Scaling the amplitudes of the circadian pattern of resting oxygen consumption, body temperature and heart rate in mammals

We questioned whether the amplitudes of the circadian pattern of body temperature (T(b)), oxygen consumption (V (O(2))) and heart rate (HR) changed systematically among species of different body weight (W). Because bodies of large mass have a greater heat capacitance than those of smaller mass, if the relative amplitude (i.e., amplitude/mean value) of metabolic rate was constant, one would expect the T(b) oscillation to decrease with the increase in the species W. We compiled data of T(b), V (O(2)) and HR from a literature survey of over 200 studies that investigated the circadian pattern of these parameters. Monotremata, Marsupials and Chiroptera, were excluded because of their characteristically low metabolic rate and T(b). The peak-trough ratios of V (O(2)) (42 species) and HR (35 species) averaged, respectively, 1.57+/-0.08, and 1.35+/-0.07, and were independent of W. The daily high values of T(b) did not change, while the daily low T(b) values slightly increased, with the species W; hence, the high-low T(b) difference (57 species) decreased with W (3.3 degrees C.W(-0.13)). However, the decrease in T(b) amplitude with W was much less than expected from physical principles, and the high-low T(b) ratio remained significantly above unity even in the largest mammals. Thus, it appears that in mammals, despite the huge differences in physical characteristics, the amplitude of the circadian pattern is a fixed (for V (O(2)) and HR), or almost fixed (for T(b)), fraction of the 24-h mean value. Presumably, the amplitudes of the oscillations are controlled parameters of physiological significance.     

The involvement of Cry1 and Cry2 genes in the regulation of the circadian body temperature rhythm in mice

The criptochrome genes (Cry1 and Cry2) are involved in the molecular mechanism that controls the circadian clock, and mice lacking these genes (Cry1(-/-)/Cry2(-/-)) are behaviorally arrhythmic. It has been speculated that the circadian clock modulates the characteristics of thermoregulation, resulting in body temperature (T(b)) rhythm. However, there is no direct evidence proving this speculation. We show here that T(b) and heat production in Cry1(-/-)/Cry2(-/-) mice are arrhythmic under constant darkness. In contrast, both rhythms occur under a light-dark cycle and/or periodical food restriction linked with spontaneous activity and/or eating, although they are not robust as those in wild-type mice. The relationship between heat production and T(b) in Cry1(-/-)/Cry2(-/-) mice is linear and identical under any conditions, indicating that their T(b) rhythm is determined by heat production rhythm associated with activity and eating. However, T(b) in wild-type mice is maintained at a relatively higher level in the active phase than the inactive phase regardless of the heat production level. These results indicate that the thermoregulatory responses are modulated according to the circadian phase, and the Cry genes are involved in this mechanism.     

Thermoregulation and the effect of body temperature on call temporal parameters in the cicada Diceroprocta olympusa (Homoptera: Cicadidae)

We investigated the thermoregulatory behavior, thermal responses (minimum flight, maximum voluntary tolerance and heat torpor temperatures) and the effect of body temperature (T(b)) on call parameters in the cicada Diceroprocta olympusa (Walker). Regression of T(b) as a function of ambient (T(a)) or perch temperatures (T(p)) suggests thermoregulation is occurring. Thermoregulation occurs through behavioral changes that alter the uptake of solar radiation. T(p) is a better predictor of T(b) than is T(a). Thermal responses (minimum flight temperature 20.4 degrees C, maximum voluntary tolerance temperature 37 degrees C, and heat torpor temperature 46.7 degrees C) may be related to the humid, grassland habitat of the species. In contrast to other acoustic insects, no significant relationship was found between the temporal parameters of the calling song and T(b) within the population of D. olympusa.     

Effects of body mass and temperature on routine metabolic rate of juvenile largemouth bronze gudgeon Coreius guichenoti

The effects of body mass (M) and temperature (T) on routine metabolic rate (m(R) ) were assessed in the largemouth bronze gudgeon Coreius guichenoti, from Three Gorges Reservoir, Yangtze River, China. The m(R) increased with increasing M by factors (b-value in the equation m(R) = aM(b) ) of 0·843, 0·800, 0·767, 0·788 and 0·822 at 10, 15, 20, 25 and 30° C, respectively. A significant interaction between M and T on m(R) was observed. The variation in the b-value at different T suggests that the b-values were not consistent with the universal allometric exponent 0·75. After controlling for M, the relationship between the normalized standard metabolic rate (m(S), mg O(2) kg(-1) h(-1)) and T was described by an exponential equation: m(S) = 9·89e((0·093T)) . The results indicate that the effects of M on m(R) depend on T. The increased water temperature induced by dam construction on the Yangtze River may cause a marked increase in energy demand by this species, with potential ecological consequences.     

Metabolism, body temperature and thermal conductance of fruit-doves (Aves: Columbidae, Treroninae)

Basal metabolic rate (MR), body temperature (T(b)) and wet thermal conductance (C(wet)) of three tropical species of fruit-doves were investigated at ambient temperatures (T(a)) of 11-33 degrees C in activity (alpha) and rest (rho) phases to investigate the possible effect of obligate frugivory on the physiology of columbids. The basal metabolic rates of Ptilinopus melanospila (black-naped fruit-dove, 94 g), Drepanoptila holosericea (cloven-feathered dove, 198 g) and Ducula pinon (Pinon's imperial pigeon, 748 g) are 20-38% lower than predicted for all birds, including granivorous columbid species from temperate and tropical regions. The MR was minimal at a T(a) value of approximately 30 degrees C (=lower critical temperature, T(lc)) for all three species, indicating that these rainforest birds are not able to withstand high ambient temperatures as well as arid-adapted members of the pigeon family. Minimal wet-thermal conductance was, on average, higher than expected, indicating poor insulation in these tropical birds. Body temperatures were as expected; however, below T(lc) the body temperatures decreased to levels of 35-36 degrees C (T(a)=12 degrees C).     

长江中游湖泊放流河蟹的生长动态

在保安湖的两个湖区(扁担塘和龙王头)和牛山湖的一个围拦湖汊中对放流河蟹的生长指标逐月采样研究,结果表明,三个水体虽同属长江中下游典型草型湖泊,但河蟹在生长末期规格(壳宽、体重)上表现出一定差异。扁担塘(瓯江种)、龙王头(瓯江种+长江种)成蟹规格较一致,群体壳宽分别为6.70±0.59、6.73±0.56cm,体重分别为155.1±36.0g、158.0±36.1g。而牛山湖湖议成蟹壳宽为5.63±0.43cm,体重为103.2±26.3g,与前两者相比,差异显著。原因可能主要是后者放养时间太晚(1997年4月26日)。从瞬时生长率来看,牛山湖湖(天津种)为0.02687g·day-1,大于扁担塘(0.00977g·day-1)和龙王头(0.00997g·day-1)。作者给出了上述三个水体2龄河蟹体重生长的逻辑斯蒂曲线方程。       

Hysteresis of heart rate and heat exchange of fasting and postprandial savannah monitor lizards (Varanus exanthematicus)

Reptiles are ectothermic, but regulate body temperatures (T(b)) by behavioural and physiological means. Body temperature has profound effects on virtually all physiological functions. It is well known that heating occurs faster than cooling, which seems to correlate with changes in cutaneous perfusion. Increased cutaneous perfusion, and hence elevated cardiac output, during heating is reflected in an increased heart rate (f(H)), and f(H), at a given T(b), is normally higher during heating compared to cooling ('hysteresis of heart rate'). Digestion is associated with an increased metabolic rate. This is associated with an elevated f(H) and many species of reptiles also exhibited a behavioural selection of higher T(b) during digestion. Here, we examine whether digestion affects the rate of heating and cooling as well as the hysteresis of heart rate in savannah monitor lizards (Varanus exanthematicus). Fasting lizards were studied after 5 days of food deprivation while digesting lizards were studied approximately 24 h after ingesting dead mice that equalled 10% of their body mass. Heart rate was measured while T(b) increased from 28 to 38 degrees C under a heat lamp and while T(b) decreased during a subsequent cooling phase. The lizards exhibited hysteresis of heart rate, and heating occurred faster than cooling. Feeding led to an increased f(H) (approximately 20 min(-1) irrespective of T(b)), but did not affect the rate of temperature change during heating or cooling. Therefore, it is likely that the increased blood flows during digestion are distributed exclusively to visceral organs and that the thermal conductance remains unaffected by the elevated metabolic rate during digestion.     

Differences in the physiological responses to temperature among stonechats from three populations reared in a common environment

The physiological response to variation in air temperature (T(a)) can provide insights into how animals are adapted to different environments. I measured metabolic rate, total evaporative water loss (TEWL) and body temperature (T(b)) as a function of T(a) in stonechats from equatorial Kenya, temperate central Europe and continental Kazakhstan, environments where stonechats have evolved different life histories. All birds were raised and kept under identical captive conditions to highlight genetically based differences and to exclude phenotypic plasticity as explanatory factor. The slope relating metabolic rate to T(a) was steepest in Kazakh stonechats and lowest for birds from Kenya, indicating that, counterintuitively, the tropical stonechats were best insulated. Taking into account variation in T(b) in response to T(a), the lower critical temperature for the three populations fell between 32.0 and 34.9 degrees C, values higher than previously assumed. Whole organism BMR did not differ among populations, but because body mass was significantly higher in the Kenyan stonechats, their mass-specific BMR was lower compared with conspecifics from higher latitude. Whole organism or mass-specific TEWL did not differ among populations. Possibly, Kenyan birds are better insulated to compensate for their limited capacity to elevate metabolic rate.     

An energy-based body temperature threshold between torpor and normothermia for small mammals

Field studies of use of torpor by heterothermic endotherms suffer from the lack of a standardized threshold differentiating torpid body temperatures (T(b)) from normothermic T(b)'s. This threshold can be more readily observed if metabolic rate (MR) is measured in the laboratory. I digitized figures from the literature that depicted simultaneous traces of MR and T(b) from 32 respirometry runs for 14 mammal species. For each graph, I quantified the T(b) measured when MR first began to drop at the onset of torpor (T(b-onset)). I used a general linear model to quantify the effect of ambient temperature (T(a)) and body mass (BM) on T(b-onset). For species lighter than 70 g, the model was highly significant and was described by the equation Tb-onset=(0.055+/-0.014)BM+(0.071+/-0.031)Ta+(31.823+/-0.740). To be conservative, I recommend use of these model parameters minus 1 standard error, which modifies the equation to Tb-onset-1 SE=(0.041)BM+(0.040)Ta+31.083. This approach provides a standardized threshold for differentiating torpor from normothermia that is based on use of energy, the actual currency of interest for studies of torpor in the wild. Few laboratory studies have presented the time-course data required to quantify T(b-onset), so more data are needed to validate this relationship.     

Restricted selection index in mice designed to change body fat without changing body weight: correlated responses

Summary Correlated responses were studied in lines of mice selected for eight generations based on the criterion of a restricted selection index. Two replicate lines were selected in each treatment as follows: HE, high epididymal fat pad weight (EF) with zero change in body weight (BW) at 12 weeks of age; LE; low EF with zero change in BW; and RS, randomly. Correlated responses showed considerable variation between replicates, suggesting that genetic drift was important. Further, correlated responses for most traits were relatively small, probably because of low selection intensity. The HE line responded as expected in component traits of the restricted index. Associated compositional traits in HE responded as predicted since traits correlated with adiposity increased and hind carcass weight did not change significantly. Feed intake increased and feed efficiency (weight gain/feed intake) decreased in HE, as predicted. In contrast, the LE line did not respond in component traits as predicted since EF did not decrease and BW increased. Consequently, LE exhibited little change in traits associated with adiposity, but hind carcass weight, feed intake and feed efficiency increased. Of the correlated responses scored for fitness traits (littering rate, number of days from pairing of mate to littering, litter size and preweaning pup survival rate), significant effects were found for decreased littering rate in LE and increased prenatal survival rate in HE. In summary, correlated responses to restricted index selection generally agreed with expectation when responses in component traits of the index were considered.The research reported in this publication was funded by the North Carolina Agricultural Research Service (NCARS), Raleigh, NC 27695-7643, USA. The use of trade names in this publication does not imply endorsement by the NCARS, nor criticism of similar ones not mentioned     

Thermophysiological responses of human volunteers to whole body RF exposure at 220 MHz

Since 1994, our research has demonstrated how thermophysiological responses are mobilized in human volunteers exposed to three radio frequencies, 100, 450, and 2450 MHz. A significant gap in this frequency range is now filled by the present study, conducted at 220 MHz. Thermoregulatory responses of heat loss and heat production were measured in six adult volunteers (five males, one female, aged 24-63 years) during 45 min whole body dorsal exposures to 220 MHz radio frequency (RF) energy. Three power densities (PD = 9, 12, and 15 mW/cm(2) [1 mW/cm(2) = 10 W/m(2)], whole body average normalized specific absorption rate [SAR] = 0.045 [W/kg]/[mW/cm(2)] = 0.0045 [W/kg]/[W/m(2)]) were tested at each of three ambient temperatures (T(a) = 24, 28, and 31 degrees C) plus T(a) controls (no RF). Measured responses included esophageal (T(esoph)) and seven skin temperatures (T(sk)), metabolic rate (M), local sweat rate, and local skin blood flow (SkBF). Derived measures included heart rate (HR), respiration rate, and total evaporative water loss (EWL). Finite difference-time domain (FDTD) modeling of a seated 70 kg human exposed to 220 MHz predicted six localized "hot spots" at which local temperatures were also measured. No changes in M occurred under any test condition, while T(esoph) showed small changes (< or =0.35 degrees C) but never exceeded 37.3 degrees C. As with similar exposures at 100 MHz, local T(sk) changed little and modest increases in SkBF were recorded. At 220 MHz, vigorous sweating occurred at PD = 12 and 15 mW/cm(2), with sweating levels higher than those observed for equivalent PD at 100 MHz. Predicted "hot spots" were confirmed by local temperature measurements. The FDTD model showed the local SAR in deep neural tissues that harbor temperature-sensitive neurons (e.g., brainstem, spinal cord) to be greater at 220 than at 100 MHz. Human exposure at both 220 and 100 MHz results in far less skin heating than occurs during exposure at 450 MHz. However, the exposed subjects thermoregulate efficiently because of increased heat loss responses, particularly sweating. It is clear that these responses are controlled by neural signals from thermosensors deep in the brainstem and spinal cord, rather than those in the skin.     

Hypoxic metabolic response of the golden-mantled ground squirrel.

We examined the magnitude of the hypoxic metabolic response in golden-mantled ground squirrels to determine whether the shift in thermoregulatory set point (T(set)) and subsequent fall in body temperature (T(b)) and metabolic rate observed in small mammals were greater in a species that routinely experiences hypoxic burrows and hibernates. We measured the effects of changing ambient temperature (T(a); 6--29 degrees C) on metabolism (O(2) consumption and CO(2) production), T(b), ventilation, and heart rate in normoxia and hypoxia (7% O(2)). The magnitude of the hypoxia-induced falls in T(b) and metabolism of the squirrels was larger than that of other rodents. Metabolic rate was not simply suppressed but was regulated to assist the initial fall in T(b) and then acted to slow this fall and stabilize T(b) at a new, lower level. When T(a) was reduced during 7% O(2), animals were able to maintain or elevate their metabolic rates, suggesting that O(2) was not limiting. The slope of the relationship between temperature-corrected O(2) consumption and T(a) extrapolated to a T(set) in hypoxia equals the actual T(b). The data suggest that T(set) was proportionately related to T(a) in hypoxia and that there was a shift from increasing ventilation to increasing O(2) extraction as the primary strategy employed to meet increasing metabolic demands under hypoxia. The animals were neither hypothermic nor hypometabolic, as T(b) and metabolic rate appeared to be tightly regulated at new but lower levels as a result of a coordinated hypoxic metabolic response.     

Metabolic, thermoregulatory, and perceptual responses during exercise after lower vs. whole body precooling.

The purpose of this investigation was to compare the thermoregulatory, metabolic, and perceptual effects of lower body (LBI) and whole body (WBI) immersion precooling techniques during submaximal exercise. Eleven healthy men completed two 30-min cycling bouts at 60% of maximal O(2) uptake preceded by immersion to the suprailiac crest (LBI) or clavicle (WBI) in 20 degrees C water. WBI produced significantly lower rectal temperature (T(re)) during minutes 24-30 of immersion and lower T(re), mean skin temperature, and mean body temperature for the first 24, 14, and 16 min of exercise, respectively. Body heat storage rates differed significantly for LBI and WBI during immersion and exercise, although no net differences were observed between conditions. For WBI, metabolic heat production and heart rate were significantly higher during immersion but not during exercise. Thermal sensation was significantly lower (felt colder) and thermal discomfort was significantly higher (less comfortable) for WBI during immersion and exercise. In conclusion, WBI and LBI attenuated T(re) increases during submaximal exercise and produced similar net heat storage over the protocol. LBI minimized metabolic increases and negative perceptual effects associated with WBI.     

How should body heat storage be determined in humans: by thermometry or calorimetry?

The aim of this study was to determine whether in humans there are differences in the heat storage calculated by partitional calorimetry (S, the balance of heat gains and heat losses) compared to the heat storage obtained by conventional methods (thermometry) via either core temperature or mean body temperatures (Tb = 0.8Tc + 0.2Tsk, where Tc is core temperature and Tsk is mean skin temperature) when two different sites are used as an index of Tc [rectal (T(re)) and auditory canal (T(ac)) temperatures]. Since women respond to the heat differently than men, both sexes were studied. After a stabilisation period at thermal neutrality, six men and seven women were exposed to a globe temperature of 50 degrees C, relative humidity of 17% and wind speed of 0.8-1.0 m.s-1 for 90 min semi-nude at rest, where T(re), T(ac), Tsk, metabolic rate, dry (radiant + convective heat exchange) and evaporative heat losses, S, heat storage by Tc (STc) and heat storage by Tb (STb) were assessed every minute. In the mean, S was equal to 350.8(SEM 49.6) kJ whereas STc amounted to only 114.6(SEM 16.2) and 196.7(SEM 32.3) kJ for T(re) and T(ac), respectively (P less than 0.05). Final STb(re) underestimated S by 49% [177.7(SEM 23.0) kJ; P less than 0.05] whereas STb(ac) was not significantly different than S [255.7(SEM 37.9) kJ]. In the women, S corresponded to a total of 294.3(SEM 23.2) kJ, a value that was very similar to the STb(ac) [262.6(SEM 31.0) kJ], whereas STb(re) under-predicated S by 35% [190.4(SEM 26.3) kJ; P less than 0.05].(ABSTRACT TRUNCATED AT 250 WORDS)     

Thermophysiological consequences of whole body resonant RF exposure (100 MHz) in human volunteers

Thermophysiological responses of heat production and heat loss were measured in seven adult volunteers (six males and one female, aged 31-74 years) during 45 min dorsal exposures of the whole body to 100 MHz continuous wave (CW) radio frequency (RF) energy. Three power densities (PD) (average PD = 4, 6, and 8 mW/cm(2); whole body specific absorption rate [SAR] = 0.068 [W/kg]/[mW/cm(2)]) were tested in each of three ambient temperatures (T(a) = 24, 28, and 31 degrees C), as well as in T(a) controls (no RF). A standardized protocol (30 min baseline, 45 min RF or sham exposure, 10 min baseline) was used. Measured responses included esophageal and seven skin temperatures, metabolic heat production, local sweat rate, and local skin blood flow. No changes in metabolic heat production occurred under any test condition. Unlike published results of similar exposures at 450 and 2450 MHz, local skin temperatures, even those on the back that were irradiated directly, changed little or not at all during 100 MHz exposures. The sole exception was the temperature of the ankle skin, which increased by 3-4 degrees C in some subjects at PD = 8 mW/cm(2). During the 45 min RF exposure, esophageal temperature showed modest changes (range = -0.15 to 0.13 degrees C) and never exceeded 37.2 degrees C. Thermoregulation was principally controlled by appropriate increases in evaporative heat loss (sweating) and, to a lesser extent, by changes in skin blood flow. Because of the deep penetration of RF energy at this frequency, effectively bypassing the skin, these changes must have been stimulated by thermal receptors deep in the body rather than those located in the skin.     

Influence of body heat content on hand function during prolonged cold exposures.

We examined the influence of 1) prior increase [preheating (PHT)], 2) increase throughout [heating (HT)], and 3) no increase [control (Con)] of body heat content (H(b)) on neuromuscular function and manual dexterity of the hands during a 130-min exposure to -20 degrees C (coldEx). Ten volunteers randomly underwent three passive coldEx, incorporating a 10-min moderate-exercise period at the 65th min while wearing a liquid conditioning garment (LCG) and military arctic clothing. In PHT, 50 degrees C water was circulated in the LCG before coldEx until core temperature was increased by 0.5 degrees C. In HT, participants regulated the inlet LCG water temperature throughout coldEx to subjective comfort, while the LCG was not operating in Con. Thermal comfort, rectal temperature, mean skin temperature, mean finger temperature (T(fing)), change in H(b) (DeltaH(b)), rate of body heat storage, Purdue pegboard test, finger tapping, handgrip, maximum voluntary contraction, and evoked twitch force of the first dorsal interosseus muscle were recorded. Results demonstrated that, unlike in HT and PHT, thermal comfort, rectal temperature, mean skin temperature, twitch force, maximum voluntary contraction, and finger tapping declined significantly in Con. In contrast, T(fing) and Purdue pegboard test remained constant only in HT. Generalized estimating equations demonstrated that DeltaH(b) and T(fing) were associated over time with hand function, whereas no significant association was detected for rate of body heat storage. It is concluded that increasing H(b) not only throughout but also before a coldEx is effective in maintaining hand function. In addition, we found that the best indicator of hand function is DeltaH(b) followed by T(fing).     

Factorial scopes of cardio-metabolic variables remain constant with changes in body temperature in the varanid lizard, Varanus rosenbergi

The majority of information concerning the cardio-metabolic performance of varanids during exercise is limited to a few species at their preferred body temperature (T(b)) even though, being ectotherms, varanids naturally experience rather large changes in T(b). Although it is well established that absolute aerobic scope declines with decreasing T(b), it is not known whether changes in cardiac output (V(b)) and/or tissue oxygen extraction, (Ca(O2) - Cv(O2)), are in proportion to the rate of oxygen consumption (Vo(2)). To test this, we studied six Rosenberg's goannas (Varanus rosenbergi) while at rest and while maximally exercising on a treadmill both at 25 and 36 degrees C. During maximum exercise both at 25 and 36 degrees C, mass-specific rate of oxygen consumption (Vo(2kg)) increased with an absolute scope of 8.5 ml min(-1) kg(-1) and 15.7 ml min(-1) kg(-1), respectively. Interestingly, the factorial aerobic scope was temperature-independent and remained at 7.0 which, at each T(b), was primarily the result of an increase in V(bkg), governed by approximate twofold increases both in heart rate (f(H)) and cardiac stroke volume (V(Skg)). Both at 25 degrees C and 36 degrees C, the increase in V(bkg) alone was not sufficient to provide all of the additional oxygen required to attain maximal Vo(2kg), as indicated by a decrease in the blood convection requirement V(bkg)/Vo(2kg); hence, there was a compensatory twofold increase in (Ca(O2) - Cv(O2)). Although associated with an increase in hemoglobin-oxygen affinity, a decrease in T(b) did not impair unloading of oxygen at the tissues and act to reduce (Ca(O2) - Cv(O2)); both Ca(O2)) and Cv(O2)) were maintained across T(b). The change in Vo(2kg) with T(b), therefore, is solely reliant on the thermal dependence of V(bkg). Maintaining a high factorial aerobic scope across a range of T(b) confers an advantage in that cooler animals can achieve higher absolute aerobic scopes and presumably improved aerobic performance than would otherwise be achievable.     

Increased heat loss affects hibernation in golden-mantled ground squirrels

During hibernation at ambient temperatures (T(a)) above 0 degrees C, rodents typically maintain body temperature (T(b)) approximately 1 degrees C above T(a), 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. T(b) was recorded telemetrically in golden-mantled ground squirrels (Spermophilus lateralis) housed at a T(a) of 5 degrees 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 T(b), 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.     

Resistance to myelin oligodendrocyte glycoprotein-induced experimental autoimmune encephalomyelitis by death receptor 6-deficient mice

Genetic disruption of death receptor 6 (DR6) results in enhanced CD4+ T cell expansion, Th2 differentiation, and humoral responses after stimulation. However, the in vivo consequences of DR6 targeting (DR6-/-) during the initiation and progression of inflammatory autoimmune disease are unclear. Using a myelin oligodendrocyte glycoprotein (MOG(35-55))-induced model of experimental autoimmune encephalomyelitis, DR6-/- mice were found to be highly resistant to both the onset and the progression of CNS disease compared with wild-type (WT) littermates. DR6-/- mice exhibited fewer inflammatory foci along with minimal demyelination and perivascular cuffing of inflammatory cells. Consistent with these observations, mononuclear cell infiltration, including CD4+ T cells and macrophages, in the spinal cord of DR6-/- mice was dramatically reduced. Furthermore, CD4+ T cells from DR6-/- mice exhibited profoundly reduced cell surface expression of VLA-4 before and after stimulation. Compared with WT mice, DR6-/- mice exhibited significantly increased autoantigen-induced T cell proliferative responses along with greater numbers of IL-4-producing and similar or slightly higher numbers of IFN-gamma-producing CD4+ T cells. DR6-/- CD4+ T cells secreted higher levels of the Th2 cytokine, IL-4, and similar levels of the Th1 cytokine, IFN-gamma, compared with WT cells. Taken together, our data demonstrate that DR6 plays an important role in regulating leukocyte infiltration and function in the induction and progression of experimental autoimmune encephalomyelitis.     

Involvement of basal metabolic rate in determination of type of cold tolerance

This study aimed to assess the relationship between basal metabolic rate (BMR) and metabolic heat production, and to clarify the involvement of BMR in determining the phenotype of cold tolerance. Measurements of BMR, maximum oxygen uptake, and cold exposure test were conducted on ten males. In the cold exposure test, rectal (T(rec)) and mean skin temperatures (T(ms)), oxygen uptake, and blood flow at forearm (BF(arm)) were measured during exposure to cold (10 degrees C) for 90 min. Significant correlations were observed between BMR and increasing rate of oxygen uptake, as well as between decreasing rate of BF(arm) and increasing rate of oxygen uptake at the end of cold exposure. These findings suggested that individuals with a lower BMR were required to increase their metabolic heat production during cold exposure, and that those with a higher BMR were able to moderate increased metabolic heat production during cold exposure because they were able to reduce heat loss. This study showed that BMR is an important factor in determining the phenotype of cold tolerance, and that individuals with a low BMR showed calorigenic-type cold adaptation, whereas subjects with a high BMR exhibited adiabatic-type cold adaptation by peripheral vasoconstriction.