-activity of intact brown adipose tissue increased after 14 days cold acclimation. Denervation did not completely prevent a cold-induced 1.5-fold increase of cytochrom-c-oxidase-activity and a 3.2-fold increase of the uncoupling protein-messenger ribonucleic acid level in denervated brown adipose tissue after 14 days of cold acclimation. In conclusion, high levels of uncoupling protein-messenger ribonucleic acid and cytochrom-c-oxidase activity in brown adipose tissue of cold-acclimated hamsters can partially be maintained without intact sympathetic innervation, suggesting a considerable contribution of trophic factors not requiring sympathetic innervation for maintenance. The cold-induced increase of cytochrom-c-oxidase activity and expression of uncoupling protein-messenger ribonucleic acid largely depends upon sympathetic innervation of brown adipose tissue.Abbreviations ANOVA analysis of variance - BAT brown adipose tissue - COX cytochrom-c-oxidase - HPLC high performance liquid chromatography - mRNA messenger ribonucleie acid - NA noradrenaline - T _a ambient temperature - UCP uncoupling protein     

Effects of photoperiod on energy budgets and thermogenesis in Mongolian gerbils (Meriones unguiculatus)

(1)

To investigate the role of photoperiod on the regulation of energy budgets and thermogenesis in Mongolian gerbils, body mass (BM), body fat mass (BFM), basal metabolic rate (BMR), nonshivering thermogenesis (NST), gross energy intake (GEI), mitochondrial cytochrome c oxidase (COX) activity and uncoupling protein1 (UCP1) content of brown adipose tissue (BAT), and serum tri-iodothyronine (T₃), thyroxine (T₄) and leptin levels were measured.     

Effects of photoperiod on energy intake, thermogenesis and body mass in Eothenomys miletus in Hengduan Mountain region

The present study was designed to examine whether photoperiod alone was effective to induce seasonal changes in physiology in voles (Eothenomys.) from the Hengduan Mountain region. Eothenomys miletus were randomly assigned into either long photoperiod (LD; 16L: 8D) or short photoperiod (SD; 8L: 16D) for 4 weeks at constant temperature (25 °C). At the end of acclimation, SD voles showed lower body mass and body fat coupled with higher energy intake than LD voles. SD greatly enhanced the thermogenic capacity of E. miletus, as indicated by an elevated nonshivering thermogenesis (NST), mitochondrial protein in brown adipose tissue (BAT); basal metabolic rate (BMR) was also raised. Although no variations in serum leptin levels were found between SD and LD voles, serum leptin levels were positively correlated with body mass and body fat mass, and negatively correlated with energy intake and UCP1 content in BAT, respectively. To summarize, SD alone is effective in inducing higher thermogenic capacities and energy intake coupled with lower body mass and body fat mass in root voles. Leptin is potentially involved in the photoperiod induced body mass regulation and thermogenesis in E. miletus. Our study shows that SD alone is effective.     

Metabolism,thermogenesis and daily rhythm of body temperature in the wood lemming,Myopus schisticolor

Wood lemmings (Myopus schisticolor) were captured during their autumnal migration in September and October. The animals were maintained at 12°C and under 12L:12D photoperiod. Basal metabolic rate and thermogenic capacity of the wood lemming were studied. Basal metabolic rate was 3.54 ml O₂·g^-1·h^-1, which is 215–238% of the expected value. The high basal metabolic rate seems to be typical of rodents living in high latitudes. The body temperature of the wood lemming was high (38.0–38.8°C), and did not fluctuate much during the 24-h recording. The high basal metabolic rate and the high body temperature are discussed with regard to behavioural adaptation to a low-quality winter diet. Thermogenic capacity, thermal insulation and non-shivering thermogenesis of the wood lemming displayed higher values than expected: 53.0 mW·g^-1, 0.53 mW·g^-1·C^-1 and 53.2 mW·g^-1, respectively. Brown adipose tissue showed typical thermogenic properties, although its respiratory property was fairly low, but mitochondrial protein content was high compared to other small mammals. The 24-h recording of body temperature and motor activity did not reveal whether the wood lemming is a nocturnal animal. Possibly, the expression of a circadian rhythm was masked by peculiar feeding behaviour. It is concluded that the wood lemming is well adapted to living in cold-temperature climates.Abbreviations BAT brown adipose tissue; bm, body mass - BMR basal metabolic rate - C conductance - Cox cytochrome-c-oxidase - HP heat production - HP_max maximum heat production - M metabolism - NA noradrenaline - NST non-shivering thermogenesis - NST_max maximum non-shivering thermogenesis - RMR resting metabolic rate - RQ respiratory quotient - T _a anibient temperature - T _b body temperature - T _lc lower critical temperature - UCP uncoupling protein - vO₂ oxygen consumption - vO_{2 max} maximum oxygen consumption     

Maximum rates of sustained metabolic rate in cold-exposed Djungarian hamsters (Phodopus sungorus): the second wind

Djungarian hamsters (Phodopus sungorus) tolerate short-term exposure to ambient temperatures (T _as) down to −70°C, but surprisingly, previously appeared to reach maximum sustainable metabolic rate (SusMR) when kept at T _as as high as ≥−2°C. We hypothesized that SusMR in Djungarian hamsters may be affected by the degree of prior cold acclimation and temporal patterns of T _a changes experienced by the animals, as average T _a declines. After cold-acclimation at +5°C for 6 weeks, hamsters reached rates of SusMR that were 35% higher than previously determined and were able to maintain positive energy balances down to T _a −9°C. SusMR was unaffected, however, by whether mean cold load was constant or caused by T _as cycling between +3°C and as low as −25°C, at hourly intervals. At mean T _as between +3 and −3°C hamsters significantly reduced body mass and energy expenditure, but were able to maintain stable body mass at lower T _as (−5 to −9°C). These results indicate that prior cold-acclimation profoundly affects SusMR in hamsters and that body mass regulation may play an integral part in maintaining positive energy balance during cold exposure. Because the degree of instantaneous cold load had no effect on SusMR, we hypothesize that limits to energy turnover in Djungarian hamsters are not determined by the capacity to withstand extreme temperatures (i.e., peripheral limits) but are due to central limitation of energy intake.     

Seasonal and daily changes in the capacity for nonshivering thermogenesis in the golden hamsters housed under semi-natural conditions

Nonshivering thermogenesis (NST) is a main source of heat for many small mammals. It undergoes seasonal changes, being the highest in winter and the lowest in summer. Such acclimatization can ensure winter survival for species living in moderate or cold climates. Nevertheless, not only seasonal, but also daily changes in the capacity for NST seem to be of great importance. In this study, the effects of season and time of day on the temperature of brown adipose tissue (T(BAT)), preferred ambient temperature (PT(a)) and activity after noradrenaline (NA) injections in golden hamsters (Mesocricetus auratus) housed under semi-natural conditions were investigated. Animals were kept in outdoor enclosures and experienced natural changes in both, photoperiod and ambient temperature (T(a)). NA-induced hyperthermia was the largest during autumn (mean increase in T(BAT) by 0.74+/-0.04 degrees C), while during summer increase in T(BAT) was similar to that recorded in control (saline-injected) animals (0.16+/-0.05 degrees C and 0.24+/-0.04 degrees C, respectively). In spring hyperthermia was intermediary (0.57+/-0.05 degrees C). Daily variations in the response to NA depended on the season. In summer, the largest increase in T(BAT) (0.45+/-0.1 degrees C) was recorded during the first part of the day, while in autumn-in the middle of the day and night (1.1+/-0.1 degrees C and 0.9+/-0.1 degrees C, respectively). In spring, all NA injections induced large increase in T(BAT) except for the injection in the middle of the night. The largest decrease in PT(a) after NA administration was recorded in autumn (mean decrease by 1.5+/-0.3 degrees C). Both, seasonal and daily changes in the capacity for NST reflect different demands for heat dependently on the time of the year and time of the day. It can be concluded that although long history of breeding in captivity, golden hamsters preserved ability to survive in natural environment.